PROJECT WINDRIGGER April 2009 Instalment
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Last October I removed my 6800mm loa fibreglass catamaran (WRC6800) from its mooring, detached the hulls and dumped its bridgedeck. This catamaran first launched in January 2002, was a good platform for testing ideas, but has outlived its usefulness. I intend to design a new catamaran incorporating following outcomes of this project - the beam-change/trailering system, biplane sailboard-sailrig, fore-and-aft kickup rudders, the vortex generators and steerable centreboards/leeboards, design a new bridgedeck for camp-onboard accommodation followed by design of new hulls. But at present I am undecided whether to design round-bottom or Dory hulls - for the following reasons:
- Sailing the round-bottom hulls catamaran was never as exciting as sailing my Dory-hulls plywood catamaran, which in 15-20 knts. wind would suddenly accelerate and throw up lot of spray - like planing when sailing a 505 and or Flying Dutchman. I had never considered Dory's to be planing hulls until recently reading a book (ref. 1) which lists them as planing hulls.
- When trialing the proa shown in Photo 1, I found its performance under outboard propulsion to be unexciting - sluggish. I designed this hull following the accepted practice of "round-bottom to minimise wetted surface and length to beam ratio of at least greater than 10, to minimise wave-making drag. At speed - it shipped a lot of water over its bow and into the cockpit due to the smooth curvature of this hull which offers no means to deflect the bow-wave water flow off the hull - so its wetted surface must increase with increasing hull speed. Contrary to this, the waterflow from the bottom of planing hulls is deflected sideways from its hull.
- According to Hullform hydrostatic data, my Dory catamaran has less wetted-surface than the round-bottom catamaran (3.1 and 3.4sqm) for the same displacement.
All of this has lead me to investigation of planing with a Dory-hull using a trimaran which I am developing for launching off a beach. It is shown in photos 2-4.
This trimaran differs from existing trimarans in that it is designed to sail with negligible heeling and to have high resistance to pitch-polling - to maximise on safety. To achieve this its outriggers are located forward of the hull centre-of-buoyancy to provide reserve buoyancy up-forward.

Photo 1

Photo 2 - DORYTRI - 3000mm loa, trailering beam 1700mm, sailing beam 3000mm. The centrecase slot has been sealed off.

Photo 3

Photo 4 - DORYTRI - Note the stern-mounted kickup-rudder.
The hull of the DORYTRI was the centrehull of my WRC 6800 mm catamaran. It is a truncated-Dory as it has a transom stern instead of the chisel-shape stern of a Dory. The two outrigger hulls were produced from a Crit 370 fibreglass/foam sailboard by sawing along its fore-and aft-centreline. They are connected to the hull by cross-arm arrangements designed to facilitate investigation of the interaction between the outriggers and hull. Lateral resistance for the DORYTRI is provided by two leeboards which are shown in Photos 2-4 fastened in their up-position. For sailing they are dropped and are free to move in accordance with water forces, or positioned manually - as shown in Photo 5. The leeboards are attached to the hull to provide about 6 degrees angle-of-attack. My decision to use leeboards followed reading pages 52-53 of Joseph Norwood's book High Speed Sailing.

Photo 5

Photo 6 - DORYTRI - hull bottom shape.
TRIAL RESULTS
I first launched the trimaran 19 Dec 2008 and the following are highlights after five sea trials.
- Under outboard power, the trimaran planes with about 1800mm of its hull forward out of the water - at a speed of 14km/hr measured onboard using a TOM TOM car-navigator.
- Its windward performance appears acceptable - the leeboards automatically change on tacking.
- Sails with very little heeling - both outrigger hulls stay in the water - no flying outriggers.
- No noticeable impacts on its hulls when sailing in the choppy waves of the River Clyde estuary.
- The tiller of the transom mounted rudder interfered with the aft stubmast as shown in Photo 6. Remedies is shown in photo 7.
- The outboard mounted as in Photos 2-4, is well-placed for controlling it by a helmsman - but at top speethe outboard leg creates a lot of turbulence and water flow into the cockpit .

Photo 7
DORYTRI RUDDERS
One problem I have encountered with the DORYTRI and my other multihulls, is accommodating the helmsman near amidships and connecting him to the rudder - shown in the following are some of my solutions and problems. I have added this section because it grew into a considerable unplanned problem.

Photo 8 - rudder control arrangement devised to overcome the tiller-interference problem shown in Photo 7

Photo 9

Photo 10 - DORYTRI on its trailer.
FUTURE ACTIVITY
I have constructed a trolley to carry the DORYTRI from its trailer across sandy beaches for off-beach launching. Essential for beaches that threaten to bog a car and boat trailer.P>
I have converted the round-bottom proa shown in Photo 1 into a reversing Atlantic proa powered by an inclined sailrig and incorporating a Dory outrigger hull. I think this is a much safer option than a Pacific-proa - it provides a fail-safe way to fly its outrigger and sail with a friend.
REFERENCE
1. SMALL BOAT DESIGN FOR BEGINNERS by Frank Bailey
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