Boat designer Bernd Kohler has just released building plans for a new sailboat he calls “Tiny Tri.” This comes on the heels of his successful “Little Tri“.
Bernd sent me the following info after I was first alerted to this new design by Brian Pearson, one of our readers. (Thanks Brian!)
Click on the images below to enlarge for better view.
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TINY TRI
by Bernd Kohler
K-designs
Here my next small outrigger/trimaran – the TINY TRI. This time a tri which is only 4m (13’3“) long.
One main reason is that I want a boat which is easy to transport on a car’s roof rack. The hull will weight about 27 kg.
Okay, a boat is for sailing and not for road transportation in the first place. The very fine hull will slide easy through and over the water. The amas are sort of big water skis. They are mounted high. The have an upwards angle in the longitudinal direction.
The amas are also mounted at an inward angle. In this way, when they touch the water, they will easily plane and generate the least possible water resistance. By the way, I, and owners of the LITTLE TRI, observed the positive effect of the angled amas.
The hull is (again) a sharpie hull. Construction is from 6 panels of 4mm plywood, good quality plywood. As usual, I use the plywood/glass/epoxy technique.
The hull and amas are build on stringers. No stitch and glue technique. Count the steps and you see what I mean.
For a stitch and glue build:
First, drill the holes to the keel and sides.
Second, wire the sides together.
Third, add fillets between the wired areas.
Fourth, remove the wires.
Fifth, fill the gaps and holes between the first fillet parts.
Sixth, sand the fillets to receive the glass strip(s).
Seven, add the bulkheads.
For the slap sided sharpie as this hull is:
First, mount and glue the keel stringers to the sides.
Second, place the bulkheads.
Third, add the keel. There is a raw hull.
The difference is obvious.
I designed wooden akas (beams) because many customers can not get correct aluminum tubes in
their countries. Connection to the hull is by Dynema ropes and to the amas by bolts.
The rudder system is more or less the same as on LITTLE TRI. The open rudder housing is very handy
when the boat is sailed onto a beach. The rudder slides back without damaging the rudder. No rudder
up and down haul because the rudder can be reached from the cockpit.
I again use an outside dagger board. That a boat with an outside board is slower than one with a
centerboard is logical … but 1/10 knot? Or how much? I don’t care. I prefer a torn outside case to a hole in the
boat if something is hit hard by the dagger board.
The dagger board can be canted forward or backwards to trim the boat. I sail the board canted forward. Reason, no ventilation and by ground contact the board slides aft and up by it self. If the board floats then use a wedge from a soft material to keep it in place.
The sail is furled by mast rotation. Nothing new here. It could be sailed without a boom but the drawback is that it’s not very efficient. Low booms can be dangerous. Never pleasant or downright dangerous when hit by a boom. So I designed for a wishbone boom rig. I like these sorts of booms. The wishbone boom is high enough not to be knocked on one’s head.
A wishbone boom needs no boom vang or mainsheet traveler to be set for any given wind angle. To have a sail which furls by mast rotation and a have the wishbone boom was the challenge.
The solution is to mount the wishbone on a pole forward of the mast. The geometry of the wishbone shape and pole position gives freedom of movement of 58° to each side. The boom has a quick to topping lift. The vang rope is mounted on a rotation device on the top of the mast not to interfere with the mast rotation.
Sail Area is a modest 7,2 m². A good quality windsurf mast is used. The mast stands free and is mounted on an Aluminum mast extension. The rotor for the furling rope is also mounted on the extension.
The drawings for the furler, mast rotator, goose neck fitting, wishbone boom are part of the drawing set. Any amateur can make them. And if need be, any good machining shop can also make them.
Construction time will be about 180 hours. Main material: 3 panels of 4 mm plywood, 1 panel 6 mm plywood, 30m fir 19×19mm, 12 m² glass clot 10 kg Epoxy.
The akas are fastened with rope to the hull and with bolts to the amas. Setting up of the boat will take about 15 minutes and can be done by one person. As mentioned, the heaviest part, the hull weights only 27 kg.
The plans consists of 33 drawings, transferred DXF CAD/CAM drawings to PDF and the construction manual. Costs US $60
Building plans are available from both Duckworks –
http://www.duckworksbbs.com/plans/kohler/tinytri/index.htm
and Bernd’s own website –
http://ikarus342000.com/Tinytripage.html
Thoughtful sail plan. I love a mainsail that furls on the mast, simple lightweight, quick to adjust. The challenge of adding a boom is handled in an interesting way. The Hobie Bravo also has a furling main with a boom option, but I haven’t examined it closely. And of course, jib booms on furling jibs have been around a long time; also addressing the problem.
I wonder at what points of sail the boom makes the most difference (being not much of a sailor myself)
On all reaching courses.
On a reach course. Sails without a boom can no longer be optimally trimmed.
Bernd
As a canoe sailor I was intrigued by your Little Tri but thought it too much boat for easy car topping. The Tiny Tri looks like it might be just what I’ve been looking for in a small trimaran. Can you provide a little additional information on the design? Will the 4 meter hull get up on plane? Does it tack easily? What speeds do you think it capable of? What are the cockpit dimensions? Does it have a self bailing floor. How is it sailed, from a seat inside the cockpit or on a tramp?
Very interested in this design, looking forward to your response.
Little Tri is a handful for car topping. It is a great boat for camping trips with a lot of room and also the ability to handle a big load. An extra weight of 170 lbs is no problem for the boat. The cockpit is 2m long and wide enough to sleep in.
Tiny Tri was from beginning designed for low weight. The hull weight a mere 27 kg. A canoe from the same length weights normally more as you will know. Only some skin on frame canoes can be
a bit lighter. The low weight comes from somewhere. So no self bailing cockpit. A cockpit floor will cost an other 3,5 kg. But it can be done of course. If a self bailing cockpit is used the seat will be very uncomfortable. I personal prefer to sail from the tramp. It is up to the builder. The cockpit is 1,35 m long and has a of 0,5m wide. Because of the big dagger board the boat will tack easy. The system has proven itself on the Little Tri which tacks like a very good dingy. The construction water line (CLW) is drawn on a sailing weight of 180kg (397 lb). At this weight the boat will be already at 7 knots in plane. The boat will be good for about 12 to 15 knots. I am always wary to give speed prediction for a small and light boat. Wave conditions will play a major role how fast the boat will be. Have fun Bernd
Bernd,
Thanks for the additional information. The design sounds perfect for car topping and the construction method ideal for a sharpie type hull. I am intrigued by your innovative use of a furling mast with a wishbone boom and your friction mounted leeboard and rudder arrangements. I will be placing an order with Duckworks and looking forward to viewing your plans and preparing for a new build.
Regards,
JW
You should use a leeboard. If it’s hit, it will pivot up and not tear up your boat. Multiple angles fore/aft to get the proper angle for the point of sail.
Sorry David, missed your post. Moved from France back to the Netherlands.
The boat has a leeboard, only camouflaged. The board can swing back and forward for proper angle of sail
it might not be applicable to tiny tri, but what are your thoughts on non submersible amas against low buoyancy types. regards Tony downs
Hi Tony,
It depends upon the center hull. Some small tri configurations, for example, are really stand-alone boats that utilize low buoyancy hulls as amas, which serve to further stabilize the center hull. Other center hulls literally cannot be used apart from larger, higher-buoyancy amas that were purposely designed to work with those center hulls. Such amas tend to be the “non-submersible” kind. These latter types of boats are really “true trimarans” in the sense that the center hulls cannot work apart from their amas.