JEM Watercraft

I had an experimental canoe with sealed end chambers. It was used off and on for 5 years. When I decided it was time to scrap it, I cut it up and opened those end chambers. No water or condensation. But if something happened where some water got in there (and I knew about it) I would have had to cut it open to clean it out.

I'd suggest a small inspection hatch it there's enough room on the deck to install one.

I could install a small hatch about 3" I guess. But I could just install a bung plug in the deck on one end with a rubber stopper or something in each one, that way if there is any condensation or seepage I can get it out. I was also thinking that if the temperature got up to 40 deg + in summer, and they were left sitting in the sun the temp could get quite high. The air pressure inside might be enough to force a small crack, but I don't know about that. There should be enough flexibility to allow for expansion of air inside. I have seen lots of hollow fibreglass pontoons with no bung plugs.

I put one of those plastic access panels on the jem paddle board. I have built a couple of other boards that are basically giant hollow surfboards and I put boat drain plugs on them. When I open the plug on a hot day air comes out. But thats a big boat. I think you would be ok leaving them sealed because they are so small. I dont think they would crack. An access panel would be cool because you could store stuff in there. Or you might look at surf board vents.

Yes I could store things in them but I don't thing that is going to be an issue with the Sabalo, it's got lots of storage capacity and with the outriggers overloading won't be an issue. Also, there is a bulkhead half way along which restricts the storage capacity, so unless I put two inspection ports in them there is limited space for storage anyway. It does seem a pity to leave about 20 litres in each pontoon unutilized though.

I'm only guessing on the volume of the pontoons, I intend to do a capacity test with water to measure the displacement before fitting the decks. If they are 20 litres each it will make it an extremely stable trimaran with an overall beam of almost 3 metres.

Actually... on thinking about the inspection port bit, I wonder if that would weaken the decks at all. There will be a fair amount of rotary stress in choppy sea and I'm going to need the deck structure to be as strong as possible. I think I will just leave them as is and make sure that the glassing is sound. I might even double the thickness of the decks to make sure of the strength. It won't add too much weight and it might be good insurance.

I'm making this up as I go so any suggestions are welcome.

you want to glue on a "doubler" disc a little bit wider than the hatch ring. Helps distribute pressure a little better.

Interestingly I'm at this stage now, waiting for 6'' deck plates to arrive.
I have the Hobie Adventure Island with outriggers, that has drain/vent plugs and they do build up pressure, hence the reason for the deck plates/hatch. Also any extra storage can be handy.[img]http://i469.photobucket.com/albums ... .jpg[/img]
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Very impressive makenmend. They are a bit bigger than mine. If I was making something of that dimension I would certainly be installing hatches. I like the outrigger arms you have there. I have been thinking about the design I want. Where did you get the design for those? I could design them myself but a bit of a guide would be helpful. The key is getting the levels right, so I need to get an idea of how deep the pontoons will sit in the water, and the freeboard height to the deck on the Sabalo under 'average' load. Matt, can you help with that?

Sabalo will draft 3-4" under average load. Midship total height is 11". So deduct accordingly.

goanywhere

the crossbars are 1/4'' *1 3/4'' strips laminated togetherwith a solid 32'' centre section and 3 1/2'' spacers with 3 1/2'' gaps then 10'' outer spacers formed on blocks screwed to bench.