Inflatable sailing catamaran with tubeclamps

[Wavewacker]

Check out the inflatables that can be custom made at "Jack's Plastic Welding" mostly catarafts but they add rocker or have straight tubes, the big ones do get pricey but not too bad.

 

[Skyak]

I got a problem... A few weeks ago one of the outer pockets teared from back to front for about 2 meter while I was using it as a raft (without the mast) on a calm river in my city (Ghent, Belgium). We were actually not moving at all at that time, just floating and having a drink (maybe too much ). We didn't hit anything it just happened like that. I don't measure the pressure (maybe I should), but from my subjective opinion the pressure was not that high. I guess the material is getting old.
The floats are constructed with an inner float of neoprene and an outer pocket made of hypalon. It was the outer pocket that ruptured (not on a seem), so the boat was still floating and stable and we managed to continue the trip back home. I managed to stitch the outer pocket (it doesn't need to be airtight and it was constructed with stitching) but my confidence is gone in these pockets, so I want to make new ones.
The fabric doesn't need be airtight but strong enough to hold the pressure of the inner tube, resistant to rocks (white water use), not soke up water, UV resistant, it should not stretch out when I inflate the tube but hold the shape. Any ideas on which fabric to use? I've been thinking of kevlar or polypropyleen but it can't be too thick because I need to be able to stitch it with a regular machine. Having it custom made will cost me a fortune and I can't buy new floats on the market here in Belgium. Using hypalon again is also an option but that will cost me around 500 euro and I have never worked with that material (I don't want to mess up 500 euro...).

I don't know for sure based on your description, but my suspicion is that your old hypalon outer tube failed due to UV sunlight degradation just because it is the most common cause of outdoor fabric failure. For a replacement I would suggest PVC impregnated polyester. There is a substantial industry manufacturing this material for trucking tarps and commercial awnings so the price is very reasonable. The material is also used in lower priced inflatable boats though there is much debate over it's value relative to hypalon. The base polyester weave fabric is the same as hypalon (or can be, there is a wide variety of denier values available) but PVC is used instead of hypalon rubber. Hypalon stretches farther before failing so it can be applied thicker and still folded without developing pin holes. PVC is also more susceptible to chemical attack by things like brake or hydrolic fluid (this also makes pvc easy to 'chemical weld). PVC does soften and melt so be careful of chafe. PVC is generally better at stain rejection and UV life but as I said Hypalon can be thicker. PVC welds and sews much better than hypalon. Since you don't need defense against pin holes PVC should work fine and cost about a third of what hypalon does.

One other option is to use polyester weave fabric and then seal it with urethane. The advantage is that you can sew a more optimal shape without darts. Pre-impregnated fabric is limited to 'conic' shapes because the weave is not free to move. I don't know the UV life of urethane but SOF kayakers use it.

Kevlar (and other aramids) is super strong and stiff but about the same UV life as polyester. I don't know of any commercially coated aramids and I don't think the stiffness is beneficial. I would use a higher denier poyester fabric for strength before I would pay for kevlar which is much more expensive.

Polypro is the opposite - much weaker and stretchier than polyester -cheaper too. I don't know of any coated polypro materials and I suspect that it doesn't work well because the adhesion needs to be greater than the stiffness of the coating relative to the base fabric.

 

[Wavewacker]

For cheap materials you might check at a sign shop for the used banners and billboards that are taken down, a PVC material, turn the vinyl printing on the inside, unless you want to look like you're sponsored by a beer company.

Another source are swimming pool companies for old liners and pool covers, might find useful vinyl and PVC there.

Trucking companies should have old tarps you could get cheap.

I have an almost new pool cover, my dad changed to an automatic cover, that I'm trying to figure out what project to donate it to, probably a SOF boat.

 

[wasafari]

Hi Dima,

Check this: http://www.minicatamaran.eu/news.html for inspiration and ideas. Czech guys made a nice job.

Oleg