I'm pretty impressed with the biplane rig designs from Schionning, Nordic
, and others. I have a question though about what I see as a potential risk with this design, and it concerns accidental jibes.
As I understand, these boats are sailed wing-and-wing downwind. Since the masts are unstayed, the two mains can be sheeted out arbitrarily far to reduce the risk of an accidental jibe. However we all know ... stuff happens. And with so much mainsheet out, an accidental jibe would result in a boom sweeping the deck
through a 180 degree angle or more. Apart from being extremely dangerous to anyone on the side deck
or near the mainsheet, the dynamic loads on the mast
bearings could be difficult to engineer
. You've also got a lot of mainsheet flying around, possibly snagging people or boat bits and causing a lot of trouble. Since the mast
is stepped way out on the beams, there's no obvious way to mount a preventer, boom brake
, or traveller to limit the energy from an accidental jibe.
Even worse, there are scenarios where the booms could impact each other. Consider a broad reach with both mains sheeted out on the same side. Then if the boat jibes accidentally and the (old) leeward rig happens to jibe before the windward rig, bang! you have damaged or destroyed both of your booms.
I can think of ways to limit these problems but not fully eliminate them:
1) Have a "stop sheeting out here" limit on the mainsheets to prevent boom interference
-- can only be exceeded once the boat is wing-and-wing.
2) Stay the hell off the side decks when sailing downwind. Without headsails, there's not much reason to go up there anyway.
3) I guess you could rig preventers through turning blocks on the bows for sailing wing-and-wing. Interesting rigging
challenge though -- the boom ends are completely inaccessible over the water
once you are wing-and-wing.
What do y'all think about this -- particulary those of you who have sailed bi-rig catamarans? And for builders, what are thoughts on how to design for these problems? Where is your mainsheet anchored? Does it keep the mainsheet away from people who might get tangled/dragged/decapitated in an accidental jibe? Is the mainsheet anchor
engineered for the load from an accidental jibe?
Just some food