Tim,

I think I understand your issue now.  When you are beam-to a sea at slow
speed or at rest, when the period of the waves is just right, you experience
a very sharp roll or snap.  Indeed, that is the nature of catamarans.  Every
boat is a compromise.

I don't think a wing/foil will help very much.  But there may be some things
that will:

• Move your weight down.  If you are storing weight high, move it down into
  the hulls.

• Get skinnier hulls.  Skinny hulls ride deeper in the water, and don't
  respond as quickly to passing waves.  The downside is that the boat is more
  sensitive to trim issues, and may have more wetted surface, thus poorer
  efficiency.

• Install a mast.  A tall object gives you a greater moment of inertia -
  resistance to rotation - and will thus slow down the roll.  And the side
  benefit is that you can hoist a bedsheet in case you run out of fuel.  But
  you might be confused for a sailboater, and you don't want THAT to happen!

• Try flopper stoppers.  Though with a cat I suspect they'd have to be
  oversized, with excessive drag.

• Add more weight.  But that of course defeats many of the cat advantages.

Bob Deering
Juneau, Alaska

On 11/16/09 9:36 PM, "Tim Chrisp" timchrispb2@gmail.com wrote:

Hull separation more than overall beam is a factor and certainly vertical
center of gravity. Putting a mast on would raise center of gravity. Does a
boat roll more or less with people in the fly bridge?. The Manta was very
stable and resistant to roll because of 21 ft. beam on 44 overall length,
tanks in the hull bottoms, and no flybridge. Skinny hulls offer more hull
separation, the difference in draft is not significant. The Manta had 11:1
ratio and a 2.5 ft. draft. You can have pretty skinny hulls with narrow hulls
with shoal draft, if you keep the weight down.
----- Original Message -----
From: Robert Deeringmailto:deering@ak.net
To: PCW Listmailto:power-catamaran@lists.samurai.com
Sent: Tuesday, November 17, 2009 2:54 AM
Subject: Re: [PCW] fin stabilisers on cats

Tim,

I think I understand your issue now.  When you are beam-to a sea at slow
speed or at rest, when the period of the waves is just right, you
experience
a very sharp roll or snap.  Indeed, that is the nature of catamarans.
Every
boat is a compromise.

I don't think a wing/foil will help very much.  But there may be some
things
that will:

• Move your weight down.  If you are storing weight high, move it down
  into
  the hulls.

• Get skinnier hulls.  Skinny hulls ride deeper in the water, and don't
  respond as quickly to passing waves.  The downside is that the boat is more
  sensitive to trim issues, and may have more wetted surface, thus poorer
  efficiency.

• Install a mast.  A tall object gives you a greater moment of inertia -
  resistance to rotation - and will thus slow down the roll.  And the side
  benefit is that you can hoist a bedsheet in case you run out of fuel.  But
  you might be confused for a sailboater, and you don't want THAT to happen!

• Try flopper stoppers.  Though with a cat I suspect they'd have to be
  oversized, with excessive drag.

• Add more weight.  But that of course defeats many of the cat advantages.

Bob Deering
Juneau, Alaska

On 11/16/09 9:36 PM, "Tim Chrisp"
<timchrispb2@gmail.commailto:timchrispb2@gmail.com> wrote:

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Pat,

A mast will reduce the snap roll Tim is talking about.

It's kind of counterintuitive, but think of a tall mast something like the
long pole a tightrope walker carries to help balance on the rope.  Your
initial thought would be that he'd be more stable with all of the weight
directly over the rope, but the long pole resists rotation (its moment of
inertia), so it slows down tipping motions for the tightrope walker,
allowing them to adjust and balance.

When monohull sailboats get dismasted at sea during a storm, perhaps due to
rigging failures, they become very dangerous and unstable.  You would think
just the opposite would happen with the lower center of gravity, but instead
the boat tends to snap roll violently and can throw the occupants overboard.
The boat is more susceptible to flipping over in the waves as well.  The
mast acts as a vertical stabilizer.

I believe a mast would have the same effect on a small cat, within reason.

Bob Deering
Juneau, Alaska

On 11/17/09 4:47 AM, "Pat Reischmann" preischmann@msn.com wrote:

Putting a mast on would raise center of gravity. Does a

Bob, I think just plain roll and stability is more important then whether it
has a quicker motion or not. A lot of money is spent in sailboats to reduce
weight aloft with high tech sails, carbon masts, and aramid rigging. Masts are
wind resistance too, causing more healing and drag. Your analogy of the tight
rope walker would be more accurate if the power cat had a deep keel to oppose
the mast for a slower roll motion, but a higher CG would not contribute to
overall stability. I can tell you that the survivability of racing sailboats
once they have lost their masts is far higher than with them. Righting moment
is improved dramatically when the mast is taken out of the equation. Yes you
can slow roll down by healing the boat with a sail and a sail would dampen the
motion, but with a lot of associated drag. Most of the power cats that suffer
from bad rolling have inadequate hull separation and a higher CG than they
should,  Now lets talk about how the mast would contribute to the pitching
motion as well.
----- Original Message -----
From: Robert Deeringmailto:deering@ak.net
To: PCW Listmailto:power-catamaran@lists.samurai.com
Sent: Tuesday, November 17, 2009 9:09 AM
Subject: Re: [PCW] fin stabilisers on cats

Pat,

A mast will reduce the snap roll Tim is talking about.

It's kind of counterintuitive, but think of a tall mast something like the
long pole a tightrope walker carries to help balance on the rope.  Your
initial thought would be that he'd be more stable with all of the weight
directly over the rope, but the long pole resists rotation (its moment of
inertia), so it slows down tipping motions for the tightrope walker,
allowing them to adjust and balance.

When monohull sailboats get dismasted at sea during a storm, perhaps due to
rigging failures, they become very dangerous and unstable.  You would think
just the opposite would happen with the lower center of gravity, but
instead
the boat tends to snap roll violently and can throw the occupants
overboard.
The boat is more susceptible to flipping over in the waves as well.  The
mast acts as a vertical stabilizer.

I believe a mast would have the same effect on a small cat, within reason.

Bob Deering
Juneau, Alaska

On 11/17/09 4:47 AM, "Pat Reischmann"
<preischmann@msn.commailto:preischmann@msn.com> wrote:

Putting a mast on would raise center of gravity. Does a

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