[MHml] Catamaran vs Trimaran

[brian eiland]

Oh, boy. I'm gonna go get some popcorn ready. I always love this 
thread; an oldie but a goodie! 

Dave 
_______________________________________________ 
Brian replied:
I think I'll join you with that popcorn Dave, particularly as I'm guilty of
bringing this subject up again.

I was just looking thru another forum and this subject jumped out at me. I
made a responce, and I thought the members of this forum might be interested
in the subject matter, so I posted a reference to this subject thread.

What has surprised me most is almost no one on this forum has extracted any
portion or quote from the other forum discussions and brought them back here
to either make or break some point of discussion??

Did anyone bother to read the attached Seahorse PDF document closely??
<http://boatdesign.net/forums/showpost.php?p=98787&postcount=39>
<http://boatdesign.net/forums/attachment.php?attachmentid=8455&d=1154576689>
 
Quoting RMG, "What I found so interesting was Schmidt and Richard's design
process. They first started out by designing the most optimal sailplan that
best suited the tricky winds of Lake Leman often ranging 360 degrees from 0-30
knots, without taking into consideration the rig, beams, or hulls. Computer
tests were then run using the already designed sailplan on optimum tri and cat
platforms. They found that in light air, the difference in wetted surface area
favors the tri only if sailing on the central hull, which is not possible. The
tri goes through an increase in wetted surface area until flying on one hull.
To fly two hulls, the tri will be heeling at the very minimum of10 degrees.
The wetted surface area of a cat only decreases with heel. The cat has a
weight advantage of 400kg in this case, 1200kg compared to 1600kg. The cat
only needs 3.5 degrees of heel to fly on one hull. What about righting moment?
Obviously a tri is going to have much more righting moment than a cat. This
was solved with 320 liters of water ballast and six crewmembers on racks. This
extra weight is movable unlike on a tri."

"This catamaran was untouchable. None of the trimarans under the same rule
came close to beating the Alinghi Catamaran. I think that this is a perfect
example of how a catamaran platform is more optimal than a trimaran platform.
It would be interesting to see this concept applied to larger racing
catamarans."


_________________________________
In reference to the catamaran type structure to support a sailplan that placed
high regards for headsails and thus tight forestay tensions, "An innovative
carbon truss/tie rod structure was used to solve the compression and torsional
deformation problems prone to cats. Two carbon trusses...meet at the mast base
and continue forward as a single truss to form the bowsprit. The structure
looks like an upside down Y. A complex system of PBO rigging was used to
support the trusses attached by tie rods."

"It was the first boat sporting a full carbon truss/tie rod structure on the
centerline, looking somewhat like one side of a mast. That takes the place of
the trimaran's mainhull, to carry the very high fore-and-aft loads generated
by the forestay, mast, and mainsheet..."

In my posting on this subject 
<http://boatdesign.net/forums/showpost.php?p=111971&postcount=71>
I was considereing this same type of sub- structure to give longitudinal
stiffening support to a cruising catamaran design, "imagine a central nacelle
flat plate , on edge, mounted down the centerline on the underside of the
bridge deck. This flat plate will act as a rib to strengthen the fore-to-aft
rigidity of the vessel, a somewhat weaker characteristic in a catamaran
structure vs. a keeled monohull. If a tow bundle (rope, etc) of carbon fiber
(kevlar, PBO, etc) was laid along the bottom edge of this flat plate, the
rigidity could be even greater...sort of akin to a bottom truss structure, or
a flange of an 'I' beam.


 


Brian Eiland

beiland at usa.net
www.RunningTideYachts.com
distinctive expedition yachts