have any of you guys been on a harryproa?
From:
Arto Hakkarainen <ahakkara@yahoo.com> Subject:
Re: [harryproa] Re: Moment of inertia To: harryproa@yahoogroups.com.au Date:
Thursday, 9 June, 2011, 16:33
Again that nice thing about boat design. Never a solution
for all the design criteria...
Talking about beautiful lines the old archipelago cruiser
rule in Scandinavia almost 100 years ago created perhaps the
most beautiful lines ever with very low and narrow boats with
extreme overhangs like this http://www.puuvene.net/saaristoristeilijat/albumit/JuhlakilpailuMeritiell/photos/photo17.html .
It was a very good rule giving a lot of freedom for a designer
with the main limitation being sail area. The boat in the
picture is designed for the 75 m2 class as you can see from
the numbers in the mainsail. Boats were beautiful and
sailed well for their time. That is beautiful but it will
never do the same things we are after in this group.
Arto
--- On Thu, 6/9/11, Mike Crawford
<mcrawf@nuomo.com> wrote:
From: Mike
Crawford <mcrawf@nuomo.com> Subject: [harryproa] Re:
Moment of inertia To: harryproa@yahoogroups.com.au Date:
Thursday, June 9, 2011, 12:02 AM
<<I mean if the design is made to go through the
waves with as little resistance as possible is it better to
dampen the pitching by having lot of inertia or not?
>> Yes. Both are better.
;-) I'd have to break it down by goal. If
you're shooting for a daysailer that you don't intend to have
out in really hairy weather, maybe it's nicer to have a more
stable boat that pitches less. If you think you might be
running into the back end of waves in a big blow, it's
probably good to give those bows every opportunity possible to
pop back up, including reducing pitching
moment. --- Robert (may he rest in peace)
and Rick have certainly sold me on the idea of wave-piercing
bows. I've always been a fan of salty
lines with a big shear and large overhangs. It's not the
most efficient design in terms of waterline, but it can be
beautiful. Some, like Wharram, will argue that it's a
good design for big weather because there's lots of reserve
buoyancy up high. I think that works in certain
weather. Perhaps you'll be both higher and drier for a
given hull length, at low speeds, in many sea
states. But I think the argument falls apart at
high speeds and/or really big seas (which lead to high speeds
surfing down waves...). That's when the bows are going
to want to drive into wave faces, and a big shear and flat
deck are going to seriously get in the way of popping the bows
back up. So if you're racing, and therefore going
quickly, or making a passage, and therefore need to be
prepared for really big weather, the wave-piercing design is
both safer and faster. In which case, it also
makes sense to reduce pitching resistance where
reasonable. Again, to help those bows raise as quickly
as possible. Not by spending thousands of dollars to
save just a pound or two by going to all titanium shackles,
but perhaps by centering fuel, water, and motors/gensets as
much as is reasonable. Plus, it's really
nice not to have the outboard on the extreme aft end, popping
out of the water in seas over three feet. That will
drive you crazy after a while. For a daysailer,
which isn't necessarily flying into wave faces at high speeds,
I'd say it's harder to form a firm opinion. Maybe
-
Mike Arto Hakkarainen wrote:
Gardner,
I agree that harryproa should provide a platform
where the negative effects of weight up in the
mast should be minimal. However, less is better always
so keep that in mind when we are talking about weight
up in the mast or bow or aft.
Still I must admit that I have no experience with
wave piercing designs and have kept on thinking
whether it is better for a wave piercer to have lot of
inertia or less. I really don't know. I mean if the
design is made to go through the waves with as little
resistance as possible is it better to dampen the
pitching by having lot of inertia or not? I really
don't know?
From:
Gardner Pomper <gardner@networknow.org> Subject:
Re: [harryproa] Span Efficiency - Another Harryproa
Opportunity To: harryproa@yahoogroups.com.au Date:
Wednesday, June 8, 2011, 4:35 PM
Arto,
I am not saying that it doesn't make any
difference, but it seems to me that fear of
weight aloft has become a phobia in the sailing
world. For a monohull, I can see arguments with
rolling and capsize, but not for pitching. If you
look at a 40' monohull, either the bow anchor (50
lbs?) or the dinghy (200+ lbs) are 20' away from the
COG. Their moment arm is 1000+ ft-lbs, vs < 50
ft-lbs for a block on top of the mast.
For a proa, the situation is even less
critical. My masthead plate might be 40' high and
weigh 4 lbs, but a gallon of water in the ww
hull is 20' from the COG and weighs 8 lbs, so it is
just as big an effect.
I don't want to come across as saying that
piling weight at the top of the mast is good, but I
have a hard time seeing why the effects on a
harryproa are not minimal, compared to traditional
(read monohull) thinking. Maybe there is an
opportunity here for the harryproas to take
advantage of some options that are closed out to
other designs. One more reason to get a harry!
- Gardner
On Wed, Jun 8,
2011 at 2:43 AM, Arto Hakkarainen <ahakkara@yahoo.com>
wrote:
Gardner,
We come back to the moment of inertia
issue. Which place on a boat is located longest
distance away from the center of gravity? Mast
head of course. All the weight there has the
longest lever arm there is when the boat is
pitching or rolling and that lever arm is quite
long. So in addition to reducing the stability
it also has all the negative effects of weight
at the ends multiplied by the longest lever arm
there is on the boat. So the winglet may improve
aerodynamic efficiency but be very careful about
adding the weight. Monohull racers talk about
removing grams from the mast head, some are even
ready to remove the halyard blocks and leave
just the axle of the block to the mast head to
reduce weight...
From:
Gardner Pomper <gardner@networknow.org> Subject:
Re: [harryproa] Span Efficiency - Another
Harryproa Opportunity
Date:
Wednesday, June 8, 2011, 2:03 AM
Rob,
Yes, the discussions of upper winglets on
monohull forums always hit the "weight in the
wrong place" argument and quit. I can see that
argument for multihulls, because of rolling,
capsize, etc. I can even see it for racing
multihulls, which may want to sail heeled over
to fly a hull. I don't see the relevance for a
cruising multihull that is never intended to fly
a hull. If the hull ever lifts, even a little,
you will do all you can to depower as quickly as
possible, so your heel angle should not even
exceed 10 degrees. (ToyyoT is heeled about 3
degrees when the ww hull flies).
So, it would seem that an extra 10 lbs at
the top of a short mast should not make a
significant difference. Am I just naive?
- Gardner
On Tue, Jun 7, 2011 at 6:16 PM, Rob Denney
<harryproa@gmail.com>
wrote:
Steve Dashew tried tarps under the boom on
his 65' mono. Reckoned they made a huge
difference. Loic Peyron tried a wing tip
at the top of an ORMA 60 tri mainsail, took them
off soon after. Top ones are a problem as
they are weight in the wrong place and because
they contribute to capsize when seriously
heeled. I have some ideas for a masthead
tip which stays horizontal which I intend to try
on El when the new mast is built.
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