A 15 foot dinghy for cruising

John Perry

10-08-01 Grey boat in cofleet creek

In Coflette Creek, above Newton Ferrers

grey boat at chausey

At Chausey Islands, south of Jersey

  

grey boat in friesland

In Friesland, 2012, with new boom and new boat tent

06-08-21 grey boat at east mersea

At East Mersea, Essex
 

  

INTRODUCTION

In about 1976 I was looking for a boat which could be trailed by a fairly small car and would be suitable for exploration of shallow creeks as well as coastal and possibly even cross channel trips. The boat needed to be suitable for camping on board using a boom tent with a crew of either one or two persons. I decided to design and build my own boat simply because I like making things and once you have decided to build your own boat it is tempting to introduce a little individuality by doing the design as well.

CAPSIZE RESISTANCE/RECOVERY

This boat was designed at about the time that Eric Coleman was completing the first Roamer, the purpose designed cruising dinghy for which you can buy plans through the Dinghy Cruising Association. A feature of the Roamer design is that it has better capsize resistance and self righting ability than most manufactured dinghies. I wanted my boat to have at least a degree of self righting ability and since I knew Eric and lived not too far from his home in Chelmsford I popped over to chat a couple of times during the period that my design work was progressing. Eric was pleased with the first trials of his boat and the obvious thing would have been to base my design on his. But I do have a tendency not to do the obvious thing and as a result my boat turned out to be different in almost all respects to the Roamer, although the design aim is similar. As for which is best, I think they are both successful boats but I can say that my boat is faster whereas the Roamer is roomier and has better initial stability.

The Roamer has unique raised 'castles' at each end which increase righting moment when the boat is capsized. The righting ability of the Roamer is due to a combination of a heavy steel plate centreboard and the buoyancy of the raised 'castles'. I could not accept the castellated profile of the Roamer aesthetically despite the practical benefits. With the aid of computer programs I calculated that I could replace the righting moment provided by the raised castles of the Roamer by increasing the weight of the centreboard and concentrating weight in the lower part of the centreboard. The centreboard of the Roamer is a steel plate whereas that for my boat is a much thicker grp aerofoil the lower part of which is lead filled, hence it is heavier and has a lower centre of gravity.

CHOICE OF HULL CROSS SECTION

A fundamental consideration in the design of any monohul sailing boat is the shape of the cross section through the mid region of the hull. A cross section through the maximum beam is usually taken as the typical section and the options range from a wide shallow 'firm bilged' box at one extreme to narrow and rounded with 'soft bilges' at the other. These shapes are extremes, most practical boats are intermediate.

The advantages of the wide flat cross section are high initial stability and hence good sail carrying ability and a boat which does not rock excessively when the crew move ar round inside. The inherent 'form stability' of wide flat bottomed hulls means that sufficient stability for sailing can be possible without the use of any ballast and hence unballasted sailing dinghies tend towards this hull shape whereas ballasted boats tend towards a narrower and more rounded hull shape. The disadvantages of a wide flat hull shape are increased hull drag under non planing conditions and a rapid fall off of righting moment at large angles of heel. Further disadvantages are difficulty in steering at large heel angles and once a capsize has occurred this kind of hull has a tendancy to be rather stable in the inverted position. The higher hull drag of a wide flat hull does not necessarily mean that the boat will be slow since the good sail carrying ability may more than compensate and if the boat is light then planing may be possible.

The narrow rounded cross section in its extreme form has too little stability to be a practical sailing boat unless it has ballast low down or the crew is prepared to be mobile enough to constantly stabilise the boat with crew weight. Given suitable ballasting, for example with a deep keel with ballast bulb, this hull form offers low drag and a righting moment which although initially low rises gradually reaching a maximum at a large heel angle. This righting moment characteristic makes it easier to avoid capsize and indeed a ballasted boat of this type is likely to be self righting from all but the most extreme angles. Examples include ballasted racing keel boats and traditional yacht hulls. The lower drag of the narrow rounded hull does not necessarily make for a faster boat since the sail carrying ability is dependant on the righting moment available at small heel angles and this may well be lower than for the wide flat hull form. Also, narrow round bottomed hulls are less likely to plane than wide flat ones.

The above paragraphs indicate that self-righting capability is more readily achieved with a narrow beamed hull having rounded underwater sections than with a wider, more flat bottomed hull. Both shapes can be made to be self-righting but the wide flat bottomed hull will need  more  ballast to achieve this and adding ballast to a small boat soon starts to reduce the available payload if displacement is to be kept within reasonable limits. I therefore chose a hull cross section with a "softer" turn to the bilge and slightly narrower beam than is normal for a modern sailing dinghy.

A plot of righting moment against angle of heel,  produced using a computer program, is included below. The position of the crew weight and other payload has a significant effect on the  righting moment of a boat of this size. For simplicity in calculating the righting moment plot I have assumed the weight of the payload to be concentrated at the centre of gravity of the unloaded boat. Under normal sailing conditions the crew weight would typically be about 500mm to windward of the centre of gravity of the unloaded boat giving about 700Nm of additional righting moment with a crew of two.

Stability curve

The stability curve is extended only to ninety degrees since for a small open boat the uncertainty of crew location makes the predicted righting moment unreliable for large angles of heel. Even at around 60 degrees of heel the position of the crew is uncertain, they could be swimming, holding on inside the boat or climbing onto the topsides or center board. Some of these crew positions would give significantly less righting moment than that shown on the stability curve and indeed possibly insufficient righting moment to prevent a capsize. To make this boat truly self righting under all conditions regardless of crew action would probably require an increase in ballast ratio by means of an even heavier centreboard.

BALLASTED CENTRE BOARD

As noted above, the center board is lead weighted to provide ballast weight low down. The centre board is about 50mm thickness and has an aerofoil section. The lower part of the centreboard is filled with lead and the upper part is wood cored. It was constructed by positioning the lump of lead and the wooden core on a bench with supports to hold them in alignment then encapsulating both parts with grp. Unidirectional rovings were included to counteract bending moment and some of the rovings were threaded through the gap between lead and wood so as to provide an interconnection between the skins on each side of the structure. The weight of lead was chosen to be about the weight of an average person, ie. 75kgs. The thinking here was that the weight of one crew member standing at the root of the centreboard of an unballasted dinghy is generally sufficient to right the boat from a 90 degree capsize. The lead is towards the tip of the keel so should be even more effective.

Most boats which have ballasted retractable keels have this keel in the form of a vertically sliding dagger board. A vertically sliding keel suits many small cabin boat designs since the keel trunking can be fitted just aft of the mast leaving at least a little free cabin space between the keel trunking and the cockpit. For this open boat design I preferred a pivoting rather than sliding keel for two reasons. Firstly, in an open boat having fairly shallow depth of hull it is difficult to accommodate  the height of a vertically retractable keel if there is to be a good depth of keel in the lowered position. Perhaps the best attempt I have seen in this direction is a new dinghy, I think from Laser, which has a foldaway 'crane' for raising the keel but even then the keel is rather an obstruction when raised. Secondly a pivoting centreboard suits a boat which is frequently used for 'ditch crawling'. The risk of damage by running the keel into the seabed is much reduced if the keel can swing backwards on impact. As first built, the fibreglass sheathing of the keel on my boat did suffer from impact against the seabed, sometimes even against rocks. I have now added metal reinforcement to the leading edge extending around the lower end and this helps a lot.

A special centreboard lifting tackle is provided since the centre board is heavier than even the steel plate centre boards used on traditional day sailing boats. The forward end of the centreboard case extends under the long foredeck and serves to support the foredeck against loading from the deck stepped mast. The forward end of the centreboard, i.e. the upper part when the board is down, provides a large lever on which the centreboard hoist can act. This reduces load on the centreboard lifting cable and also reduces the contact loads between board and case when the boat is heeled. The center board is raised and lowered by a 2:1 wire tackle lead over pulleys to a winch conveniently mounted on the centreboard case at the front end of the cockpit. This winch is of stainless steel and bronze and is of a type which used to be sold for davits on large yachts. It makes an excellent winch for a heavy centreboard but I don't know if it is still available. Rollers fitted into the centreboard reduce friction between the side of the board and the side of the centreboard case. This refinement may not be essential, plastic sliding surfaces would probably be adequate.

This centre board control system has proved to be effective, allowing the centreboard to be raised and lowered almost as quickly as an unballasted wooden centreboard. Indeed, this centreboard is quicker and easier to raise while sailing than are most wooden ones since the winch easily overcomes the effect of weight or water pressure acting sideways on the board. With a conventional wooden centreboard such as on a Wayfarer it is not unknown to have to luff up so that the centreboard can be adjusted. But one point to watch out for is not to let go of the handle of the centreboard winch without the ratchet being engaged, otherwise the handle will fly round and could cause injury. This is an inherent problem with this style of winch and applies also to most of the winches used on boat trailers. It is possible to have a winch which locks the drum as soon as the handle is released but I have never seen such a winch in a fully water resistant marine version.

The unusually thick centreboard needs to work in a correspondingly wide centreboard case. A disadvantage of this is that when the boat is sailing fast water sloshes around in the centreboard case and I am sure that this turbulence must be a source of drag. The access cover on the top of the centreboard case has to be fitted with rubber seals to prevent surging water squirting out. The original idea when the boat was designed was to fit a hinged flap to the aft end of the centreboard, this flap being weighted so that when the board is fully lowered it closes off the bottom of the centreboard slot and when the board is fully raised it sits above the centreboard at the top of the centreboard case. I still think that a flap like this would be a good idea but I never did get around to making it - the diagram below shows how it would work.

Centreboard with hinged flap to close slot

The lead for the centreboard was purchased as scrap roofing sheet from a scrap merchant. The original intention was to melt it down and cast the ballast weight in a mould made by placing cement around a wooden former. Making the mould then casting the lead seemed quite a complicated operation. There are also possible health hazards in breathing fumes from the moulton lead, although if one were to do the job outdoors I think that the problem would be minimal. Since the lead was supplied in sheet form I decided to see if the casting operation could be avoided altogether by making up the ballast weight in layers. The first stage was to clean the sheet lead and flatten out folds and wrinkles with a mallet. It was pretty dirty having been on a roof for many years. Then shapes were cut out from the sheet and stacked to form the required shape of the ballast weight. Odd bits of lead left over were fitted in as best as possible. The layers of lead were fixed together by a few home made rivets made from soft aluminium rod. The ends of the rivets were sawn with slots so that they could be splayed out with a hammer. Finally the lead sheets were compacted a bit with a hammer and the shape trimmed with a surform. This method appears to be a reasonable alternative to lead casting if one is starting with sheet lead. The aluminium rivets may not be the best way to join all the laminations together, perhaps they could be stuck together by painting with epoxy.

SELF-DRAINING CAPABILITY AND BOUYANCY TANKS

I wanted the boat to be self draining and this required the floor inside the boat to be above the waterline with a sealed space beneath. A self draining boat is a big advantage being able to quickly recover and continue sailing if swamped and there is no problem with rain water collecting if the boat is left on a mooring. There are however potential disadvantages to a self draining layout. Firstly, having the floor above the waterline means a relatively shallow cockpit unless freeboard is higher than normal. The shallow cockpit feels more exposed and crew weight is carried higher. The side decks probably become the main seating since there being little point in having benches inside the cockpit as such benches would be at similar level to the side decks. A second disadvantage of a self draining boat is that it may well be harder to right from a capsize due to the necessity to have a large volume of sealed buoyancy space under the floor and low down in the hull. For ease of righting it is desirable to have buoyancy high up in the hull and the buoyant 'castles' on the Roamer design exemplify this. The self draining facility is very useful immediately after you have recovered from capsize but if it means that you won't recover in the first place then it is hardly a benefit.

To offset the disadvantage of having a lot of buoyancy low down there are large side tanks which extend up to deck level. At 90 degrees heel, ie. knock down with the mast close to the water, most of the weight of the boat is supported by one of the side tanks and in this situation the righting moment is better with the side tank than with only the under floor buoyancy. However the side tanks themselves create a further problem at even greater angle of heel. If the boat were rolled right over it would float on the two side tanks and since these are at the extremities of the beam the boat would then have excellent stability in the fully inverted position. Righting could then be difficult even with the help of the ballasted centre board.

To help in this fully inverted situation a water transfer system is included. A water intake channel leads from an opening under the centre of the fore deck to one of the side buoyancy tanks. This buoyancy tank has an air vent which is normally closed by a weighted flap. The idea is that if the boat is inverted the air vent will open and the side tank will flood until the boat turns back on its side, perhaps with some help from the crew. After the boat has righted the flooded tank could be drained by removing an inspection hatch allowing it to empty into the self draining cockpit.  The system has not been tested, perhaps fortunately. Water ballast tanks for self-righting used to be installed in many RNLI lifeboats; the arrangement in my boat is a simplified version.

There is a drain channel with loose fitting covers running athwartships across the floor of the cockpit. The cockpit floor is slightly sloped towards this drain channel. A large self bailer is centrally fitted amidships at the bottom of the drain channel. When the boat is level and stationary with the self bailer open the drain channel will fill with water to just a few millimeters below floor level. If the boat then heels there will be some water over the floor but normally the boat will be moving when the boat is heeled with the self drainer open and the self drainer will then lower the water in the drain channel so that the floor remains dry under most sailing conditions. The self bailer is homemade and is opened and closed through a linkage worked by a small lever mounted at the back of the centreboard case. In the event that a large amount of water is taken aboard, the water level in the cockpit may be above the top of the centreboard case. The crew can then supplement the action of the self bailer by unclipping the removable top cover to the centreboard case which gives a drain opening about 60mm wide and 600 mm long straight through to the sea allowing rapid emptying of the cockpit. The original idea was that this cover being made of wood would float off automatically if the boat were swamped but this was found to be not a good idea since water surging in the centreboard case lifted it off when sailing!

On a couple of occasions the boat has been blown over to about 90 degrees when sailing in strong winds and on both occasions it self-righted with some water inside then rapidly self drained. The boat was also once swamped by steep breaking waves from astern when entering a river across a bar. This was frightening for the crew but the water drained out in seconds and by then we were through the worst of the breakers.

To make the boat unsinkable in the event of collision the buoyancy tanks under the floor are divided into watertight sections each of which is filled with polyurethane foam. This large volume of foam weighs at least 25kgs so it provides a little ballast as well as buoyancy. A strange thought that lightweight plastic foam can act as ballast but in a sense it can if there is a lot of it low down in the boat. Also fitted under the floor is a 10 gallon freshwater tank which must contribute as ballast when full and provides a fresh water supply to a pump tap. Additional sea water tanks under the floor could be worth considering, they would give the option of increasing stability and slightly lowering the centre of gravity for rough conditions and yet could be emptied so not to add to displacement in light weather or to trailing weight.

General arrangement drawings LOA 4.57m     Beam 1.6m    Displacement 475kg (at maximum design load)

GROUNDING

The boat is designed so that it can dry out level, a most useful feature for cruising. Most dinghies having either a Vee bottom or a full length external keel dry out at a slight angle which is a nuisance for camping on board, especially if the boat falls from side to side as the crew moves around. My boat has a flat bottom panel from midships to the stern, this flat panel blending into a Vee shape towards the bow. There are two shallow bilge keels/rubbing strakes, about 80mm deep, each side of the flat bottom panel amidships. These little keels are shod with stainless steel. The boat sits sits firm and level when grounded and the keels help to protect the bottom. The flat bottom and bilge keels are also an advantage for trailing. The road trailer can be a simple design with a cross member which supports the boat under the bilge keels, no special supports are needed.

COCKPIT LAYOUT

The cockpit is flat floored and a little over six feet long so as to allow space for sleeping under a boom tent. The width of the cockpit is a little under four feet and it is rectangular apart from the front end which is bounded by swept back washboards at the aft end of the long foredeck. Although the cockpit is small for the size of boat it is uncluttered and comfortable for a crew of two. The only furniture in the cockpit is a removable rowing thwart. Once the boom tent is in place this thwart is usually taken up and stowed out of the way on one of the side decks. The main sheet horse is stern mounted rather than centrally mounted so that it does not intrude on cockpit space. I prefer a stern mounted mainsheet anyway, I think it makes it easier to get a temporary grip on the sheet with the tiller hand and to my mind it is easier for tacking. Seating while sailing is normally on the side decks, except in light winds when it is comfortable to sit on cushions on the flat floor. The centreboard casing is little intrusion into the cockpit since all but about 80mm of it is below the floor level.

A useful detail in the cockpit is a line which runs in a loop right around the cockpit guided through small plastic fairleads and which can be clipped to a hook on the tiller. This allows steering from any position in the cockpit, useful when adjusting halyards etc single handed. The line is tensioned with a length of elastic and there is enough friction in the fairleads that it can be used to secure the tiller in a fixed position. Since the boat is well balanced it will then steer itself in light winds and has sometimes done so for and hour or two at a time on long passages.

Another detail is that the removable rowing thwart is in the form of a shallow box into the middle of which is mounted a compass visible through a flush perspex access cover. There are small storage compartments to each side of the compass and these are useful for small items which may be needed in a hurry, eg. sail ties, spare lines, torch (but nothing in these compartments should be magnetic). As originally built, the lids of these compartments were on stainless steel piano hinges. These soon seized and got broken (they may not have been a high grade stainless steel) and were then replaced by lids which hinge on short webbing straps which are much more satisfactory - the James Wharram school of technology!. The compass is a gimballed Silva type 33 which is a grid compass allowing one to set a course on a graduated bezel then steer by aligning the compass needle with a grid. Actually, a fixed compass is far from essential on a dinghy, unless you are going to use it for race tuning. If your boat does not have provision for a built in compass you can manage well enough with a pocket compass such as the ones used in the sport of orienteering.

STOWAGE

Commercially manufactured sailing dinghies generally have insufficient storage space for long distance sailing. Even in craft such as the Wayfarer dinghy the available storage space tends to be packed solid when cruising making it impossible to extricate  equipment in a hurry. Approximately 35 cu.ft. of  storage space was designed into my boat, about 16 cu ft being in a watertight compartment under the stern deck and the remainder in the space under the large fore deck. This exceptional volume of stowage space is at the expense of cockpit space but I am happy with that compromise, the cockpit is still adequate for two persons.

The space under the long fore deck is divided by the center board case which extends to deck level to support the mast. The area to the port side of the center board case is a "galley". A large drawer pulls out from under the foredeck on plastic runners, this drawer containing a single burner gas stove and most of the food and cooking utensils aboard the boat. Beneath this drawer there is space to sit a plastic storage box down on the floor and this tends to be used for sailing boots etc. but could be used for more food storage. The pump which draws freshwater from the tank below the floor is mounted alongside the centreboard case. The lower end of the pump extends directly down into the water tank so no plumbing is required. The water tank is filled through a removable inspection hatch with an 'O' ring seal, this is of the type used for dinghy buoyancy tanks. A built in water tank is rather a posh luxury on a dinghy but quite useful for long trips. It can be filled from a marina hose and one can then cruise for at least a few days without needing to top up. The water tank is not used for short weekend trips since emptying it at the end of the trip (desireable to minimise trailing weight if nothing else) is more trouble than it saves. The space under the foredeck on the starboard side of the center board is a large open storage for sails, two anchors and anchor warps, fenders, small inflatable tender etc.

The stern locker is rather more voluminous than on a Wayfarer and takes up the space under the tiller which is little used space on most dinghies. The hatch on the stern locker is of a sliding type so that it can be opened and closed without interfering with the tiller and cannot be lost overboard. When the lid is slid fully into the closed position it can then be clamped down onto a rubber seal by means of two levers working an 'over centre' mechanism at each side of the hatch. There is a fiddled shelf along one side of the space inside the stern locker. With such a large locker it is useful to have such a shelf to hold small items eg. tools, books, car keys. If an outboard motor is carried this can be stowed in the stern locker located by a chock and held down with a lashing so that it cannot move about when the boat heels.

ROWING

The sides of the cockpit are straight in the fore and aft direction and this allows the oars to be stowed on brackets each side of the cockpit with the blade ends of the oars under the foredeck. This built in stowage allows oars of about nine feet length which are more effective than the short oars used on most sailing dinghies. The oar stowage is above the thwart which is convenient if the oars are needed in a hurry. The rowing position is further aft than on many boats but this does not seem to matter at all. The bulkhead at the aft end of the cockpit makes a footrest for rowing and is fitted with a couple of wood strips to protect the varnish work from the rower's boots. The rowlock sockets are fitted into the side buoyancy tanks so have to be a sealed type. Plastic rowlocks are used and are not ideal, sometime they will probably be replaced with metal ones.

RIG

The rig is a gunter sloop which can be converted to a small bermudian rig for sailing in strong winds. The picture below shows the full gunter rig. The conversion is done by stowing the gunter yard and sail in the hull and hoisting a low aspect ratio bermudian sail with slides fitting the grooved aluminium mast. This method of sail reduction takes longer than reefing but gives a little less weight and windage aloft in strong winds. Both the gunter and the bermudian mainsails have one set of reef points giving four possible mainsail areas, although the smallest of these has never been used. I find that for sea sailing I use the small and large mainsails about equally. In any wind at sea the usual rig is the small mainsail set unreefed and without a jib. This is a comfortable fairly low aspect ratio rig which balances the helm nicely. Since the boat sails well without a jib in strong winds there is no need to carry a storm jib or to have a roller reefing jib.

full sail

The short mast of the gunter rig, only a few inches longer than the hull, is a significant advantage for storage ashore, for road trailing and for passing under bridges. The mast can easily be stepped single handed, either ashore or afloat. When the boat is on the road trailer the mast is stowed above the hull supported on two props, one prop being attached to the bow fitting and the other being built into the number plate/road light support. When the boat is stored in the garden the mast remains in the trailing position and makes a ridge pole to support a rectangular polytarp cover. I find that this type of cover needs replacement every few years but it is cheap to replace and hence more cost effective than a custom made fitted boat cover.

The mast is deck mounted and can rotate, the angle of rotation being limited by contact with the shrouds and also by tension in the kicking strap which is attached to a bracket on the aft side of the mast foot. An advantage of a rotating mast with gunter rig is that the mast and yard stay roughly in alignment. This can be expected to be aerodynamically beneficial and also allows a fitting running in the mast groove to connect the lower end of the yard to the mast. This is perhaps neater than traditional gaff jaws.

The mast is supported by a forestay and aft swept shrouds at the top and by inner shrouds at mid height. The inner shrouds are not swept back. The lower anchorage for the main shrouds is near the gunwhale, the inner shrouds are anchored inboard and the jib sheets lead between the inner and outer shrouds. All shrouds are attached to fittings on the front of the mast so that the mast can rotate, this is similar to the arrangement seen on many small catamarans. The use of inner shrouds is fairly unusual for a dinghy but it does give a robustly stayed rig and avoids the need for any spreaders.

The length of the gunter yard is such that it only just stows in the boat lying on the floor alongside the centreboard case. Stowed this way one end of the yard is tight up against the bulkhead to the stern storage compartment and the other end is right in the bows, housed in a 'tunnel' protruding into the forward buoyancy space.

The gunter yard is intended to be hoisted until it is absolutely parallel with the mast so that the sail shape is virtually the same as for a bermudian rig, although the sail maker probably should allow for a double kink in the luff ar round the fitting which connects the yard to the mast. There are two attachment points for the main halyard to the yard so as to allow for taking in a single reef in the gunter mainsail. I have found that the halyard has to be very well tensioned if the yard is to stay tight up against the mast. The halyard is now 6mm diameter Spectra which is much better than the prestretched polyester originally used. Even the Spectra halyard needs to be re-tightened by a couple of inches a few minutes after first setting the sail. This may be due to slippage in the cleats or between the sheath of the rope and the load bearing core. I have now made a halyard adjuster to help with keeping the main halyard tight. This is a halyard cleat fitted to a slide which runs in a short track on the mast with a 3:1 pulley arrangement to haul the cleat downwards.

As originally built, the gunter yard was sitka spruce although the mast was aluminium, a rather odd looking combination. The yard was built as light as possible, the idea being that since it is only used in light winds it does not have to be all that strong. However it was far too flexible which spoilt the set of the full mainsail. When the spruce yard split along the luff groove I took the opportunity to change to an aluminium version which was made up by Needlespar of Warsash using an experimental tapered section they happened to have lying around. This new yard is stiffer than the original one but an even stiffer yard would probably help. I have recently made carbon fibre spars for another boat and I have thought that eventually I would like to make all carbon spars for this cruising dinghy.

DECK LAYOUT

Since this is not a racing boat the deck is free of rig tweaking gadgets. At the prow there is a custom made fairlead for the anchor warps and this incorporates the attachment for the forestay and a pulley for a wire jib tack downhaul the tail of which is lead aft to a Highfield lever. From the prow back to the mast the large foredeck is clear of all fittings and is coated with non slip paint. Just aft of the mast there is one large cleat which is used for the anchor lines and forward mooring ropes. Since I often use two anchors perhaps two cleats would be useful but on the other hand I think it is nice to keep such fittings to a minimum. Fairleads and cam action jammers for the jib sheets are mounted on the side decks and are positioned to allow the sheets to lead directly from the fairleads to a large genoa jib. When the working jib rather than the genoa is in use the sheets are lead through 'barber hauler' pulleys to the fairleads. In practice I don't use the genoa jib since it takes up more space than it seems to be worth. Hence sometime I could move the jib fairleads forward and remove the barber haulers.

Back at the stern are two quarter cleats for mooring lines, one each side of the aft hatch. Across the stern there is a rope horse for the lower mainsheet block. The degree of slack in the rope horse can be adjusted to give some control over how far the boom moves off centre when tacking to windward. Less slack in the horse allows the boom to move a bit further. The lower mainsheet block is a fiddle block with an integral cam action jamming cleat. I have ignored the advice of those who say never to use jamming cleats on the sheets of a dinghy at sea. If you are going to read a chart or make a picnic while sailing I don't see how you could really manage without them.  But it is important that the jammers work properly and can always be released.

The rudder is of heavier than usual wood construction and has a lifting blade which can be hoisted to above the horizontal position so that when the boat is grounded the rudder blade is well above ground level and unlikely to be damaged on uneven ground. The rudder stays in place once the boat is afloat, with a permanently attached tiller it is a bulky item which would take up too much space if unshipped and taken into the cockpit.

CONSTRUCTION

The hull is of double chine plywood construction with glass reinforced polyester sheathing on all exposed surfaces ap part from some brightwork inside the cockpit. The sheathing has proved to be durable and I think is well worthwhile for a boat which is intended to take the ground in all kinds of harbours. Today, I would certainly choose epoxy rather than polyester resin for this sheathing application, but at the time of construction epoxy resin was little used and not readily available for boat building. I did roughen the ply before sheathing using various home made tools with spiked or serrated edges to ruthlessly rip up the surface to provide a mechanical key for the sheathing. One exception was the side decks where I was in a hurry and skipped the roughening of the ply. Sure enough, in hot weather, the sheathing in this area separated from the wood in a few places and bulged up in raised bumps. This has now been cured by cutting across the bumps with a knife, trickling in some epoxy resin, placing a plastic sheet on the deck then pressing down with bricks laid over a pad of folded cloth until the epoxy sets. I think that this has successfully cured the problem.

The boat is strong and probably unnecessarily heavy. The internal structure of buoyancy tanks makes the hull very ridged. Most small craft can be felt to distort slightly when one walks about inside with the boat ashore, whereas walking about in this boat feels like walking on a concrete floor. The floor of the cockpit is actually quite thin ply, 6mm thickness overlaid with a sheath of fibreglass cloth. This would not normally be a strong floor but in this boat the foam expanded into place beneath makes it solid.

One might question the wisdom of having large sealed spaces within the hull, these being virtually inaccessible for maintenance short of major rebuilding. The side buoyancy tanks can be ventilated by removing small plastic hatch covers when the boat is not in use but the large space under the floor is filled with polyurethane foam and so has to remain permanently sealed without ventilation, not that ventilation would help assuming that the foam has expanded to fill pretty well the whole space. All I can say is that there have been no problems that I know of so far and the boat is now over twenty years old.

The hull was designed using a computer programme to generate the lines and calculate the dimensions of the sheets of plywood. The boat was designed in 1976 so it would be one of the first small boats to be designed by CAD and one of the first, or perhaps even the first, boats to be built using computer generated panel shapes to skin a chine hull.

CRUISING RECORD

This boat has been used for weekend cruising on the Essex, Suffolk and North Kent coasts and on the Solent together with occasional longer trips to Scotland and other areas of the UK. The boat has also made a number of trips of one or two weeks duration sailing from South coast ports to the Channel Islands, the Cherbourg peninsula and North Brittany and one short exploration of the French canals around Dunkerque. It has been a lot of fun. It has also been a cheap boat to run requiring little maintenance and being stored in the garden when not in use.

The maximum speed of this boat is modest and it is quite incapable of planing due to the heavy weight and the considerable hull rocker which is needed to carry this weight. But it seems to sail at near to its maximum speed under a wide range of conditions and passage times have been almost identical to those of the HSC Wayfarer dinghies. This is perhaps surprising since it is both shorter, narrower and heavier than a Wayfarer. Despite being of heavy displacement for its size it has good performance in light wind.

CLICK HERE to read about some of our cruising with this boat

WHAT I MIGHT DO DIFFERENTLY ANOTHER TIME (MAYBE!)

Although I consider this to have been a successful design there are some changes I might consider if I were to develop the idea further. To start with I would try harder to keep down the weight of the structure and construction materials now available would help here. I would certainly use epoxy resin rather than the polyester resin that was the only option at the time the boat was built. I would also make use of lightweight filled epoxy fillets in place of much of the wood framing and I would use really light plywood for lightly loaded parts of the boat such as the sides of the cockpit. The foredeck could also be built a lot lighter. A lighter built boat would be less robust but I could accept that. I might even consider a foam sandwich construction, ideally with carbon fibre skins over a foam core, but this could be a lot more work than the plywood stitch and glue method.

Having made a substantial weight saving in the structure I might well then choose to throw away that weight saving by having more lead in the ballasted centreboard. The boat as built is a bit of a compromise between a dinghy and a keelboat. If the ballast ratio could be further increased then perhaps it could become a true mini keelboat with virtually guaranteed self-righting under any conditions. Combined with a self draining cockpit that would make a very nice boat for coastal cruising. Increasing the weight of lead in the centreboard would need a wider chord (ie broader) centreboard if the section is not to be excessively thick. A broader board would mean a higher top to the centreboard casing which would then protrude more into the cockpit but this would not really matter, it might make a good footrest. I think the existing centreboard lifting gear is quite strong enough to handle a heavier ballast weight.

The hull is more barrel shaped than most sailing dinghies, that is it is more keelboat shaped. Since the ballast ratio of the boat as built is less than most keelboats perhaps the bilges should be just a little firmer to give more initial stability. But I am not sure about this, there is a danger that firmer bilges on this heavy displacement boat might kill the light wind performance which would be a pity.

As for the rig, I might or might not keep the gunter arrangement. The best point of the present rig is that when the gunter yard is stowed away the small flat cut low aspect ratio bermudian sail set on the short well stayed mast is excellent for strong winds. Rigged like this the boat has happily sailed up the Solent tacking against the tide plus a force eight head wind. The disadvantage of this twin mainsail rig is that changing from the gunter mainsail to the smaller bermudian sail takes a lot longer than reefing.