cat bridge joints

[yipster]

cat bridge joints
bridging a multi hull with piping that is detachable for transport takes clamps or joints. i've been thinking some up, wiser to look whats been done allready but cant find much... anybody with some links, pointers, ideas?
thanks, yipster

[tspeer]

Derek Kelsall has an interesting approach with his Amkat: http://www.kelsall.com/amkat.htm

The hull tuck under the bridgedeck, and have wheels mounted in them. Unfolded, they're built-in fenders. Folded, the boat becomes its own trailer.

[yipster]

Tom,
i noticed Derek Kelsall inventive design before and like it. some small cats use vertical pipe sleeve's to get a elevated platform but thats not needed here now. what i am looking for is outrigger to deck/frame fittings, if such exist incl. locks etc than there is no use in making it new. scafolding and stage building i'm checking also, i'm thinking of some joint like in this rough sketch...

yipster

[Tim B]

I believe the Dart 18 (see www.lasersailing.com) uses a tube (well, piece of straight mast) as the fore and aft deck-beam (smaller piece aft). In this case, it simply slots into a moulded socket and is bolted in place. I presume it has internal structure to prevent crushing, but I have not looked inside one. An added advantage, is that if a mast with a sail-slot is used, then it is very easy to add the trampoline. If we are discussing a big (20ft+) multi, then the accepted way seems to be to bolt arched cross-beams to a bulkhead (or two or more, depending on materials and load) in either hull. From there, the rest of the super-structure/mast or whatever, can be loaded onto the beams.

Another thread worth cecking out would be:
Folding multihull design...
http://forums.boatdesign.net/showthr...=&threadid=969

Cheers,

Tim B.

[yipster]

thanks Tim, that looks attractive, can even be flush, i'll ask the brochure for details and more ideas are still invited!

[grob]

How big is the boat? more importantly how large do you want the beam.

I am building a folding beachcat, I am using 3" Diameter tube for the beams. It is easy to get extruded aluminium in a variety of thicknesses. Also if you want to go slightly higher tech there is plenty of pullwound carbon fibre tube availalble.

For the joints I have used 3 1/4" Dia. 10 SWG tube (giving an inner dia just under 3") with a 3x1 channel section welded to it. If you cut a slot in the tube it will slide over the 3" tubular beam and the channel gives you a flat 3"x3" square to join the next joint too.

have a look at www.fourhulls.com for more details.

If you want I can attach some photo's to show you what I mean.

All the best

Gareth

[yipster]

3" tube sounds about rite to me and thanks for reacting Grob, i'm also following your "fourhull".

my puppy -beam about 3.60 metre- is under the "some ideas " option2 thread.

got the "legs" about ready, now have to bridge them, frame bulkheads, clamps, slots etc. yes show me more please, guess i can learn a thing or two from you.

yipster

[yipster]

...

i've been talking to a aluminum guy (who likes boats it seemed).

alu pipe in 6 metre, pipe dia 110 milimeter, wall 5 mm comes to 26 kg and cost E/$ 35 a metre. pipe 120 dia by 10 mm wall is 56 kg (6 metre) and E/$ 73 a metre. alu welding E/$ 45 a hr.

forgot to ask what grades there are, maybe i need marine grade? looked at standard knie's etc but that only came in sizes of some 4 centimer diameter was said but did have slots of some sort i have to check better like bending loads. he would call me back with a weight and price on galvanized / anodized steel also. sleeve slots or "buttons" as fourhulls mentions in his site i havent figgered out yet.

so here another very rough napkin of my cat bridge joint construction, please inform me when you see shortcomings or improvements in my seemingly fast going along now...

yipster

[Tim B]

Um, yipster, how big is this thing? and if you can get hold of duralumin (aircraft-grade ali), then it supercedes both ali and steel. Aluminium supersedes steel anyway in my opinion. Be careful how you attach it though. Corrosion can be a problem, so remember to use steel bolts with steel, and something non-corrosive with Ali, otherwise you get a big battery. I have some values for corrosoin between metals somewhere.

Good Luck,

Tim B.