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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