Subject: [harryproa] Re: leepods - pro
From: "petermirow" <petermirow@hotmail.com>
Date: 2/11/2006, 8:40 AM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

Yes.
A leepod on a Harryproa doesn´t seem to make much sense. Capsize
seems very unlikely anyway. And if do the buoyant mast seems to take
care of the business.
Best,
Peter



--- In harryproa@yahoogroups.com.au, "colcampey" <colcampey@h...>
wrote:
>
> IMHO a leepod on a Harryproa is as incongruous as training wheels
on
> a touring bike.
> The only time there's a risk of lifting the windward hull of a
> cruising Harry is if you're
> 1. racing, or
> 2. way over powered for the conditions when cruising, or
> 3. in severe weather conditions.
>
> In the first case you should be concentrating, especially if you're
> near the limit.
> In case 2. you can be conservative with sail area on Hp and still
go
> quick, and
> in case 3. you'll have all sail down and have a drogue/sea anchor
> deployed (same thing on a proa), so if you still capsize, a pod
> would be unlikely to make much difference.
>
> My 'pod money' will be spent on a wing mast - with anough buoyancy
> and strength to hold the boat at 90 degrees  (hopefully) - again,
in
> such conditions Mother Nature has the final say.
>
> Regards,
>
> Col Campey
>
>
>  --- In harryproa@yahoogroups.com.au, Mike Crawford <jmichael@g...>
> wrote:
> >
> > <<Boats have been knocked down and righted.  Including the
amusing
> case
> > of one of Russ' friends falling asleep on his watch and waking up
> to
> > find the boat happily loping along in the pod immersed
condition.>>
> >
> >   Good point.  I'm not impressed by arguments that boats are safe
> > because they have made ocean crossings.  Safe miles at sea are
> often
> > more a product of good seamanship and good luck than actual boat
> > safety.  But actual knockdowns and recoveries say something.
> >
> >   For the record, I've been a fan of the "Dutch Proa" ever since
I
> first
> > saw the web site, and would like to see more people work on the
> > concept.  I think it's neat that you can have a training wheel
> which
> > will increase righting moment to give you time to loosen the
> sheets.  As
> > Han Biljard points out, this removes the temptation to push the
> boat
> > past its limits because you slow down as soon as that leepod
> starts
> > creating drag.  What a great combination.
> >
> >   I'd want a relatively short aka length, though, and a low
> > displacement.  This would provide some additional righting moment
> which
> > serves as a warning, progressively getting buried further and
> further as
> > you push the boat too hard.  This would be a lot better than the
> 150%
> > buoyancy amas we see on some trimarans, which will raise the
whole
> boat
> > and make a capsize much more dangerous.
> >
> >   If the leepod is integral to the leeward hull, such as on
> Jzerro, then
> > it's not inconceivable that it would fit these criteria.
> >
> >   The challenges of a leepod on a harryproa would then be twofold:
> >
> >
> > A) Structure and complexity
> >
> >    The leeward hull in a harryproa has a lot of stress going
> through it,
> > and you'll need some solid structure if you're going to want to
> put
> > storage or accommodations inside the leepod.  This is not
> impossible,
> > but it adds complexity to what is a very simple (and easy to
> construct)
> > design.
> >
> >
> > B) Increased requirement for righting moment
> >
> >   A Jzerro design is great for a leepod because it has most of
its
> > weight in the leeward hull.  Even with water ballast in the
> windward
> > hull, there's not a whole lot of weight up there in the event of
a
> > knockdown, and it is angled in such a way as to contribute to
> righting
> > even when the mast hits the water.
> >
> >   The harryproa has more than half of its weight to windward,
> though,
> > and with standing headroom and a cockpit there, that weight is a
> lot
> > higher up.  Between the additional weight and its angle to the
> leeward
> > hull, this will create a lot more heeling moment than a Jzerro
> design if
> > the boat goes past 90 degrees due to sea action or wind pressure
> on the
> > upturned hull.
> >
> >   It's this heeling moment that the leepod would have to counter,
> and
> > that's different than with Russ Brown's boats.
> >
> > ---
> >
> >   With enough design time and experimentation it's probably
> possible to
> > overcome both of these challenges.  The resulting design would
get
> away
> > from Rob's criteria of maximum speed, accommodations, and
righting
> > moment for a minimum of weight, structure and complexity, but no
> one
> > every said that every single one of Rob's criteria is sacred.
> >
> >   I think the key is in getting data on how a leepod would affect
> a
> > weight-to-windward proa once it's in a capsize condition of 90+
> degrees
> > heel.  If there were some solid calculations or real-world tests
> of this
> > combination, I believe a number of people would consider adding
> leepods
> > to their designs.
> >
> >         - Mike
> >
> >
> >
> > proaconstrictor wrote:
> >
> > > > > "My objection is the use of the lee pod as I believe
> > >
> > > > > 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.
> > > >
> > > > 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.
> > >
> > >
> > > The rig never slows you down, the leepod does all the righting
in
> > > combination with the CG.  You need to scale this
realistically. 
> If
> > > you are actually talking about a wave that is as wide as the
> boat is
> > > wide and the mast is tall, and extremely severely sloped, and is
> > > there for a period long enough for the capsize to occur, because
> > > there is a timing element also, then I'm not objecting, every
> boat
> > > has it's limitations, but this sounds like a situation where it
> isn't
> > > so much the leepod that is a failure as the sea conditions are
> > > savage, and a number of boats might be at risk.
> > >
> > >
> > > >
> > > >
> > > >
> > > >
> > > > >
> > > > > "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 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.
> > >
> > >
> > > It's not as though this is an untried technology.  It's been
> around
> > > for 40 years, and quite a few ocean crossings and a fair amount
> of
> > > cruising has been undertaken.  Boats have been knocked down and
> > > righted.  Including the amusing case of one of Russ' friends
> falling
> > > asleep on his watch and wacking up to find the boat happily
> loaping
> > > along in the pod immersed condition.
> > >
> > > Math doesn't get us very far, because one has to be able to
> design
> > > the boat in the first place beforeo n can run the numbers.  You
> can
> > > do the math and get the wrong result just because you don't get
> the
> > > design, which by your own admission you don't.  It is perfectly
> clear
> > > that there is a pod of some size say 300 feet on a 30 foot bat
> that
> > > makes lee capsize impossible, OK trim it back till it is a
little
> > > more manageable and you feel comfy sailing it all over the
> Atlantic,
> > > and across the Pacific over a period of 25 years.  Now run some
> > > numbers.  I'm not trying to be insulting but I have seen far to
> many
> > > failures of numbers to take much stock in the situation simply
> > > because the actual working principles are not understood.
> > >
> > > Absolute security is an illusion.  I can't tell you what boat is
> > > right for the Bass strights, probably every type of boat has
been
> > > thrashed there are one time or another.  Local boat designs vary
> > > because not every type is as suited to every environment.
> > >
> > > >
> > > > 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?
> > >
> > > This is the fantasy diagram example.  Phill Weld's 60 Gulf
> Streamer
> > > was capsized by a rogue wave.  Bad stuff happens.  One can
always
> > > draw a picture of the point of no return in any boat.  This
kind
> of
> > > weather is only survivable in a multihull with a para anchor
> out.
> > > You still have to get the boat way past 90 degrees to capsize
> it.  As
> > > a mater of degrees, the boat has to be orders of magnatude more
> > > rolled over than the capsize trigger point for a cat or tri. 
> That
> > > said, I haven't heard of any situations in whcih proas dealt
with
> > > huge nasty conditions with a para anchor.  A lot of these guys
> just
> > > don't talk about what they have done so the data is not deep.
> > >
> > >
> > > >
> > > > I am sorry if my explanation is not clear enough as the
> mathematics
> > > > are clear enough for me.
> > > >
> > > >
> > > > Regards,
> > > > Robert
> > > >
> > >
> > >
> > >
> > >
> > >
> > >
> > > ----------------------------------------------------------------
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