more questions on powercat design

[northerncat]

is it easier to drive an assymetric catamaran or a panga longboat that have identical beams?
sean

[northerncat]

well i built a scaled down version of my 6m cat to serve as a dinghy and to see what if anything i might like to change, at the moment im thinking of adding a foil to it to see whether i would gain any performance increase would this be worthwhile do you think? if i do are there any opinions on how wide the length of the foil ie skinny or wide also is it better to go witha symmetric foil like a naca 12 or to use a more of an aeroplane wing shape?
some photos here
http://www.hostmybb.com/phpbb/viewto...=0&mforum=easy
sean

[yipster]

Originally Posted by Pericles

I often wondered why the Tasmania built InCat fast ferries have a bow shape under the bridge deck, suspended above the sea, by the wave piercing hulls. I am sure you can find the pictures. http://www.tomw.net.au/2004/tas2004/index.shtml

The reason are twofold. The first is to provide buoyancy to prevent pitch poling should the hulls go too deep in very rough seas and to a lesser extent, to reduce the sound of wave slap. The other reason is to be opened to allow vehicles to roro.

It occurs to me that you could re-create this shape, much as a Tolman lower hull is built and bond it to the under bridge components. http://www.backporchboat.org/Hull002.html

This would provide additional internal volume, plus strengthen the whole vessel and prevent twistiing.

Please don't chew my ears off, if these words do not meet with your approval.

Regards,

Pericles

Originally Posted by northerncat

its an interesting idea but im basically trying not to add anything on the boat that i dont need to so as to keep the weight down im more looking at preventing twist by making a thicker bulkhead, im just not sure that 18mm is thick enough, im considering using 2 sheets of nine mm and seperating them with a timber 42*19 frame i was kinda hoping someone would chime and say yeah ive built 6 m boats before and 18mm is heaps for a bulkhead
sean

my take is long strong triangled beams plus all the above ( and asymetric hulls ;-)
edit: added some bulkheads pics alla shuthleworth

[Bullshipper]

We need a lot more information to even attempt to answer these questions.

A lot depends on
Whether the hull has a cabin or is a CC.
Total weight to figure panel loading
Distance between centers on frames running port to starboard
What ply are you using, what is the layup schedule
Motor size, top speed expected.
Floor thickness and glue/putty system, stringer type and centers under floor boards
Spacing, size on stringers to form box inner under gunwhales from bow to stern, linered or unlinered gunwhales
tunnel width, beam, planning sponson, height between tunnel and deck? Are there any steps on the deck?

[masalai]

Oh for the love of it? You are in the home of performance powercats - why not BUY one? sharkcat, powercat, plus a dozen or so more manufactured and ready to go - even with survey to commercial standard - used by coastguard and a lot of other folk who have proven the design.... a home build powercat, I think, will not be usable in Australia. check current design rules.... there are changes.... Sail boats are still left to amateur builders not power...

[northerncat]

Originally Posted by Bullshipper

We need a lot more information to even attempt to answer these questions.

A lot depends on
Whether the hull has a cabin or is a CC.
Total weight to figure panel loading
Distance between centers on frames running port to starboard
What ply are you using, what is the layup schedule
Motor size, top speed expected.
Floor thickness and glue/putty system, stringer type and centers under floor boards
Spacing, size on stringers to form box inner under gunwhales from bow to stern, linered or unlinered gunwhales
tunnel width, beam, planning sponson, height between tunnel and deck? Are there any steps on the deck?

actually for the moment im just chasing info for a foil for the dinghy, so this is where im coming from will i get a performance gain with a foil given im only powering it with a 3.6hp and if so how long should i make the foil etc

[northerncat]

Originally Posted by masalai

Oh for the love of it? You are in the home of performance powercats - why not BUY one? sharkcat, powercat, plus a dozen or so more manufactured and ready to go - even with survey to commercial standard - used by coastguard and a lot of other folk who have proven the design.... a home build powercat, I think, will not be usable in Australia. check current design rules.... there are changes.... Sail boats are still left to amateur builders not power...

actually it is for the love of it that i would build one(that and the fact that it would work out significantly cheaper for me (3000) to build than buy) i have looked into the new boating plate and this is part of the reason for going to 6m, theirs a few hoops to jump through now for a powerboat but its not insurmountable(means i dont need to calculate bouyancy), sharkcat is going to cost in the region of 30-40000 and thats probably just the hull
sean