The Multichine Proa
by Othmar Karschulin

(translated from the original German by the author, from the websites at: and

1. Building Report        2. Sailing Report

Part I - Building

Basic Concept
The conception of the P5 is a light car-toppable proa for 1 to 2 sailors. Both hulls are multichine designed for plywood/epoxy (stitch&glue) building. The total weight should be 70-75 kg. The basic idea of the boat is borrowed from Gary Dierkings strip planked TARAWA.

Cutting Plans
The main hull has three parts: lee plank, luff plank up and luff plank down. Every plank could made from mirrored halfs from 4mm plywood. Next step is to glue a stringer (20x20mm) along the upper edge of the lee plank (may be a second one into the middle) and of the upper luff plank for fitting the decks later. Annother stringer should fixed at the below edge of the upper luff plank. For more stablity use a keel batten (20x20 mm) as backbone. Then the traditionary holes through the below edges of the lee plank, keel batten and below luff plank.

 Please Note: All cutting plans and instructions are only proposals!

Building Pictures


Cut out planks with bulkheads

Main hull set into the support???. It's useful to build the support very strong,
 because the multi chine hull is unstable before gluing.

First the put the lee plank into the support, then the keel and the lower luff plank. Next, stitch all together with copper wire. If all is perfectly arranged glue it together with epoxy putty/glue. After the glue has dried strengthen the keel section and the connection of the luff planks with stripes of 200 gr fiberglass.

If the hull is stable, you can insert the cockpit floor and the beam fittings. Pay attention to the paddle fittings. They should be match the length/diameter of the paddle you use.
See details

Finally, fit the small decks and the wood poles for the webbing between the beam fittings. Now all woodwork has finished and you can start sanding the surface ...
The ama is built just like the main hull (aka). It's simpler because the hull is symmetrical and it straightens itself after putting the bulkheads in.

Ama ready for sanding and coating. Here you can clearly see the arrangement of the poles between the beam fittings.
See details

For the first time both hulls are fitted with the surf mast beams and with the 'test' sail made of polytarp.


The rig functions like a seesaw. By changing the bow after shunting you pull down the yard with the sail to the new bow.

A good example is this rig at the homepage of Gary Dierking    or in the Gibbons-Special at This Gibbons/Dierking rig has a simpler handling in opposite to the Crab Claw sail. Also you should do easier maneuvers at the overcrowded lakes here (Remark: This I thought before I tried it in reality. See 'sailing experiences' below).

Fittings and running lines 1
Fittings and running lines 2


The Gibbons/Dierking rig has the advantage (like the Crab Claw) of needing no shaped camber, so you can cut it yourself. I used a white standard polytarp like you can get here in homeworker shops, double glued tape like you use for carpet and to protect the overlapping parts, a special repair adhesive tape.

Cut of the sail out of a minimal tarp
Cut of the sail measurement (for first test)

Detail Views

Drawing - Hull Arrangement
Drawing - Beam fittings, Webbing
Drawing - Construction - Paddle fittings
Drawing - Yard connection
(now out of date, because no bamboo was used.
Used windsurfer masts are cheaper in Germany)

The plans of the P5 are free for building a boat for private use. Commercial replication is not allowed. For rightness of all plans and advices are no guaranty is given. Most parts in this descripton have only a character of proposal and must be verified by the builder himself. Be creative and courageously - and you can sail a P5 like me!

Part II - Sailing

The Difference between Theory and Reality

The boat was finished to the extent that we did not know what else could be done.  From here, only experience would show us what was missing: and this is exactly what happened.

Before the sailing story, some hints for building:

  • Use 1-2 stringers for every hull side, otherwise the 4 mm plywood makes visible cambers between the frames. The sleight additional weight more will be justified by a better view and naturally, more stability.
  • The windsurfer masts we used for beams an mast were not stable enough. They will not break, but they are too limber for this application. The whole structure of the boat would be too flexible, which would have a bad influence on the rig and sail shape. A stiffener of carbon roving makes it somewhat better, but for a future boat I would use alloy pipes with a diameter of 50 mm and 3 mm thickness.

At last we were ready for launching. Transporting on top of the car is absolutely easy. The beams rest on the side to side braces of the car top carrier.  In ten minutes the boat was ready to go on the car's roof....

....and in a half hour, the boat was assembled and ready for sail.

The First Trip

It was a beautiful day, except that the wind was gusting to force 5.  Nevertheless, this was the day!  As soon as we assembled the boat, we were on the water - a little prematurely - but we would finally sail.

(The first contact with its element. Here you see the large leeward bend of the mast made among others by the curve of the beams)

For us, however, fate had prepared something else. Because of the tendency of the boat to luff,  we made a big curve directly into the foot bridges of the nearby marina. We stayed ashore until all the lines were sorted.  Fearlessly we pointed the bow toward the middle of the lake, and ran, close hauled, into the 'open sea'. In fact pretty successfully, as we sailed very fast, although the two of us were 2/3 of the total displacement.

Steering, by moving our bodies along our sitting plank to change the center of displacement, was very hard because of the gusty wind and the boat's tendency to luff. The steering paddle seems to have no effect. The result was that we sometimes got a gust from the 'wrong' side and the rig came down to the wrong side too. But because it was held by rubber ropes, nothing was damaged. The wind had, in the meantime, reached permanent force 4 and we had no chance to set up the rig again. The paddling home I don't need to describe ... we we used the time to talk about the 'Why'.

(The yard is bend to much astern. But in principle the 50 $ sail looks good)

The Experiences And The Redesign

Basically, it was a positive experience. The boat floats almost exactly at the theoretical CWL and carries two sailors who weigh about 150 kg (with a boat weight of nearly 75 kg). The asymmetric multichine hull allows it to sail close hauled with acceptable leeway. The hulls/beam connection with a simple webbing proved strong enough. Also the polytarp sail was effective enough to give a good speed.

The following figures show something about the 'accidental research'

The figure above shows how the curve of the beams and the sitting plank, where the mast stands, cause the mast to bend. Additionally, stretching of the shroud exacerbated this effect.

Moving the CE by shortening the sail and controlling the clew at the boom should optimize the sail shape.

Problem after the mast extension. The Schot angle becomes smaller and the sail is more strongly distorted.

 Additional trim possibilities

Following changes were made before the next test sail:

  • Stiffening the beams and the mast via carbon rovings
  • Stiffening the sitting plank
  • Lengthening the mast by 50 cm to bring the CE nearer to the bow by arranging the yard more vertically
  • Clew control at the boom
  • Doubling of the rubber ropes to make the rig stiffer
  • Shortening all lines to their necessary minimum for simpler handling and to prevent catching oneself ;-)

Second Test

It was a beautiful summer day at the Brombach reservoir for the second sailing test. The wind offered a 2-3 force breeze - great conditions! After an hour of sailing we came back to our starting point. In that time we had an eventfull trip. We tested the steering by moving the center of gravity and controlling the sail trim. It functioned well. Moving to the bow causes the boat to fall off, and moving astern means heading up. But all must be done alertly and with a lot of feeling. The boat accelerates rapidly - you must immediate close in the sail - and in the same time move back with your body(s). The P5 is no boat for 'coffee sailors' (which in German means 'cushy'), you are continually occupied. If you are sailing with two aboard, permanent cooperation is needed:

Go to front, go back, pull here, etc.' , especially during shunting maneuver.

After the first test run I risked a single-handed trip. Alone, you are much more tranquil because you quickly get the right feeling for the boat and move automatically in the right direction.  Also the speed increases naturally with less weight aboard and so I could sail the first meters with a flying ama.

Of course, this Bavarian lake is not the original home of a proa. Constant turning and gusty winds are not useful conditions for sailing such a boat. As quickly as it accelerates,  it stops - and if in the meantime the wind turns - you get it from the wrong side. The only potion is to turn the boat with you paddle. BTW, as an Atlantic proa the P5 runs surprisingly fast ;-).

At last, a word about the steering paddle. On a close reach you don't need it, it hinders more than it helps. By moving the center of gravity you can steer until you are on a beam reach. Downwind, you must use the paddle.

Here you can clearly see that the lower part of the sail has too much 'belly'.


The P5 is a basically well-tried boat. It's a fun machine for sailors who need an alternative to 'boring' beach catamarans. With a better sail shape and maybe better sail cloth, I believe the P5 should sail as fast as a comparable beach catamaran like a Hobie 14. And if not, I promise you will sail it with at least twice the joy.

Next year we will change the rig to a Crab Claw Sail to compare the rig types. We will inform you.

Othmar Karschulin/Phil Young