The two large rudders suit the offset rig with enough lateral restraint aft of the sail to avoid getting stuck in irons. The problem is managing the forces in the supporting structure that allows them to be raised.
Blind Date (now Campaen) had three iterations of rudders and the current version are supported in a heavy duty structure consistent with the forces that a large, high aspect blade can generate:
The dagger board on the 18m proa has a pivot under the deck on the windward side of the lee hull. It has a faired tubular brace that is connected just below the waterline and comes back to the longitudinal beam that carries the lee side of the cockpit well. This arrangement has well defined load paths with a good lever arm to resolve the forces on the blade.
Rick
On 4 Nov 2018, at 12:57 am, Mike Crawford mcrawf@nuomo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:You can pinch to 40 degrees? Nice! That's trimaran territory.
I don't think I've ever seen 100 degrees VMG on the catamaran.
That's most comforting.
My plan is to skip the daggerboard and go with longer rudders, raising them a bit most of the time. Waters near us are either deep or not, so there's no penalty in drawing 4' instead of 3', particularly if the rudders can be raised. Maybe we go for the greater depth 1/4 of the time -- when headed to windward in light summer winds.
But we'll see. A leeboard an always be added on later if theory doesn't pan out in reality.
- Mike
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Posted by: Rick Willoughby <rickwill@bigpond.net.au>
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