Subject: Fw: [harryproa] Re: sailing Elementarry
From: "Robert" <>
Date: 1/30/2006, 7:22 AM

--- In, "proaconstrictor"
<proaconstrictor@y...> wrote:
> "My objection wasn't with the Pacific proa. I have great fondness
> it after my time in PNG. I believe it has its place but not for long
> haul cruising."
> That is a fair point, but it falls into the same category as a
> ship passenger wondering why someone would cruise on any sailing
> multihull.  Russ Brown doesn't recomend that you or I do it, you
> to want to do it for whatever wacky reason.
Fair comment

> "My objection is the use of the lee pod as I believe
> that it is an unseaworthy attachment. I can almost see some value in
> it for flat seas as training wheels and as a lee platform for
> drifting conditions but not once there is any swell. I can't see how
> it can help prevent combination wind/wave capsize."
> Right answer, wrong question.  It's not aobut capsize, but self-
> righting, and it doesn't prevent knock down it just rights from it.
> "On the side of a wave the boat would have to be about 90 degrees
> before the leepod contributed to righting moment."
> Right at the point where a PP without one might become stable in
> knock down position, it is doing it's work.  Somewhat similar to
> ballast does in the same situatiom.

This is where we have a difference of opinion
On a side of a wave by the time the leepod STARTS to work the boat is
pretty close to 90 degrees, not when it has any significant bouyancy.
By the time it provides significant bouyancy you are probably past
dead center and by the time the rig slows you down you're over and
the leepod is actually preventing the return.
This is my interpretation of the mathematics.

> "In breaking seas, if hit from the
> side by a breaking wave it could dig in and flip the boat."
> Not heard of that happening, doesn't seem to be a serious
> Reminds me of the Wharram/Boon drawing of a tri perched ona 
> wave about to get rolled over.  It might happen, but it either
> doesn't or they have the sea anchor out, one hopes the literature
> not full of that kind of capsize.

There are not many leepod boats out there in Bass Strait conditions.
My experience of breaking seas over many years in pretty nasty
conditions coupled with my experience surfing all sorts of craft
(including many capsizes in craft that weren't meant to be surfed)
suggests it is a real possibility.
This could be tested by making a scale model of a PP with a leepod
and taking it down to a beach with a small to moderate surf. I am
sufficiently convinced by the mathematics and my own experience to
think that a leepod is at best useless, except in flat seas and at
worst a trigger for a full capsize

If my reasoning doesn't make sense to you , so be it, but at least it
is out there for people to at least think about.

> There isn't much evidence of the pods digging in either, depends on
> the exact shape, but generally they seem to rise out of a wave.
> "It also
> makes the boat less likely to be stabilised by mast bouyancy from
> going over further."
> Right, stabilizing with mast bouyancy is not what one wants in the
> kind of situation that causes a capsize in the first place.  Self-
> righting is the proven concept, or as with conventional cruising
> multis a very high resistance to capsize.  Low resistance to
> combined with high stability in the capsized or KD position is not
> winner.
Who said anything about low resistance to capsize. Again my argument
is that the lee pod does not prevent capsize on the side of a
moderately steep wave and encourages the boat to go way past 90 in
this situation, preventing its return back to 90. Wouldn't it be
better to be stabilised at 90 degrees in that situation?

I am sorry if my explanation is not clear enough as the mathematics
are clear enough for me.


Yahoo! Groups Links