Folding catamran construction

I've been fooling with Gary Dierking's fun and functional Tamanu design for the last two years and took it down to the Texas 200 for it's first launch. It was fun, but I tried to use too much of the Hobie 18 and suffered some breakdowns. We ended up cracking the main beam from the Hobie 18 in the luff groove that holds the tramp and having to throttle down for the rest of the trip. I was sold however on the Tamanu as cat idea. I loved the wide beam, the huge hulls, the freeboard, and the drier ride. I didn't like the long setup time and light but wimpy crossbeams.


For the next iteration I waffled over a fixed beam 8'6" boat or a folder. I was sold for a time on the 8'6" boat and began beam construction, but was conserned about two items--it can't fit in the garage and it took forever to assemble at 9'6" (the width it needed to be to reuse the Hobie tramp)



I'm thinking of using the Woods' Sango, Wizard, Skoota folding method shared by The Tomcat 6.2 and the Tennant turbo 6. This could make a folder with narrow beam for garage storage into a wide beam cruiser with limited assembly time. It'll be longer assembly than the fixed version at 8'6", but not too bad since most everything stays attached. It's quite a bit smaller than Wood's Wizard, but otherwise would fold the same way.

I'm torn between the idea of one big hard deck surface or splitting the surface into two tramps taken from the H18 and using a central spine for an outboard mount.

Thoughts on tramp vs. hard deck? Insight into the folding concept?

Dan

 

You sound confused.

Perhaps you can say what you want, rather than have others tell you what they want? As much as you have done with the cat you have, it looks as if you already know what works and what doesn't for your needs.

 

I think Dan is here, like most of us, to learn what we think and what we think we know. That doesn't mean he has to take anyone's advice, but he's a smart guy. Like most smart guys, he'd rather learn from the mistakes of others.

Dan, as we discussed, you'll have to have pretty sturdy framing for the platform to which your beams will be hinged, unless instead of pivoting them from heavy bolts at the platform edge, you do something like TF Jones did with Brine Shrimp and connect the beams with heavy blocking when they're down in place for sailing. That might allow you a less sturdy (lighter) platform, if all it has to deal with is holding the boat together on the trailer.

 

this is from the cat2fold boat

 

I'm about to build a boat, and basically it's just like yours but smaller, so were thinking along the same lines. There's different ways to go about folding a boat as I've seen, but it's not all that many.

attached is another way to fold,
http://www.ikarus342000.com/KD800page.htm
and it keeps all the beams on the same plane hinging to a center pod. Hinged off each side of the pod/platform can be the rest of your hard deck. I'm thinking you can use your existing cross beams for this to keep costs down?

When it's time to fold, flip up each side platform to the center pod, unbolt the mounts on each part of the beam and fold the hulls together, the center pod will be right on top of the hulls. Total width of the boat would be like 5ish feet?

I'm not sure how you'd attach your mast though, as I'll be using a biplane rig.

 

Perhaps so as I've never sailed a folding cat. However, deciding between a tramp that would need to be divided to reuse my H18 tramps or figure out how to support a hard deck of approximately 7'6" width x 8'-9'.

I do know what works for what I've done before, but not what I plan on doing--a folder with either a tramp or a solid deck.

Dan

 

Cool, but too complicated for what I'm planning. Think Woods Wizard with a hard deck.

Dan

 

Is this for your UFC boat? I'm looking to avoid any bolting or anything else that would slow down assembly.

Have you found your rigs? I have a Raptor 16 rig I'm thinking of using on my Ulua or even one of the Tamanu hulls--but right now they are spoken for with the cat mode.

Dan

 

I like Bernd's stuff, but the bolting puts me off in terms of a speedy assembly. I also wonder about the single bolt at the deck of the cat, but it seems to be working for the Seaclipper 20. In fact, you might get enough displacement for your proposed craft by building the Amas and no vaka from the Sea Clipper--and having your hard deck for sleeping over that. Getting it to fold quickly seems important though. I wonder if an over center latch with some sort of mouse to avoid unlatching at sea would work.

Dan

 

Good points. I'm thinking the beams will be a large box beam central section with U shaped ends. They will pivot on a large bolt. The deck has yet to be resolved, but light is good. If I can find some sturdy bolt rope channel section, I may use my H 18 tramp with a sentral spine like you are contemplating. It gives some structure to the motor mount as well. Alternately, I can build a ply/foam/ply deck or a ply/ply honeycomb (like a hollow core door)/ply deck. All those options will be heavier than the tramp, but still reasonable.

I did see on wikiproa a neat idea for a semi rigid deck. John had strung some rope between his beams and laid some ply on top of that. It sags some, but the caternary curve isn't too offputting.

Dan

 

Hey Dan--

Yes, bolts can be a pain, but my new boat will use them. The idea only requires 4 bolts in all, so I think that can be done in just a couple of minutes with a ratchet.

Many of the compromises I've chosen have to do with the goal of allowing the boat to be folded with the rig in place, to allow the use of narrow slips and dry sailing. That's also why the kind of folder that tucks the hulls up under the center deck is not an option for me, because the hulls have cabins, and I don't want to have to unload the hulls every time I fold the boat briefly. This is also why I'm going to try out a central board and rudder, because then the boat can be motored while folded, and with only a central ruder, the tiller bar does not have to be removed for folding, because no tiller bar is necessary.

 

Well the SeaClipper20 is pretty much what I'm trying to do .... and your idea of leaving off the vaka, perfect!
This video shows it well:
http://smalltrimarans.com/r/seaclipper-20-trimaran.html
I'll have to add this to my thread!

 

There is already a version of Wizard with an open deck


Richard Woods of Woods Designs

www.sailingcatamarans.com

 

Has anyone built one with the open hard deck Richard? Any pics?

 

Beware

Just a quick note re the swing arms under the cabin - they will be very hard to move. When you make as folding cat model the self weight of the whole structure is very low. You grab the thing and its the geometry you are trying to get right. BUT

Do a mind experiment - Imagine you can cut down the centreline of the cat with a light sabre. What would happen? Each half would fall inwards. As the Cat2fold and other folding cat is folding they somehow have to cope with the huge load of the beams, mast, people, cabin that wants to fall straight down and rotate the hulls top inward. They can probably be sized to do this when extended and not move but to swing the beams with a large load on them is asking for trouble. Mr Francke got rid of the central mast on Cat2fold. My guess is that it put too high a load on the folding beam.

I think this is why there are lots of drawings of folding cats and not many sailing versions. If you want to do the cabin with the swinging arms under be aware that the fold will be under many tens of times higher load than a Dragonfly setup. It will require significant engineering to swing whilst under a large off axis load

cheers

Phil