Integral fuel tanks

[PatriciaLynn]

OK, I am looking to understand the good, bad and ugly of integral fuel tanks, ie. Fuel tanks that use the skin of the boat as one or more of the sides of the tank.

I am looking into moving up into a larger rig and for my future goals will want to carry 400+ gallons of fuel. Anyone ever build a fuel tank into the boat rather than build seperate tanks and mount them in the boat?

 

[Scooby]

My 37 west bay has them integral both sides. He also put an opaque vertical view strip to see fuel level if needed. See photo.

 

[Genius]

My 37 west bay has them integral both sides. He also put an opaque vertical view strip to see fuel level if needed. See photo.

View attachment 154361

That’s pretty cool!

 

[c1steve]

Integral tanks would not produce as much condensation, so less water in the fuel. However this is more of an issue when the boat is hauled out than when in the water.

On the West Bay, how easy is it to see the fuel level?

 

[Genius]

Integral tanks would not produce as much condensation, so less water in the fuel. However this is more of an issue when the boat is hauled out than when in the water.

Imo, that’s a myth anyway. The amount of water that would condensate from a “trapped” air pocket is sooo insignificant.

 

[c1steve]

I had a boat stored on a trailer in a rainy area, Washington State. Went to use it one weekend, engine died after a while. Secondary filter was completely full of water, and there was more water in the bottom of the tank. Total water removed was probably 1.5 quarts in a 65 gallon tank.

 

[Scooby]

You can see the fuel level in the photo a few inches above the horizontal piping strip. The brown translucent panel gets darker below that.

 

[enginecom]

Integral tanks can be a major problem especially if the boat grounds. I used to support them for metal welded hulls until all the problems with single skin tankers. A double layer of metal is now a requirement on tanks for stationary generators which never move once installed. The boat being a moving vehicle is vulnerable on collision with anything near or at the tanks. Check with your insurance company and a local boat surveyor on their opinions.

 

[Provincial]

OK, I am looking to understand the good, bad and ugly of integral fuel tanks, ie. Fuel tanks that use the skin of the boat as one or more of the sides of the tank.

I am looking into moving up into a larger rig and for my future goals will want to carry 400+ gallons of fuel. Anyone ever build a fuel tank into the boat rather than build seperate tanks and mount them in the boat?

That's how we've been doing it for 40 years and 400 boats. These tanks are over 700 gallons combined.

 

[Bill]

Heres some that I built, you just thicken up the hull where you are building them you arent gonna have an issue, tons of boats do it this way it adds structure to the boat and you arent dealing with mounting the tank, foaming it in or whatever.. In a diesel boat I think all the tanks should be integral.

27 T Jason

That thing has a deep keel, looks like she can swing a bigger wheel than my 30!! what can she swing under there? 22" is max diameter on the "original" 25 T Jason. Bill has extended the keel...I bet he can swing maybe a 24" wheel if it warranted.

downeastboatforum.com

 

[leaky]

I think the water in fuel problem is mostly a gasoline one, due to ethanol, which really really wants to eat up water. Integral fiberglass tanks, even if it was a concern made worse - that's not gonna be gasoline.

Never seen integral fuel tanks except in welded aluminum boats. Funny though one of those boats, it did have a terrible problem (with gasoline) and water condensation. Owner fixed it by insulating the deck with a piece of carpet, which was the actual top of the fuel tank in that boat, ie issue was the deck and not the hull.

I'd think one concern would be similar to integral exhaust parts, if the boat flexes so do these parts that might fatigue and crack, then leak.

I'm not sure it buys you much over a custom tank done to a tight fit though. You can form a fuel tank right in the hull where it's going to sit and you do not lose much capacity beyond the little bit that the skins take up and whatever gap is left. The 1/4 skin of a 200 gallon tank might be 10 gallons of capacity lost, given a little gap here and there, probably a ballpark of 10% in the end if done truly tight & custom when the deck is off.

 

[Genius]

I had a boat stored on a trailer in a rainy area, Washington State. Went to use it one weekend, engine died after a while. Secondary filter was completely full of water, and there was more water in the bottom of the tank. Total water removed was probably 1.5 quarts in a 65 gallon tank.

Not from air IMO

 

[Jay Michaud]

OK, I am looking to understand the good, bad and ugly of integral fuel tanks, ie. Fuel tanks that use the skin of the boat as one or more of the sides of the tank.

I am looking into moving up into a larger rig and for my future goals will want to carry 400+ gallons of fuel. Anyone ever build a fuel tank into the boat rather than build seperate tanks and mount them in the boat?

My Provincial 42 was built with integral tanks. Now on my third engine, but have NEVER had a single issue with the fuel tanks. I admit, I was skeptical when I had her built, but it turned out to be a blessing. 400 gallons with no extra "nooks & crannies" under and around the two the tanks. Provincial did an outstanding job.
Before haul-out, I do fill the tanks to prevent any chance of condensation forming during seasonal lay-up, however I would do that with any tank, integral or traditional, metal or fiberglass. Provincial molded large clean-out ports on each tank, but I've never had to use them.

Jay Michaud
MarinSurveys.com

 

[Jay Michaud]

Spelling error!
MarineSurveys.com

 

[Scooby]

I would say they are well proven then. Mine are great as well.

 

[Diesel Jerry]

Greg with you being more proactive on maintenance than the average boat owner integral tanks should not be a problem. Use good treated fuel. Use the boat to get enough “traffic” in the fuel tank and you will be all set. I usually don’t like integral tanks for the fear of potential replacement. But all the tanks I have replaced were due to poor fuel quantity. Just a couple were leaked and it was a ton of work to get them out of the boat. If intragal they could have possibly repaired with some glass work.

 

[stimmy]

I have a 1990 Hatteras, built with 1500 gallons of integral fuel (diesel) tanks. They have worked without issue for 33 years; however, Hatteras uses rubber liners.

 

[c1steve]

Not from air IMO

It was practically in a rain forest, on Bainbridge Is. Only used the boat 1-2x/ year, as I lived out of state. 99.9% sure it was from condensation. Deck fill never seemed to be a problem, it was o-ring sealed, was in good condition. It would pick up this much water over a year without being used.

 

[Genius]

It was practically in a rain forest, on Bainbridge Is. Only used the boat 1-2x/ year, as I lived out of state. 99.9% sure it was from condensation. Deck fill never seemed to be a problem, it was o-ring sealed, was in good condition. It would pick up this much water over a year without being used.

the physics of water vapor depositing water in the tanks doesn't make sense. Volumes, air flow and amount of water vapor air can hold.