Tuesday, April 28, 2009

The Tahitian sprit sail



Certainly one of the most intriguing rigs to be observed during early European contact was the sprit sail used by the Tahitians and in a less radical form by the Hawaiians. It has a very high aspect ratio and a very interesting top shape. (Tip vortex reduction?)
It was not convenient to use and had to be tipped up fully rigged like a windsurfer sail. There does not seem to be a way to reef it. It is possible that the sail could be brailed up against the mast if the boom were removed.
Painting by Herb Kane.



I built a small version of this rig for my Ulua some years ago. Instead of a sprit along the leech to support the head, I used some fiberglass rod battens in curved pockets to support the head. While very efficient it still could not be lowered out on the water or reefed.



I came up with another version of this rig for a 27' Tahitian tipairua (catamaran) that I built for a client. This is actually a cross between a sliding gunter rig and the Tahitian rig. It had full length battens throughout and could be reefed while underway. I used a sprit boom to reduce the twist from a very high aspect sail like this. It goes very well to windward.

4 comments:

Proafile said...

Looking at your Tahitian sprit for the 27' cat, I was struck by how much it resembled a "crab claw". Quite strange, considering the obvious engineering/aerodynamic differences between the other crab claw. And yet, they could both be called 'crab claws", and it reminds me how the ancient navigators were navigating symbolic seas as well as the Pacific.

Cheers, Michael

Keith said...

Great stuff! Could the boom have been fabricated from some kind of flexible spar material? In the pictures I've seen, it appears to my uneducated eyes that the half-crabclaws had a brailing line between the recurved leech of the boom and the mast.

I'm interpreting this from what I've read in Naomi Chun's "Hawaiian Canoe-Building Traditions".

Thanks for the beautiful images! Regards

Gary.Dierking said...

On some drawings you'll see a lashed scarf joint close to where the boom or sprit turns upwards. It seems to me that you could untie this and brail up the whole thing against the mast. Drawings of larger tipairua always show climbing steps on the mast that may have been used to help furl the sail.
Gary

Anonymous said...

OK - here's my theory. The curved part is the leading edge -opposite
of the western type sail - the Tahitian mast being the trailing edge of the sail.
The top of the sail is more or less flexible - which bends the top part of the sail
into a reverse winglet shedding the tip vortices. If you have a socket type attachment- the bottom of the leading edge can go past the mast - and you can wrap the sail up like a hang glider sail - then you don't have to take the whole sail down. This also gives you a way to reduce the sail area - effectively giving you a way to brail the sail up/down.I reckon the single hulled version of this sail could of been the downwind lagoon hotrod...LOL!
A lot of work and resources went into this sail - and they're not going let the sail flog itself to death on the shoreline when not being used.Heck I can remember how my relatives got super upset when a number of tapa cloths weren't stored correctly.
OK got to go and build one...