Monday, April 30, 2007
Forward Buoyancy Compartment
Here's a look into the forward watertight buoyancy compartment. The area between the diagonal stringers is reinforced with a ply web, as shown in the plans. The inside edge of the stem is deeply buried in a large fillet of thickened epoxy, with 3 overlapping layers of glass tape over it. A waterproof inspection hatch will be fitted in the hole cut in bulkhead 6. I don't plan to put any fixed foam floatation in any of these sealed compartments, as many Wharram owners have found this can lead to rot. I also want to be able to get to the inside of the hull at any point, in case of damage that needs repair from the inside. I'm thinking of filling these compartments with empty plastic soda bottles, each one sealed tightly with the cap. These can be packed in through the 6-inch inspection hatches one by one, and removed the same way if access is needed. Filled with air, dozens of these bottles in each compartment would provide lots of positive floatation in the event of a holing.
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I decided to revisit the Wharram cats today (I've considered building one on and off for ten years or so) and have been browsing the web looking at different pages. It looks like you are making excellent progress (I've read up to April something so far).
I've heard the soda bottle flotation method before and one thing always struck me wrong about it: If you take an empty soda bottle, cap it, then squeeze it, you will find that it compresses quite a bit, negating some of the buoyancy.
There is a solution, I think. Before capping the bottle, put it in a freezer with the cap off for a few minutes. More cold air fits in a bottle than warm air. Take it out of the freezer, cap it, and when it warms up it you will end up with compressed air in the bottle. My biggest concern at this point would be the quality of the caps seal. If I where doing this I think I'd experiment a bit and if the bottles leaked at a high ambient temperature I'd try sealing the cap with 5200 or epoxy or something.
It seems to me that the smaller bottles also seem sturdier and would probably fit in tighter than 2 liter bottles.
(Probably just what you wanted...unsolicited advise. Sorry!)
Keep up the good work! You never know, you might push me over to the dark (read: multihull) side.
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