I was looking at a boat down at the marina today that had a wishbone boom and was wondering what are the advantages and disadvantages over a conventional boom
Regards Don
Look like my avatar Don?
The wishbone is one of the few things I haven't changed or modified on Kankama. It works well for my type of sailing on a cat.
Cats can't have vangs as the cabin gets in the way. They also would probably break a boom as they are very stiff and have roachy mains. This means you have to control twist with sheet loading, so loadings can get really high - similar to the boat's displacement.
So designers put long travellers on cats. But they aren't long enough for a broad reach so you sometimes see cats with mains way oversheeted or with bits of rope to hold the boom down when eased. The ropes don't work too well and the main slowly wears itself on the stays as the boom goes up and down every wave and gust.
So the wishbone gets around these problems. The wishbone acts as a pusher vang. 49ers and other skiffs have pusher vangs. A wishbone is just like a pusher vang pushed all the way to the end of the boom. So you don't need a normal boom.
Kankama is probably the only 38ft 4000kg cat with a 4:1 mainsheet system and no winches. She doesn't need them. I can trim the main with one hand up to 12 knots and two hands until I reef. The wishbone also protects the main from rigging chafe and, as it swings in and out like a door, the clew doesn't go up and down so the main is very well cared for at all times.
With the little storm jib up, I can sail the boat to windward in 22 knots without a winch handle, the storm jib sets better with a grind or two but it can be done.
I don't know why more cats don't have wishbones, as they really suit the large high load mains. You can't tighten your forestay with the sheet loading as there is little. I have made the central sheet position higher with a composite loop to have the same effect as pulling the traveller to windward - much any skiff or sports boat.
So I saved money in deck gear (no boom, traveller and winches - made the wishbone out of excess hull material) , got an easier boat to sail and a faster one (at least downwind) as well. So yeah, I reckon wishbones are pretty good for a boat with high sheet loadings. Kankama still sails pretty nicely to windward, I don't think we will see them on race boats but you mono guys have nice and low load mainsheets all the time. I race monos and love vang sheeting, the wishbone gives you vang sheeting without the huge loads.
PM me if you want a closer look
Phil
Hi Phil
Thanks for the information
As you suspected it was your Cat i was looking at
Is there any disadvantages of the wishbone boom on Cats or Mono's over a conventional boom and is there any reason why they are not used more
Regards Don
Yeah, you are spot on Don, with your inquiry, "why we don't use it more often"?
Well, Sun Toy uses it with his cat rig, (Graham Radford) Nonsuch designs use it since the beginning of times as well.
I think Kankama's set up is really handy and l could not imagine another reason not having more boats set up like this just because we are a conservative lot not really fond of innovations.
Sun Toys 70k carbon fibre mast and wishbone might be another reason but the set up on Kankama proves it otherwise.
The huge sheet load on a mono would demand a pair of good winches but that's all. 
Sun toy is a great example [ if expensive ] way to use the wishbone setup. Wylie cats in America have been using wishbone rigs on their Wylie 30 yachts for years.... If you look at the Radford web page it states "Graham Radford worked in conjunction with designer Tom Wylie at Wylie cat in San Francisco and Watsonville, CA to develop a suitable rig for the new 12m design." I personally believe it makes more sense short handed sailing... Why not so popular ? Most yacht racing you see have teams 5 - 10 bodies , hiking ,swapping genoas running about not 2 -3 people sitting comfortably looking up at the sail as the mast self depowers in the gusts.... my 2 cents worth.
Wishbones are not that great on smaller boats with smaller foot lengths on the mains. On many racers, the ability to constantly adjust leech tension is important to avoid head stall. Also you might want more twist in choppy conditions. The wishbone limits the ability of the rig to do this.
You will probably only see wishbones on long footed mains on monos, sailboards (of course), and one or two cats. Most cats sailors are happy to trim less than me, so they often set and forget. My not reasonably fast cat, often gets sailed in tricky areas so the ability to quickly trim the main correctly makes it more pleasant to sail as well as making the boat faster because the main is better trimmed. But if you are not an ex-racer trim worryer it may not be so important.
As KK says, his rig works brilliantly but smaller racing monos need to have more ability to adjust twist. The other issue is that while freestanding rigs can depower by themselves, many racers want the ability to adjust the extent of the depowering. When fractional rigs first started to dominate ocean racing years ago, the Kiwis used to set them up so they would depower dramatically automatically, but later they shifted to a more controllable setup.
When you race windsurfers, you notice the problems that come with being unable to adjust twist in the same way that a conventional rig can. And racing on or against the few classes that sail as cat (main only) or sloop rig really underlines the huge aerodynamic benefits that a jib can give, and its huge light air power - lots of development dinghy classes have tried to use cat rigs but they just don't go as fast.
Finally, lots of us just like having another sail to play with, and with a modern short overlap rig you can easily handle the heady yourself and sail under main only when it's windy.
Select to expand quotesirgallivant said..
we are a conservative lot not really fond of innovations.
I'm not sure if that's the issue, at least with racing boats. When you look at developments like assymetric kites you can see that they caught on very quickly; in fact a lot of the time they were used before they were really working properly. Lots of people in the sailing industry went into hysteria over shortboard windsurfers, production skiffs, sportsboats, canters and foilers. They were not just fond of the innovations, but they claimed that they were "the future of sailing" and ignored the downsides.
I've done a huge amount of research into the history of developments in dinghy sailing and a lot of research into yacht sailing. Sailing has often been very leading edge - it was into carbon fibre the same time as Formula One was, for example. It lead Formula One in terms of computer-aided design, I think. When we ignore innovations it's normally because they are impractical and not worth it, IMHO.
