Low Aspect Bermuda Rig

BLUF:
My question is: Wouldn't a bermuda rig with similar AR offer these same characteristics with most the additional benefits of the bermuda rig?

I have pouring over Marchaj's wind test, as well as a bunch of other material on oceanic rigs (de Piazza et al, M. Georges, etc) and how certain rigs out preform the bermuda rig. The reasoning seems to center on the vortex lift generated by quasi delta sails. If you compare these sails to the wings on the Concord you can see the similarity:
Thamakau of Fiji https://www.herbkanehawaii.com/product/thamakau-of-fiji-2/

https://www.heritageconcorde.com/the-wing
And the fact that the crab claw is a low stress rig.

I'm picturing a rig with a large possibly boomed/poled jib/genoa and a smaller main, a mast height similar to the length of the boat stepped midway fore and aft. (the boomed genoa would be for on a proa)
Thanks for your thoughts.

BMP said:

BLUF:
My question is: Wouldn't a bermuda rig with similar AR offer these same characteristics with most the additional benefits of the bermuda rig?

Click to expand...

Sorry, I do not understand the question. You appear to be comparing a bermudan rig to a bermudan rig?

Sorry, I was wondering if a Bermuda rig with a similar AR to a crab claw would generate the vortex lift while still having the benefits of being a Bermuda rig.

I think the vortex lift requires a highly swept leading edge so the answer is no. There has to be a vortex somewhere if there is a pressure difference between each side of the sail, usually at the head of the sail, and another at the foot unless you can close the gap between the foot and the deck. The ultimate low aspect bermudan is probably the American catboat with the mast up in the bow (or do they all have a gaff?). I imagine these boats need a giant rudder to counteract the offset of the thrust line when sailing downwind; maybe a catboat sailer can tell us...

To my knowledge nobody has been able to replicate Marchaj's test and prove the superiority of crabclaws. Just use whatever type of sail you want, low (and high) aspect ratio bermudans have been used successfully on proas, in every possible configuration. The big advantage of crabclaws for proas is their ability to vary the CE in all directions, wich is a little bit more complicated to emulate with a jib/main combination.

Thanks so much for the input.

alan craig said:

I think the vortex lift requires a highly swept leading edge so the answer is no

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I was wonding if the swept luff of the headsail would generate the vortex if it was at the same angle as a crab claw. Or if an aft(ish) mast rig would also work.

Rumars said:

To my knowledge nobody has been able to replicate Marchaj's test and prove the superiority of crabclaws.

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Here is a pdf of just such a test:
View of Wind Tunnel Measurements of the Performance of Canoe Sails from Oceania. https://thepolynesiansociety.org/jps/index.php/JPS/article/view/109/pdf
The caveat is that while the crab claws numbers are better you only get the one sail, unlike the bermuda's horses for courses sail inventory.
The performance and low stress/tech aspect of the crab claw is very appealing as well as the less precise sheeting needed, but the lack of true reefing is kind of a deal breaker. Brail lines work to a surprising extent and lazy jack allow for almost instant dousing, but don't allow for less sail area with decent sail shape. A swept headsail with a boom and roller reefing is an appealing thought hence the Bermuda question.

Thanks again.

While the autors of that article quote Marchaj with “the practically extinct crab claw type of sail -once used by the Polynesian seafarers—is superior to the fiercely guardedproduct of racing and rating rules”, they do call it a hypotesis. More importantly they don't test any form of bermuda sail, so the article never compares oceanic traditional forms with it.

The low stress/tech is deceiving, woven sails are actually not flat and the rig has multiple running and standing stays.

You are correct, the pdf only duplicates Marchaj's results with the Santa Cruz sail not compares it to the bermuda. So would it be possible to make a bermuda rig with the weak materials that can be used for crab claws?

The triangular "bermuda" rig has been around from some time, and it's predecessor the lateen even longer. Synthetic sail material is barely 70 years old, before that it was all natural materials, the sailmaker was a regular crewmember and sail mending was a normal recurring activity. So yes, you can make a bermuda sail from woven palmleafs and use coir cordage, it's durability would be the same as a crabclaw, as would be the necessary construction techniques. The ideea that the bermuda rig is high stress and high tech by definition is false, it just evolved to that as our materials improved.

Great reply. Thanks

BMP said:

BLUF:
My question is: Wouldn't a bermuda rig with similar AR offer these same characteristics with most the additional benefits of the bermuda rig?

I have pouring over Marchaj's wind test, as well as a bunch of other material on oceanic rigs (de Piazza et al, M. Georges, etc) and how certain rigs out preform the bermuda rig. The reasoning seems to center on the vortex lift generated by quasi delta sails. If you compare these sails to the wings on the Concord you can see the similarity:
Thamakau of Fiji https://www.herbkanehawaii.com/product/thamakau-of-fiji-2/

https://www.heritageconcorde.com/the-wing
And the fact that the crab claw is a low stress rig.

I'm picturing a rig with a large possibly boomed/poled jib/genoa and a smaller main, a mast height similar to the length of the boat stepped midway fore and aft. (the boomed genoa would be for on a proa)
Thanks for your thoughts.

Click to expand...

Big picture, you are comparing two triangular sails, point at the top vs point at the bottom. The point at the bottom has the advantage of presenting more sail area to higher wind speed up high -that is all. The rest of the assertions about efficiency, stress, and lift I would question because you can't separate the performance of the sail from the boat. The reason for putting the pointy end up is that sail power is often righting limited so you can put up more sail pointy side up and get higher aspect ratio- not to mention that the lift distribution is closer to elliptical optimum. Multihulls typically have more righting, less drag, and wider structures that allow more direct rigging angles -that is where the lower stress comes from.