"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 objection.
This is probably more of a problem in theory than in practice, but
hey, that's why we're all here batting the ideas about.
Leeward-pod proas have been through some pretty heavy weather, so we
know they can be seaworthy in good hands. I still like to keep
challenging the design, though, to eliminate as many potential problems
as possible.
"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
Could you explain this in more detail? I think that self-righting is
a wonderful thing, but don't yet see how a leeward-pod proa would right
itself in a knockdown or wave-induced capsize.
Rob's explanation of a harryproa recovery makes sense: the boat
floats at 90 degrees supported by mast buoyancy, the windward hull
weathercocks to leeward, and then a kite or weight is used to pull the
windward hull back down. I wouldn't want to try it on a bad day, but
at least it's possible. Something like that would never, ever happen
on most cruising cats.
I can see how the leeward-pod proa will work well for a wind-induced
capsize, especially if the knockdown isn't complete. Forgetting the
rig, that pod will keep the boat from going over in many or most cases,
so there's no need to worry about mast buoyancy.
But what about a more extreme condition, such as a massive gust, a
large steep wave, or a combination of the two? If something were to
push a leeward-pod proa past 90 degrees, how could it be
righted again? I would think that anything that extends past the hull
would make it more difficult to flip the boat back upright..
It seems to me that a) the harryproa will normally have
a greater righting moment when sailing, b) while the leeward-pod proa
will be more resistant to capsize if you push the boat past 30 degrees,
but c) the harryproa will have a much greater chance of
getting back on its feet if pushed to 90 degrees.
It's a series of tradeoffs I like the harryproa approach, but I'm
clearly biased. However, if I can learn how a leeward-pod proa will
self-right, that could certainly change things.
- Mike
proaconstrictor wrote:
"My objection wasn't with the Pacific proa. I have great fondness for
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 cruise
ship passenger wondering why someone would cruise on any sailing
multihull. Russ Brown doesn't recomend that you or I do it, you have
to want to do it for whatever wacky reason.
"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 the
knock down position, it is doing it's work. Somewhat similar to what
ballast does in the same situatiom.
"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 objection.
Reminds me of the Wharram/Boon drawing of a tri perched ona rbeaking
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 is
not full of that kind of capsize.
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 capsize
combined with high stability in the capsized or KD position is not a
winner.
Yahoo! Groups Links