Graeme, your approach to dinghy building surely is more practical and hands-on than mine. I start with the numbers. Still, since I keep my own lack of skills as a boatbuilder in mind, I try to make it as simple as possible. This is much helped by using a 2D CAD-program which doesn’t invite to fancy curves in plywood. The pram shape lets one get away with constant deadrise, for instance. Also note that some of the curves are identical, so if one starts with lofting the bottom-side planks, these can be used to scribe the curves on both the bottom plank and the lower edge of the topsides.

I am not sure if I will build Halibut, but I surely will build a 1:5 scale model of it, and then I will try to assemble it in the same order as a full-size boat could be built.

Hopefully that will encourage me to “go 1:1 “...

Arne

PS to David. We don't design dinghies because we have to  -  we do it because it is fun, and because we may learn something in the process. I, at least have still a lot to learn  -  I've learned...

 

Part 4

The hull (bottom and bow) is plywood planked in four pieces, two each side of the strong-back. This is unconventional, but easy to do, and being curved, its strong and rigid when finished.

Some fairing/bevelling of the cleats, near the forefoot and “stem” – and on the fore part of the chines, is now done with a chisel and plane. A straight-edge between stem and chines is used for a guide (see straight lines drawn on photograph below.) This is the only bevelling or even slightly challenging joinery in the build.

Explanation: this wrapped-around surface, which is marked with straight lines, is part of a cone. (In a larger vessel this section could be cross-planked with planks which are tapered and not bent at all). The rest is flat. (at the bow) or a simple roll (aft).

Laying the plywood over this simple shape is hard to explain but believe me, its easy to do.

However, that bow/bottom panel is not straight forward to loft. These days people seem to do it with computer software. Otherwise, a cardboard mock-up of the bow/bottom piece may be cut and fitted, to ascertain the correct shape The ply is now cut, glued and fastened to the bevelled cleats. (If the ply is difficult to wrap around the curve, the surface can be score-cut with a sharp knife, through the outer layer of the plywood, along the lines shown in the above photograph. These cuts should be on the outside of the hull, they will open somewhat when the ply bends, and can be filled with thickened epoxy later.)

The more simple, rectangular aft bottoms are cut and fitted, its a simple and easy roll and no bevels are required here. The two bow/bottom and aft/bottom panel pairs are joined with a simple butt strap join, from plywood offcuts. 

After the bottom/bow is completed, the chines can be dressed with epoxy and fibre-glass bandage, the outside of the hull painted and the hull turned right way up.

The outside part of the off-centreboard case needs its own panel, so a compete case is fastened to the vertical side on the inside of the hull. The slot for the off-centreboard is now cut.

Now the sheer line can be cut, further timber strips placed where necessary: gunnels, belting, thwarts, breast hook or fore-deck, lands for buoyancy tanks etc.

The off-centreboard can be permanently installed, with a hardwood pin glued in, so it can't leak, and provision made for a “push rod" for raising and lowering the board, before the case is capped. A swing up rudder must be made and fitted with suitable hinge detail: gudgeons or Wharram-type lashing.

If the hull is over-length, 100mm can be trimmed off the bow with a vertical cut, and a simple transom fitted in this place, as shown here. Buoyancy tanks may be fitted if desired, joinery will be simple and mostly square.

Finally the rig – I think the sail plan designed by Arne is the obvious choice – and as this design competition is, in my opinion, all about finding a suitable, simple junk rig (not the hull, of which there are plenty of choices and which is therefore a mere detail) I believe Arne should be declared the winner of the competition.

This is just a frivolous entry. I don't think I am going to build it though I have had discussions about the idea with Marcus, from time to time - it would go well in davits, with Havoc. Marcus thinks he might eventually build a bigger one as a load-carrying tender for Havoc - its length would match Havoc's beam (which is of course, being a NZscow, is the width of the transom)- bigger than would fit within the parameters of the dinghy design competition.

Part 2

I don’t have skills or software for drafting (though not much drafting is required) so it remains in concept form, and these photographs of a model, and some sketches, will have to suffice for the moment.

This dinghy is based on a NZScow, an interesting model in that it is a box barge, but with 1 level of improvement – a “sharp” (though bluff) bow. The bow is truncated here, simply to get a bigger dinghy within the maximum length permitted by the committee.

Apart from aesthetics, the shape of a vessel under 3m is (within reason) almost irrelevant to performance. It must be able to turn aside a short chop and not be stopped dead by it. Nothing else is going to make much difference to its performance under oars or sail. (Differences emerge quickly as the vessel becomes larger in size.)

Box barges, such as the Bolger Brick, are the ultimate in simplicity but perhaps not the best in choppy conditions.

3 or 5-plank dinghy designs are the most aesthically pleasing, but already quite numerous, and not quite as simple to build as this one.

Conventional stem dinghies are a little more difficult to design well, and to build – and not particularly well suited to very small size.

The NZScow, is a fresh approach, maybe a good compromise on all counts, it will be a superior load-carrier, simple to build, with high initial stability, and the hull shape is proven to be a rather more easily-driven shape than some people might think. It could be a new addition to the pantheon of boat tender designs.

I would build this dinghy about 100mm longer than the maximum length permitted, then after the hull has been built, put a vertical cut 100mm back from the stem-head as shown in the above sketch, and retrospectively fit a small triangular transom bow. This will have no effect on performance but will bring the over-all length back to what is permitted, while giving a slightly bigger dinghy.

It will have a single internal off-centre board built into one of the vertical sides. The board will swing down to a maximum of 45 degrees. The swinging board is most convenient for sailing in shallow water and can be left permanently in the case. (Dagger boards and leeboards are just so much extra clutter when not sailing). (Unless put to other uses such as moveable thwart – or bait cutting-board!)

The little scow is intended to meet the following particular requirement of the committee: “Simple and cheap to build, (think along the lines of building on a beach…”) – it is debatable whether any of the other designs so far can make this claim. Almost no boat-building skills are required, and in keeping with the original concept (by the late Brian Donovan) it can be built from construction ply and house-building lumber, with just a plane, a sharp chisel, a screw driver, a hammer and a hand saw with plenty of "set". (Though a battery-operated sabre-saw and a battery-operated drill would speed things up somewhat).

The build will require 1/2 sheet of 15mm construction ply, 2 (edit: probably 3) sheets of 6mm construction ply and a small stack of short lengths (off cuts) of 48mm x 24mm or similar, thinner if available. Waterproof glue and fastenings are required – if “building on a beach” is the job, then galvanised clouts will do, and galvanised screws of the type which can be driven with a drill and a square-head bit. Of course, epoxy glue, fibre-glass cloth and ss fastenings would be better, but not essential. In a few places in the forward sections where a small amount of bevelling is required, it will be wise to remove the fastenings after the glue has cured. Final finish with alkyd house paint from discarded non-empty tins. (Old Olly Goodwin used to collect near-empty tins of paint from the dump – when he had enough, he would mix it all together and paint his boat. Year after year it always came out about the same shade of brown!)

Since I am finishing with building my Carabela 650 - ANNA LUCJA 2, and have some xps panels 60cm wide left I plan on to make a small and lightweight dinghy out of it. I am sketching the boat around a three persons sitting close each other - two on a central bench and a helmsman. Looks like 2m x 1,2m would suffice. 10 cm of drought gives over 200 kg displacement-plenty. Rowing, sculling and junk sail will power it. 3 plank, leeboard. I'll try to make it a nesting dinghy.

... and you don't get much forward motion!