Thinking ahead about the "limbers", the manual says all bulkheads limbered to drain aft to the bilge area except for the fuel tank compartment. How does water flow around the fuel tank?
I believe any water from anchor / windlace locker will drain into the hull and travel aft until it hits the bulkhead for the fuel tank, then what?
Hey ... good question and great illustration! I should make this more clear in the manual.
Ok, so first ... why keep water away from fuel tanks? Well, perhaps I didn't make my 'aluminum tank' assumption clear! You really want to avoid standing water in or on or around aluminum tanks. That includes water that is 'trapped by capillary action' between two surfaces, one of which is your aluminum tank. This will absolutely eventually cause tank failure / leaking. My aluminum tank assumption is based on the idea that while you can find off-the-shelf tanks for the aft belly tank, the
forward belly tank span will likely be a custom tank, e.g. welded aluminum. This is because the forward end of the tank is going to be shallower than the aft end of the tank and I doubt you can build a tank (reliably) with something like poly welding and plastic etc. Using an off-the-shelf tank for the forward position will likely limit your fuel capacity. Some people choose to paint the aluminum tanks with something like
Zinc Chromate Primer by Moeller and then with a good submersible-grade non-ablative paint ('hard bottom paint') before installation of the tank. This will add a LOT of relatively cheap and easy insurance that'll help guarantee a good long life for aluminum tanks. Combine that with preventative measures such as allowing for drainage out from under tanks and for preventing water collection on the surface of the tank, and you're in like Flynn.... be proud!
Alright, so much for homework ... back to the under-deck drainage questions. First, I do recommend that you CAN drain water through the fuel tank compartments but you should do so only if a) you can plug the limbers to prevent it (boat plugs and 15/16" round limbers), and b) you have provided some sort of access and/or ventilation that'll help dry out even the capillary-action trapped water that might be in the tank compartments somewhere. Easier done that said. For this reason, even without limbers into the fuel tank compartments, I suggest always providing good ventilation - even if only used when the boat is in dry storage.
Another approach is to block water from the fuel compartments and just sponge out whatever collects outside the bulkheads. Or, provide ventilation together with f'w'd bilge pumps to move water out of those areas where it can be trapped ... either to an area that *does* drain, or over the side. Thinking ahead and providing access is key. On one boat that I had, the 'access' was a small deck plate and I could 'just barely' fit a Shop Vac hose down in there to suck out the water that collected, and then I'd duct tape a cloth on a broomstick to reach in and 'sponge out' the remaining bits of water. When you build your own boat, you can do better than that, right?
Brian
