Questions Wishbone - Birig, Rotating, Unstayed Wing Masts - Catamaran

[jorgepease]

I've read every thread on wishbones but I am left more confused. Some people say wishbone rigs suffer upwind, others point at Wyliecats and say not a problem, very simple, inexpensive.

- Who is right?

- Does a Wishbone boom sound like a good option (compared to a rigid boom) for a bi-rig unstayed rotating wingmast on a 75 foot performance cruising catamaran.

- Will a Wishbone boom work well with long aspect ratio sails.

- Do you know of any similar boats rigged this way?

This is the boat I would consider rigging a wishbone on

 

[Doug Lord]

Two very modern trimaran foilers--the TF10 and the SuperFoiler use half wishbones-less weight and still very effective...........
Stb. tack wishbone half visible:

Port tack no wishbone visible:

 

[Angélique]

Hi Jorge, check out these of Bernd Kohler's K-designs . . .

- 4.25 m - DUO 425 - Wishbone boom - Bi-rig
- 8.00 m - DUO 800 - Wishbone boom - Bi-rig - = - an option in the plans
- 11.50 m - Pelican - Wishbone (boom or gaff ?) - Sloop
- 10.00 m - DUO 1000 - Rotating masts - Bi-rig - Wishbone gaffs
- 12.00 m - KD 122 Voyager - A-frame mast - Wishbone boom - Sloop​

 

[PAR]

The wishbone boom doesn't affect performance, unless it's a straight stick and only then in very light air. It is heavier than a more conventional approuch, though it can save some rigging, as a trade off to a degree. I use and make 1/2 wishbones regularly, which saves some weight, though special attention needs to be made in regard to compression loads, changing the shape of the boom.

 

[Doug Lord]

The half-wishbone seems like a good solution for use with a deck sweeping main.

 

[jorgepease]

That's interesting Doug, that answers the high aspect ratio question. So looking at those Trimarans the tack of my sail would connect down at the base of mast like those shown and it would just clear the salon, I like that. The angle of those wishbones looks pretty flat though?


Angelique, I have seen these designs, love his innovative approach to so many things. Just spent an hour re-reading all his site. Very interesting A frame mast but I don't want to make anymore changes on things settled lol )

Par do you stow the sail on a half wishbone? I'm thinking to build mine of carbon fiber, don't think weight should be too great and I hear it's nice with the wishbone to let it catch and stow the sail there.

 

[Angélique]

Hi Jorge, check out these of Bernd Kohler's K-designs . . .

Just saw the 8.6 m (28' 2½") KD 860 now also has a Wishbone sloop rig option, but here it's not the boom, but a Wishbone gaff, to create a squarehead.

This could be similar to the Wishbone rig of original Pelican in post #3.

Here's a KD 860 slideshow vid, it shows a drawing of the original sloop rig at 0:11, and the squarehead wishbone gaff sloop at 0:23.

 

[Angélique]

Angelique, I have seen these designs, love his innovative approach to so many things. Just spent an hour re-reading all his site. Very interesting A frame mast but I don't want to make anymore changes on things settled lol )

Since you're not buying it, I'll conclude I've done no harm here yet . .

 

[jorgepease]

Yeah I saw that, very cool. Also cool video, now I see about the asymmetrical hulls.

 

[hump101]

Wishbone booms do affect performance, because they don't allow the sail to twist off in the same way as a regular boom and track arrangement. This is generally a good thing on a high performance boat, as you don't want twist, which is why a track is used with a normal boom as a kicking strap can't easily cope with the forces involved in a big high aspect rig. The wishbone eliminates the need for a track or kicker, and massively reduces the mainsheet loads, but if you are looking to induce twist, e.g. to account for wind shear, you need to do so via tuning the mast stiffness and leach shape, combined with a powerful downhaul. All well understood by a decent sailmaker so you shouldn't have a problem getting a suitable sail made.

On high performance boats like yours, the apparent wind dominates at low windspeeds, and hence the need for sail twist is not so marked, hence a wishbone boom is a good solution, particularly with rotating unstayed masts as you don't need twist to dump the sail in extreme conditions.

 

[Gary Baigent]

I did a half wishbone, metre high mounted boom on Flash Harry back in the 1980s. The mast/boom attachment was a stainless ring epoxied slightly forward and to one side of mast track.
Oops, wrong photograph, will search - but this is the boat. Here's the correct image with half boom. No that too is later photograph, will search some more. Finally.

 

[jorgepease]

That is good to hear hump101

 

[redreuben]

Jorge;
The Robin Chamberlain Cirrostratus 10 Trimaran used the Wishbone rig, not a lot of information out there I'm afraid, here's what I have,

Rob Denney at Harryproa uses them a lot on his rotating unstayed masts and would probably be a good person to bounce ideas off.

 

[redreuben]

Hump 101; Surely you can open the leach by letting the wishbone run up its mast track a bit ? Aah yes but that would also make the bottom fuller. Hmmm
just thinking allowed.

 

[jorgepease]

Thanks, I googled that and found a few more pics of it.

Yeah, I emailed Rob and he was the one that suggested it as the most logical option. I just wanted to bounce it off others to gain a little better understanding. I am now thinking it's the right way to go as well and I actually like the look of it once I drew it with the boat.