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**David M** · 05-07-2012, 15:43

I need to extend the range of my ski boat, which I also use for fishing. It only has a 90 mile range, which means I can only go 45 miles out and back, when I feel lucky.

So I am looking at semi-clear plastic fuel tanks. The reason I like the semi-clear plastic tanks is that I can see the actual fuel level just in case the fuel gauge is inaccurate.

It is not possible to remove the existing fuel tank for a larger tank, there is not adequate space in that location.

The boat I have came with a plastic fuel tank so I know that the type of plastic that the tank is made of meets Coast Guard requirements for a recreational boat. I also have another boat at work with the same thing.

The problem is, when I look up Polyethylene and Polypropylene in the Chemical Resistance Tables, neither of these materials are satisfactory for gasoline.

I need a custom tank so the higher of the two tanks, the new one, will pour into the older tank. The custom tank needs two larger plastic pipe nipples, one at the top and one at the bottom. I also need a smaller air vent nipple at the top of the tank.

Existing gas tanks will not work because they lack the two larger nipples that I need. I am not interested in bringing the gas nozzle into the enclosed space of the engine compartment to fill the auxiliary tank. This is too dangerous if there is a spill.

So my question is, what type of material are plastic fuel tanks made of and where would I find someone who can make me a custom tank. I found one manufacturer but they only make custom polyethylene tanks.

http://www.borealisgroup.com/pdf/che...ce-hdpe-ld.pdf

http://www.borealisgroup.com/pdf/che...chemtab_PP.pdf

Stumble · 05-07-2012, 18:01

Most plastic fuel tanks are polyethylene.

Take a look at http://www.moellermarine.com/sites/m...Tank_Sheet.pdf which is Moeller's custom tank work sheet.

Astral Blue · 05-07-2012, 18:33

Quote:

Originally Posted by David M

I need to extend the range of my ski boat, which I also use for fishing. It only has a 90 mile range, which means I can only go 45 miles out and back, when I feel lucky.

So I am looking at semi-clear plastic fuel tanks. The reason I like the semi-clear plastic tanks is that I can see the actual fuel level just in case the fuel gauge is inaccurate.

It is not possible to remove the existing fuel tank for a larger tank, there is not adequate space in that location.

The boat I have came with a plastic fuel tank so I know that the type of plastic that the tank is made of meets Coast Guard requirements for a recreational boat. I also have another boat at work with the same thing.

The problem is, when I look up Polyethylene and Polypropylene in the Chemical Resistance Tables, neither of these materials are satisfactory for gasoline.

I need a custom tank so the higher of the two tanks, the new one, will pour into the older tank. The custom tank needs two larger plastic pipe nipples, one at the top and one at the bottom. I also need a smaller air vent nipple at the top of the tank.

Existing gas tanks will not work because they lack the two larger nipples that I need. I am not interested in bringing the gas nozzle into the enclosed space of the engine compartment to fill the auxiliary tank. This is too dangerous if there is a spill.

So my question is, what type of material are plastic fuel tanks made of and where would I find someone who can make me a custom tank. I found one manufacturer but they only make custom polyethylene tanks.

http://www.borealisgroup.com/pdf/che...ce-hdpe-ld.pdf

http://www.borealisgroup.com/pdf/che...chemtab_PP.pdf

I agree with Greg with respect to Moeller Marine. They offer the largest variety of sizes and shapes; and I have used their tanks in the past and will be using one for my repower. They are of excellent quality.

I do have concerns with what you are proposing. If I understand your post correctly, you are going to locate the new tank above your existing one...and will be running a fuel line to the existing tank, enabling the fuel to pour into the existing tank....correct? Will your new fuel tank be mounted on the deck?

If this is the case, there are considerations. First, I would obtain the ABYC standards for auxiliary fuel systems to determine whether that configuration is compliant. This might be necessary for insurance considerations. Besides compliance issues, there are a few items to consider. If the new fuel tank's level is above your existing tank's vent, the hydraulic pressure from the fuel in the new tank will push fuel out of your vent. Another consideration is the location of the port on your new tank that feeds into your old one. Both Coast Guard and ABYC standards require that fuel be drawn from the top of the tank via a tube extending to a point slightly above the bottom. The only way to enable transfer between tanks would be through the use of a pump.

The simple and most straightforward solution is to have two separate fuel tanks, a fuel switching valve, and a dual fuel gauge (or a single fuel gauge connected to both senders).

Also, the polymers used in the construction of marine fuel tanks are quite effective for the first 10 years. All polymers for fuel tanks will eventually allow fumes to permeate; and each tank manufacturer will be able to provide specific information regarding the ratings of the polymer used for the specific tank.

Hope this helps.

**David M** · 05-07-2012, 18:58

Thanks. That is some very helpful information.

Edit: I have learned that what I want to do is not approved by ABYC. Gasoline tanks cannot have drains. All fittings must be at the top of the tank according to the standards. What this means that there are no gasoline fuel tanks that have been tested and certified that have a drain, they would not be legal. The rules also require all tanks to be certified to certain pressure, shock and fire resistance standards. Therefore a custom made tank would never fly...the designs all have to be lab tested.

This is where I found my info: http://newboatbuilders.com/pages/fuel.html

I like your idea of two separate fuel systems where you select which fuel tank you want to draw from. It seems to be okay with the CFR's and ABYC. At least I don't see anything prohibiting this setup. I could probably put a Y-valve in the pour hose so that after one tank is full I could switch the valve over to fill the other tank. A Y-valve on the pour hose would mean I never have to take the fuel pump nozzle below deck, eliminating a potential source for a spill and possible fire.

So does this seem safe and legal with respect to the CFR's and according to the ABYC's guidelines?

Cheechako · 05-07-2012, 19:09

having an outlet on the bottom is a recipe for disaster.... a big noisy loud one.... Maybe a a 3 way fuel valve drawing from the top of both tanks would be better?

**David M** · 05-07-2012, 21:05

Do you mean an A-B-Both valve? I like the idea.

Astral Blue · 05-07-2012, 21:09

Quote:

Originally Posted by David M

Thanks. That is some very helpful information.

Edit: I have learned that what I want to do is not approved by ABYC. Gasoline tanks cannot have drains. All fittings must be at the top of the tank according to the standards. What this means that there are no gasoline fuel tanks that have been tested and certified that have a drain, they would not be legal. The rules also require all tanks to be certified to certain pressure, shock and fire resistance standards. Therefore a custom made tank would never fly...the designs all have to be lab tested.

This is where I found my info: New Boatbuilders Home Page - Fuel Systems

I like your idea of two separate fuel systems where you select which fuel tank you want to draw from. It seems to be okay with the CFR's and ABYC. At least I don't see anything prohibiting this setup. I could probably put a Y-valve in the pour hose so that after one tank is full I could switch the valve over to fill the other tank. A Y-valve on the pour hose would mean I never have to take the fuel pump nozzle below deck, eliminating a potential source for a spill and possible fire.

So does this seem safe and legal with respect to the CFR's and according to the ABYC's guidelines?

You are best to avoid any installation that requires you to take a fuel nozzle below the deck. Safety and convenience are powerful incentives here.

A few considerations regarding the Y valve for the fuel fill... All boats I have seen with two fuel tanks have a separate deck fill and dedicated fill line for each tank. When fueling, you want to minimize the inconveniences associated with the process. Having to go below deck to turn a Y valve while at a fuel dock is something you might consider avoiding. The prospect of an accident occurring while opening the hatch, stepping in and out of the engine compartment, accessing the valve, etc. can be high during the presence of wind or a wake. Imagine performing this during a small craft advisory. Also, you want to minimize the number of connections between the deck fill and the tank. More points of connectivity invites a higher degree of risk for leaks, compromises in the integrity of the hose, and more maintenance in general. This is not an area you can afford to have fuel leaks. And lastly, marine grade fill hoses are INCREDIBLY difficult to work with. They are very rigid and do not tolerate bends well at all. Just a few things to think about...

And to answer your question about the Y valve being safe and legal. The safety issue is addressed above. But as far as legality is concerned, I doubt it will be compliant. I performed a rudimentary search for Y valve rated for marine fuel fill lines, and had no success finding anything for that purpose. If it was legal, most marine supply houses would carry them. There are plenty of Y valves for switching between tanks, but none for fuel fills.

One option you might consider is an above-the-deck fuel transfer tank. It is the least costly and quite easy to install. It can be filled and left there. You can create a closed system with a pump plumbed to your existing tank. When your existing tank is depleted enough, simply activate a fuel transfer pump and the fuel from the transfer tank can make its way to your existing tank. The nice part about this arrangement is your ability to remove and replace your new tank with minimal effort and minimal impact on your boat. If you find yourself not needed it, you can simply remove it and not worry about dealing with the holes you made in your hull for the deck fill and vent. You might want to research the certification requirements for fuel transfer tanks, but I don't believe they need to meet USCG (CFR) requirements for marine fuel tanks. The transfer tank will also be vented, so there would be no need to run a vent line and penetrate your hull.

Hope this helps.