Subject: [harryproa] Re: mast bouyancy
From: Mike Crawford
Date: 2/12/2006, 2:24 PM

<<My guess is that mast buoyancy or leepod are only good to deal with errors of judgment in moderate conditions.>>

  I agree.  I'm not sure that anyone here views mast flotation, or masthead flotation, as a solution that is meant to take the place of sound seamanship.

  Mast flotation is great if you're pushing the boat in relatively calm seas to compete either with the clock, the gps, or with other boats.  In that case, it's easy to envision popping the boat back up after a knockdown.  Far easier than doing the same thing with a cat or trimaran.  Self-recovery in most large multihulls is simply not going to happen an any type of knockdown.

  An easyrig harryproa will have enough mast flotation in most cases to prevent going past 90.  A schooner rig with wing masts should be able to keep a harryproa from going turtle even if it heels to 110 degrees.  Mast flotation alone then covers most cases, so discussions of additional mast flotation border on intellectual exercises.

  However, if seas are big enough to endanger a 15m proa with a positive righting moment at 70 degrees, one ought to be taking real precautions.  This means both setting a sea anchor to avoid reverse pitchpoles when climbing the leeward face of waves, and towing drogues in order to prevent  pitchpoles when surfing down the windward face.  When conditions are this bad, no amount of righting moment or mast flotation will matter.

  As many have pointed out, after a certain point it's foolish to pretend that the boat will just take care of us without any action on our parts.  No boat is going to be able to passively stop a pitchpole, or proaconstrictor points out, a capsize where the leeward hull goes over the windward hull.

  I would definitely spend some time figuring out how to make my boat liveable when turtled.  That makes a lot of sense.  As far as righting it from turtle, though, that seems to be a bit of a challenge.  That might be exceedingly difficult without flooding a hull and rigging up some righting spars underneath.

  In the end, it's better to sail carefully than to count on any of this.

       - Mike


robertbiegler wrote:
--- In, Mike Crawford <jmichael@g...>
>   Very solid arguments for fixed masthead buoyancy.

My guess is that mast buoyancy or leepod are only good to deal with
errors of judgement in moderate conditions.  If you flip a cruising
multihull by carrying too much sail because you need to get off a lee
shore, the conditons are likely rough enough that your masthead
buoyancy breaks your mast, unless te mast is specifically engineered
for the purpose.  (Relevant case study is a 12 m Apache catmaran in
the Round Britain Race which failed to climb a wave in a force 7, slid
backwards and capsized over the lee stern.  The masthead float kept
the boat on its side for while, until the mast broke.)  If the boat
gets flipped by a wave, it is very unlikely the the wave will transmit
just barely enough energy to the boat for a capsize without lee pod or
mast head buoyancy.  That little bit of extra capsize resistance would
help for only a small proportion of the spectrum of wave sizes.  If
you are not willing to accept a low probability of flipping the boat
in the first place, I think you have to accept that the boat will go
over all the way and design the boat so that, first, it can survive
this without significant structural damage, and second, so that it can
be righted frum a fully inverted position. 


Robert Biegler

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