belowdecks gasoline tank for an outboard motor

[Tod Mills]

Hi,

Any thoughts or references on properly installing a gasoline tank for a 4 stroke ouboard motor?

Clearly the simplest thing would be to keep the tank out in the open air, but I would like to keep the weight as low in the boat as possible. I'm thinking of a tank on the order of 20 gallons (I know that sounds like a lot; the only reason for so much is if I happen to be working aboard and need power for a computer, etc. I also detest gerry jugs on deck)

Down where the inboard engine used to be seems like a good place:



It seems like three fittings on the tank: a fill, a vent, and supply to the motor. Somehow, hose clamps seem less than suitable. What about SAE type fittings? For the connection to the motor, some kind of adaptor to a regular section of hose with the push-on fittings at the transom...

How about a blower? Theoretically, it would only be needed in event of a leak in tank or hose, so when would it ever be used unless you happened to smell gas? How about some kind of containment/isolating box with it's own natural ventilation system to keep any vapors from ignition sources?

I suppose it is good practice to keep any electrical switches up as high as practical (nearer the nose, so to speak)?

Thanks!

Tod

P.S. almost have all the fittings off. A couple of cleats, chainplates, and the genoa tracks plus some odd wood trim yet. Got the thru-hulls out along w/ the cockpit drains (the hoses were so rotten they are like tissue paper...wonder she didn't sink on the test sail!) Also got some interior wood removed:

[Tim]

Tod,

You've asked a deceptively simple question. There are many considerations to take into account when installing any gasoline fuel system. I'll do my best to summarize what might apply to your situation. By no means is this to be construed as a complete list, either. I am sure I have overlooked something.

For general reference, here are the applicable standards and recommended practices that cover gasoline fuel systems and ventilation of boats using gasoline:

ABYC H-2: Ventilation of Boats Using Gasoline
ABYC H-24: Gasoline Fuel Systems

First, the blowers. Blowers are not required to ventilate a space that contains a gasoline fuel tank, and are not required in your case since you are using an outboard motor. Blowers are of course required for any space containing a gasoline engine.

However, if you choose a non-metallic tank, your gasoline fuel tank space must be vented naturally to the atmosphere according to the standards of ABYC H-2.5.3.3. The remainder of ABYC H-2 goes on in excruciating detail about the various ins and outs of the ventilation options, and is too involved to properly address here without more information.

Suffice it to say that the often-seen cowl ventilation system (a couple clamshell-type cowl vents on the coaming, with corrugated blower-type hose leading to the compartment) is probably adequate to provide the required natural ventilation, but the size of the compartment, type of fuel tank, and whether or not it vents into adjacent compartments that might be considered "open to the atmosphere" all come into play.

Metallic fuel tanks are not susceptible to these ventilation requirements. Why? Because plastic fuel tanks are semi-permeable, and allow gasoline vapors to escape (slowly, of course). Metallic tanks are non-permeable.

Now on to the fuel system.

In the most general terms:

1. Fuel tanks should not provide support for any part of the boat's structure.

2. Metallic fuel tanks should be mounted above normal bilge water accumulation, and horizontal surfaces of the tank should allow for drainage without pooling. This is to help avoid corrosion. You also don't want the tank to sit directly on a flat platform, which can promote corrosion in the tight space between tank and platform. Always raise the tank off any platform with risers or cleats. Plastic tanks, on the other hand, generally require the full support of a platform to prevent distortion.

3. The tank must be securely fastened. If metallic straps are used on a metallic tank, isolating gasketing must be employed.

4. There is nothing wrong with using hose clamps in the fuel system, as long as they are of appropriate quality and are installed properly. SAE fittings are fine, but they are less serviceable on the fly. Use rolled-band clamps like AWAB clamps; these have a smooth edge and non-perforated band that doesn't tend to cut into the hose like cheap clamps.

5. Use A1 fuel hose (J1527) for all supply lines, regardless of whether it is technically required or not. (It's probably not technically required in your case, meaning you could use any other grade of fuel hose if you wanted. But I never saw a reason to use anything but the highest-rated A1 hose.)

6. Install a shutoff at the tank end.

7. The fill hose must be A2-type hose and secured with double hose clamps at each end. The tank fitting for the fill must be on top of the tank.

8. You can use A1, A2, B1, or B2 hose for your vent line. (A1 or A2 are required on any fuel line or vent line running through an engine room).

9. The tank and fill plate, if metallic, must be grounded.

10. Obviously you don't want any spark-producing equipment in the fuel tank space.

11. Install a good fuel filtration system. Don't rely only on the little one inside your outboard.

A properly-installed tank should never vent fumes to the boat's interior. Using the proper materials and properly maintaining the tank will prevent this, though of course unforeseen events can occur.

For your proposed installation, I'd suggest an aluminum fuel tank (typically 0.090" 5052 aluminum). Depending on the shape of the tank, you might want to consider a tank containing internal baffles. I'm all for making the tank as big as practicable, as no sailor likes to make extra trips for fuel. However, be sure that you can use up your tankful each season, at a minimum, so that your fuel doesn't become overly stale and full of varnish. 20 gallons is probably good--not too big, but large enough to avoid the need to refuel often.

I've tried not to get overly specific here, but it's important to ensure that gasoline systems are installed safely. Usually, following the generally accepted recommendations of ABYC is a good bet, though don't fall into the trap of thinking that all of these practices are necessarily "required". Some are, but many are not. We can sort that out if need be.

[hesper]

Tod-

Real quick observation is that my new/used Honda 5hp outboard's book says to keep tank ""within 6 feet of the outboard motor" and no lower than 3 feet "below the fuel connector on the outboard motor." I'm no mechanic so I don't know if there is or is not a fuel pump but you should check that specification out on your engine before hand or you may be sucking air...

Jim

[Tod Mills]

I can see that this is going to take a lot of forethought if I want to end up with a topnotch installation, which I do. Some of the idea behind changing to an outboard was to get the heat and fumes out of the cabin. The original motor was a Kermath Sea Pup, 5 hp four stroke water cooled inboard which I have removed. It's cute, but still....

When I was first aboard the boat, the owners were there, running an ordinary household fan in the cabin. They had just filled the tank and the whole boat smelled of gasoline; I had a headache in no time. Here's the reason for the fumes:



As you can see, the inlet was rusted badly and fuel no doubt leaked all over creation and vapors ran rampant. Boat sinking or exploding, take your pick. They were both pretty darn close.

Tim, I'm printing out your post for future reference. There's a ton of info there. Are you a member of the ABYC? I just visited their web page for the first time and see that if a body wanted to buy some of their guidlines, it wouldn't take too many before membership would pay for itself.

Jim, I was wondering whether I would need a fuel pump. The OB will probably be a 9.9 Honda; I've had real good luck with my Honda 5. I'm sure I'll have no problem meeting the 3' of head limit; the 6' distance is probably meetable w/o changing my plans but I better check it to be sure, as well as see if the figures are different for the 9.9 motor.

Thanks, guys!

[Tim]

Tod,

Your photo above should be the poster child for "how things should not be done"! What's more frightening is how common similar situations are. People tend to neglect their boats' systems, but none of the systems are maintenance free or ever-lasting.

I am a member of ABYC and have the standards. Within reason, I am happy to offer you (or anyone) information on any particular standard, or even provide you with a copy of the standard itself for important things like gasoline or propane installations, or whatever the need.

I've never been a believer in quoting chapter and verse on standards that may or may not be applicable, but with a vast amount of misinformation circulating around the boating world about what is "required", and what is not, I will often research a standard to clear up these misunderstandings. Very few things are actually required by federal code or law. My pet peeve is hearing how such-and-such is required when, in fact, there is no such requirement, which is why I will often quote the applicable section of ABYC or some other governing body to clarify the requirements vs. recommended standards. The standards are a good reference, but common sense must be applied to the job as well. Not every part of every standard is practicable, or applicable, to "your" job.

For example: with a gasoline fuel system, all that is required for safety, in the most general terms, is to:

1. Ensure that the fuel stays in the tank and hoses, and cannot leak out

2. Ensure that excess vapors caused by expansion can escape safely

3. Provide the necessary means to ensure that, in the unlikely event that the first two needs are somehow not met, or otherwise compromised, there is not a negligent means of spark creation that could create a catastrophe.

The ABYC standards, if followed, are certainly a good step in this direction, but are not necessarily the end-all. ABYC has no enforcement power, and nothing in and of itself in the ABYC standards is required--except when the wording of a certain standard has been incorporated by reference into the US Code or Code of Federal Regulations sections that apply to recreational boats. There are a few cases where this is true, but not that many. I belive the standards to be an excellent starting point, but there are sometimes other ways to accomplish what is intended by the spirit of the standard. Use of the highest quality materials and installation practices will get you 90% of the way every time--and, coincidentally, will virtually assure that you also meet the voluntary standards of ABYC.

Specific questions regarding the standards themselves should be posted in the "Technical Data" section of this site, as practicable. Free access to the ABYC standards--the only standards widely accepted in the marine industry and the generally accepted minimum benchmark for installations--is a small service I like to provide. I can see no harm in the spread of this information, and feel that the standards should be easily accessible to regular boatowners to promote safe and sound installations rather than the Mickey Mouse stuff so often seen.

Sorry to go on and on here. I can really get going on this topic sometimes...

[xroyal]

Tod, thanks for this subject.

Tim, thanks for your input. I got my first plastic gas tank for 7.5 ob with the Santana I recently bought. Appreciate your comments, and just may revert to a newish metal tank I have. Bottomline, you've got me thinking more about safety in this area.

[Tim]

Plastic tanks can be perfectly fine, but they should be stored in appropriate areas--lockers open to the atmosphere (common for portable tanks), or lockers that are otherwise designed to accommodate the permeability of the tank.

I didn't mean to scare anyone away from good plastic tanks. The point was that there are considerations to take into account depending on the material from which the tank is made.

[Dan H]

. Obviously you don't want any spark-producing equipment in the fuel tank space.

Is the shore power receptacle considered a spark-producing device? I would think not because there are no contacts to create a spark but I'm not sure. I am thinking I will move mine so it is not in the fuel tank compartment at all.

The biggest problem I am dealing with is the location of the ignition switch for the engine and the bilge blower switch. They are mounted through the side of the cockpit well. The back side of the switches are in the fuel storage compartment. The fuel tank is metal, and brand new. I'm not sure if this is acceptable.

My Off-1-2-Both switch is in the engine compartment but it says it is ignition protected. Is this foolish abandon or will this be OK? I will need to turn this switch on to start the engine room blower.

I also purchased the new fuel vent combination unit from Attwood. I e-mailed them and asked if they had a fitting that fit this fill vent unit so I could pressure test the fuel system to 3 psi. They shipped me the fitting for free! I plan to test the system each year.
Thanks for your help,
Dan

[xroyal]

Plastic tanks can be perfectly fine, but they should be stored in appropriate areas--lockers open to the atmosphere (common for portable tanks), or lockers that are otherwise designed to accommodate the permeability of the tank.

I didn't mean to scare anyone away from good plastic tanks. The point was that there are considerations to take into account depending on the material from which the tank is made.

Thanks/agreed. I was thinking of taking permeability out of the equation since I have the option.

Truth is the 7.5 Evinrude is unnecessary on a 22'er like mine. I'm hoping to crank my old 6hp ls, and sell off the 7.5 and plastic tank. My 6hp Johnson a fair amount lighter too. Heck, on this lake maybe I should use my electric trolling motor to get away from the dock.

[Tim]

Is the shore power receptacle considered a spark-producing device? I would think not because there are no contacts to create a spark but I'm not sure. I am thinking I will move mine so it is not in the fuel tank compartment at all.

The biggest problem I am dealing with is the location of the ignition switch for the engine and the bilge blower switch. They are mounted through the side of the cockpit well. The back side of the switches are in the fuel storage compartment. The fuel tank is metal, and brand new. I'm not sure if this is acceptable.

My Off-1-2-Both switch is in the engine compartment but it says it is ignition protected. Is this foolish abandon or will this be OK? I will need to turn this switch on to start the engine room blower.

Most switches that should be on a boat will not produce a spark when thrown, including the battery switch. Battery switches must meet ignition protection requirements, and are frequently located in engine rooms or other areas that might potentially contain gasoline vapors.

The problem with having any electrical wiring whatsoever in a gasoline fuel tank space is that there is always the chance that a malfunction in the wiring could create an unsafe condition. For this reason, it's best, when practicable, to avoid having wires and terminals inside the fuel tank space. This is not always possible, of course, given the space constraints on boats. Most boats, by necessity, have some form of electrical equipment somewhere near a gasoline tank--and often a lot of it. Still, boat manufacturers and weekend warriors often choose the easiest--rather than the best--location or installation. Sometimes things can be rearranged.

The diabolical side of this is that large areas of many boats are actually, by nature of the design of the compartments, open to the fuel tank space. Many fuel tanks are located in the relatively open area beneath the cockpit, and by definition this means that all adjacent open spaces are considered the fuel tank space. The purpose of wiring installation standards and ignition protection requirements is to help prevent the possibility of a spark that could create a safety issue.

Marine shorepower receptacles have caused plenty of fires when they are improperly installed or impropery maintained. The condition of the marina's wiring, which leads eventually to the shore power receptacle, is also a factor. The receptacle shouldn't spark on its own, however, as long as the wiring is good and the receptacle is the proper type and in good condition.

These are all worst-case scenarios. Proper installation and maintenance will virtually assure that there will never be a problem. That's why it's important to use quality materials and do the job right, and why older installations should often be considered suspect. It's not hard to build safe systems. Most older boats are full of minor hazards that will probably always be OK...but might not. Gasoline fires or explosions don't just happen--there is always some chain of preventable events or issues that leads to the problem.

To adopt a common tool-usage mantra: if it looks unsafe, it probably is!

[cliffg]

At a Coast Guard Auxiliary meeting a while back someone mentioned that ethanol gas will eat up plastic/synthetic gas tanks. Supposedly a report had been issued somewhere. I don't know this for certain but the guy that provided the information is usually pretty knowledgable.

[xroyal]

At a Coast Guard Auxiliary meeting a while back someone mentioned that ethanol gas will eat up plastic/synthetic gas tanks. Supposedly a report had been issued somewhere. I don't know this for certain but the guy that provided the information is usually pretty knowledgable.

Thanks cliffg. Will keep my antenna up on the ethanol/plastic tank issue.