An Unconventional Boat
by Horst Werner
(click HERE for Folding Tri study plans)

It all began when I went sailing with my small ballasted cabin cruiser in a 5-6 Bft. wind. A knockdown, man-over-board and the complete inability to get the boat back into harbour without help left me so scared that I didn't dare to go out on that boat with my wife and my baby any more.

The safer alternative would have been a bigger boat, about 20 feet long with a weight of at least one ton. On the other hand, I already found the hassle I had slipping the 350 kg boat annoying. Furthermore, such a big boat doesn't fit well to the small and partially shallow lakes in my region, and it would eat up lots of money for marina and maintenance.

So what did I really want? A boat that didn't exist.

  • A lightweight trailer boat, ready to sail in about 20 minutes.
  • shallow draft and beaching capability
  • minimum heel even in strong winds
  • capacity for up to six adults (and a handful of small kids)
  • stowage for a one-week trip
  • self-draining cockpit
  • unsinkability and unswampability
  • a small cabin for the kids, ideally big enough to sleep two adults
  • ideally, the potential to exceed hull speed
It was clear that only a multihull could provide the stabilty I wanted for a light-weight trailer boat. And I think I got infected by the multihull virus when I made experiments with my canoe converted into an outrigger boat before buying a "real" sailboat. A catamaran like Wharram's Tiki 21 seemed attractive, but would not offer the comfort I had in mind and wouldn't be a real trailer boat. As for trimarans... well there seems to be an unwritten law that trimarans are uncomfortable racing machines with extremely slim center hulls.

But what if you build something like a cruising centreboarder with stabilizing floats? It turned out that it would be feasible, but that a really light planing hull would require the cockpit to be more or less in the middle, since crew weight determines the location of the center of gravity to a high degree. On a short boat, there would be no way of getting a reasonably sized cabin in front of the cockpit since the first two feet are too narrow to be of any use. So I came to the idea of having an aft cabin and the resulting design looked like this: 

With a hull length of 5 m and a weight of about 250 kg it was a really small boat, but by extending the cabin under the seat bench, it would offer 2m berths and a 1,80 m cockpit right in the middle of the boat. A 20 cm layer of styrofoam in the bottom and two drain pipes would ensure that the boat can't be swamped or sink.

And a sophisticated folding mechanism including floats rotating by 180 would reduce the width from 3,50 m to 1,90 in a few minutes.
I submitted the design to Duckworks Magazine's 2000 design contest. It earned me a honourable mention (thank you, Chuck!), but the reader's poll was, well, desillusioning. But hey, I was the only person who needed to like it. So I prepared myself to build my boat.

I bought the plywood and a used trailer in spring 2001. Unfortunately the trailer was a bit to short for the boat, but I thought I could get away with it if I shortened the boat to 4.70 m. At the same time, my wife stated clearly that she would not sleep in such a small boat, and thus the aft cabin became obsolete. I changed the design by doing two straight cuts through the given hull lines (my father had already made the stem and I didn't want to throw it away): I cut off the last 30 cm and the top structures.

With the new straight deck line, the platforms could fold 180 degrees, so the floats didn't need a rotating mount any more. In the changed design there is still enough space for the children under the foredeck and they can even sleep under the aft deck.

Now the actual construction was a very long process since my wife wouldn't let me invest all my spare time in the boat. In fact, without the help of my father, my brother and my sister, I would never have finished the boat (I think my father put twice as much time into the boat as I did). We started in summer 2001, and maybe we spent more time talking than actually working, but it was well worth the time.

The following pictures show some stages of the building process:

Since the hull is made from Okoume, we glassed almost every part of the surface (they say it rots really fast). Although I always used latex medical gloves, I finally got allergic against epoxy. My hands appeared like cauliflower and itched for two weeks! In March 2002, we had to get the boat out of the workshop, which was not easy since the workshop was in the basement. Here is how we did it:
In July 2002, the main hull was finished and we made the maiden voyage with a trolling motor on a nearby lake. We were six adults and three kids and we didn't feel cramped. The main alone is already very stable and you feel safe in it. But I didn't want a motor boat... so I went ahead. The floats were glued together of 1m x 0,5m x 5cm styrofoam plates with a 3 cm bottom of blue foam. Then the project was waiting till April 2003, when I started taking regularly single days of vacation in order to visit my father and work on the boat. We shaped the floats mainly by clamping plywood templates to both sides and then drawing a hot wire along the plywood edges. It worked very well and only about an hour was needed to bring both floats to the final shape with a disc sander.

We laminated them with two layers of 200 g/m^2 glassfibre. Although I used thick rubber gloves, protective paste and wore a gas mask, I got an allergic reaction on the hands again. Maybe it was due to walking in the room without gas mask after the work was done. It is really hard to have that allergy if you're bitten by the boatbuilding bug!

The leeboards are very unconventional too: They hang under the platforms and pivot around an axle made of 1" aluminium tube that runs crosswise through their top an is glued in with epoxy. A diagonal strut which is bolted to the leeboard just above waterline forms a triangle together with the leeboard and the axle which can cope with the high bending momentum.

The proper leeboard is mostly hollow and approximates a NACA012 profile. Each is made by bending two 5mm plywood sheets around a center strip and glueing them to a trapezoidal "nose strip" and a triangular "tail strip". Next time I'd take 3 or 4 mm plywood since the bending required really high forces.

Cross section of leeboard (and no, it's not meant to be asymmetric)

The leeboards are glassed on the outside so that they are very strong and very light - they must be held down in the water against their buoyancy by strong rubber bands pulling them forward and a rigid line running aft. The lines end has several knots and is led through a U-slot so that its length (and thus the position of the leeboard) can be easily adjusted.

The platforms are also sandwich structures with a 40 mm styrofoam core in a lumber frame and two 5 mm plywood sides which are additionally glassed with 200 g/m^2 fabric. Each platform complete with the float weighs about 25 kg. So the boat is at least 50 kg heavier than a 16' unballasted monohull dinghy.

The mast was a gift from a friend and has formerly been used on a 505 dinghy (as far as I know... with only 4,80 m it's suspiciously short). To save time, I used the sails of a small fishing dinghy I had a chance to buy really cheap. They fit well to the short mast... but they have only 7.5 square meters, that is only half the area in my plans. Well for first trials maybe not a bad idea. To avoid jibe-caused headaches, I mounted a surfboard's sprit boom instead of the boom belonging to the mainsail.

The mast is stayed by two aluminium tubes which lead lateral forces directly to the floats and two additional galvanized steel stays which should only transmit the forward-directed parts of the sail force.

Finally the day came when everthing was finished and we went off for a two-day trip on a lake in France. The boat can be folded and unfolded by one person if necessary, but setting the mast up is easier with two persons. The whole setup takes about 20 minutes after a bit of training.

Mid of October is maybe not the best time for such a trip, but after all that work we wanted to try it out! It was only 11C, but we had sun and wind. Lots of wind, I estimate 4-5 Beaufort. The trolling motor could hardly cope with the boat under these conditions and I felt really uncomfortable when we set sails...

After half an hour of completely upright sailing under full sails, I got more confident. The boat behaves very well, it tacks on a dime (having a boom at the foresail and the lack of necessity to change sides makes tacking a pretty negligible manoevre) and even when beating upwind against some nasty waves the cockpit stays dry (apart from occasional drops). As for speed, we probably went at hull speed most of the time but didn't get her to plane. We'll see what happens with 15 square meters of sail.

A really useful feature is the "hawse hole" mounted to the bowsprit. It allows to let the anchor hang from the bowsprit all the time, with the chain in a box in the upper part of the bow. So you don't get dirt into the boat and the anchor can be dropped very quickly.

But still better than anchoring is beaching! We went ashore at the lee side of an island, collected some wood and prepared a barbecue. Maybe beaching is actually the best part of sailing... at least when it's cold and windy.
I know that now a long phase of tinkering with experimental sails and improving details begins. But the boat already meets my expectations completely, I only think it was too much work (estimated 400-500 hours). If I had to redo the design, I'd leave out the styrofoam double bottoms, which means having no self-draining cockpit and no self-draining stowage boxes. With the two floats and the sandwich platforms the boat is already unsinkable, and the only way to get water into the cockpit is by sailing in the rain.

Im also thinking about a deck tent that includes the foredeck and the platforms. It would offer full standing headroom in the cockpit and allow two persons to sleep on the platforms (which are 1,90 m x 85 cm each). Together with a cockpit table that would mean caravan comfort on a 16 foot boat!

(click HERE for Folding Tri study plans)