# Fuel tank and battery in same compartment?



## RobertKWFL (Apr 3, 2009)

My catamaran has transom-hung outboards. I'm thinking about the best location for the starting batteries and permanently installed below deck fuel tanks. We currently use portable tanks above deck. They are always tripping people, fouling sheets, or otherwise in the way. Each hull has a compartment at the stern with a bulkhead sealing it off from the rest of the boat. These compartments would be the perfect size and location for battery and tank. Assuming the battery is installed correctly (strapped down in leakproof box; vented; no ignition sources, etc) and assuming a permanent below deck tank is installed correctly (strapped down; properly installed deck fill and vent, etc), would it be illegal/unsafe/unwise to have battery and gasoline tank side-by-side in the same compartment?


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## Barquito (Dec 5, 2007)

> would it be illegal/unsafe/unwise to have battery and gasoline tank side-by-side in the same compartment?


Yes.


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## tommays (Sep 9, 2008)

Well

Not sure if you really mean touching or in the same compartment 


Unwise as it may be its sort of the way a lot of boats were and still are built 

There are a fair amount of ventilation requirements that may come into play and i had a survey guy stop by my boat before i got to far into it to get and idea what would pass


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## Barquito (Dec 5, 2007)

> Fires and explosions require three conditions before they can occur. This is called the fire triangle. It is, oxygen, a source of ignition, and fuel. On boats the oxygen obviously is present, the source of ignition is usually the boats electrical system, and the fuel is generally gasoline. So, if one side of the fire triangle can be eliminated, then the explosion and fire can be prevented. Each of the standards dealing with fuel systems, electrical systems and ventilation is designed to eliminate one of the sides of the fire triangle.


Kind of simple. But, it makes sense. Would it be possible to build a glassed-in box that is ventilated to the outside for the gas tank?


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## tommays (Sep 9, 2008)

If you install a proper fuel tank its already a sealed unit










And then install the proper fill and vent hoses










And locate the fill and vent so they do there thing overboard WHICH has a bunch or rules as to were

If you have smells something is broken


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## RobertKWFL (Apr 3, 2009)

Well, I've read all the AYBC/USCG/ISO regs I can find regarding battery installation and permanent fuel tank installation. AYBC says the battery can't be directly over or under the fuel tank, and there are specific rules about fuel hoses running over batteries. Otherwise I can't find anything specifically about battery/fuel tank proximity. The only issue I know of is that all electrical devices in the compartment have to have ignition protection certification. I guess batteries don't have that certification, even if under normal conditions they are not an ignition source. So the batteries will have to move to another home.


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## tommays (Sep 9, 2008)

Battery s are allowed but as i said before i would consult with a good survey person before making such a big change as you have no motor down there the ventilation requirements are the issue that's up in the air


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## Minnewaska (Feb 21, 2010)

I can't count the times that I've had a little arc when removing or replacing a 12v battery. Can't imagine wanting that to happen in the proximity of a gasoline tank, vented or otherwise. Yikes.

Can you put the batteries in one hull and the tanks in the other and just run wires and plumbing across?


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## P35juniper (Feb 11, 2010)

How big are these compartments? are they just lockers or are they someplace you could install inboards if desired? 
My batteries are about 3ft from the fuel tank, diesel now was gas, in the engine bay, all that seperates them is a peg board and 3ft. 
can you split the compartment in some way to devide it as a removeable bulkhead?


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## Michael K (Feb 27, 2006)

*Another reason...*

Robert,

With the safety precautions already noted above by others, here's another reason your idea may not be so good. I'm not certain how large your catamaran is but fore-aft hull trim is key to catamaran performance, and so you may not want to concentrate too much weight in aft. compartments. Both fuel and batteries are heavy and might cause your transoms to drag.


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## RobertKWFL (Apr 3, 2009)

Thanks for all the input. A couple of thoughts.

1) These are outboard starting batteries. With the engine off, there is no current draw at all and therefore no arcing when connecting terminals. Also, to reach the battery, I have to open a hatch large enough to qualify the compartment as open to atmosphere by the CG definition.

2) Crosslinked PE tanks and approved fuel hoses do have some small amount of vapor permeation, but we're not talking about much. The tank vents to the outside as required by the rules. 

3) I would love to move battery weight forward, as this is a light displacement boat. Fore-aft trim is a big concern to me. But on a 36' boat, just moving batteries to the center means about 40' of awfully heavy wire. Added weight and cost might negate the benefits of better trim. Moving fuel tanks forward might be easier, but I just don't know how much a small outboard can pull fuel through a long hose, and adding an extra fuel pump seems risky and complicated. 

For now at least, I'll look for a better battery location and put the tanks at the stern.


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## jhaley66 (Nov 4, 2008)

*Do you need a bulb with this installation?*

I am considering the installation of a permanent fuel tank in my boat. Is there a way to avoid the manual fuel pump bulb with a permanent tank or do you still have to prime the engine with a few squeezes of the bulb?


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## pdqaltair (Nov 14, 2008)

Certainly, I would get a surveyor's opinion. Code matters, but so does a surveyor's probable reaction.

* Batteries are NOT an ignition source. If they were, hydrogen explosions would be epidemic.
* Tight electrical connections are not an ignition source.
* Battery location restrictions vs. fuel tanks and hoses are because H2SO4 fumes and leakage can damage hoses and the tank.

Separation would be nice, but not strictly required. That said, battery cables have started many fires in boats and cars/trucks (they were routed poorly and chafed in most cases); be VERY careful with wire routing and required fuses.

Is it possible to place the tanks and batteries in the bridge deck, such that spills and fumes can be vented down and OUT of the boat? This an option catamaran owners have and often take advantage of. Good for propane tanks too.


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## RobertKWFL (Apr 3, 2009)

You do have to prime. I plan to use a small pump such as Facet Posi-Flo #60104 followed by a fuel-water separator. The pump will be controlled by a momentary contact switch in the cockpit. Instead of squeezing a bulb, you just push the switch for a few seconds. I suppose, out of an abundance of caution, adding a squeeze bulb in series with the pump might be a good backup in case of pump failure or power loss.


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## tommays (Sep 9, 2008)

You should really do and abovedeck outboard primer bulb as that fuel pump has a bunch of stuff like (Built in Anti-Siphon Valve) that is going to be to restrictive for the outboards fuel pump to draw through


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## pdqaltair (Nov 14, 2008)

RobertKWFL said:


> You do have to prime. I plan to use a small pump such as Facet Posi-Flo #60104 followed by a fuel-water separator. The pump will be controlled by a momentary contact switch in the cockpit. Instead of squeezing a bulb, you just push the switch for a few seconds. I suppose, out of an abundance of caution, adding a squeeze bulb in series with the pump might be a good backup in case of pump failure or power loss.


And the primer bulb should NOT be below deck. Not convenient, but more to the point, not code and too failure prone.

Do remember that the fuel line requirements for an outboard and below decks are different. Double clamps, CG approvals... be safe!


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