Section 1 Description and appraisal of the Thames sailing barge

 

Contents

 

Introduction

 

The basic principles of sailing

 

Sailing and sails

 

The sailing rigs used on the Thames sailing barge

 

The standing rigging

 

The mizzen sail

 

The sails

 

The sprit and the mainsail

 

The foresail

 

The secondary rig

 

So how good is the rig on a Thames barge?

 

The hull of a sailing barge

 

The rudder

 

Leeway

 

The small mizzen sail

 

The fore-sail

 

Summing up

 

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Introduction

Before decisions can be taken about modelling a Thames sailing barge we ought really to know how a barge actually works. To this end I have prepared this introductory section.

 

The Thames sailing barge seems to me to be the end product of a long period of engineering by cut and try methods. This is not a criticism because no other method was available. I do not suppose that all the people who designed and built barges could read or write but that did not stop them from finding out how to make a working boat that was extraordinarily successful. No doubt the Thames sailing barge evolved from many forerunners but it seems to me that the unique conditions that led to the Thames sailing barge were the size of the Thames (as distinct from most other rivers in Britain) and the mainly sand, mud and gravel beaches right round the South East coast. The beaches and river-banks permitted the use of a flat-bottomed hull that could be beached almost anywhere without rocks breaking through the hull. The size of the river permitted the widespread use of a barge that was large enough to be more easily driven than the smaller barges used on smaller rivers.

 

Given these two factors we must now recognise that Thames sailing barges were working boats that were designed to be robust, to be cheaply made, and to be capable of operation by a minimum of crew. The two designs that emerged filled these criteria very well indeed and could be sailed quite well even in the hands of the skippers of any ability. They were the sprit-sailed barge in figure 1 with a staysail and no bowsprit and the sprit-sailed barge with a bowsprit and no staysail shown in figure 2.

 

The designs evolved in the nineteenth century in yards that were primitive by any standard and the principal building materials were wood, mostly locally felled, iron that would have been smithed on site to work it, cast iron and sails and ropes from natural fibres. Some items were bought in like the winches and windlasses and the ship’s boat but in the main the yard made most of the barge in house.

 

There are books on the construction of barges that are more informative than I can ever be. Here I am interested in understanding the Thames sailing barge so that it can be modelled to a scale of 1/24 as a working model.

 

We need to understand how the Thames sailing-barge actually sailed if we are to make a successful model of it. We shall see that the Thames sailing barge turns out to confound the usual intractability of mechanical things. Let me start with an explanation of sails and how they work.

 

The basic principles of sailing

Sailing boats rely on energy extracted by the sails from the wind to make progress. Sails usually work in sets, i.e. rigs, although there are useful working boats and racing boats using just one sail. The rig of sails interacts with the wind to produce a net force that will have a useful component in the direction of the course of the boat and a component, that is not wanted but is unavoidable, that acts across the boat. The first component drives the boat and is resisted by the drag on the hull due to skin friction and wave making. The second makes the boat heel and move sideways. The resistance to the sideways force is provided either by the hull or by a keel or both. Any boat can be analysed to see how these forces are produced. We need to analyse the Thames sailing barge and in order to do so we need to know how sails actually work.

 

Sailing and sails

We expect any vehicle we build to be able to go in any direction that we choose. This is quite possible for cars and aeroplanes and powered boats but, whilst sailing boats can proceed upwind, they do so with varying degrees of difficulty. Sailing boats used to be designed for transport either of goods or people and their designs were compromises between the requirements imposed by their working function and the requirements of an efficient sailing rig. Sailing boats that have been designed solely for speed with no payload and only the minimum of creature comfort have appeared only relatively recently. We are here concerned with the working boat.

 

Whilst it is true that most sailing boats can go in any direction it is not just a matter of being able to sail directly upwind. Boats must tack repeatedly and follow a zigzag course into the wind. They can sail down wind (run) and across wind (reach) easily and refinement of sail shapes does not have great affect on boat speed unless the boat is a racing boat. The real problem for all sailing boats is sailing upwind (beating). This can be seen by contrasting the square-rigged ship with a modern racing yacht. A square-rigger, for example Nelson’s Victory in favourable conditions might have been able to make 18° upwind, that is 72° to the true wind, but a modern racing yacht can make about 35° to the true wind. Figure 3 shows the difference between these two levels of performance. The square-rigger had to beat for 100 miles to make 32 miles of progress against the wind; the modern yacht can make 82 miles upwind if it beats for 100 miles. Clearly it is important to get any sailing boat, whatever its rig, to beat as close to the wind as is possible in order to make better progress upwind. The sailing barge is no exception and when we look at its rig we must look to see how well it can beat upwind and not be so concerned about how it runs and reaches.

 

First we must look and see just what has changed to produce this extraordinary improvement in the performance of sailing boats and to see where the sailing barge fits into the development of sailing rigs. The two most obvious changes are the change from square-rigged sails to pairs of triangular sails working together as in the ubiquitous Bermuda rig and the elimination of every piece of rigging that is not essential in order to reduce the drag on the sailing rig. This latter change is crucial. Just look at the rigging in photos of Cutty Sark as it used to stand at Greenwich. If, for such a boat, the wind were to be so strong that no sails could be set to control the course of the boat the drag produced by the wind on the vast array of spars and cordage would drive the boat quite quickly but only more or less downwind. (and I understand that such a boat could be tacked). Hence the lee shore problem. The drag on this cordage does not disappear when sails are set, it just reduces the performance of the rig. The sailing barge has a significant array of spars and cordage and sails are normally stowed aloft so it has a drag problem.

 

Now we need some understanding of the way that sails work and the focus of our attention must be on beating.

 

Some claim that sails are really aerofoils but that seems to me to ignore the fact that aerofoils are rigid and have thickness whereas sails are floppy and comprise one thickness. Furthermore aerofoils do not work in a stalled condition like sails that are always stalled. We can see that this is the case by calling on our experience.

 

It is convenient to use the term “angle of attack” borrowing it from aerodynamics. In aerodynamics it is the angle that an aerofoil makes to the direction of flight or, if it is an aerofoil in a wind tunnel, to the centre line of the tunnel. In figure 4 I have shown the angle of attack when it is used for a sail and it is between the direction of the undisturbed wind and the line joining luff to leech which is called the chord line. When our barge is sailing with all sails filled every sail must make an angle of attack (though not necessarily the same angle of attack) to the relative wind. The angle is quite large simply because it has to be big enough in the first place just to fill the sails. Let us stop just to consider what happens when a sailing boat goes “into irons”.

A boat may be sailing into the wind as close to the wind as it can and an attempt made to change tack by turning the head through the wind[1]. If the boat has too little way on it, it will stop turning and come to rest with the sails just flapping in the wind. The boat is in irons. The way to get out of irons is to centre the rudder and wait. The boat will fall off the wind one way or the other and, eventually, the sails will be seen to fill and start to drive the boat again. We can, by doing the same thing on the other tack, gauge the angle to the wind at which the sails first fill[2]. It is certainly greater than 20°(refer to figure 5 to get a mental picture of 20°). The very best aerofoils stall at about 16° and others at less than 12° so our rather primitive sails, that must operate at angles considerably greater than 20°, are always stalled when they are working.

 

We need to make an attempt to put a size to the angle of attack of the mainsail of a Thames barge. The Thames sailing barge can make quite respectable progress against the wind but the nearest it can point to the wind is between 50° and 60° to the true wind. From this we can make a stab at the angle of attack for beating. I have drawn the diagram for a barge beating at 6 mph at 55° to the true wind of 15 mph. The relative wind then makes 15° to the true wind. The boat will be skewed to its course and I have let this angle be 7°. This means that the relative wind blows across the barge at 33°. The barge is beating so the mainsail at least will be sheeted in fairly close to the centreline of the barge at perhaps 10° and of course to leewards. The smallest angle of attack is 33° minus the angle the sail makes to the hull. As this angle is about 10° the sails will be working at an angle of much more than 20° and inevitably they are stalled with the flow eddying on the leeward side. As a result these sails are not very efficient. But they are very tractable, they do not respond violently to veering or backing of the wind as an aerofoil would, and we get the drive for nothing. I do not think that sails should be regarded as second best to aerofoils. (See my section on the wing-sailed yacht.)

 

Now that we know the angle of attack we can go on to see how two sails working together permit a boat to beat up close to the wind. Let me start by explaining the flow over the two sails by looking at the mainsail first. Figure 7 shows the flow pattern over a mainsail without a foresail. It is not guesswork but comes from pictures of smoke trails over aerofoils in a wind tunnel. The sail is operating at a high angle of attack just as it would on a barge. The direction of the wind is shown as the direction of the undisturbed flow. The obvious feature is the complete breakdown of the orderly flow on the leeward side of the sail. The air in the dotted space is just eddying in a random way just as water does behind a bridge pier with a general tendency to circulate forwards towards the mast over the surface of the sail and then, after turning, to flow from the mast along the line of mixing. There are very few examples of wings being used practically in this stalled condition yet it is normal for sails. When it comes to working two sails together the important feature of this flow is the behaviour of the wind as it approaches the sail. Some imagine that air just carries on in straight lines until the sail cuts it like butter but this is a long way from the truth, indeed the behaviour of sails cannot be explained at all along these lines. We can start by noting that the air ahead of the sail will obviously have to split, some to go over the leeward side of the sail and some to go over the windward side. Then, as the diagram shows, most of the air that is affected by the sail is actually diverted to leewards ahead of the sail, even the air that will eventually flow over the windward side. The air that flows over the leeward side converges with a drop in pressure that is greatest just above the mast. The air that flows over the windward side of the sail diverges as it curves upwards to increase in pressure. This air then converges as it passes the leech.

 

There is no reason at all why a single sail like this one should not be used to drive a boat, for example a wherry, but such a sail will not beat as close to the wind as a mainsail and a foresail working together. The reason for this is inherent in the flow pattern round the single sail. We have to look in the diagram at the region of flow a little forward of the mast and to leeward that I have shown shaded in figure 8. Any sail set in this region works in a wind that has been diverted upwards by several degrees, and, whilst such a sail will still work at a high angle of attack and be stalled, the force produced by the sail acts forwards by those several degrees to be more effective in driving the boat. This is the key to understanding how two or more sails can combine to improve the performance of a rig when it is beating and so let it sail closer to the wind. Races are often won on the ability to point closer to the wind. As the boat changes from beating to running the angles of the sails to the centreline of the hull increase and the interaction between the sails becomes much less and eventually they become independent.

 

In figure 9 an appropriate position for the foresail is shown on the first flow pattern. Now we must see what the presence of this sail does to the flow pattern. The combination is shown in figure 10. It is evident that the flows over the two sails are quite similar and the main effect on the mainsail is to perhaps reduce the pressure a little more in the region of the mast. The flow from the foresail now mixes with that over the mainsail but the patterns round the two sails are fairly similar. We end up with two diffuse, eddying wakes that will join at some point downstream. The overall effect is that the foresail works in the diverted flow ahead of the mainsail and the force that it produces is at a better angle to drive the boat. When the boat is beating as close as it can to the wind it is unlikely that the mainsail is making any contribution to driving the boat but it is diverting the flow so that the foresail can produce drive that would not be possible if the foresail were to be so far ahead of the mainsail as to be unaffected by it.

 

As the sails are sheeted out in response to a change in the course relative to the wind so that the boat first reaches across the wind and then swings towards the run they get further apart and interact much less. Then both sails make much the same angle to the wind and both drive the boat.

 

This is the underlying principle of the Bermuda rig. Where there are two or more jibs attached to a bowsprit, each jib is set at a slightly greater angle to the one behind it and the leading one is at a very useful angle to the ship. Once all this is understood it becomes easy to see how the sails of a three-masted clipper ship are set. On a barge where there will be jibs as well as a foresail they must all be made to work when the barge is beating.

 

We must now look at our sailing barge and try to see how the sails work.

 

The sailing rigs used on the Thames sailing barge

The sailing rigs have to work in two environments. The first and obvious one is in the open river and perhaps round the coasts and second is in the confined waters of docks. As the docks grew the buildings that were erected interfered with the wind and only sails mounted high up could catch the wind. We must expect to find tall rigs on our spritsail barges.

 

As far as I can tell only two basic designs reached general acceptance, the spritsail rig with its two variations both used for river and inshore coastal work and the boom-sail rig that developed for the North Sea and was then used for longer sea passages.

 

The two versions of the sprit-sail barge are easily distinguished because one has a bow sprit. This leads to two different sailing rigs.

 

Let me start with the spritsail rig with a staysail. Figure 11 is a picture taken of the sailing barge May before she was fitted with a bowsprit again when she would probably have had no staysail and a jib sail as well as the foresail. In this version she has five sails. The mizzen sail is not an essential part of the sailing rig but was fitted in the days before auxiliary engines to assist the rudder during a tack and to give a measure of self-steering. That leaves the other four. The big one on the mast is the mainsail, the one above it is the main-topsail. Forward of the mast there are two sails, the lower one is the foresail and the upper one is the staysail. The rig is tall.

 

All the sails are made from sailcloth with their edges sewn to ropes called bolt-ropes. Without these bolt-ropes the sails would take on all sorts of unwanted shapes simply because the sailcloth has ordinary warp and weft construction which offers little resistance to diagonal forces.

 

The mainsail is propped at the top outer corner on a massive[3] spar called the sprit. It is easily seen in the picture. The luff of the mainsail (the front edge against the mast) is attached to the mast using a jackstay and shackles and the clew (the lower outer corner) is tethered to a horse (a curved rail running right across the deck) by a system of rope and pulleys so that it can be adjusted. The sail is said to be loose footed and this can be understood from the absence of boom to which the sail is lashed over the whole length of its foot.

 

The main topsail is attached to the topmast also with hoops, and lashed to a short spar at the masthead called the headstick and its clew is attached to the top of the sprit.

 

The picture shows clearly that the foresail is attached by links (hanked) to the forestay, which is a very stout wire that runs from the stem to the top of the mainmast. The foresail clew goes to a ring on the fore-horse and a short loop of chain.

 

The luff of the staysail is attached by rings to the stay that supports the topmast. Its clew is tethered to cleats on the bulwarks.

 

I do not know the history of this rig but there are some constraints that seriously affected what was possible and may well have dictated the evolution.

 

A barge carried most of the cargo in a hold under the mainsail. Loading and unloading was made easier by using the sprit as the jib of a crane with a block and tackle roped to it. Of course the mainsail was lashed to it (brailed up) out of the way. This dual use of the sprit is a powerful incentive to retain it whatever disadvantages there may be elsewhere.[4]

 

For commercial reasons the Thames sailing barge had to be capable of getting under low bridges. To this end the whole rig has to be lowered. This was done by hinging the mast at its foot and then lowering it towards the transom under the control of a very substantial multi-rope pulley system, the falls, in the forestay.[5]

 

A spritsail barge was normally worked by a crew of two with perhaps a boy so the rig had to be simple to hoist and set and be such that the men were capable of actually raising and lowering the sails and rig without any auxiliary power.[6]

 

Now we must try to understand how this rig was actually worked so that we can decide what is important when we try to model it. It looks to me to be two rigs, one, the primary rig, comprising the mainsail and the foresail and the other, the secondary rig, is the main topsail and the staysail. In figure 12 I have drawn a line across the rig of the May to separate the two rigs.

 

The lower rig that I have called the primary rig looks exactly like what used to be called a stumpie rig. The stumpie rig was much used by the Admiralty on small boats that worked between the docks and boats at anchor. It is a handy rig that works well and is low down which makes it suitable for heavy weather. I suppose that, on the admiralty boats, this was really a Bermuda rig and the two sails worked together. On the sprit sail barge this is not the case. It was so important to make tacks with confidence with a small crew that the fore-sail was attached to the fore-horse by a loose chain and set in only two positions at the two ends of the horse one to port and one to starboard. During a tack the fore-sail clew was lashed to a halyard on the lee side and held there during the tack when it would become the first sail to fill to drive the head round. Then the fore-sail clew was released and the sail swung across the deck to its new position on the opposite tack. Fortunately, or by design, this corresponds to a good setting for beating. It is deficient when reaching and running. I think that it is likely that the bowsprit barge was developed to get over this constraint.

 

Above the line we can see the two upper sails that form the secondary rig. This looks like another pair of sails that can work together and here both are filled and pulling with the staysail at the greater angle. It is like a Burmuda rig and the staysail has been made to work because, when the barge is beating, the staysail is potentially more powerful than the topsail. This is also the part of the rig that might be used in confined waters.

 

So how shall we look at the staysail rig? If we look at the whole rig comprising four sails, except for the restriction on the fore-sail, we might view it as a form of Bermuda rig with the equivalent of the mainsail being in two parts and the equivalent of the jib being in two parts. We might also view it as two rigs to be used as one for light weather or to have its topsails removed for heavy weather. We might even see the top rig as the one to set in really light weather when the drag of the heavy drooping mainsail is too great and yet the wind too light to fill the heavy sail. Then the lighter topsails might be best.[7]

 

Now we must look at this rig from the side so that we can see the proportions. In figure 13 I have included a picture of Marjorie taken at Maldon in 1999. This picture shows the sails stowed. The mainsail is brailed up to the mast, the main topsail has been lowered to the foot of the topmast, allowed to hang, and lashed. The foresail has been twisted like an umbrella and tied to the horse and the white staysail has been stowed in a similar way. What is left for us to see is the standing rigging outlining the spaces in which the four sails must operate. It also shows the relative sizes of the primary rig and the secondary rig. Give or take a bit the point of action of the drive produced by the secondary sails is more than twice as high up as the point of action of the force of on the primary sails. In a wind they would have a very large upsetting moment compared with that from the primary rig and they would be taken in. The staysail has an area about equal to that of the foresail and topsail has an area about 2/3 of that of the mainsail. The topsails are a significant portion of the rig and not just an extra.

 

This picture also shows us what seems to me to be a weakness in the sailing rig of the Thames sailing barge. If we look more carefully at the topmast it is clear that it is quite slender and not stiff enough to carry sail in heavy weather and further that, whilst there are two running backstays going from the bulwarks to the head of the topmast, these stays make too small an angle to be effective. (The topmast appears to bend forwards although this is not always the case.) Somehow it must be stayed when it is in use.

 

The bowsprit barge has the same arrangement of mainmast and forestay as on the staysail barge but of course it has a bowsprit. This makes a significant change to the triangles into which sails might be fitted.

 

In figure 14 the topmast forestay now goes to the end of the bowsprit instead of the stem and a new top forestay has been added. This creates two new triangles that might be used for sails. From our knowledge of how sails work it seems that the fitting of a staysail is unlikely to be effective because the staysail is too far in front of the topsail to be in the curved flow ahead of it. Instead it is used to set a spinnaker for running before the wind. The “triangle” between the two forestays does let us fit a jib that is in the flow that has been diverted by both the foresail and the mainsail acting together even though the fore-sail is not at its best angle. The jib will have a greater angle than the foresail and, as this turns the force it produces even further towards the bow, it will be a very useful sail when going to windward and for reaching and it can be trimmed for beating. This sail must have justified the extra complexity of the bow-sprit which might have been fixed or arranged to be lifted inboard when alongside a wharf.

 

This rig takes us away from the standard Bermuda rig by working an extra jib in front of the foresail. Other sailing rigs including the boom sail barge often used two extra jibs. Potentially the bowsprit barge is a better sailer than a staysail barge.

 

The standing rigging

We have seen the standing rigging on the Marjorie. It is important for us to understand this rigging and how it permits the sails to function properly. Let me construct the rigging bit by bit.

 

The starting point is the pulpit or mast box fixed to the deck. The pulpit is just an open sided box made in cast iron as shown in figure 15. The foot of the mast is squared to fit into the pulpit and the foot is radiused so that the mast can be lowered.

 

Now let us look at the arrangement, shown diagrammatically in figure 16, that holds the primary rig. The essential elements are the mast that is hinged in the pulpit, the forestay and the sprit. The sprit is mounted on the mainmast at the foot as in figure 17 using a muzzle, which is a short chain attached to a collar and is supported from the top of the mainmast by a rope or wire called the stanliff. A second rope called the yard tackle from the top

of the main-mast goes to the middle of the sprit to control the angle of the sprit. The forestay has a pulley system called the falls shown in figure 18 that permits the raising and lowering of the rig.

 

The sprit supports the top corner of the mainsail. The luff of the mainsail is hanked to a jackstay behind the mainmast and the clew (the bottom of the leech) is roped through a system of pulleys to a ring on a horse. The foresail is attached by hanking to the forestay at its luff with a halyard and a downhaul to tension it. The clew is attached to a horse by a loop of chain.

 

Clearly this arrangement is unstable from side to side and must have stays. As the whole rig has to be lowered to aft the stays can only go in line with or behind the mast.

 

The first addition is the set of six shrouds that are attached to the mast at the joint with the topmast and through deadeyes and halyards to the bulwarks and, by straps, to the gunwales as shown in figure 20. The shrouds are looped round the mast as in figure 21 and have ratlines on the starboard side to form a ladder to give access to the top of the mast for stowing the sails. See figure 22

The mast has to withstand most of the force produced by all of the sails to drive the barge as well as the sideways force. The only means of stopping the mast from leaning forwards is the weight of the sprit and of the mainsail. The shrouds are in the right position to resist the sideways force but more shrouds attached further aft would impede the sail as it swings out for running before the wind. This presents something of a problem because the weight of the sprit and sail may not be enough in a blow. The solution that is adopted is to use one of two running backstays, the one on the windward side, as shown in figure 23.

 

The running backstay is hooked to a fixing on the gunwale on the windward side. The other running backstay is made off to a suitable point to keep it under control.

 

The outcome of all this is a quite simple structure that can support the two sails and withstand the forces exerted by the sails of the primary rig on it.

 

However the sprit can swing around the mast like the jib of a crane but, so far, we have nothing to limit its travel. Two vangs are fitted for this purpose. They go between the top of the sprit and fixing points on the gunwale or deck as in figure 24 and the photo in figure 25. The vangs can be seen at the top right hand corner.

 

The sprit and its two vangs which are just ropes are shown in mid position in full lines. The angle between the vangs at the top of the sprit is very small and the force in the vangs would be very large if an attempt were to be made to hold the mainsail in this position. But the sail is not needed to be on centre and the vangs are used by extending the windward one to let the sprit slew and letting the other go loose. The mechanics become more practical as the angles increase. Of course, whilst this lets the sprit swing round the mast, the shape of the sail will be determined by the length of the rope going to the horse and the angle of the sprit.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

These are all the parts that go to operate the primary rig. We should note that there is a significant weight being supported jointly by the topping lift and the wire rope that goes through the head of the main-sail. The weight is that of the sail, the sprit itself and any downwards force in the vang. As a result the top of the sprit is so difficult to lift that it can be treated as a fixed point swinging round the mast and a very suitable point to attach the topsail.

 

Now for the secondary rig. It obviously goes on to the extension to the lower structure. To this point the mast has been shown as having two parts, the stout mainmast and the more slender topmast. They are joined with an overlap called the doubling. If we are to set up a second rig above the first using this topmast we must start by staying the topmast. Whilst a pair of simple stays may be thought to be adequate in fact, two spreaders are fitted as well, as shown in figure 26. The stays are called the standing backstays. A second forestay is fitted to the top of the topmast going down to the stem head again.

 

This is all that is done to support the topmast as part of the standing rigging. It is clearly not stayed to resist a forward force.

 

Now we have to add the secondary rig to the barge. We have seen the arrangement of the sprit-sailed barge in the first diagram. There the top edge of the topsail is attached to the headstick that can be hoisted using a halyard going to the head of the top- mast. Its clew is attached to the top of the sprit. If that headstick is hauled up, tension will be applied to the bolt-rope in the leech of the topsail and to the luff[8]. However it will only work if the headstick makes a sensible angle, say 20° to the topmast. The tension in the head rope will easily be resisted by the weight on the sprit and it will tighten the top forestay. The top forestay must be in tension if the staysail is to set properly so it appears that the tension in the forestay is provided at least in part by the tension in the rope to the headstick of the topsail. Clearly the topsail and the top forestay provide some stability to the topmast. In a way the undesirable weight aloft in the sail and the sprit has been put to good use.

 

There is another way of stabilising the topmast. Jock had (It has been broken up.) an extra running backstay (see photo) that goes from the head of the topmast to a point on the gunwales abreast of the aft end on the main hatch. Whilst this can stabilise the topmast it is not as practical a solution as one might have hoped to find because only the windward stay can be in position because the sail has to swing out to leeward. At least it is pulling in the right direction. It is yet another stay to be attached niftily during a change of tack which is a good reason for wanting to avoid fitting it. The presence of this extra running backstay indicates that the lack of a fixed stay for the topmast to aft was an inherent weakness in the rig that required the constant attention of the crew.

The mizzen sail

As I have said the fore-sail was restricted as part of the primary sailing rig to let it be used during tacking. The mizzen sail was used, amongst other jobs, to aid tacking as well. I wrote up the mizzen separately for another purpose. I have added it in its entirety as Appendix 1

 

The sails

The sails were made from sailcloth and more recently from man-made fibres dyed to the correct colour. The practical design probably goes back centuries. The basic problem that confronts sail makers is that cloth made from woven thread is very weak on the slant. In order to see the difficulty just try pulling your handkerchief between adjacent corners and then between opposite corners. As we have seen the desirable shapes of sails is not a simple square but a triangle or a quadrilateral. As the fixing points for the sails of a Thames sailing barge are the corners, except for the luff adjacent to a mast, some means of imposing a shape on the sailcloth is required. The bolt-rope is used for this purpose. Sailcloth was made in bolts of about 40 yards in length but only about 24² wide. It had to be joined to make sails. The seams were made between selvedges where the weft (the thread that runs transversely and is carried by the shuttle during weaving) returns at the edge. The seams were quite stiff and imposed some stiffness on the large area of cloth in the sail.

 

I have drawn a sketch of the main-sail in figure 24. The bolt-rope goes right round the sail with cringles (eyes) fitted at the corners. The seams run parallel to the leech of the sail presumably because this was found to be the best option.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The bolt-rope should be seen as a part of the standing rigging and everywhere under tension. Then the sail has slightly curved edges and the sail maker will vary the way in which it is sewn on so that the sail will have whatever is seen to be the best shape when it is set and filled by the wind. The bolt-rope is sewn to the edge of the sail not in the middle of the turning. If the sail is not to slip along the bolt-rope the thread used for sewing must go over each strand in turn as shown in figures 29 and 30. Figure 29 is of the bolt-rope near to the cringle where it was doubled for strength and may well be the joint and figure 30 is of the transition to the normal rope.

 

Figure 31 shows the common ways of joining lengths of cloth to make sails.[9] The stay sails and jib sails are always made in two panels because they have to curve in two directions. The critical joint is the middle one between two edges that are both very slightly curved.

 

For the record the bolt rope is always sewn on to the port side of the sail supposedly so that they could be sorted out when setting them at night.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The sprit and the mainsail

I have said that the sprit is very heavy. It is either a wooden spar or a steel tube. We have seen that it has to be held up on the rig and arranged so that it can swing, under control, round the mast and support the mainsail. The amount of swing is controlled by the vangs. As I have pointed out the angles made by these vangs are quite small by engineering standards. (eg one would use larger angles to stay a radio mast.) This means that attention must be paid to the movement of the sprit during a change of tack.

 

There can be no doubt that sails seem to work best when they are curved (cambered) from luff to leech over the whole length of the sail. They also seem to require some twist but it is hard to know how much. For the mainsail to have a progressive twist the sprit and the clew must be in the correct relative positions. This means that the position of the sprit and of the clew must both be adjusted during sail changes. The sail control arrangements on the Thames barge do not seem to be suited to letting the mainsail right out for running before the wind. They are more suited to sailing down wind as distinct from running.

 

The vangs can control the position of the head of the mainsail. The clew position must be adjusted by altering the distance between the clew and the horse and we need to look more carefully at the horse.

 

The horse seems to be a simple mechanism involving a curved pole fixed across the deck between the bulwarks and a ring called the traveller sliding along it.

 

In practice the clew and the traveller are not joined by a single rope. The mainsail is too big a sail to be controlled by a single rope and a multi-pulley system is required to give sufficient advantage to be able to pull the sail in or indeed to let it out. Usually barges used one rope over a three pulley block as shown in figure 32. The block at the traveller has a pin through it and the rope is made off using this pin as shown in figure 33 because the block needs to be unhooked from the ring when the sail is brailed up. This arrangement of three separate connections to the luff of the mainsail must have given the skipper some control over the shape of the sail beyond that which is possible with a single connection to the clew. No doubt a skilful skipper would have found out how to adjust this rope to get the best out of his sail. In the absence of a restraint the traveller appears to have only two fixed points and they are at either end of the horse. I do not know whether the traveller was allowed to run its full travel and only the sheet adjusted but we only need to know the arrangement to the point where we can adapt it to suit remote control. Certainly restricting the travel of the traveller gives potential for improvement of the set of the sail especially when beating.

 

The foresail

On the spritsail barge the luff of the foresail is hanked to the forestay. The clew is attached to the traveller using a short loop of chain. We have seen that there is advantage if foresail can be set in the proper position relative to the mainsail if it is to drive the barge when it is beating but this is over-ridden by the need to ensure that the barge will tack through head to wind as I have already noted.

 

I am sure that skippers of sailing barges knew all about striking a balance between getting the utmost from the rig by making lots of adjustments and managing the rig with just a crew of two.

 

The secondary rig

It is easy to see where the two sails of the secondary rig fit into the standing rigging.

 

The main topsail can be regarded as a continuation upwards of the mainsail. The fact that it is attached to the topmast by mast rings with an uphaul and downhaul means that the set of the sail depends on how it is cut and on the position of the top of the sprit. It is a sail that appears to need no continual adjustment provided that its shape blends with the mainsail as an extension.

 

The staysail is clearly not an extension of the foresail. It is a separate sail and just as the foresail works in the air that bends to leewards to flow over the mainsail the staysail works in the air that bends to leewards to flow over the main topsail. The shape of the staysail is determined by the cut of the sail, whatever curvature there may be in the top forestay, and by the position of the clew as set by the adjustment of two ropes that pass over the forestay and are made fast to suitable cleats inside the rail. If the top forestay goes slack the shape of the staysail changes and probably suffers a reduction in its drive.

This is the problem that seemed to be so evident in our models.

 

I have shown the arrangement of the staysail in figure 34 but it is figure 35 that shows how the sail is set. The two sheets are made off to the windward and leeward gunwales and the fact that the windward one rests on the forestay separates the effects of the two sheets to give excellent control of the position of the clew. In effect the windward one sets the angle of the sail and the leeward one sets the camber.

 

 

 

 

 

 

 

 

 

So how good is the rig on a Thames barge?

I do not think that anyone would claim that the arrangements fitted to the barge to set the sails is as good as it might be if there were to be a crew of five or more to man it. Nor would anyone claim that the use of horses is ideal. If it were to be all racing yachts would have them. The main and unavoidable problem is the high drag from the spars and cordage. This drag has to be overcome by the sails before the barge can move forwards at all. The result is that when the barge is beating the mainsail and the foresail are sheeted out more than they would be on a racing yacht and the barge cannot get so close to the wind. Nevertheless we are looking at a design that is forgiving whilst having a very acceptable performance. My guess is that the barge can probably beat at about 50° to 55° to the wind and that the mainsail would be set at something less than 10° to the centre line of the barge when beating. It is a rig that has a proper place in history and it is hard to see any way that it could have developed any more and still do the job for which it was built.

 

The hull of a sailing barge

Everybody who takes an interest in boats will eventually run across Froude’s ideas about wave-making and its contribution to the resistance to motion of a boat. He observed that as the speed of an ordinary displacement boat, such as a barge, increases, the resistance first increases slowly with speed and then the resistance rises very rapidly. We can see this in the graph which is for one particular hull. Froude also noted that as this region of high resistance to motion is approached a big wave forms in front of the hull together with a large wave that is shed sideways. Froude found that the wave was usually fully formed when the boat reached a critical speed that can be related to the square root of the length of the boat. On the diagram I have included the critical speed calculated from the length. We can also plot a graph of the way in which this critical speed varies with length.

 

I have drawn this graph for hulls up to 300 feet in length and it is evident that a barge that is typically 80 to 100 feet in length has a critical speed of 15 mph that is over a half of the 27 mph for the 300 foot boat ie for a boat that is three times as long as the barge. Now displacement boats do not move at these critical speeds. The larger powered vessels go at the speed that makes the best economic balance between the cost of fuel and the journey time. Typically this is about 20 mph. The barge goes as fast as it safely can and in a typical wind of 15 mph this speed will be about 6 to 8 mph. In sheltered waters and higher winds they will do better still. Smaller boats do relatively badly when compared with a barge.

 

Once more the Thames sailing barge seems to have hit the happy medium. There is little to be gained by becoming longer and a lot to be lost by getting smaller[10].

 

The design of the hull of a barge is a compromise. The barge is designed to carry a load and, for this, the best shape is the shape of a shoe box. In order to make the barge easy to drive it should have fine bows and to make the most effective rudder it should have fine lines aft. The combination of a box and the fine bow and the fine stern would give a long hull. Unfortunately the cost of wharfage increases with length and so the practical design must have bluff bows and the run aft must be as short as is effective. This shape is typical of working, as distinct from racing, barges. It is a good compromise.

 

Now it is quite remarkable that this simple hull could be sailed in quite difficult sea conditions without either a load or any ballast. Not many hull shapes can do this and ballast was an expensive commodity to get and often difficult to discard. This cannot have been the result of scientific design so we are left with another advantageous facet of the barge that came about by good luck. The barge turned out to increase its ability to carry sail in proportion to the load that it was carrying. As the power required to drive the barge increases with the weight of the barge the ability to carry sail increases in just the way that is required. There is no need to overpower a barge whatever its load.

 

The rudder

Contrary to intuition, a force acting towards the centre of the turn is required to produce a change in course. The rudder clearly produces a force acting outwards so the inward force must come from the hull or the sails. The offset of the rudder upsets the flow over the whole hull, produces leeway, and so causes the hull to produce an inward force.

 

It seems to me that the rudders fitted to sailing vessels were much too small to be the sole or perhaps even the primary means of steering. Trimming the sails seems to have been the main way of setting a course with the rudder used continuously to correct the veering caused by the cyclic fluctuation in the direction of the wind. This would let the ship move most easily[11] in response to wind and waves. Even with so few in the crew, barges could be made to sail easily in the open sea but they were known to be difficult to handle in confined waters so they could not have been very responsive to rudder action and sail trimming could not have been a very speedy process.

 

As the Thames sailing barge was for working off beaches and riverbanks its rudder could not extend below the keel. As is well known the rudder is a simple flat board made from wood mounted on the sternpost and operated by either a crude system of chains or an equally crude screw and linkage arrangement. It is by no means as large in proportion as the rudders fitted for instance to wherries. This relatively small unbalanced rudder does not require an excessive force to turn it or to hold it in position. It would not operate at all without the shaping of the hull to give a smooth flow on to the rudder. Even the swim headed lighter has an approximation to fair lines at the stern. It is fortunate that this shaping does not involve serious encroachment on the volume amidships devoted to the hold for the cargo.

 

Leeway

We have seen that when the wind interacts with any sailing rig that is properly set up to drive a boat the total force produced on the rig has components in the forward direction and across the boat. We do not want this transverse component but must accept it. However a transverse component can only exist if there is a resisting force to balance it out. This has to be generated by the boat as it moves through the water. It can only be generated if the boat has its bows pointed by a few degrees to windward relative to its course. The diagram shows the attitude of the barge to its course. The simple fact that the barge is skewed to its course means that the symmetry of the flow round the hull is destroyed and the level of the water at the bows on the leeward side will be above that on the windward side. This produces a sideways force and a flow underneath the hull from leeward to windward. The barge looks as though it is moving sideways[12] and if you want to think about it this way I suppose that it is. However it will be more help later to see that it is the barge skewed to the course. The skewing does not take place automatically. It is either the result of rudder action or of sail action or a bit of both. The forces produced on the sails act on the boat at various points, the mast box, the horse, the rails where ropes to the sails are made fast, the winches and so on. When the rig is correctly placed on the hull the net effect of these is a force tending to push the bow gently to windward. The rudder can produce the same result but only at the cost of greater drag caused by the rudder. So the best arrangement is for the hull to be turned primarily by the rig and “fine-tuned” by the rudder. The small sail on the stern and/or the rudder can also be used to “balance” the barge. It is quite near to the helmsman for him to adjust it.

 

Clearly a hull that is deep in the water will offer more transverse resistance than a lightly loaded one. This is what is required.

 

Barges are fitted with leeboards and this must mean that under some conditions, probably when sailing light, the hull and rudder were not adequate to limit the leeway. The leeboards have to do the same job as a centreboard on a dinghy. These leeboards are boards that are fitted one on each side of the hull and are pivoted so that they can be lowered into the water. Normally only the one on the lee side is lowered. The board was flat in most cases but later barges used boards that shaped in cross-section like a symmetrical aerofoil only it is now called a hydrofoil. What it does is produce a force from leeward to windward as a result of going through the water at an angle to the course of the boat just as a wing lifts an aeroplane. The hull and the leeboard now share the job of providing a resistance to the transverse sail force and the net effect is that the angle that the hull makes to the course is reduced. (It reduces the leeway.)

 

The small mizzen sail

Sprit-sail barges were nearly always fitted with a small mizzen sail mounted between the wheel and the transom. It is clearly not an integral part of the sailing rig like the mizzen of a ketch-rigged barge. It is placed so that it can be trimmed by the helmsman. It seems to have been fitted to augment the rudder.

 

This mizzen looks to be the most interesting sail on the barge because, given the direct control of the helmsman, it can be set with its boom to windward. [13]. Its function requires explanation. I have done this in appendix 1 of Section 6 of this book.

 

The fore-sail

The practice of using the foresail to ensure the success of a tack meant that it could not be set in the normal manner to work with the mainsail for other points of sailing. It seems likely that the foresail was correctly set when at its limits for beating but was not properly set for reaching or running. No doubt the foresail contributed something to the drive when reaching made but could not be set correctly for other points of sailing, It is doubtful whether the foresail was much use when running anyway because it works entirely in the lee of the mainsail. In truth the mainsail cannot be sheeted out far enough using only the sheet attached to its clew. The foot comes against the shrouds and even if the shrouds were not there sheeting out a loose-footed sail just increases the camber without increasing the area presented to the wind. There are photographs of barges running with the clew of the mainsail propped way out to leeward. I presume that, normally, skippers chose to sail in a long zig-zag down wind and not use props and then a jib sail on a bowsprit would be an asset and this may have been the incentive to use the bowsprit. The jib is better placed and can be set for any point of sailing.

 

Summing up

I have drawn attention to the essential features of the Thames sailing barge and to the contributions that they make to the sailing of the barge. It turns out to be more complex than one might think at first. If we are to model a sailing barge we cannot just ignore the way in which the real barge achieves its functions and we must attempt to recreate all these various facets of the design in miniature if we hope to make the model sail like the full sized barge. Every decision to simplify affects the ultimate performance of the model but fortunately any practical model can be made to sail passably well.