sorry, I posted this in the maintence thread and made it drift away. I'm reposting it here because it's a much better fit, thanks John for making a new thread!
I had a friend who is a marine
architect (formerly with Farr and now up in Canada) and also building his own multihull
go through the specs for our boat two weeks ago and tell us for our boat when we would start to lift
. The numbers he came up with I thought might be of interest to other multihull
With our full main up and Genoa
(around 1200 sq ft of sail area) were we on a beam reach in 25 knots of steady wind
we would be in danger
of starting to lift
a hull. Think of what that looks like, it's not a subtle wind
, white horses are everywhere, moderate waves have been building up, it's painful to look into the wind. To be conservative, we reef when winds have built up to a steady 20 knots (25 knots is 1.6 times the force of 20 knots). By the way, we'd be sailing then at 14 knots. At 25 to 30 knots of wind we'd reef again.
I've personally been in 70 knots of winds, not by choice, and we were bare poles motoring into the wind which was a very strong thunderstorm. I was very white knuckled and very happy that I had two engines instead of one. Fortunately I wasn't in the open ocean and it lasted only for around 15 minutes. For open water the most wind I've seen is 30-35 knots and reefing conservatively.
This is also not to say that if you are on a multihull and you are in those winds you will always flip. Last weekend a friend of mine on his PDQ
42 was sailing with his spinnaker
and full main in 30 to 35 knots of wind. He was sailing at 120 degrees off the wind and was foolishly seeing how fast he could go (called me on his cell phone
screaming about how fast he was going (15 knots). Anyway, he got through it without incident because at least he realized he shouldn't go beam to with his sails
. At the same time, 20 miles away another multihull was in the same wind and in the lower chesapeake flipped because they were beam to.
So there are two example of the math and the experience of showing how our rules of thumb to reef at 20 actually make sense and should be followed. (I've never been able to personally point at two catamarans I know about in similar winds where one made it and the other flipped). By the way, the flipped boat was towed within hours to a nearby marina to be righted.