DIY inflatable catamaran

[gregkn]

Hi,

 

Inspired by Tim’s catyak http://www.cubenmaker.com/?2

I wanted to make an easier to assemble catyak, with minimal rigid frame. I knew I will face difficulties and failures but hoped to find solutions. So after a lot of thinking and  welding , I made it . Unfortunately as you can see at picture, the fabric sockets holding the crossbars preventing pontoons to roll, and also the welded dyneema rope , to prevent outward forces, ripped off 🙁 I used 210d 275gr/ SQM tpu nylon from extemetextile, I am located in Greece, for the whole project. My question if anybody have experience is,  if I make the sockets and welded dyneema rope, by heavier tpu nylon, 450gr/ sqm ( extemetextile doesn’t have any heavier, if anyone in Europe knows any other source bof heavier tpu nylon, please write it), would the heavier fabric withstand forces applied and won’t rip off? Thanks in advance

Topic

[Alpo]

I’d propose a different construction, though it’s a bit of a heretic idea to make holes in the hull…

Use longer aluminum crossbars and make them go through the whole hull, using plastic boat thru-fittings:
https://www.amazon.co.uk/through-hull-boat-fittings/s?k=through+hull+boat+fittings
I’d imagine if you cut off the unnecessary length in the hull fitting and choose tight fitting tubing size, it would be pretty airtight.  Perhaps with some glue between fitting and hull fabric. I don’t promise it will work, but if it does, that would make quite a solid connection.

The 450g nylon from Extremtextil is much stronger than their 275g or even 370g versions. Bigger difference than the numbers indicate.

[gregkn]

Thanks Apo from your out of the box Idea. But I am afraid to try it, I think not even helaplast glue, will hold  fittings you suggested onto the fabric.

[Alpo]

Fittings are screw and nut type and will seal well to the fabric, with perhaps a little glue or a rubber gasket. I’ve used those for attaching inflation tubes. Problem is more likely between fitting and crossbraces as it’s not easy to find exactly matching sizes. And perhaps if your fabric is on the thin and flexible side then the hole in the fabric could stretch and come out of the fitting. For Extremtextil 450g nylon I would trust it while for thinner fabrics some reinforcements could be useful.

But yes, making more holes in airtight hulls is not exactly the safest bet.

[Torgil Benigh]

Well, I don’t think a heavier TPU material will work with your current construction. The forces applied ar simply too much, even with heavier material for the sleeves.

I look at the dyneema rope. The sleeve for the rope has ripped in the hole where the rope comes out. If you would have a small diameter piece of aluminium tubing in the sleeve instead of the rope, and then tied the poktoons together with rope around the pieces of tubing, it will hold up much better. Doing so will distribute the force over the whole section abd not just around the hole, because the stiffness of the aluminium. It would probably be enough with 12-15mm diameter tube.

About the construction, i have to ask: is the dyneema rope to prevent the pontoons from rolling outward, and the crossbraces to prevent the pontoons rolling inward, yes?

[gregkn]

Nearly Exactly , crossbraces prevent also the outward forces. I add dyneema rope to distribute outward forces from only the cross braces, but it wasn’t enough. If I can  think of a way to insert not permanently welded , aluminium tubing, instead of dyneema rope, it will be a good alternative. Thanks for the idea

[Author]

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