Subject: Re: [harryproa] Re: mast bouyancy
From: Mike Crawford
Date: 2/7/2006, 3:01 PM

  I agree.  Beyond the lower righting moment when reefed, buoyant sails would also be less useful once you uncleat the sheet in order to right the boat, allowing the masts to fall further.

  I've had conversations with three racer/cruiser open deck catamaran manufacturers about masthead flotation systems.  All three chose to avoid them because the extra windage that high is pretty significant, and also because they wanted to avoid weight at the masthead.

  One manufacturer decided to avoid righting systems altogether, one went with a compressed-gas system that will inflate a bag at the masthead, and one has yet to unveil its new righting system.

  A schooner rig with wing masts would likely offer enough flotation.  I'd still consider a compressed-gas system as well.  Either that or I'd keep an inflatable dinghy ready, as well as a spare halyard, and make sure I had a system to hoist it up the masts when the boat is on its side.

  Of course, it's unlikely an additional system would ever be needed.  I'm not aware of cruising multihulls this size that can be righted in the event of a capsize, and a harryproa is likely to have a better righting moment at a higher degree of heel than most.  As Robert points out, as long as the loads are properly distributed in the hulls, mast flotation will probably be enough.

  But what the heck -- why not brainstorm additional safety systems?

       - Mike

Dave Howorth wrote:
On Tue, 2006-02-07 at 02:02 +0000, Robert wrote:
> Hi Carlos,
> My own experience with lots of capsizes in small boats and
> windsurfers is that the sail damps the initial rotation and then if
> you don't uncleat you have a hard time of it getting it back as it
> tends to hold onto the water pretty hard. I have seen bouyant panels
> sewn into the tops of dinghy sails and they seem to work to avoid
> turning over completely.

Brian Phipps does it successfully with Darts, AFAIK. But a standard Dart
will not normally turtle immediately anyway.

>  Theoretically it should work on a bigger
> boat but scaling up often brings suprises. I am assuming a capsize
> from carrying too much sail in pretty strong winds such as one does
> when racing. On the other hand a racing boat would have a taller mast
> and therefore more mast bouyancy set higher, while a cruising boat is
> extremely unlikely to go over.  I have seen the bouys on the top of 
> masts but have no idea of the cons.

Don't forget that in strong winds the sail is likely to be reefed, so
the righting arm will be decreased and the heel angle at which it has an
effect will increase. All of which means you may need a lot more
buoyancy if it's mounted in the sail. Consider the strength of the sail
and fittings required to withstand the impact as well. Mounting a float
at the top of the mast overcomes this; designing the mast to incorporate
the buoyancy does even better.

>  Is the extra windage that much of a problem or not?.

As well as the windage, it also seriously affects the shape of the top
of the sail (aka ruins it). Again, mast-based buoyancy is better.

Regards, Dave

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