Why don't catamarans have boom vangs?

[chrisr]

we are another cat that does use a boom vang. in our case a rigid / spring loaded vang. tends to be a bit 'set & forget' as my days of fussing over the last little bit of sail trim are behind me...but it does get used

in our case at least 50% of the function is to support the boom will reefing etc. we have a topping lift as well 'cause i'm a belts & braces kinds guy...but the result of having the boom come down on all those solar panels does not bear thinking about.

in passing : if we ever re-rig the boat i intend to give some serious thought to a wishbone rig. has some interesting advantages for short-hand cruising. has anyone ever tried one with in mast furling ?

cheers,

[Andy B]

Most performance cats have rotating mast and fat head full batten main.
Rotating mast and gooseneck on boom with rotation limiter or control lines make a boom vang impractical.
Tripod standing rigging and full batten main preclude backstay.
Wide main traveller and boomend main sheet are required for forestay tension .

[markiobe]

Originally Posted by Stephen Ditmore

Would love to see more about your custom multihull build, Markiobe!

It isn't actually a custom, it will be hull #2 of a new design with a small production line. The builder already has an existing design production line of about 25 boats so far. Hull #1 (the prototype) is on the water but our build hasn't started yet, (some design issues to still work out) but hopefully starts soon.

Originally Posted by Stephen Ditmore

Also more about above-the-boom vangs, including what Google search term to use to see more about various arrangements. If one doesn't have or want a 2 sided pocket in the main, I'm thinking something akin to a mini-wishbone boom except probably a simple rectangle with a little rounding at the corners just to avoid sharp edges. This would come slightly beyond both mast and boom with "soft" rope connections & control down the front of the mast. Yes there could be a bolt through the boom, but drilling the boom might weaken it in exactly the wrong place.

No idea what search term to use as I've never searched for them! I'm from a dinghy racing background and many skiff/foiling boats use an above boom vang for various reasons. They typically use a fixed attachment at the mast and a track at the boom adjusted by a line, or a 2 piece system where one is a lever arm that has a line at the end (see 49er). Either way you either have 'bad' and 'good' sides (4000) or a small double skin (49er). They are very elegant systems, however, as has been mentioned on this thread, the biggest issue when trying to scale up to a cruising cat size are probably the forces involved which may make it too much trouble.

Obviously the easiest way to make it work on a larger scale is to increase the lever arm, hence the leg-o-mutton or wishbone set up. For our boat I'm still undecided as to what to do, will no doubt have some deep conversations with the rig providers when the time comes.

Originally Posted by Stephen Ditmore

I'm also intrigued by boomless catamaran mains (are America's Cup foilers going to this)?

They already are! For such a high performance boat where aerodynamics play an enormous role, having a deck-sweeper main is so advantageous that removing the boom becomes almost mandatory.

Originally Posted by Stephen Ditmore

If one has a clean & workable traveller control arrangement perhaps a boom becomes unnecessary - a batten along the foot will suffice.
And if the latest innovation in sail making is a "structured luff" how about a "structured foot"?

I had an early catapult catamaran with no halyard that had a wishbone boom hinged in the middle with a control line that passed through a grommet in the middle of the sail. That was an interesting arrangement.

The Italian AC boat with the boom under the deck and other things I've seen lately cause me to suggest: what if the boom we're in the coachroof? By 'in", I mean the upper coach roof is solar panels on beams as necessary to support them. The boom swings under the solar panels & beams. Perhaps the beams run fore & aft so the structure supporting the traveller at the back is also what the beams land on (perhaps the boom swings under that as well, so the boom is connected to it by a car on top of the boom). Then there is a liner under the boom that serves various purposes including keeping the hot air under the solar panels out of the crew/passenger enclosure.

The issue is that it needs a seriously powerful arrangement to provide both downward force for twist control as well as rearward force to flatten the sail. Doing that without a fixed attachment point (the boom) is a real PITA and hence why the AC boats use hydraulic rams and some serious traveller arrangements. The below boom option is kind of a jury-rigged way of doing the same thing and I'd be surprised if any of the 2nd gen AC boats use one as it compromises all sorts of other things.

All that said I can't see it being of any use whatsoever in a cruising cat (even performance focused) as the complexity wouldn't be worth it for the dubious performance benefits at the speeds we operate at. A deck-sweeper main is kind of pointless when a) you're not racing and b) you top out at 15-20kn with averages in the high single digits or low teens.