Re: Advanced Sharpie design explanation in a nutshell
- Hi Patric,
Most seagoing boats are long, narrow and flat-bottomed without a
ballast keel i.e. just about all cargo ships.
Google will find you plenty of information on hull stability e.g. at
You can see from the picture there that while there is a positive
righting arm ("ra") there remains some static stability. Depending
on where the cg lies and where the cb moves to as the boat heels,
even a flat-bottomed design could be stable beyond 90 degrees. The
idea is to have weights down low, short light masts and buoyancy up
high. It's important that the watertight volume remains watertight.
Some people say a boat without a salient keel is safer in extreme
conditions than one with a deep keel because the shallow hull will
be pushed along the surface like a cork whereas the deep hull will
have waves breaking over it like a "half-tide rock", as they say.
Breaking waves can breach the hull sides allowing water in and
sinking the vessel.
--- In email@example.com, "Patric Albutat" <albutat@...> wrote:
> Hi all,
> this is my first post on the group. If all of this has been
> over and over I apologize but I'm not quite sure I got it right.
> Obviously Bolger requires some out of the box thinking! At the
> however I feel like it might be slightly beyond me.
> From where do you get the required righting torque when heeled
> a boat with no keel? They don't get their stability from beam
> (like multihulls), quite the contrary. The righting arm curve
> it's maximum at somewhere around 30° which doesn't sound terribly
> seaworthy to me. Hardly any righting moment to stop the boat from
> capsizing after that? The internal ballast won't work beyond 90° as
> opposed to deep keels (Hmm the same could be said for bilge keels
> I've got to be making a mistake somewere). I forgot how much
> foot-pound of righting force you ought to have at 90° but I think
> righting from 120° was considered a minimum requirement for
> I guess this is where the high freeboard/buoyancy comes in?
> They won't stay upside down like a cat or tri though, that's
> definitely a good point.
> Also read that stability will increase by x^4 with waterline lenght
> whilst the drag coefficient raises at x^2. Frankly I don't
> why a long narrow boat will have any advantage there.
> If somebody please could shed some light on this?
- "Aside from Herreshoff's experiments in
the early 1900's, multihulls didn't really begin to develop until after
I know what you mean though there is a tendency to overlook thousands
of years of development in the rest of the world. There were other
westerners pre-Herreshoff and on a much larger scale. There have also
been many important experimenters from below the yachting radar between
Amaryllis and the post war
"and for much of the last century were sort of a counter culture boat.
take a few more years for multihulls to become mainstream."
Never owned one, but from what I understand the Hobbie was the largest
category of sailboat in it's day. Sailing multihulls are now
frequently on the covers of yachting magazine, particularly those that
emphasize cruising. In Europe multihull yacht racing has some
considerable prominence with financial institutions using the coverage
of boat ownership to snake their way onto public television, the whole
fast ferry industry has gained momentum, there are catamaran cruise
ships, there is the big day charter cattlemaran phenon. Dennis Connor
owned a bunch of those sailboats. There are little niches like
coaching boats for watersports and pontoon boats. Do we get to claim
houseboats on two pontoons? Sailing yachts are my main interest and I
don't see a time soon when multihulls will replace monos since they are
expensive to dock. They are a far better bet for those who actually
use their boats. They may be reaching a point where they have a
mainstream level of mindshare. People don't care about them one way or
the other, but if faced with a trip on one they don't pull out a dog-
eared copy of Herreshoff's biography and start sputtering indignantly.
"Our combative correspondant thinks it has
because they are good investments. I doubt that because I never met a
was a good investment, because pleasure in non-tangible."
Right, then neither drugs nor gambling will ever amount to anything.
Good tip. I did not say they were a good investment I said there were
a lot of them being bought as an investment. In Canada during the same
period there was a government program designed to promote boat building
(in the absence of a nuclear navy etc...) that gave government
subsidies to people buying boats. People would buy these boats and
rent them out. In the extreme, three college students created a huge
business building houseboats that popped up everywhere. In the French
case, the charter business led to the creation of several powerhouse
cat companies like Privilege. Insurance was available to secure the
loans, both relative to the crossings from France, and subsequent
"Your tone remains insulting,"
Get over it. I don't know you, and you don't know me. I sincerely bear
you no ill will. I think you fired the first arrow against the
multihull, I'm firing back with equal force. If some imaginary actuary
gets caught in the crossfire, why should anyone care? Bolger is a
designer of multihulls among other things, and the author of Boats With
an Open Mind. That's all this is about, certain choices made by the
great one, and open minds.
"Multihulls are small in number and have (compared to monohulls) a
short history. They have often been built by inexperienced amateurs who
less than ideal materials and sometimes suspect design/construction
As a result, there have been many boats which have either failed
or simply gone missing."
Right you are, though adjusted for scale, this sounds like a summary of
Bolger boats also.
"Insurers and actuaries are not comfortable with these
exposures and either refuse to insure them or charge higher premiums."
This is where it gets tricky. Do we know this for a fact? Is it world
wide, or a one country, one state, one office thing? Does the
insurance industry really keep these kinds of stats?. I have been on a
bunch of the multihull boards, and also done survey work, and even got
quotes for insurance that would have been a rider on my household or
car policy, and was cheap, though I decided to self insure for the
reason that I boat in a large lake in NB where there are virtually no
other boats. I don't remember a problem about this ever. In southern
Ontario we have at least 5 multihull factories (none of which I have or
have ever been connected to) business seems OK. We have a strong club,
not a member there either, but the people there seem very normal I
don't know what they pay for insurance, never came up. The only
problems I have had related to the boats being wood. There is a bias
against wooden boats. People will tell you that one can't get those
I have learned one interesting "fact" in all this. In the multihull
world Amaryllis is fondly remembered as a triumph that was only held
back by the conservatism of the day. I did not know that there was an
alternative spin. I wonder which was the revisionist interpretation.
Speaking of prejudice or conservatism in yachting. I think that is a
far more likely lens through which to see this kind of thing today and
for the last century or so.