I asked Phil on the Boatdesign forums what he thought of the wishbone boom on his Robin Chamberlain design catamaran Kankama, he likes it, here is his reply.
I love my wishbone and was happy to see Keisha fitted with a wishbone/boom hybrid. Interestingly Stanton used to own Songlines - the cat that got me onto wishbones.
As the original poster says - every normal mono has a vang so why don't cats. I think it is because beach cats don't and that the cabin gets in the way on larger cats. Add to that the extra loads of non heeling and a stable platform and it gets too hard for the engineers.
Kankama has had a wishbone for all her 12 years. In that time I have rebuilt her cockpit, added a new cabin, changed the steering twice, built a back deck and am in the process of building new dinghy davits. I would change the boom if needed but the wishbone is wonderful.
You get fingertip control of the main - no winch needed, you save thousands of dollars - no travellers and winches, no boom and gooseneck, increase crew safety - no boom and no traveller near fingers and you go faster. So you go faster, save thousands and its easier - should be an easy sell but it's not.
A wishbone makes downwind sailing faster as you can ease out the main fully and the sail swings out like a door with no twist. The sail is protected from chafe by the wishbone. Upwind you get less twist and so keep speed up too.
A couple of my friends came out sailing with me before they ordered their rigs. They liked the wishbone but felt it was too way out to put on their boats but for me the advantages are obvious and stark. You need a different rig setup. The three stay a side no spreader rig is required - this saves even more money in mast hardware. The lowers should be about 30 percent of the distance up the mast to handle the wishbone's forward thrust. I almost sold Kankama years ago but that meant I would have had to got a cat without a wishbone and I couldn't do that.
Here is a link to a youtube video of Phil giving a tour through his boat some neat ideas integrated there.http://www.youtube.com/watch?v=XEiIQn6Ikls