open bridgedeck catamaran design

brian eiland · Jan 19, 2026

catsketcher said: ↑

The wishbone system makes taming the main very easy. I love the spreaderless rig as it cheaper, allows the use of a staysail (we furl the genoa above 18 knots and sail with the storm jib to windward), has the same amount of wire as a double diamond rig, allows me to reef and pull the mainsail up on a square run in 25 knot tradewind conditions (no spreaders to poke into the sail), wishbone means you have nothing to brain yourself on, saves thousands on deck gear (traveller, blocks, winches) vangs downwind beautifully, prevents mainsail chafe (no mainsail oscillating up and down with the waves), and cleans up the cockpit no end. For me the lack of wishbones on other cats and the design of the cabin was one reason I never thought of selling Kankama when we weren't cruising for 12 years.
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Just reading back thru this subject thread, and found this posting rather interesting,...taming that mainsail

PS: more from Catsketcher

Sweepback is 30 degrees for shrouds - pretty common I find.

As for chafe and the wishbone. I ease the main out till the wishbone touches the intermediates. If there was no wishbone I could maybe ease another 5 cm BUT and this is a big but I could never do this as the chafe would be terrible. Even vanged down and tied off with a preventer your average mainsail will move up and down causing chafe so the main gets pulled on more. I can ease out the wishbone main at least as far as the same rig with a boom and get no chafe - my 15 year old main gets a bit of work every 4 years, the photo was taken 6 months ago and the main looks good. The wishbione protects it well.

As to the Vee the main is sheeted to - it is an old idea from 505s and skiffs. As thew wishbone does not need a traveller you can use a bridle. This is what vang sheeting dinghies do to raise the mainsheet position up high. The higher you can raise the mainsheeting position the more it is like pulling the traveller up to windward. So I made a composite bridle (properly called a Loveday Loop after the 505 sailor who did it in the 70s) and sheet the main to it. It is like permanently having the traveller to windward meaning I need even less tension to get the main to where a normal main gets to. One handed pull in 15knots, it gets hard (need to heave a bit) just when I have to reef in a tradewind 22-25 knots. Then the staysail goes up too and the rig is bulletproof. we use this rig of reefed main and staysail when it blows a heap and we feel awfully snug and safe.
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....and more,..

As to the questions

- staysail. The typical double diamond rig used on a boat this size has no inner forestay (leading to the intermediate hounds). This rig design needs an inner forestay to stop the mast inverting. The inner forestay leads about 50% of the distance from the mast to the forestay allowing the genoa to pass through pretty easily - much easier than a proper cutter like a Searunner when tacking. We don't use the rig like a cutter. When the wind blows up we furl the genoa and raise the staysail(storm jib). This brings the CE aft on the headsail which is exactly what you want when you reef the main and its CE comes forward. The boat stays balanced.
- the designer - Robin Chamberlin - calculated the amount of wire as being the same. A double diamond rig will have 5 or 6 wires keeping the mast in column as well as the caps. We have 6 and two of these are very short - no spreaders too which may help.
- Going to the main chainplates with intermediates and lowers - don't do it. I have been on cats with this and you get a faceful of wire every time you walk forward. It is really annoying and maybe dangerous on a dark night. The staying angle with the chainplates at the cabin side is still very wide.
- Reefing - I have a reef that is about 1.2 metres which would bring the head to the hounds - but I never use it and go straight to the next one. Remember the inner forestay means the rig never even thinks about inverting - it is pretty bulletproof and gives great security. On my old Twiggy rig the mast would invert as soon as I reefed making the main very full which was not what I wanted. We fly the storm jib and trundle to windward as fast as we can handle - about 8 knots max in big winds, You don't want to go any faster on a 4000kg cruising boat or your crew will get off next stop and you may break expensive things.
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PS; still more good suggestions from Catsketcher,

I also would move the inner forestay aft to about 50% of the J. Where you have it will be a pain to tack with. Searunners are like this and whilst I dearly love them you almost need someone to run the genoa around the inner forestay because the inner forestay is far forward. I would move it aft, put a storm jib on it and use it only in heavy weather.
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