The problem with these fine hulls, of course, is that once there is
enough lateral force to completely submerge a hull, any further force
will greatly submerge it further. The buoyancy of a submerged hull is
the same whether it is submerged one inch or six feet!
Gary
I'm sure that Malcolm can articulate it better, but while the pounds per
inch (PPI) of immersion of the hulls is probably low, the overall
displacement of the boat looks really low too, so relatively I'm guessing it
works out.
More interesting to me is the reference in the article to flexible hulls
that move independently of each other. The wording in the article obscures
the concept, but I'm guessing that the long "spider legs" attaching the
hulls to the cabin are what really flex, which would help prevent one hull
from being submerged by forces from the other hull. I'll bet the ride is
better too.
How about it Malcolm? Ever considered a cat (or tri) with "independent
suspension" hulls?
Bob Deering
Juneau Alaska
Robert Deering.
Dear Robert,
A number of my sailing catamaran and trimaran designs are flexible in a
similar way to the original polynesian vessels and those of James Wharram.
In this James and I follow a very honourable tradition as all of the
catamarans designed by the various Herreshoffs, and their contemporary
Thomas Fearon, were flexibly coupled. Similarly, a number of Meade Gougeons
trimaran designs had flexibly coupled floats.
Some of the early steel and aluminium ferry boat designs had the
superstructure mounted separately on air suspension bags. This was mostly to
isolate the engine noise in these all metal structures. It is no longer done
because you essentially had to build two structures that had to be capable
of standing alone separately and the result of this was that the overall
structure was heavy.However this is not the same as a "flexible suspension".
If you are designing/building a vessel that is completely open with very
little accommodation like the blowup boat then such flexibility can be
relatively easily achieved. However if you want a vessel with the usual
amount of accommodation then it is much more difficult. It will be heavier
and much more expensive as flexible couplings will be needed for all piping
etc[ unless each module is completely self contained]. Unless the boat is
for some highly specialised purpose where such flexibility is considered to
be an advantage,then the added complexity, weight and cost just doesn't seem
to be worth it.
Regards,
Malcolm Tennant.
Malcolm Tennant Multihull Design Ltd
PO Box 60513 Titirangi,
Waitakere 0642
NEW ZEALAND
ph +64 9 817 1988
fax +64 9 817 6080
e-mail malcolm@tennantdesign.co.nz
www.tennantdesign.co.nz
www.catdesigners.com