Fuel Tank Setup

[Hiptrip]

Hello everyone.

My name is Zol & this is my 1st of many threads I'm sure. Very well informed & fascinating forum I must say.

I am fully restoring an 'x' coastal patrol boat....an old Australian classic fibreglass single deep V hull cruiser called a Savage Marlin. It's 21ft long & is powered by a 350 Small block Chev. It used to have an OMC gearbox but I have since re-designed the propulsion setup with a Doen Jet. A DJ80 which is also an Australian design. I've removed the stringers, bearers & transom. In otherwords fully gutted the boat due to rot & major hull fractures. It's been a 4 year project for me as I've never built or restored a boat in my life. All I wanted to do was to buy a big boat to go fishing. Not to rebuild one. But I'm sort of addicted & devoted to building her into a fine looking vessel.

The boat has just been sprayed & is ready for the running gear to go in. But the first thing I need to do is set up the fuel system.

Just a brief description so that you understand my setup.
I have glassed the floor with room to fit 2 stainless steel tanks in the center of the floor. Length ways. Once covered they will sit flush with the rest of the floor. At the moment I have drainage access for water to flow from the cabin all the way through & under the tanks & out to the back under the engine. It flows openly. I glassed the floor thats beneath the tanks in a 'V' channel so that the water is guided to the rear.

I'm wanting to change this setup.
I want to close off ANY access for drainage to flow beneath the tank. Then I want to permanently cover the fueltanks with plywood lid & then glass it so that the floor is flush . I'd have predrilled portholes for filling, guage wires & breather. Have a sealed porthole for access by unscrewing. Fill the cavities around the tanks with 2 part polyurethane foam (closed cell). And ofcoarse...properly closing off the drain holes on each end of the cavity to make it FULLY SEALED.

I would also fit PVC pipes in the cavity accordingly which I would use to feed the rubber fuel hoses & breathers through. This is to make changing fuel hoses a simple process. The other way I thought was to fit brass or alloy fuel lines & make it permanent.

The reason I want to do this is to keep fumes away from underneath the floor. Even more floating safety. No hinges.one peice carpet...etc

Some friends are telling me that it's not a good idea to close it off in case of tanks cracking. They don't seem to know of this setup. I haven't either.

Is this the wrong way to do things? Do stainless tanks crack that easy? Is there a better set up? Are there things that I have not considered? Does the 2 part foam react with leaking fuel & absorb it creating a more hazardous situation or will it act as a secondary seal?

Any opinions would be helpful as I don't have the luxury of being a shipwright. So I'm following my logical instincts.

Cheers
Zol

[yipster]

hello hiptrip
why do you want to change the drainage setup? its a common concept that leads water to the bilge that must have a driftervalve actuated pump system. my shower even drains that way
ah, fumes, yeah... and bilge bulkhead as high as the freeboard? i'll hope / am sure others will add to this reply but i allready ask to see a pic (of the doen jet also?) yipster

[Hiptrip]

Hi Yipster

I've got some photos but my scanner isnt up. But I'v got some digi pics of the Jet for ya while I sort the scanner out.

[Hiptrip]

And one more

as far as the fitting go...use copper and copper pipes.

The fuel tanks (at least in the U.S.) cannot be completely sealed unless you're running diesel fuel. Rules aside, I think if you plan on encapsulating the tanks under plywood you need to realize that if any happens to the tanks or more likely to the fittings you may have a difficult time replacing them.

I did something similar to what you are proposing but actually made the tanks out of fiberglass and incorporated them to the hull itself (yes...that's a no-no) but who cares.

If you plan on permanently covering the tanks I would suggest bedding them in using two-part polysulfide...if they happen to leak for any reason the polysulfied will maintain the seal. This needs to be two-part not one part polysulfide.

You can get this at most marine outlets and is generally used for bedding teak planks...orginally made for sealing fuel tanks.

[Hiptrip]

That sounds interresting. Any sites around that show this kind of setup?

I can't refer you to a site that specifically talks about permanent fuel tanks in boats.

I decided to make my tank permanent because I needed as much fuel capacity as possible in a limited amount of space. Putting a stainless steel or alum tank inside the well area and then closing it off did not sound very appealing to me either.

After looking at your pics I think the best course of action is to try a more conventional approach...lid, hinges and all. Good luck, and if you decide to try and go the permanent built in approach let me know...maybe I can post a few pictures.

[gonzo]

Stainless steel tanks do crack easily. Aluminum is a better material. If you must use stainless, have the edges bent instead of welded. However, check out local regualtions. They may not allow stainless for gas. Also, the vent, fill, pickup line and gauge need an access plate.