Subject: [harryproa] Re: mast bouyancy
From: "Robert" <>
Date: 2/12/2006, 6:48 PM

A fully flooded Harry lw hull will have in the order of 300-450kg
bouyancy and you would need to move ~9 tonnes of water to fill the
hull. It would be easier to lift the 350kg weight of the hull (add
another 100kg or so for masts and rudders), especially encouraged by
mast bouyancy. This is only 700-900kg off a 3m gantry. You only have
to work a distance of 4m or so. This is no more than I have done
hauling vehicles up a slippery slope. With the right winch,
exhausting but doable- or maybe you could fly a kite ;-)

I've been reading the Jordan series drogue website and the
recommendation is that the drogue is to go over the stern as it gives
the windage and the under water resistance such that the boat doesn't
tack up on the rode to end up side on. On a Harry, slight rudder down
on the end where the waves are coming from and a tiny bit of rag on
the opposite end mast would similarly stabilise the boat I think the
reports on the website well worth a read 


--- In, Mike Crawford <jmichael@g...>
> <<My guess is that mast buoyancy or leepod are only good to deal
> 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
> sound seamanship.
>   Mast flotation is great if you're pushing the boat in relatively
> 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
> 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
> righting moment at 70 degrees, one ought to be taking real
> This means both setting a sea anchor to avoid reverse pitchpoles
> 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
> 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
> our parts.  No boat is going to be able to passively stop a
> or proaconstrictor points out, a capsize where the leeward hull
> over the windward hull.
>   I would definitely spend some time figuring out how to make my
> liveable when turtled.  That makes a lot of sense.  As far as
> it from turtle, though, that seems to be a bit of a challenge. 
> might be exceedingly difficult without flooding a hull and rigging
> some righting spars underneath.
>   In the end, it's better to sail carefully than to count on any of
>        - Mike

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

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