Dipper 16 fuel tank under sole?

Does anyone have experience with building hatches in the cockpit sole for a fuel tank in a small cruiser? I am to the place in building my Devlin Dipper 16 where I need to make a decision.

According to the Devlin's plans I should put a 6 gal tank in one of the "bin" style lockers on the port side of the outboard engine well. The location is about as far from the galley and future wood stove site as possible on this short boat. I like that since I was once one of the damage control officers on a Naval Vessel). What I don't like about the locker is the 6 gal size. So, I have secured a nice Marine aluminum 18 gal tank (gas) that fits nicely between the longitudinal bulkheads of my cockpit sole. I know in Devlin's book "Build any Boat Stitch and Glue," he mentions that he puts the Surf Scooter tank under the cockpit sole, but goes into no detail. Something in me does not want to place the tank where I cannot access the connections. Yet my plan is to put it in an area where I expect regular water.

What I see that I will have change in the plans are the following: 1. No open access from in the pilot house to the under sole area of the cockpit to prevent any transfer of fumes or water if it floods. 2. Build an under sole locker with what I would call "coped up sides" like a hatch on a sub. 3. Build a fully removable hatch cover that fits over the coped sides, 4. Place a rubber gasket around the gutter. 5. Use flush levered dogs to secure the hatch. 6. Epoxy seal everything.

This hatch could be placed all the way aft so the 1/4" wide and 1" deep channel around the hatch could be at the right level to dump into the centered transom cockpit scope. It would mean that I would raise the sole about 1" on the forward, port and starboard sides of the hatch to everything would be flush. A nice detail would be to have a 2" wide 1" deep channel around the entire deck flushing out the scope.

All venting of the locker would be as far back as the Devlin design. Even if the locker did fill with water should the hatch wash away, there would not be enough water there to even make the transom squat and water would go out the scope before into the pilot house.

Sound like a good plan?

I am posting a picture of the tank before the longitudinal bulkheads were installed. You can see where they go by the pencil marks on the pilot house bulkhead.

 

You have hit on one of my pet peeves. Most boat manufacturers bury the fuel tanks where you can't get at them, can't inspect them, and if you ever have to replace it you have to cut big holes in the sole or a bulkhead to get at the tank. In the case of a metal tank it is especially important to mount it where it is not in bilge water, water cannot collect on top of it, and air can freely circulate around it.

So your idea has merits. But I wouldn't mount it flat on the bottom as in your photo. There should be airspace under the tank. There should be a way for any water that gets in that space to immediately drain out. Aluminum does not like wet. If it stays wet it corrodes. If it stays dry it doesn't corrode.

Yes you do want no air flow between the compartment the tank is in to any other compartment in the boat, especially if there is electrical equipment in the space.

Here's a link to rules for gasoline fuel tanks. The ABYC standards for diesel tanks are similar. http://newboatbuilders.com/pages/fuel.html

 

Unfortunatly you have an aluminium tank resting in the bilge. Aluminium doesnt like to be wet...it will corrode. Block up the tank to keep air under it and give the tanks a good coating os epoxy primer

As far as inspection hatch, I see no need for daily inspection. I would go with conventional floor boards and screw them down

 

Great thanks, the picture what mostly to show that what where and how much room. But I glad to know that I can indeed block it up. I was thinking hard rubber and maybe stainless straps over the top. Do I have to worry about dissimilar metals? If so I could use rubber there too?

 

Since your floor boards will be removable and the tank is small, you can easily inspect for corrosion each year.

On a small skiff I prefer plastic tanks and tank instations that are not in the bilge.

 

You might consider having tabs welded to the tank that will allow you to secure it to a bulkhead or stringer rather then using SS straps.

MM

 

How the tank will go under the sole

Here is what I decided to do. The tank fits nicely between these wooden bunks. There is a 4x4 beam that goes over the top and provides support for the removable inspection panel. Oh, and nice limber holes under the bunks.