Thinking About Proas

A Proa is a style of boat which is very fast and very efficient. Proas are symmetrical lengthways and always sail with the same side to the wind, reversing direction and moving the sail when changing tack. On the windward side is a small outrigger (ama) which is weighted by the crew. Multihull.de has a gallery of traditional proa designs from various parts of the pacific.

I wonder if a more modern design could take the form of a trimaran with sliding aka (crossbeams), so the ama on the leeward side is pulled next to the main hull and the ama on the windward side extends away, pulling on the mast via sprung cables. Fresh water is then pumped as ballast into a tank on the windward ama. As a conventional trimaran heels away from the wind one of the amas is pushed deeper into the water, increasing drag and causing the boat to want to turn. Sliding akas could reduce this (I think).

If the wind were on the same side long enough to warrant the effort - thinking of a large boat - stores and equipment could be moved into lockers on the ama to further increase speed. This gives some of the efficiency of a proa but uses more conventional sails and has a stern, rather than two bows. Being able to move the amas may also make the boat easier to right if it capsizes, though I recall reading somewhere that trimarans should be righted bow-over-stern instead of sideways.

Picture is of Queequeg 18, a rather attractive design by Michael Schacht of ProaFile, modified to illustrate the idea. (Queequeg was the noble savage type in Herman Melville's Moby Dick)

Update: This has been done before, Timothy Colman's Crossbow had a sliding aka design and set the world speed record in 1972.

Created 2007-09-30 00:49:36 by strix and filed under things

Comments

Michael writes...

Hi Strix, got your note. Cool idea - as you've found out, Crossbow had that set-up. Frankly I don't know which is more hassle - the "normal" (snicker) proa shifting rudders and rig, or the sliding ama + water ballast trimaran. Maybe half of one, six dozen of the other?

-Michael

website: http://www.proafile.com posted: 2007-09-30 18:37:45

strix writes...

@Michael: Thanks for the reply :-) It is quite possibly an obtuse thing to do, especially considering all the other ways there are to improve on a boat (better sails, handling, hull finish, etc), will let you know if I ever get to building one.

website: http://strix.org.uk posted: 2007-10-1 21:26:32