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Use of Two Masts on a Multihull

QUESTION: "Hi Mike, I live in Wellington NZ - famous for lots of wind and wild water. I have been looking at various parallel rigged cats, like the Kohler 8m duo and Jeff Schionning's 'Radical Bay', primarily from the stand point of lower centre of effort - thus increased stability and safety. My question is, 'Could a suitably designed/constructed trimaran carry a cantilever mast in each ama? And if so, would it share the same advantages/disadvantages as the same rig on a cat?'"

ANSWER:
Yes, these rigs are certainly interesting for a cat and do indeed offer increased safety from lower heeling moment. This is particularly important for a catamaran as this type of boat has a sharp peak on its stability curve, meaning that it can more easily capsize, once the windward hull leaves the water.

Unstayed masts also act a cushion against sudden gusts ... though they store this energy for delayed release. (See comment below)

As far as planting similar unstayed masts in a trimaran, it's not something that I would recommend. The loads from such a mast are pretty high and the X-section of the typical ama is just not big enough to handle them without a lot of hi-tech material built in. The relatively low depth would also mean a very high load on the lower part of the mast. I would recommend you contact Eric Sponberg on the mast design for such a rig, as he's a specialist on unstayed CF masts… www.sponbergyachtdesign.com/Masts.htm.

The sails and rigging would also be far out on a trimaran and not as accessible as on a catamaran. Also keep in mind that the leeward ama of a tri is often underwater or nearly so, making access to the sail for adjustments etc, a very risky, wet affair. Trimarans generally heel slightly more also.

One other option you might wish to look at, would be to use two masts, fore and aft, like Chris White used on his trimaran Juniper. (Click here to see a photo of Juniper.) This is much more workable for a trimaran that on a cat. However, if you're limited to 8 metres, that's rather short for 2 masts though doable if you feel it's really the way you want to go. Keep in mind that a trimaran has a little more stability and a more gentle stability curve than a catamaran, so it's easier to predict a potential capsize situation. If you keep the mast about 1.25 - 1.3 times the overall length, and organize for easy reefing, you should be fine even in rough water.

Today there are many trimarans that are less skittish than the Buccaneer 24 you say you once sailed ... and yet somewhat faster too. But trimarans are sweeter to handle in my view that most catamarans ... turning easier and having a more responsive feel at the helm. Catamarans enjoy going straight and also provide larger social areas on board for good times in port and above 10m ... more private, divided accommodation.

Here's what Chris White says about his experience of trying two ketch rigs on his 52' Juniper "Two different rigs were tried on Juniper 1. An unstayed cat-ketch rig and a more powerful stayed ketch rig with rotating spars. Each has its advantages, but in a nutshell, the stayed rigs can be more powerful although they are more expensive and require more effort to sail".

When Jim Brown and Mark Hassall were invited on Juniper's maiden sail, here is what Mark wrote about his experience with the flexible, unstayed rig: "Though we spent the better part of the day trying to find wind. Late in the afternoon, it found us. The free-standing masts suddenly bent at an alarming angle and then twanged upright again. Juniper shot forward at such an incredible speed that we all grabbed at whatever was handy to keep from falling overboard! "17 knots!" yelled Chris. "My God, she went from 0 to 17 in a couple of seconds! Have I got a boat or have I got a boat?" "It's no boat," I yelled. "It's a goddamned slingshot!"

Hope this helps,

Mike

Now, please email your mast story to Mike Waters.


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