I installed a 52 gallon ‘belly’ tank mounted with its front right at station 6. The tank is 60” long, so extends quite a ways back. I did not want to raise the floor any more than necessary, so the tank fittings are slightly above floor level. I covered the fittings with a ‘curb’ or ‘chase’ that I will run the hoses in. The chase is 6” wide and 3” high. Before committing to it, I made sure it does NOT get in the way of standing up to steer or getting in and out of the cuddy. The tank sits right on the bottom of the boat and its V shape is an almost perfect match of the hull’s V shape.

I reinforced the area underneath the tank with a layer of 24oz biax that wraps all the way up onto the main stringers. I put a thin layer of polyethylene foam under the tank but none at the very center to allow water to drain (The tank is flat at this point too and so is no where near the boat bottom in the center). The front, back and sides of the tank compartment are padded with a thickness of foam to allow 2-3% expansion in all directions as required by the tank MFG. This foam is quite firm and is impervious to gas.

The plywood tank cover sits on plywood ledges on both sides and at the rear and is made of ¾ plywood, but is unsupported for almost 30” across. Since its part of the main walkway I had to stiffen it. (Its too close to the tank to add strips of wood underneath). So I epoxied 3 layers of 10oz glass on the underside for support and 1 layer of 10oz on top. This *completely* eliminated any bounce or sag when walking on the tank cover! In addition, the cover had a bit of a ‘bow’ in it. Before glassing the bottom of the cover, I screwed 2x4’s to the ‘topside’ to hold it flat. (I applied tiny pieces of masking tape to the screwheads so they wouldn’t get filled in. After the epoxy cured, I used a small forstner bit to drill the glass above the screws – which I will fill in later) After the 3 layers of bottom glass had cured for 3 days, I removed the 2x4’s and the plywood remained perfectly flat! Awesome.

I spaced everything so that the tank cover is also the tank hold down. It will be very very close to the top of the tank. So I glued a thin layer of polyethylene foam to the underside of the tank cover, too. I also used a 1.5” high by ¾” wide mahogany strip at the front of the tank cover to provide support from sagging when somebody steps there. This is all under the curb.

If you look closely at the pictures of the ‘curb’ over the tank, you can see that I used ‘inverted’ finish washers. Instead of sticking up like a typical finish washer, they go ‘down’ into the wood. This allows for good screw support on screws that may be removed a number of times, but also allows the floor areas to still be flat - because eventually the floor will be coated with a rubberized non-skid and I didn’t want the screw heads sticking up through it.

I used these same washers on the tank cover and they make for a nice flat floor. Those washers are a little hard to find. These are stainless and came from an aircraft supply house. Since pine and/or plywood doesn’t do well with screws that are removed a number of times (it can strip out), all of the screws that may be removed for tank/hose servicing screw into mahogany strips below. None of the ‘curb’ pieces will be epoxied in place. Instead, I will use something like boatlife caulk that will waterproof and paintable but will still be removable in the future if needed. Since it has to be removed fairly often for inspection, the top curb piece directly above the tank fittings and sender will be gasketed or sealed very sparingly with silicone only.

The fill and vent hose will be run to port and about 3' aft so that the deck fill will be within reasonable reach of the cockpit for easier “on the water” filling if necessary. The fuel hose will run to starboard and then in its own UV protected (gray) pipe under the gunnell to the stern. Since the fuel pickup fitting is at the front of this tank, I added a longer fuel pickup tube that reaches back to about 1' from the stern end of the tank. This will ensure good fuel pickup even with the bow up when the boat is on plane.