<<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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