Best Material for Experimental dual hull Dinghy Outriggers?

[Roy M]

You can make curved cross arms, to avoid clipping wavetops, that are very stiff. A simple shape is that of an I-beam with the top and bottom made of 1/8" ply, reinforced with carbon fiber tow (a Gougeon Brothers West System epoxy product available at West Marine), and the vertical web made of 1/4" plywood with lots of large lightening holes (like you see in aircraft frames). Then you can attach it and dismantle it using wing nuts and bolts for ease of conversion.

[Cadence]

Originally Posted by captain-cowboy

I'm connecting two self bailing kayaks together into something of a convertible outrigger canoe. That way I can dismantle my dinghy and store it on board (no painter or davit), make use of a single kayak when most convenient, or assemble the whole raft when it's time to row dry goods or gear over from shore.

We used pine 3x2's to prove the concept, it worked brilliantly, so now it's time to invest in final materials. I need outriggers that won't flex and warp too badly. Right now I'm looking at 1/8'' wall 3X2'' aluminium rectangular tube. does that seem robust enough? Round pipe would be more similar to the out riggers on a small catamaran, but a squared shape fits into our setup really well, and it's cheaper.

If the 2X3s work beautifully use them. Probably over build. Why get exotic?

[captain-cowboy]

Originally Posted by Cadence

If the 2X3s work beautifully use them. Probably over build. Why get exotic?

the kayaks as pontoons worked beautifully. the pine 2x3's will rot and warp in short order.

[nimblemotors]

I'd make a gently curved rectangle, or maybe just an oval, if you are up for the time, as it would be a lot of work, compared to just using some tubing.
However, fiberglass tube can work too, if big enough, but perhaps a truss using the glass tube might be a little less work, to get the stiffness you need.


Differnt methods to sizing, get engineery and try and compute it,
or slightly less techy and use your existing wood and find its strength,
or the easy way just overbuild it and be done, or underbuild it and see if it is not strong enough, and then go bigger.

How about instead of catamaran, just tow the second one behind if you need to carry transport more load, use a trolling motor instead of paddles.

Originally Posted by captain-cowboy

Hey friends, nimblemotors has nearly sold me on using fiberglass tube; anyone know what OD and wall thickness I should be using? there will be 6 feet of trampoline between the pontoons, 2 feet of outrigger laying on each pontoon to fix to, and about two feet between the outriggers.

Thanks for the help all!

[captain-cowboy]

Originally Posted by nimblemotors

How about instead of catamaran, just tow the second one behind if you need to carry transport more load, use a trolling motor instead of paddles.

thanks for the lattice suggestion, that could help a lot, actually.

I've towed the second one behind before to bring things to the boat, but they're self bailing, so anything you put in them (including your backside) sits in a few inches of water for the whole trip. separately they're perfect to store on the deck, and to go ashore to a beach for a camping trip. But to bring two people and a paper bag of groceries and a portable fuel tank, it's too wet and too tippy. when we put them together with wood, we had two men in excess of 200 lbs and a light load of building materials, and you could stand up on the thing and walk around. when they're together, you can sit on the cross bars and keep your ass dry, which makes things a lot less annoying than putting a dry bag of clothes on your head EVERY SINGLE time you come ashore.

this is what the kayaks look like if that helps cement the situation:
http://www.backcountry.com/images/it...0032/ALYEL.jpg

[HopCar]

What ever exotic material you decide on, you might find Well Nuts useful to fasten the cross bars to the hulls. It doesn't look like you can get inside to put nuts and washers on.

[nimblemotors]

My idea and approach is instead of two kayaks, I built a proper catamaran that disassembles for easy stowage, and you ride on the cat, not in the hulls.
Carbon fiber and secret material and this boat is very lightweight.
You can't use just one hull though, need both.
A further refinement was to make the hulls tanks to store water or fuel during a passage. Didn't get a lot of enthusiasm for the idea on here..

[Snore]

Nimble- the black at looks interesting. Storage inside the hulls?? The bridge decks could be built like take apart paddles, with two joints and the hole thing packs super small.

How does it paddle?

[a64pilot]

Originally Posted by onestepcsy37

I went to visit him in the hospital and he confided to me that he was making a DOWNWIND landing! In an ULTRALIGHT! Said "I should have known better". All I could think of was, here's a guy whose got thousands of hours in crop dusters...

Maybe he was transitioning back to the Ag plane, they almost always land downwind.
Taxiing wastes time so you want to position the loader truck on the downwind end of the runway so you land downwind, but get to take off into the wind. Remember your 1,000's of pounds heavier with a full hopper.
Can't move mix tanks though so it only works if your putting out dry because that is loaded from a truck.

I'd use aluminum, exotic materials only make sense for exotic boats.

[Cheechako]

I wonder if clear VG cedar 2 x 4 would work? You wouldn't have to coat it with anything as it's highly resistant to water. Lightweight too. There are cedar fenceposts in t he ground up here in t he wet PNW that have been there since I was a kid.... so that's at least 50 years!
One caveat though... the fast growth cedar they mostly sell now wont last as long...

[captain-cowboy]

Thanks for all the response, everyone. Spoke to some of my buddies here locally that have some expertise with this kind of thing. I'm going to go with 1/8'' walled aluminum. Now I'm just working on whether I want 2'' square or 3x2''

[Cadence]

Originally Posted by captain-cowboy

Thanks for all the response, everyone. Spoke to some of my buddies here locally that have some expertise with this kind of thing. I'm going to go with 1/8'' walled aluminum. Now I'm just working on whether I want 2'' square or 3x2''

Good decision. 2" square aluminum will still be over built with a 1/8th wall.

[HopCar]

"Maybe he was transitioning back to the Ag plane, they almost always land downwind."

You're probably right. Crop dusters only fly when there is almost no wind. I think he forgot that part.

[nimblemotors]

Originally Posted by Snore

Nimble- the black at looks interesting. Storage inside the hulls?? The bridge decks could be built like take apart paddles, with two joints and the hole thing packs super small.

How does it paddle?

The crossbeams are attached like you describe (I think), disassembles pretty easily. I have not tried to paddle it, my intent is having electric propulsion.
Heck I've barely put it in the water, have moved on to other things at present. Will get back to it sometime after a few other projects get done.
Thanks.

[Captivy]

Originally Posted by captain-cowboy

man, wish I'd thought to take a picture, but sorry no such luck. The reason I didn't want to stick with wood is because it rots and warps. by the time I over-lay some marine quality lumber with west systems, I'm approaching the cost of aluminium which would be stronger anyway. the wood was strictly just to test the viability of the sit-on-tops as catamaran pontoons. thanks for the suggestion of carbon fiber. it's a little out of my price range, I'm afraid. It would be nice to cut down on the weight, that's for sure. I originally was hoping to find some kind of perforated channel, but I can't find it in aluminum.

B-LINE makes aluminum perforated strut, ask at an electrical distributor:

http://www.cooperindustries.com/cont...AluminumSS.pdf