IRPCS for Sailors: Who Gives Way, Who Stands On and What Happens in a Narrow Channel?

Sailing would be much simpler if we always had the river, lake or sea to ourselves. In reality, we share the water with other sailing boats, motor cruisers, rowing boats, paddleboards, safety boats, commercial vessels and sometimes boats whose intentions are far from obvious.

That is where the International Regulations for Preventing Collisions at Sea come in.

Usually known as the IRPCS or COLREGs, these regulations provide a common set of expectations. They help vessels behave predictably when they meet, cross or overtake one another.

However, the rules are not simply a hierarchy that gives one boat an absolute “right of way”. They are a system for preventing collisions. Even the stand-on vessel must remain alert and may eventually be required to act.

For those of us learning to sail on a comparatively narrow and busy river, this is particularly important. A sailing boat may theoretically be the stand-on vessel in one situation, but its skipper must still consider the riverbank, moored boats, bridges, other traffic, wind shadows and whether a larger vessel has enough room to manoeuvre.

The real objective is not to prove that we were correct.

The objective is to avoid the collision.

What Are the IRPCS?

The IRPCS are the International Regulations for Preventing Collisions at Sea. They are also commonly called the Collision Regulations or COLREGs.

They cover subjects including:

• maintaining a proper lookout;

• travelling at a safe speed;

• assessing the risk of collision;

• actions to avoid collision;

• sailing vessels meeting one another;

• overtaking;

• crossing situations;

• narrow channels;

• responsibilities between different types of vessel;

• navigation lights, shapes and sound signals.

UK guidance confirms that vessels and watercraft operating at sea, or in waters connected to the sea and navigable by seagoing vessels, must comply with the Collision Regulations. Authorities can also make special rules for harbours, rivers, lakes and inland waterways.

This distinction matters on the Thames. The non-tidal River Thames is governed by Environment Agency navigation byelaws, which contain rules closely related to the IRPCS but adapted to the river environment. Local restrictions, event directions, bridge instructions and navigation notices must also be followed.

The Most Important Rule Comes Before “Who Gives Way?”

Before deciding whether another vessel must give way, we must first decide whether a risk of collision exists.

Four fundamental principles apply to almost every encounter.

Maintain a Proper Lookout

Every vessel must maintain a proper lookout by sight, hearing and any other appropriate means available.

On a small sailing boat, this means more than looking straight ahead. The helm and crew should regularly look:

• ahead and to leeward;

• behind the mainsail and jib;

• astern for overtaking vessels;

• towards side channels and moorings;

• around bends;

• through bridge arches;

• towards boats that may be hidden by other traffic.

A large sail can create a significant blind spot. Moving one’s head, changing position briefly or asking a crew member to check the obscured side can reveal a boat that would otherwise remain invisible.

Travel at a Safe Speed

A safe speed is not necessarily the maximum speed permitted.

It is a speed at which the vessel can take effective avoiding action and, where appropriate, stop within a suitable distance.

The correct speed depends on visibility, traffic, available water, the vessel’s manoeuvrability, wind, current and nearby hazards. The IMO places proper lookout, safe speed, assessment of collision risk and positive avoiding action at the centre of the Collision Regulations.

Assess Whether the Bearing Is Changing

A useful practical test is to watch the other vessel against a fixed part of your boat or the distant background.

If the other vessel remains on approximately the same bearing but appears to be getting larger, a collision risk may exist.

A changing bearing does not guarantee safety, particularly at close range or when approaching a large vessel or a tow. If there is doubt, the rules require the navigator to assume that a risk of collision exists.

Take Early and Obvious Action

Avoiding action should be positive, made in ample time and large enough to be readily apparent to the other vessel.

A succession of tiny course changes can create confusion. The other skipper may not know whether we have seen them or whether our movement is simply the result of waves, wind or poor steering.

A clear alteration, made early, communicates intention.

Which Rule Should We Apply?

A common mistake is to begin every situation with the statement:

“Sail gives way to sail according to the tack, and motor gives way to sail.”

That is only part of the story.

Before applying the familiar sailing rules, ask the following questions:

1. Is either vessel overtaking?

2. Are we in a narrow channel or fairway?

3. Is either vessel unable, restricted or severely limited in its ability to manoeuvre?

4. Are both vessels sailing?

5. Are both vessels power-driven?

6. Is one under sail and the other power-driven?

7. Do local navigation byelaws or directions alter the situation?

The overtaking and narrow-channel rules may apply before the more familiar relationship between a sailing boat and a power-driven vessel.

When Two Sailing Boats Meet

Rule 12 covers two sailing vessels approaching one another when there is a risk of collision.

Boats on Different Tacks

When the boats have the wind on different sides, the boat with the wind on its port side must keep out of the way.

In normal sailing language:

The port-tack boat gives way to the starboard-tack boat.

A boat is normally described as being on starboard tack when the wind is coming over its starboard side. Its boom will usually be carried to port.

A boat on port tack has the wind coming over its port side, with the boom usually carried to starboard.

A useful memory aid is:

Port keeps clear.

Boats on the Same Tack

When both boats have the wind on the same side, the windward boat must keep out of the way of the leeward boat.

The windward vessel is the one nearer the direction from which the wind is coming.

The leeward vessel is farther away from the wind.

A useful memory aid is:

Windward gives way to leeward.

This makes practical sense. The windward boat generally has more opportunity to alter course without being forced directly into the leeward boat.

When the Tack Is Uncertain

A vessel on port tack that sees another vessel to windward, but cannot determine the other vessel’s tack with certainty, must keep out of the way.

In other words, uncertainty is not a reason to continue and hope for the best.

It is a reason to create more separation.

These sail-to-sail provisions appear both in the international regulations and in the Environment Agency’s Thames navigation byelaws.

Sailing Boats and Power-Driven Vessels

Under the general responsibilities between vessels, a power-driven vessel underway normally keeps out of the way of a sailing vessel.

This is the origin of the familiar phrase “power gives way to sail”.

However, it is not an unrestricted privilege for the sailing boat.

A sailing vessel must keep out of the way of vessels that are:

• not under command;

• restricted in their ability to manoeuvre;

• engaged in fishing as defined by the regulations.

A small sailing boat must also avoid impeding a vessel that can safely navigate only within a narrow channel or fairway. The overtaking rules apply regardless of whether the overtaking boat is powered or sailing.

A yacht that is being propelled by machinery as well as carrying sail must not behave as though it is operating solely as a sailing vessel. The regulations also require the appropriate cone, with its apex pointing downwards, to be displayed by a vessel proceeding under sail while also being propelled by machinery.

The practical lesson is simple:

Never assume that displaying sails automatically gives a boat priority.

Following and Overtaking

The overtaking rule is one of the clearest and most important regulations.

A vessel overtaking any other vessel must keep out of the way of the vessel being overtaken.

This applies regardless of vessel type.

Therefore:

• a sailing boat overtaking a motor cruiser must keep clear;

• a motorboat overtaking a sailing boat must keep clear;

• a fast sailing dinghy overtaking a slower sailing boat must keep clear;

• a safety boat overtaking a rowing boat must keep clear.

A vessel is considered to be overtaking when approaching from more than 22.5 degrees abaft the other vessel’s beam. At night, it would be in a position from which it could see the other vessel’s sternlight but neither sidelight.

If there is doubt, the approaching vessel should assume that it is overtaking.

Most importantly, the overtaking vessel remains responsible until it is finally past and clear. A change in the relative angle does not suddenly turn the encounter into an ordinary crossing situation.

A Practical River Example

Imagine that we are sailing a dinghy downriver and gradually catching a motor cruiser.

It may be tempting to think:

“We are under sail, so the cruiser must keep out of our way.”

That would be the wrong starting point.

Because we are overtaking, we must keep clear.

We should choose a side with adequate room, consider our wind and the cruiser’s wash, pass at a safe distance and remain clear before returning to our preferred course.

The slower boat should behave predictably, but responsibility for the overtaking manoeuvre remains with us.

Power-Driven Vessels Crossing

When two power-driven vessels are crossing and there is a risk of collision, the vessel that has the other on its starboard side must keep out of the way.

It should, where circumstances allow, avoid crossing ahead of the other vessel.

A useful memory aid is:

If you see the other vessel on your right, you give way.

The give-way vessel should take early and substantial action. It might alter course to starboard, reduce speed, stop or pass astern, depending on the circumstances.

The stand-on vessel initially maintains its course and speed so that its movements remain predictable.

These crossing and give-way principles are covered by Rules 15 and 16 of the international regulations.

Narrow Channels Change the Situation

Rule 9 applies to narrow channels and fairways.

A vessel proceeding along a narrow channel should keep as near to the outer limit on its starboard side as is safe and practicable.

More importantly for small-boat sailors, a sailing vessel or vessel under 20 metres long must not impede the passage of a vessel that can safely navigate only within the channel.

A vessel should not cross a narrow channel if doing so would impede such a vessel.

This is where “power gives way to sail” can become dangerously misleading.

A yacht may be under sail, but it must not tack repeatedly across the path of a large vessel that is constrained by the available depth, width or bridge opening.

The larger vessel may have:

• limited room to turn;

• a significant stopping distance;

• strong current acting upon it;

• a deep draught;

• restricted visibility from the wheelhouse;

• no safe route outside the marked channel.

The small sailing boat may be much more manoeuvrable, even if altering course is inconvenient.

Applying This on the Upper Thames

The Upper Thames is not an open sea. It is a relatively confined river with bends, bridges, moorings, shallows and boats travelling both upstream and downstream.

The Environment Agency’s Thames byelaws contain several particularly relevant provisions.

Power-driven vessels proceeding up or down the river should, where safe and practicable, keep to the starboard side of the fairway or mid-channel.

A vessel crossing from one side of the river to the other, or entering the fairway from a side channel, must choose an appropriate time and give way to vessels navigating up or down the river.

An overtaking vessel must keep out of the way of the vessel being overtaken.

Actions to avoid collision should be positive, made in ample time and result in the vessels passing at a safe distance.

Tacking Across the River

A sailing dinghy may need to tack frequently while beating against the wind.

On a narrow river, each tack can take the boat from one side of the fairway to the other. The sailor therefore needs to look well beyond the immediate manoeuvre.

Before tacking, ask:

• Is a cruiser approaching from upstream?

• Is a rowing boat hidden behind the sail?

• Will the tack place us directly in front of another vessel?

• Is another sailing boat already committed to a manoeuvre?

• Will we emerge from a wind shadow with enough control?

• Is there room to complete the tack without being swept towards moored boats?

The rule should not be interpreted as “I am sailing, so everyone else must move”.

A better interpretation is:

“I must sail predictably and avoid obstructing vessels already proceeding along the river.”

What Must the Stand-On Vessel Do?

The term “stand-on vessel” is often misunderstood.

It does not mean a vessel with an absolute right to continue regardless of danger.

The stand-on vessel has three stages of responsibility.

Stage One: Maintain Course and Speed

Initially, the stand-on vessel should maintain its course and speed.

This allows the give-way vessel to predict where it will be and make an effective avoiding manoeuvre.

Unexpected alterations by the stand-on vessel can make the situation worse. The give-way vessel may already be planning to pass astern, only for the stand-on vessel to slow down or turn into the same space.

Stage Two: The Stand-On Vessel May Act

As soon as it becomes apparent that the give-way vessel is not taking appropriate action, the stand-on vessel may take action by its own manoeuvre.

It does not have to wait until collision is inevitable.

This is one of the most important parts of Rule 17. The stand-on vessel is permitted to intervene while there is still room to make an effective and controlled manoeuvre.

Stage Three: The Stand-On Vessel Must Act

When the vessels are so close that avoiding action by the give-way vessel alone can no longer prevent a collision, the stand-on vessel must take whatever action will best help to avoid the collision.

At this stage, standing on is no longer an acceptable option.

In a crossing encounter between power-driven vessels, a stand-on vessel acting independently should, where circumstances allow, avoid altering course to port for a vessel on its own port side. Turning to starboard, slowing or stopping may produce a clearer and safer result, although the skipper must consider the whole situation.

The practical sequence is therefore:

Maintain, monitor, intervene and, if necessary, evade.

Being Stand-On Does Not Remove Responsibility

A stand-on vessel must continue to:

• maintain a lookout;

• monitor the other vessel;

• check whether the avoiding action is effective;

• consider other surrounding traffic;

• prepare an escape manoeuvre;

• avoid creating a second collision while avoiding the first.

It should never continue towards danger merely to demonstrate that the other boat was supposed to move.

There is little satisfaction in being technically correct while repairing a damaged boat—or dealing with something much more serious.

What Should the Give-Way Vessel Do?

The give-way vessel should take early and substantial action to keep well clear.

The best action is normally:

• early enough to avoid alarm;

• large enough to be obvious;

• consistent rather than hesitant;

• easy for the other vessel to understand;

• followed through until both vessels are past and clear.

Reducing speed can be extremely effective. Sailors sometimes focus entirely on changing direction, but slowing down may create more time, allow the other vessel to pass ahead and reduce the consequences of any mistake.

On a dinghy, slowing may involve easing the sails, heading slightly into the wind or, where safe, stopping almost completely.

On a powerboat, it may mean reducing throttle, moving into neutral or using astern propulsion when appropriate.

Five Practical Scenarios

1. Two Sailing Boats on Opposite Tacks

Champagne is on port tack and another sailing boat is approaching on starboard tack.

Champagne is the give-way vessel.

The helm should take clear and early action. Depending on the circumstances, this could involve tacking, bearing away or passing astern.

The manoeuvre should not be left until the last few seconds.

2. Two Boats on the Same Tack

Two dinghies are beating upriver on starboard tack. Our boat is to windward.

The windward boat must keep clear of the leeward boat.

We should not squeeze the leeward boat towards the bank, moorings or another obstruction.

3. A Dinghy Catches a Cruiser

Our sailing dinghy is travelling faster than a cruiser and approaches from astern.

We are overtaking.

Despite being under sail, we must keep clear until finally past and clear.

4. A Sailing Boat Tacks Across the Fairway

A cruiser is proceeding steadily upriver while our dinghy is preparing to tack across its route.

The sensible action is to time the tack so that we do not obstruct the cruiser. We might complete the tack earlier, continue briefly on the existing course, slow down or pass safely astern.

The narrow river and local fairway rules matter more than trying to insist upon a simplistic “sail over power” rule.

5. The Give-Way Vessel Does Nothing

We are the stand-on vessel and initially hold our course and speed. The bearing remains steady and the other vessel is getting closer.

We continue monitoring.

When it becomes apparent that the give-way vessel is not acting appropriately, we make an early, clear avoidance manoeuvre while sufficient space remains.

We do not wait until there is only one desperate option left.

Common Misunderstandings

“Sailing Boats Always Have Priority”

They do not.

Overtaking, narrow-channel rules, restricted vessels and local navigation byelaws can all change the relationship.

“The Stand-On Vessel Must Never Alter Course”

Initially, it should maintain course and speed.

However, it may act when the give-way vessel is failing to respond, and it must act when collision can no longer be avoided by the give-way vessel alone.

“A Small Change Is Enough”

Small, repeated changes can be difficult for another skipper to detect.

Avoiding action should normally be positive and readily apparent.

“The Other Skipper Has Seen Me”

Never assume this.

You may be hidden by their cabin structure, sails, passengers, equipment or another vessel. They may also have misunderstood your intentions.

“We Are Racing, So Other Boats Must Keep Clear”

A racecourse does not create a protective bubble around the competitors.

Racing sailors must continue to observe navigation requirements, local directions and the presence of non-racing traffic.

A Simple Collision-Avoidance Routine

A practical routine for a dinghy, yacht or powerboat is:

Look

Maintain a proper lookout in every direction.

Classify

Decide whether the situation involves overtaking, crossing, meeting head-on, sail against sail, sail against power or a narrow channel.

Assess

Ask whether the bearing is steady and the distance is decreasing.

Decide

Identify which vessel should keep clear—but never stop considering what you will do if the other skipper makes a mistake.

Act

Make any avoiding action early, positive and obvious.

Check

Continue monitoring until the other vessel is finally past and clear.

The Deeper Lesson: Predictability Prevents Collisions

The IRPCS are not intended to encourage arguments about priority.

They are designed to make boats behave predictably.

The give-way vessel acts early and clearly.

The stand-on vessel initially maintains a predictable course and speed.

Both vessels keep a lookout.

Both monitor whether the action is working.

Both remain responsible for avoiding collision.

As I have gained more experience on the water, I have realised that knowing the basic rules is only the beginning. Applying them requires judgement.

On the Upper Thames, the wind may change abruptly. A boat may emerge from behind an island or around a bend. A dinghy may lose speed in a wind shadow. A cruiser may be committed to a bridge arch. A boat that appeared well clear may suddenly become a risk after one unexpected tack.

Good seamanship is therefore not simply knowing who should give way.

It is recognising risk early, making intentions clear and always keeping a safe alternative available.

Conclusion: Never Use the Rules to Sail Into Danger

The most important lesson from the IRPCS is not that one boat is “right” and another is “wrong”.

It is that every skipper has responsibilities.

A give-way vessel must take early and substantial action.

A stand-on vessel must remain predictable, but it must also remain alert and be prepared to intervene.

An overtaking vessel keeps clear, regardless of whether it is powered or sailing.

A small sailing boat must not obstruct a vessel that can safely navigate only within a narrow channel.

Local river byelaws and navigation directions must always be considered alongside the international principles.

Knowing these rules should make us more confident, but never overconfident.

The safest sailor is not the one who insists most strongly upon being stand-on.

It is the one who sees the developing situation early enough that no emergency manoeuvre is ever required.

This article is an educational overview rather than a replacement for the official Collision Regulations, local navigation byelaws, current navigation notices or recognised practical training.

 

Hidden in Plain Sight: The Survey Mark Beneath the Mast at Upper Thames Sailing Club

There are times when an interesting discovery is not found out on the river, aboard a boat or inside the workshop. Sometimes it is quite literally beneath our feet.

At Upper Thames Sailing Club, at the base of the mast on the lawn, there is a small circular hole accompanied by a black, three-part arrow. It would be easy to walk past it without giving it a second thought. Once noticed, however, it immediately raises questions.

Is it a trig point? Why was it placed there? What was it used to measure? And why has such a small mark survived when the methods of surveying Britain have changed so dramatically?

The answer takes us into the history of mapping, engineering and the remarkably precise measurements that underpin the modern world.

First, Is It Actually a Trig Point?

The mark is likely to be described casually as a trig point, but the photographs suggest that it is more precisely a survey benchmark, possibly a rivet or pivot-style benchmark.

The distinction matters.

A traditional trig point, or triangulation point, records a precisely established horizontal position. In Britain, the most recognisable examples are the concrete triangulation pillars found on hills and other prominent locations.

A benchmark, by contrast, records a precisely measured height.

Ordnance Survey explains the difference simply: trig pillars established accurate eastings and northings, while benchmarks established height above Ordnance Datum. Many trig pillars also carried a separate height mark, which is one reason the two terms are often confused.

The small circular feature and arrow at Upper Thames appear more like a horizontal benchmark than a conventional trig pillar. Confirming its exact type and original recorded height would require locating it in the Ordnance Survey benchmark archive or an earlier surveying record.

Nevertheless, it is certainly part of the same fascinating family of fixed survey markers.

What Does the Arrow Mean?

The three black shapes form a stylised broad arrow pointing towards the circular reference point.

Traditional benchmarks were often cut into walls, bridges, churches, milestones and other durable structures. On vertical surfaces, an arrow normally pointed towards a horizontal line. That line provided a repeatable position for a levelling staff.

On a horizontal surface, the precise reference could instead be a metal rivet, bolt or small depression. Specialist descriptions of these markers explain that some depressions were designed to accept a standard-sized steel ball, creating a repeatable point from which a measurement could be taken.

In the photograph, the arrow directs attention to the small circular point above it. The hole may be the original pivot, or it may once have contained a rivet that has since disappeared. That cannot be confirmed from the image alone.

The arrow is therefore not merely decorative. It tells the surveyor, “This is the point that matters.”

What Is a Trig Point?

“Trig” is short for trigonometrical station.

During the retriangulation of Great Britain, surveyors established a network of accurately positioned points across the country. Between 1936 and 1962, around 6,500 familiar concrete trig pillars were constructed. Each pillar provided a stable platform for a theodolite, an instrument used to measure horizontal and vertical angles.

Surveyors began with a very accurately measured baseline. They then observed other distant points and measured the angles between them.

If one side of a triangle and its angles are known, the remaining sides and positions can be calculated. The surveyors could then move to the next point and build another triangle.

Repeated across the country, those triangles created a connected national framework.

This was not simply a collection of isolated pillars. It was an enormous mathematical network supporting accurate map-making.

Why Were Trig Points Needed?

Imagine attempting to create a detailed map before satellite navigation existed.

A surveyor needed to know exactly where every town, road, railway, river, hill and significant building belonged. Local measurements were useful, but all those individual surveys had to fit together consistently.

Trig points gave surveyors reliable control positions from which other features could be measured.

They helped establish:

• national map coordinates;
• the locations of settlements and landmarks;
• the shapes and positions of roads and railways;
• boundaries and major structures;
• the positions of coastlines, rivers and hills;
• a consistent framework connecting local surveys.

A survey carried out in Buckinghamshire had to agree with one conducted in Oxfordshire, Berkshire or Cornwall. The triangulation network made that possible.

What Is a Benchmark?

A benchmark answers a different question.

A trig point helps establish:

Where is this point?

A benchmark helps establish:

How high is this point?

Ordnance Survey benchmarks record heights in relation to Ordnance Datum Newlyn, the national height reference for mainland Great Britain. That datum originated from measurements of mean sea level recorded at Newlyn in Cornwall over a six-year period.

Once the height of one benchmark had been established, surveyors could transfer that height to another location using precision levelling.

A simplified levelling calculation is:

Height of new point = height of known point + backsight reading - foresight reading

The measurements could be repeated from benchmark to benchmark, gradually extending a network of known heights across the country.

Why Is It Called a Benchmark?

The name has a very practical origin.

Traditional marks included a small horizontal cut. A levelling staff or supporting fitting could be positioned against that line, forming a stable and repeatable “bench”.

That physical bench gave us the word benchmark.

The term is now used much more broadly. Businesses compare performance against benchmarks, computers are benchmarked for speed, and schools may use benchmark assessments. In each case, the basic idea remains the same: there is a fixed reference against which something else can be measured.

Ordnance Survey records show that more than 500,000 benchmarks were created across Great Britain. Many have disappeared as buildings have been demolished, roads widened and structures replaced.

Why Put One at the Bottom of a Mast?

A benchmark needs a firm, durable and recognisable location.

The concrete foundation beneath a mast offers several advantages:

• it is unlikely to move during normal use;
• it provides a solid horizontal surface;
• it is easy to describe in survey records;
• it is reasonably accessible;
• it is less likely to be disturbed than a mark placed in soil;
• the tall mast makes the general location easy to identify.

The mark may predate the present mast, may have been incorporated when the base was constructed, or may have been installed because the mast foundation provided a particularly suitable permanent structure.

Without finding its original survey entry, it is impossible to say precisely when or why this individual mark was created. Its position, however, makes good surveying sense.

Why Accurate Height Matters Beside a River

Finding a height benchmark at a sailing club beside the Thames is particularly appropriate.

Precise height information can support work involving:

• river and flood levels;
• bank and pontoon construction;
• drainage gradients;
• building foundations;
• road and path levels;
• bridge clearances;
• utility installation;
• environmental monitoring;
• land and topographical surveys.

A difference of only a few centimetres may matter when water levels rise, when a drain must flow correctly or when a new structure must connect with an existing one.

Today, accurate height data also contributes to flood modelling, infrastructure projects, communications systems, renewable-energy planning and three-dimensional mapping.

This small mark may look unimportant, but it belongs to a system that helped engineers and map-makers describe the land in three dimensions.

How Would Surveyors Have Used It?

A survey team using the benchmark would place a levelling instrument on a stable tripod at a suitable nearby position.

A graduated levelling staff would be placed on the benchmark’s exact reference point. The surveyor would take a reading through the instrument.

The staff would then be moved to another point, where a second reading would be taken. The difference between the readings revealed the difference in height between the two positions.

The process could be repeated along a road, through a town, beside a river or across a construction site.

Accuracy depended upon:

• keeping the instrument level;
• placing the staff vertically;
• using the exact benchmark point;
• keeping sighting distances sensible;
• checking readings;
• repeating or closing the levelling route to detect errors.

It was careful, methodical work. A small mistake at one stage could travel through the rest of the survey.

Are These Marks Still Used?

Most of the historic benchmark network is no longer maintained for modern national surveying. Ordnance Survey warns that old benchmark values may have been affected by movement, redevelopment or subsidence and should not automatically be treated as current precision control.

Modern surveyors generally use Global Navigation Satellite Systems, including GPS, connected to the OS Net network of permanent reference stations. Ordnance Survey says this technology allows new map detail to be positioned to within a few centimetres without relying on the old triangulation pillars.

That does not make the old marks unimportant.

They remain physical evidence of how Britain was mapped before satellite positioning. They connect mathematics, geography, engineering, history and the landscape itself.

A Practical Investigation for Students

This discovery could form the starting point for an excellent geography, mathematics or physics activity.

1. Locate the marker

Photograph the mark from a distance and close up. Record its position relative to permanent features such as the mast, clubhouse and river.

2. Record its characteristics

Measure the diameter of the circular point, the dimensions of the arrow and the size of the concrete base.

Do not damage, deepen, repaint or alter the mark.

3. Find its approximate coordinates

Use a phone or handheld GPS receiver to record an approximate latitude, longitude and OS grid reference.

A phone will not normally provide professional surveying accuracy, but it can provide enough information to search historical records.

4. Search the archive

The Ordnance Survey maintains a searchable archive of historic benchmarks. Searches can be made using a postcode, grid reference or coordinates. The archive is no longer maintained as an active national control network, but its records remain available.

5. Compare measured heights

A simple optical level, laser level or suitable surveying instrument could be used to compare the marker’s height with the clubhouse threshold, riverbank, pontoon or other fixed positions.

This should be treated as a relative educational exercise rather than an attempt to recreate an official datum.

6. Discuss measurement uncertainty

Students could investigate why readings differ and consider errors caused by:

• an uneven or moving staff;
• instrument alignment;
• reading the wrong graduation;
• long sighting distances;
• thermal effects;
• ground movement;
• using an approximate rather than an official benchmark value.

That turns a small mark in the ground into a lesson about scientific measurement, uncertainty and the importance of repeatable reference points.

The Mathematics Hidden Beneath Our Feet

The mark also demonstrates how abstract mathematics becomes something practical.

Triangulation uses angles and calculated distances to establish horizontal positions. Levelling uses differences in staff readings to establish vertical positions.

Together, these provide three essential pieces of information:

• east-west position;
• north-south position;
• height.

In modern language, we might call these x, y and z coordinates.

Surveying therefore brings together geometry, trigonometry, optics, careful observation, instrument design, data recording and error analysis. The maps we use so casually are the final product of all that work.

A Personal Reflection

I have probably walked past this marker at Upper Thames Sailing Club many times without noticing it.

Attention at a sailing club is normally directed upwards towards the flag, across the river towards the wind or down at the boats and equipment. It took a closer look at the base of the mast to reveal something quite different: a small piece of Britain’s surveying history.

That is one of the pleasures of investigating the familiar. A feature that initially looks like a hole and three patches of black paint opens a path into trigonometry, national mapping, sea-level measurement, flood planning and modern satellite navigation.

It also reminds us that useful discoveries do not always require a journey to an unfamiliar place. Sometimes they require us to look more carefully at places we already know.

Conclusion: A Small Mark with a National Story

The feature beneath the mast at Upper Thames Sailing Club may commonly be called a trig point, but its appearance suggests that it is more likely a rivet or pivot-style benchmark used to identify a precise height reference.

A traditional trig point established horizontal position. A benchmark established height. Both were parts of the surveying systems that allowed Britain to be mapped consistently and accurately.

Modern satellites have largely replaced the daily use of these old markers, but the physical marks remain. They are small monuments to the surveyors who measured the country using theodolites, levelling staffs, mathematics and extraordinary patience.

The next time you see an arrow cut or painted onto a wall, bridge, stone or concrete base, stop and look more closely.

You may be standing beside a surviving reference point from the system that helped map modern Britain.

 

Does My Company Run on Batteries?

Sometimes I look around Philip M Russell Ltd and wonder whether the company actually runs on electricity—or whether it really runs on batteries.

Batteries are everywhere.

They power the cameras used to record science experiments, sailing videos and workshop projects. They run microphones, lighting accessories, electronic test equipment and PASCO scientific sensors. They power drills, saws, garden equipment and portable tools.

Even the quieter parts of the business depend on them. Radio-controlled clocks, remote controls and several pieces of scientific equipment still rely on ordinary alkaline batteries.

Then there is the largest battery system of all: the one helping to run the house.

During the day, our solar panels generate electricity and recharge the household batteries. At night, when the panels are producing nothing, those batteries take over and provide much of the electricity we use.

The cameras have their batteries. The power tools have theirs. The garden equipment has another collection. The scientific equipment has still more.

It sometimes feels as though the whole company is connected by one invisible battery network.

From a Tiny AA Battery to a Whole-House System

The word “battery” covers an enormous range of devices.

At one end is the humble AA alkaline battery in a clock. It may provide a tiny current for a year or more before needing replacement.

At the other end is our household battery bank, storing electricity generated by 26 solar panels and releasing that energy when the house needs it.

Between those extremes are dozens of specialist rechargeable batteries:

• camera battery packs;

• power-tool batteries;

• garden-tool batteries;

• rechargeable AA and AAA cells;

• batteries built into scientific sensors;

• microphone and recording-equipment batteries;

• emergency and backup batteries;

• batteries in laptops, tablets and mobile phones.

Each battery is doing essentially the same job: storing chemical energy and turning it back into electrical energy when required.

However, the way each battery is used is very different.

A clock needs a very small, steady current. A camera recording high-resolution video may demand considerable power. A cordless saw may require a very large current for a short period. A household battery must repeatedly charge and discharge many kilowatt-hours of electricity while communicating with solar inverters and energy-management systems.

There is no single battery that is ideal for every one of these jobs.

Why We Still Use Alkaline Batteries

Rechargeable batteries are usually the greener choice when a device is used frequently. However, alkaline batteries have not disappeared—and there are good reasons for that.

Radio-controlled clocks use very little energy. An alkaline AA battery can work reliably for a long time without needing a charger or any attention.

Some scientific equipment is also designed specifically around the voltage produced by alkaline cells. For example, PASCO manuals for some instruments explicitly specify AA alkaline batteries, while many newer rechargeable PASCO products use lithium-polymer battery packs.

Rechargeable nickel-metal-hydride AA batteries normally provide about 1.2 volts, compared with approximately 1.5 volts from a fresh alkaline cell. Many devices work perfectly well with that difference, but some clocks, sensors and older electronic instruments do not.

That means replacing every disposable battery with a rechargeable one is not always as simple as it sounds.

My approach is to use rechargeable batteries where there is regular, significant demand, while retaining alkaline cells for very low-drain devices where they remain the most practical option.

The important point is that used alkaline batteries should not simply disappear into the general rubbish. UK government guidance says household batteries and battery packs should be taken to appropriate battery collection or recycling points.

Lithium Has Quietly Taken Over the Company

Most of our rechargeable equipment now relies on some form of lithium-based battery.

Lithium-ion batteries have several major advantages. They store a considerable amount of energy for their size and weight, deliver useful levels of power and do not suffer from the severe “memory effect” associated with some older rechargeable technologies.

That makes them ideal for cameras, power tools, garden equipment and portable scientific instruments.

Without lithium batteries, many of the things we now take for granted would be far less convenient.

A battery-powered camera can be carried around a sailing club, mounted on a boat or positioned beside an experiment without requiring a mains cable.

A cordless drill can be taken directly to Champagne, our Thames A-Rater, without running an extension cable across the workshop or towards the river.

Battery garden tools start immediately, avoid petrol fumes and are far quieter than many traditional alternatives.

Our household batteries allow solar electricity generated in the afternoon to be used during the evening and overnight. Instead of exporting all our surplus electricity when the Sun is shining and buying it back later, we can store a substantial proportion of it.

The battery is therefore not merely an emergency backup. It changes when and how we use the electricity generated by the house.

The House Charges by Day and Discharges by Night

Our home energy system has changed the way I think about electricity.

Traditionally, electricity was something that simply arrived through a wire. We turned on an appliance and the electricity was there.

Solar panels and batteries make energy much more visible.

On a bright day, I can see the solar panels powering the house, heating water and recharging the batteries. As evening approaches, solar generation falls. The batteries then begin supplying the house.

During spring, summer and early autumn, we can generate nearly all the electricity we need. The batteries effectively carry daylight into the night.

This also changes our behaviour.

We can choose when to run the dishwasher, washing machine or heat-pump tumble dryer. In summer, it often makes sense to use appliances while solar generation is high. In winter, an overnight time-of-use tariff may make it cheaper to recharge the batteries and run certain appliances when electricity prices are lower.

The battery is not just an object bolted to a wall. It becomes part of the daily management of the house.

Batteries Have Made the Business More Flexible

The same principle applies on a smaller scale throughout the company.

Battery power means equipment can go where it is needed.

When recording an experiment, a camera can be positioned above the bench, beside a measuring instrument or close to a reaction vessel. When photographing wildlife, there is no need for a nearby power supply. When filming from the Whaly safety boat or an A-Rater, batteries make the entire recording system portable.

In the workshop, cordless tools allow us to move quickly between boat repair, cover making, 3D printing, laser work and general maintenance.

That flexibility is easy to overlook.

We notice a battery when it is flat, but rarely appreciate how much freedom it provides while it is working.

The Less Convenient Side of Battery Power

Running so much equipment on batteries creates its own problems.

There are always batteries waiting to be charged. There are charged batteries that need identifying, partly used batteries whose condition is uncertain and older batteries that appear full on the charger but collapse quickly under load.

Camera batteries are particularly noticeable because video recording can be demanding. High-resolution recording, image stabilisation, autofocus, bright displays and wireless connections all consume power. Heat generated by prolonged recording can add further stress.

Power-tool batteries face a different challenge. They may sit unused for days and then suddenly be asked to deliver a very high current.

Garden batteries may spend part of the year in storage before being used heavily during spring and summer.

Household batteries work more predictably, but they experience repeated daily cycling and must be managed by their battery-management system.

A company that uses this many batteries needs to treat them as equipment rather than disposable accessories.

What Are Battery Dendrites?

One of the most interesting—and potentially serious—battery problems is the formation of dendrites.

The word comes from the Greek word for tree. Under certain conditions, metallic lithium can begin to form branching, needle-like structures inside a battery.

During normal charging, lithium ions should move through the electrolyte and settle into the structure of the negative electrode. If charging conditions are unsuitable, lithium can instead plate onto the electrode surface.

Research identifies low-temperature charging, excessive charging rates, overcharging and some system faults as conditions that can encourage lithium plating.

If deposits continue growing, they may develop irregular or dendritic structures. In the worst case, a structure could penetrate the separator between the battery’s electrodes, creating an internal short circuit.

However, an important qualification is needed.

When one of my camera batteries loses capacity, refuses to charge or behaves unpredictably, I cannot look at the outside and confidently say that dendrites caused the failure.

Capacity loss can have many causes:

• chemical ageing;

• prolonged exposure to heat;

• repeated deep discharge;

• storage while fully charged;

• over-discharge during long storage;

• increased internal resistance;

• deterioration of the electrolyte;

• failure of the battery-management electronics;

• physical damage.

Dendrite formation is one possible internal failure mechanism, but it is not the explanation for every failed lithium battery.

Warning Signs That Should Never Be Ignored

Battery ageing is normal. Physical distortion is not.

A battery should be removed from use if it:

• swells or changes shape;

• becomes unusually hot during normal use or charging;

• gives off an unusual smell;

• leaks;

• has damaged or corroded terminals;

• has been crushed, punctured or seriously dropped;

• repeatedly causes charger errors;

• loses power suddenly and unpredictably.

Lithium-ion battery failures can, in rare circumstances, lead to thermal runaway—a self-heating process that can result from internal short circuits, electrical abuse, mechanical damage or excessive heat.

A swollen camera or tool battery should not be forced back into its compartment. Neither should it be dismantled as a home experiment.

It should be isolated from combustible materials and taken through an appropriate battery recycling or specialist disposal route.

How We Try to Look After Our Batteries

No battery lasts forever, but good management can extend its useful life.

Avoid Unnecessary Heat

Heat accelerates many of the chemical processes that age lithium batteries.

I avoid leaving batteries in direct sunlight, in a hot vehicle or beside equipment producing significant heat. Camera batteries used during long recordings are allowed to cool before being recharged.

The same applies to power-tool batteries. A battery that has just powered a demanding saw or drill may already be warm. Connecting it immediately to a rapid charger may add further heat.

Do Not Store Everything Fully Charged

A full battery is convenient, but leaving a lithium battery at maximum charge for months can increase chemical stress.

For long-term camera battery storage, Canon advises keeping batteries in a cool, dry, ventilated place and aiming for approximately 50% charge rather than a full charge. It also recommends checking and recharging batteries periodically to avoid damaging over-discharge.

That does not mean every working battery must always be stopped at exactly 50%. A battery needed for tomorrow’s recording should be charged sufficiently to do the job.

The distinction is between preparing a battery for immediate use and storing it for several months.

Avoid Charging Very Cold Batteries

Cold conditions can make lithium plating more likely because lithium ions move less readily through the cell.

A battery brought in from a cold shed, boat or vehicle should be allowed to reach a suitable temperature before charging. The manufacturer’s specified charging-temperature range should always take priority.

Remove Batteries from Seldom-Used Equipment

Alkaline cells can leak after long periods, potentially destroying contacts and circuit boards.

Rechargeable batteries can also continue to experience a small drain while left in equipment. Canon warns that leaving a battery in an unused camera for a prolonged period can contribute to over-discharge.

Removing batteries from equipment that will not be used for months can prevent an unpleasant surprise later.

Label and Rotate Battery Packs

With several similar camera batteries, it is easy to use the same two repeatedly while others remain untouched.

Numbering the batteries makes it possible to rotate them and identify a pack that is repeatedly underperforming.

A simple label such as “R5C-1”, “R5C-2” or “Workshop Drill-3” can reveal patterns that would otherwise be missed.

Keep a Battery Register

For a business with many battery systems, a simple battery register is surprisingly useful.

It can record:

• equipment name;

• battery type;

• date purchased;

• charger used;

• approximate number of cycles;

• observed running time;

• storage location;

• faults or unusual behaviour;

• date removed from service;

• recycling or disposal route.

This does not need to become complicated. A small spreadsheet or labelled storage system may be enough.

The aim is to stop batteries becoming anonymous objects scattered between drawers, bags, chargers and equipment cases.

The Environmental Contradiction

Batteries are helping us reduce our environmental impact.

Our house batteries make better use of solar generation. Rechargeable tool batteries reduce our use of disposable cells. Battery garden equipment avoids storing and burning petrol. Batteries allow electric boats and other equipment to be charged using electricity generated at home.

Yet batteries also require raw materials, energy-intensive manufacturing and careful end-of-life treatment.

That creates an important contradiction.

Batteries can support a lower-carbon lifestyle, but they are not environmentally free.

The most sustainable battery is not necessarily the one with the newest chemistry. It may be the battery that is correctly sized, responsibly manufactured, properly maintained, used for many years and then recycled through the right system.

Are Better Batteries Finally Arriving?

Researchers and manufacturers are developing several alternatives to conventional lithium-ion batteries.

Sodium-ion batteries are particularly interesting because sodium is abundant and does not require lithium, nickel or cobalt in the same way as many established battery chemistries. In April 2025, CATL announced its Naxtra sodium-ion battery and described it as the first mass-produced sodium-ion battery of its kind.

That does not mean sodium-ion batteries will immediately replace every camera, drill or household battery.

Different applications have different requirements. Cameras need compact, lightweight batteries with high energy density. Power tools need very high power delivery. Home storage places less emphasis on weight but needs long life, safety and competitive cost.

A technology that works well for stationary energy storage may not be the best choice for a camera.

Solid-state batteries are another promising development. Replacing a conventional liquid electrolyte with a solid material could improve safety and may allow the use of higher-energy electrode materials.

However, solid-state batteries still face manufacturing, interface, pressure, durability and cost challenges. Even solid electrolytes do not automatically eliminate every possibility of dendritic growth.

Toyota and Idemitsu have said they are working towards initial commercialisation of all-solid-state vehicle batteries in 2027–28, followed by larger-scale production. As of August 2026, that target is still in the future rather than evidence of widespread availability in everyday equipment.

Flow batteries, lithium-sulphur systems, lithium-air batteries, improved lithium iron phosphate batteries and several other chemistries are also being developed.

The future will probably not be built around one miraculous replacement for lithium-ion. It is more likely to involve several battery chemistries, each matched to a particular task.

What I Would Like from the Next Generation of Batteries

For cameras, I would like batteries that:

• last considerably longer during video recording;

• create less heat;

• retain their capacity for more years;

• report their true condition accurately;

• use standardised formats rather than a different pack for every device;

• can be repaired or recelled safely;

• use materials with lower environmental and social costs.

For power tools and garden equipment, I would like greater compatibility between products. At present, buying a tool often means buying into another proprietary battery and charger system.

For scientific equipment, replaceable battery modules are preferable to equipment being discarded simply because an internal battery has reached the end of its life. PASCO already provides replacement information and tools for the batteries in several of its products, which is a much better approach than treating the entire instrument as disposable.

For household storage, I would like long-lived batteries designed around repairability, modular replacement and straightforward recycling.

Most of all, I would like battery health to become clearer. Too many batteries appear normal until they suddenly fail.

A Battery-Powered Company Needs a Battery Strategy

Perhaps the greatest lesson is that batteries should not be treated as an afterthought.

They are part of the company’s infrastructure.

Without them, cameras stop recording, tools stop working, sensors stop collecting data and solar electricity cannot be carried so effectively into the night.

A sensible battery strategy therefore means:

1. choosing the correct battery for each task;

2. avoiding unnecessary disposable batteries;

3. buying reliable batteries and chargers;

4. storing batteries appropriately;

5. monitoring ageing and unusual behaviour;

6. replacing damaged batteries before they become hazardous;

7. recycling every battery through the correct route;

8. considering battery compatibility before buying new equipment.

Those actions will not create a perfect battery system, but they can reduce waste, expense, disruption and risk.

Conclusion: The Hidden Infrastructure of Modern Life

My company does not literally run on batteries alone.

It runs on ideas, teaching, practical science, photography, engineering, music, boat projects and the willingness to keep learning.

But batteries make a remarkable amount of that work possible.

They carry solar energy from the afternoon into the night. They allow cameras to record away from the studio. They power tools beside the river, sensors on an experiment and equipment around the garden.

The smallest battery may quietly move the hands of a clock. The largest may help power an entire house.

We often think of batteries as accessories. Increasingly, they are infrastructure.

They deserve to be selected carefully, maintained properly and recycled responsibly.

Better alternatives are arriving—but unevenly and for different applications. Until those technologies become widely available, the best approach is not simply to wait for the perfect battery.

It is to make the batteries we already own last longer, use them intelligently and recognise just how much of modern life now depends upon them.

 

Creating Champagne’s Cover: Measuring and Cutting

Making a new cover for Champagne may look like a straightforward sewing project, but the work that happens before the first stitch is just as important as the sewing itself.

A boat cover has to cope with rain, wind, sunlight, dirt, movement and the awkward shape of the boat beneath it. It must be large enough to fit properly without becoming a loose sheet that fills with water or flaps violently in the wind. It must also allow us to reach the fittings we need, secure the cover quickly and remove it without turning every visit to the boat into a wrestling match.

For Champagne, our Thames A-Rater, the cover also needs to protect a long, narrow and unusually shaped racing boat. This makes the measuring and cutting stage a practical engineering project in its own right.

Before we begin stitching, we need to turn a three-dimensional boat into a collection of accurately shaped, flat fabric panels.

Why Champagne Needs a New Cover

The existing cover has already taught us several useful lessons.

It is tight in places, awkward around some of the fittings and has developed holes where the material has been placed under stress. A temporary tarpaulin can keep off some of the weather, but it is not a satisfactory long-term solution.

A loose tarpaulin can flap, collect water and rub against varnished or painted surfaces. It may also allow wind-driven rain underneath. The purpose of making a fitted cover is not simply to improve the appearance of the boat. It is to provide better and more reliable protection.

A good cover should help to protect:

• the cockpit and internal structure;

• wooden and varnished components;

• ropes and fittings;

• control systems;

• exposed deck surfaces;

• equipment stored inside the boat;

• areas where standing water could cause damage.

The cover also needs to be practical. A beautifully fitted cover is of little value if it takes several people and half an hour to put it on.

Beginning with the Shape of the Boat

Champagne does not have the simple rectangular shape of a trailer, garden table or box.

She is long and narrow, with curved sides, changing deck heights, a cockpit, mast supports and numerous fittings. The cover must rise over the centre of the boat to create a tent-like shape so that rainwater can run away rather than forming pools.

This means that the cover cannot simply be made by measuring the maximum length and width and cutting one large rectangle.

The final shape needs to account for:

• the overall length;

• the maximum beam;

• the narrowing bow and stern;

• the height of the central support;

• the cockpit shape;

• the position of the mast and shrouds;

• cleats, sheets and control lines;

• the gunwale and rubbing areas;

• any projecting fittings;

• the points where the cover will be tied down.

The challenge is to decide where the fabric should follow the shape of the boat and where it should bridge over it.

Creating the Tent Shape

A tent-shaped cover needs one or more raised support points.

Without enough height, the centre of the cover will sag. Rainwater will then collect in the low sections. Even a small depression can become a considerable pool during prolonged rainfall.

Water is heavy. A litre of water has a mass of approximately one kilogram. A pool containing 20 litres of rainwater adds about 20 kilograms of load to the cover and its supporting structure.

That weight can:

• stretch the fabric;

• pull on seams;

• distort the cover;

• damage supports;

• push the material against the deck;

• cause the cover to collapse further and collect even more water.

The centre line therefore needs to be high enough to create a reliable slope towards both sides.

The best shape may not be a perfect symmetrical triangle. The bow and stern have different profiles, and the cockpit may require a higher or wider section. We may need several support positions rather than one continuous ridge.

This is one reason why the cover has to be designed on the boat rather than entirely on a table.

Measuring the Boat Properly

The first stage is to take a full set of reference measurements.

These should include the obvious dimensions, such as length and maximum width, but also measurements at regular intervals along the hull.

For example, we can mark positions along Champagne at intervals of 500 mm or one metre and record:

• the width of the boat;

• the height from the gunwale to the proposed ridge line;

• the distance over the top from one side to the other;

• the shape of the deck beneath the cover;

• the position of important fittings;

• the intended lower edge of the cover.

This creates a series of cross-sections.

Instead of thinking about the boat as one complicated shape, we can think of it as a sequence of smaller shapes that gradually change from bow to stern.

It is similar to taking slices through a three-dimensional object. Each slice gives us information about how the fabric will need to change.

Measuring Over the Shape, Not Through It

One easy mistake is to measure straight-line distances when the fabric actually needs to travel over a curved surface.

For example, the horizontal width of the boat is not necessarily the same as the amount of fabric needed to pass from one side, over the raised ridge, to the other side.

A tape measure can be laid over the proposed shape of the cover. This gives a more realistic measurement of the required fabric length.

We must also decide how far down the sides the cover will extend.

Should it finish just below the gunwale?

Should it cover more of the hull?

Will a deeper cover offer better protection, or will it make the cover harder to fit and more vulnerable to wind?

These decisions change the size and shape of every panel.

Using Temporary Templates

Fabric is expensive, and mistakes made during cutting cannot always be corrected.

Before cutting the final material, it makes sense to create a temporary pattern.

Possible pattern materials include:

• inexpensive plastic sheeting;

• old fabric;

• decorators’ dust sheets;

• paper or card for smaller sections;

• lightweight tarpaulin;

• pattern-making material.

A temporary pattern allows us to test the shape directly on Champagne.

It can be pinned, clipped or taped into place. Excess material can be folded away, while tight sections can be marked and adjusted.

This stage can reveal problems that are difficult to predict from measurements alone.

For example:

• a panel may pull diagonally around a fitting;

• the ridge may be too low;

• the bow section may need a dart or shaped seam;

• the cover may be difficult to remove over a projecting component;

• a tie-down point may sit in the wrong place;

• a seam may lie directly over a sharp or heavily loaded area.

A pattern is not wasted effort. It is a cheap prototype.

Deciding Where the Seams Should Go

The position of the seams is one of the most important design decisions.

Seams are necessary because the fabric roll may not be wide enough to cover the whole boat, and because shaped panels fit better than one large flat sheet. However, every seam is also a potential weak point and a possible route for water.

A seam should ideally:

• follow a logical line in the cover;

• avoid low points where water may collect;

• avoid sharp corners and fittings;

• be easy to sew;

• distribute tension evenly;

• allow the panels to be cut efficiently from the fabric;

• be accessible for future inspection and repair.

A central ridge seam may appear logical, but it would also sit at the highest and most exposed point. Rainwater would run away from it, which is helpful, but the seam may experience considerable tension.

Alternatively, the cover could use a wide central panel with seams positioned partway down the slopes. This might reduce stress along the ridge, but it could introduce more complicated panel shapes.

There is rarely one perfect answer. The design is a compromise between fit, waterproofing, strength, ease of manufacture and efficient use of material.

Planning the Fabric Panels

Once the seam positions are chosen, the cover can be divided into individual panels.

These might include:

• a central top panel;

• port and starboard side panels;

• a shaped bow panel;

• a stern section;

• flaps around the mast or support structure;

• reinforcement patches;

• protective sections around high-wear areas.

Each panel needs to be labelled clearly.

It is surprisingly easy to cut two panels that appear similar but are actually mirror images. Marking “port”, “starboard”, “bow”, “stern”, “inside” and “outside” can prevent confusion later.

Reference marks should also be added to show where panels align.

These are sometimes called registration marks or notches. When two long curved edges are being joined, alignment marks help ensure that the panels are sewn together in the correct position rather than gradually drifting out of alignment.

Remembering the Seam Allowance

The pattern represents the finished shape of the cover, but additional fabric is required wherever two panels will be joined.

This extra material is the seam allowance.

If we cut precisely along the finished seam line without adding an allowance, the completed cover will be smaller than planned.

The amount needed depends on the type of seam and the method of waterproofing. A simple seam may require less material than a folded, overlapping or reinforced seam.

The important point is consistency.

Every pattern piece should show:

• the finished seam line;

• the cutting line;

• the seam allowance;

• the direction of the fabric;

• the location of reinforcement;

• any fold lines or hems.

It is much safer to mark these before cutting rather than trying to remember them afterwards.

Choosing the Direction of the Fabric

Some fabrics behave differently depending on the direction in which they are cut.

They may stretch more across the roll than along it. The surface coating may also have a preferred direction, and printed or woven patterns may need to align.

The direction of greatest strength should normally be considered when positioning the panels.

Long sections of the cover may be under tension from bow to stern, while the tent shape creates tension across the boat. We need to consider both.

Efficient use of the fabric is important, but saving a small amount of material is not worthwhile if it produces a cover that stretches badly or places weak directions across heavily loaded sections.

Where Reinforcement Will Be Needed

A cover rarely wears evenly.

Some areas experience much more stress than others. These high-wear locations should be identified before the main panels are cut.

Likely reinforcement points include:

• the bow;

• the stern;

• the top of the ridge;

• corners;

• tie-down points;

• areas around cleats;

• positions where the cover passes over fittings;

• mast openings;

• places where support poles touch the cover;

• sections that may rub against the gunwale.

Reinforcement does not necessarily mean adding a very thick or rigid patch. A patch that is too stiff can transfer stress to its edges and create a new wear point.

The reinforcement should spread the load gradually.

Rounded patches are often preferable to patches with sharp corners because sharp corners can concentrate stress. The reinforcing material should also be compatible with the main cover fabric.

Tie-Down Points and Wind Loads

The cover has to remain secure in strong winds.

This does not simply mean adding as many ropes as possible. Poorly positioned tie-downs can distort the cover, create deep folds and place excessive stress on individual points.

The tie-down system should hold the cover down while maintaining its intended shape.

Possible approaches include:

• webbing straps;

• reinforced eyelets;

• buckles;

• shock cord;

• rope loops;

• straps passing beneath the hull;

• attachment to suitable trailer or cradle points.

Elastic systems can accommodate movement, but too much elasticity may allow the cover to flap. Rigid straps hold more firmly, but they must not be overtightened.

Every attachment point must be reinforced because a small eyelet in unsupported fabric can tear out surprisingly quickly.

We also need to consider whether the cover will remain on the boat during transport. A cover designed for storage is not automatically suitable as a towing cover. The wind loads during road travel are much greater.

For Champagne, the immediate priority is a secure storage cover rather than assuming it can be used at road speeds.

Planning Around the Mast and Fittings

A boat cover is often complicated by the things that pass through it.

If the mast remains stepped, the cover may need a collar, slit or shaped opening. This area must close sufficiently well to prevent large quantities of rain entering.

Possible solutions include:

• an overlapping flap;

• a zipped opening;

• hook-and-loop fastening;

• a laced section;

• a shaped collar;

• a separate mast boot.

The opening must also be easy to use. There is little benefit in creating a perfectly sealed system that takes twenty minutes to assemble.

The cover may also need to fit around shrouds, forestays, control lines or support frames.

Every opening is another potential wear point, so these areas need careful shaping and reinforcement.

Will the Seams Be Waterproof?

Waterproof fabric does not automatically produce a waterproof cover.

Needles create holes, and seams can allow water to pass through. The type of thread, stitch length and seam construction all affect water resistance.

Possible waterproofing methods include:

• using water-resistant thread;

• folded or overlapping seams;

• seam-sealing tape;

• liquid seam sealer;

• waterproofing compound;

• protective flaps over vulnerable seams.

The cover may not need to be completely watertight in the same way as a dry bag. Some ventilation is desirable because trapped moisture can encourage condensation and mould.

The real goal is controlled protection: keeping most rain out while allowing the boat to breathe.

Ventilation Matters Too

A cover that traps damp air can create its own problems.

Moisture may already be present inside the boat when the cover is fitted. Temperature changes can also produce condensation underneath the fabric.

Ventilation can be created using:

• covered vents;

• raised sections;

• gaps beneath the lower edge;

• breathable fabric;

• vented support caps.

The vents must be positioned so that they do not become easy entry points for rain.

This is another engineering compromise. We want airflow without creating leaks.

Marking and Cutting the Final Material

Once the prototype has been fitted and corrected, the pattern can be transferred to the final cover material.

The fabric should be laid on a large, clean and flat surface. This may be easier said than done when working with panels several metres long.

Before making the first cut, we need to check:

• the orientation of the fabric;

• which side faces outward;

• the position of every panel;

• whether mirror-image panels are correct;

• all seam allowances;

• all hems;

• reinforcement locations;

• fastening positions;

• registration marks;

• the total number of pieces.

A useful rule is to measure twice, inspect once more and cut only when completely satisfied.

Cutting tools also matter. Depending on the material, we might use sharp scissors, a rotary cutter, a hot knife or another suitable tool.

Some synthetic fabrics can fray at the edges. Heat cutting may seal the edge, although it must be done carefully and with suitable ventilation and fire precautions.

Making the Best Use of the Material

Good panel planning can reduce waste considerably.

The pattern pieces should be arranged on the fabric before any cutting begins. Smaller reinforcement patches may fit between larger curved panels.

However, fabric economy should not overrule strength or correct grain direction.

Offcuts should also be saved.

They can be useful for:

• testing stitches;

• adjusting sewing-machine tension;

• practising seam construction;

• testing waterproofing products;

• making reinforcement patches;

• carrying out future repairs.

A few apparently insignificant offcuts may become very valuable once the cover is in use.

Testing Before Sewing the Whole Cover

Before committing to several metres of stitching, it is sensible to make test seams.

The tests should use the actual cover material, thread and reinforcement layers.

We can then examine:

• stitch quality;

• thread tension;

• skipped stitches;

• puckering;

• needle size;

• how easily the material feeds;

• seam strength;

• water resistance;

• the effect of multiple layers.

This may reveal that the original seam design is too bulky or that the sewing machine struggles at reinforced corners.

Finding this out on a test strip is much better than discovering it halfway along the main ridge seam.

What We Have Learned Before Stitching Begins

The main lesson is that sewing is only one part of making a boat cover.

The project combines:

• measurement;

• geometry;

• material science;

• pattern making;

• prototyping;

• load distribution;

• waterproofing;

• practical design;

• risk reduction.

We have also learned that the current cover is a valuable source of information. Its damaged areas show us where the greatest stresses occur. Its awkward sections reveal where more space or a different fastening system is required.

Rather than simply copying the old cover, we can use it as a prototype that has already completed several years of real-world testing.

Accepting That the First Design May Need Adjustment

Even with careful measurements and a full-size pattern, the finished cover may need some modification.

Boats are difficult objects to cover. Fabric moves, stretches and behaves differently once several long panels are joined together.

The sensible aim is not absolute perfection on the first attempt. It is to create a cover that is strong, practical, repairable and significantly better than the existing solution.

We can also design the cover with future alteration in mind.

For example, extra allowance in selected areas can make it easier to adjust the fit. Replaceable reinforcement pads can be added at rubbing points. Straps can be repositioned if the original tie-down system proves unsuitable.

A Practical Engineering Project

Creating Champagne’s cover is another example of how owning and restoring an older racing boat involves a wide range of skills.

The project begins with a simple requirement: keep the boat dry and protected.

That requirement quickly develops into questions about geometry, forces, materials, weather, water flow, abrasion, stitching and ease of use.

It is a reminder that practical engineering is rarely about solving one isolated problem. Every decision affects something else.

A tighter cover may flap less but be harder to fit.

A deeper cover may protect more of the hull but catch more wind.

A heavily reinforced patch may resist wear but create stiffness.

A completely sealed cover may exclude rain but trap condensation.

The best design will balance all these competing needs.

Conclusion: The Cut Determines the Cover

Once the fabric has been cut, many of the major decisions have already been made.

The fit, seam positions, reinforcement areas and overall shape are largely determined before the sewing machine begins its work.

That is why measuring and cutting deserve time and care.

For Champagne, this stage is about more than producing pieces of fabric. It is about understanding the shape of the boat, predicting where the cover will be stressed and learning from the weaknesses of the old design.

The next stage will be to turn the individual panels into a complete cover through careful stitching, reinforcement and fitting.

For now, the challenge is to make every measurement, mark and cut count.

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