Installing molded plastic FUEL CELL.

Hello everyone.

I have tried to search the threads about installing my molded plastic fuel cell (Manufactured by Moeller Corp.) with no luck. I've tried to email Moeller too... with no response. So I'll ask here.

I've built an enclosure under the bed in the cabin to house the 25 gallon molded plastic fuel cell. There are literally no instructions regarding the installation of this thing other than the warning about it being mounted & grounded properly (and I've read some controversy about grounding a plastic fuel cell too).

Anybody have any advice on this subject (mounting & grounding) ?

Below is a quote from Dereksireci...> http://boatdesign.net/forums/showthread.php?t=4513&highlight=plastic fuel cell
"Don't forget that a plastic tank grows after it reacts with the gasoline"

Is there any truth to this ? If so, how much expansion can be expected from a cell that is 47" x 18" x 7.5" ?
My enclosure is made of 3/8" ply measuring 48" x 20" x 10". I was originally planning to lay a thin rubber mat (1/8") under the cell and surround the thing with a spray in type foam (Polyurethane - resistant to gasoline and other solvents) to prevent the cell from shifting side to side or fore & aft. Two beams across the top (athwartship) screwed & glued in solid would prevent the cell from moving up or down (even if capsized ).

Am I on the wrong track ?

 

Plastic Fuel TANK !

O.K. So there's a big difference in running a search for a FUEL TANK as opposed to a FUEL CELL (which is what I was doing wrong...).

I've consiquently been able to find a couple of threads that have answered some of my concerns.

A plastic fuel TANK will expand approx. 3% when filled with gasoline.
I do not understand how this is since the tank is vented and thus cannot be pressured up (unless the vent tube is plugged).

Quote from Ike ... > http://boatdesign.net/forums/showthread.php?t=11403&page=2&highlight=plastic fuel tank
April 26, 06
"Don't even consider foamimg a plastic tank. FIrst the stuff won't stick to them, second they expand when you fill them and third vapor permeates through the tank wall and destroys the foam."

Ike, if your out there, I am certainly not a proffesional and am of limited knowledge but as I understand this... Polyurethane Foam will stick to ANYTHING. Also, Polyurethane Foam cannot be "desolved" or broke down by anything...solvent or otherwise. Dow Chemical makes this claim about their product. In fact, they expressly warn you not to get this stuff on you because, as they claim... there is NOTHING that can take it off after it cures.

I'm not trying to start an arguement here, only wish to understand and keep my boat safe as well as comply with specified saftey regs.

Somewhere, it was suggested that one could foam in only the corners of a plastic tank thus, allowing for expansion. This is what I'll probably do. The aft side of the fuel cell's enclosure will be open for drainage at the bottom in case there is any condinsation build up in the enclosure.
I've also kept in mind being able to inspect the connections / fittings as well as the tank itself. It will be fully accessable with minimal effort.

Unless somebody tells me otherwise, I think that I've got a reasonable plan for installing my fuel cell now... I have been concerned.

Now, can anybody explain the grounding issue. Plastic tank... Plastic fill tube with a metal cap & chain. How do you ground a plastic tank ? Ground wire from tanks sending unit to a ground buss or ignition switch ? Ground buss or ignition switch grounded to the battery and or engine... ? Is there anything that connects the ground circuit to the "water" or "earth" ? I need to understand the exact circuit.... as I don't want to screw this up.
I'm not ready to hook this all up yet... it will be awhile but, I've got to take everything into consideration while I'm constructing things. I hate backing up...

 

I'm here. Just lurking. A plastic, actually roto molded cross-linked polyethylene, tank permeates some fuel vapor through the walls of the tank. It's not enough to be concerned about from a safety viewpoint, but it results in a couple of things. First it causes the walls of the tank to swell, so when you design clamps or starps to hold the tank down, you need to leave a little slack in them. The best way is to put tank in, fill it and let it swell then readjust the clamps or straps.

Ground on a plastic tank is only from the sensor gauge to the fuel guage on the instrument panel. There should be a ground connector on the fuel sensor. You could also run a wire to the ground buss if your boat has one.

As for the fill. it depends on the fill you have. If the fill fitting is metal or chrome plated it should be grounded. However, if it is plastic and the boat is a trailerable boat and going to be fueled mostly at land filling stations, then it shouldn't be grounded. Read this: http://www.uscgboating.org/alerts/alertsview.aspx?id=27

The idea here is that when liquid fuel is flowing through a rubber fuel hose it creates a static charge on the fuel hose. By grounding the metal fittings that the hose is connected to, this charge is dissipated. However, it doesn't work that way if a boat is sitting on a trailer. You can get a really nasty static discharge from the boat to the fuel nozzle at the gas pump.

I don't care what the foam manufacturers say, 20 years of experience with this stuff has shown it will not adhere to a plastic tank, especialy when the tank swells and vapor permeates through the tank walls. I have talked to them about this, and mainly it's advertising hype. Some boat builders still foam in metal tanks (also stupid) but no one foams plastic tanks.

First place, for a foamed tank (metal or plastic) to work properly the bond between the foam and the tank wall has to be stronger than the foam itself. That is so the foam itself will fracture before the bond does. Initially this was written into the Federal regs and ABYC standards because everyone was using metal tanks, and if the bond fails you get moisture between the foam and the tank and the tank corrodes. But when plastic tanks came along in the 80's people tried foaming these things, and found very quickly that it doesn't work. You foam the tank in, fill it, the tank expands and fractures the foam. Besides I believe that foaming in any tank is only an excuse for not providing a good mounting system. Metal tanks need airspace around them to keep them dry. Plastic tanks need space because of the expansion and permeation issues. Any way, I've ranted enough.

One other thing, make sure there is some space above the tank. If the top of the compartment the tank is in is in contact with the tank, it will actually push the top of the compartment up. I have seen these tanks actually lift decks that were too close, up a little. If you put those beams across the top of the tank it will proably either bend them or they will cut into you tank top. The only leaks I have ever seen in plastic tanks were from human error, drill holes or screws protruding through the deck over head, or the walls of the compartment. Tanks have been damaged by just such an arrangement as you propose too. The best way to hold these things down is metal clamps, or straps around the tank.

Here is a link to a pdf file about tanks and tank installation. It covers all tanks but has some very good info on plastic tanks and how to mount them. http://zimmermanmarine.com/docs/tanks.pdf

 

Sorry about all the editing. I kept forgetting to put in the URL for the pdf file.

 

Thanks Ike.
Much good infomation there. As for the securement of the tank, I was sold a strap package with the fuel cell (4 metal straps about 5" long... L shaped on both ends [opposing L's... one this way ... one that way]) but, there isn't anyplace on the fuel cell for the "L" to hook to like MOST plastic fuel cells sold. If that makes any sense !

This is why I constructed the box. Their is approx. 1" clearance on all 4 sides and 2"-3" clearance on top. This should be enough to accomadate a 3% expansion, would you agree ?

As for the USCG's alert...http://www.uscgboating.org/alerts/alertsview.aspx?id=27 yes, I am aware of this and have had it saved for some time now... just haven't been sure that I understood it correctly.

Thanks a bunch Ike........

 

By the way, once you have installed the tank and before you put fuel in it you should do a system pressure test. This is fairly simple to do and doesn't require a lot of pressure, max is 3 psi. Here's another link that has lots about tanks, and describes how to do a pressure test. http://www.boatus.com/goodoldboat/tanksalot.asp

 

Roger the pressure test.