[User 09]

  I am considering converting the space where my two 50 gallon water tanks are in the living area to fuel tanks. Currently I have two 50 gallon water tanks, one under each settee.

I want to buy two brand new aluminum tanks, same exact size and shape and just drop them in place and convert them to diesel. My only concern is if there is going to be a problem with diesel odor if i do this and how bad it might be.

My current tank is under the quarter berth and I can definitely smell the diesel slightly when I sleep in that bunk. Since I am live aboard, smelling that 24/7 in the main cabin if I do this conversion might be an issue.

My question is, if I replace everything with new and keep everything very tidy, replace hoses occasionally, prevent leaks etc...etc...do you think the diesel will still permeate the hoses and fittings and the smell become noticeable? Am I being unrealistic to expect to be able to contain the odor?

Im sure part of the problem with my current tank and location is the fact thats its old and fittings or hoses have not been checked in a couple decades or more. Possibly the hoses are permeated or leaking or there have been spills in the past.

I would love to hear any recommendations or suggestions on how it might be possible to maintain the odor if you guys think its doable. My initial thought was to build sealed boxes around the tanks with sealed access hatches to try and help, but this does not take into account the hoses that will run outside these containers.

[glenn.225]

If all is done "right" you should not have any odors. But that is the catch getting it right, there is almost always some little seep somewhere. Me, I don't mind or sometimes even notice a little diesel smell (I was a mechanic for 20 odd years). My wife on the other hand can smell that "sink" from metres away, so I may have to redo and wash installations a couple of times before it is acceptable. YMMV

[fox9988]

If it doesn't leak and is properly vented, there will be no odor.

[MikeHoncho]

I would not install a aluminum tank if you can do it with a poly tank. My aluminum tank corroded on the bottom and I believe it had been leaking for several years giving me a diesel smell in the engine compartment and quarter birth. With a new poly tank no more smell.

[Tsuru]

What fox said.....Our main diesel tank is under the salon with no odor. (zero, none, zip). Good luck with your conversion.

[gonesail]

i have aluminum fuel tank under my settee .. zero odor from it.

[User 09]

Thank you for the replies. This is encouraging. It sounds like I will be good to go.

Thanks for suggestions on the poly tank but i'm going to stick with aluminum because the original manufacturer can still make the exact same shape tank, and still sells them. It will make a seamless and easy drop in replacement.

[User 09]

Originally Posted by MikeHoncho

I would not install a aluminum tank if you can do it with a poly tank. My aluminum tank corroded on the bottom and I believe it had been leaking for several years giving me a diesel smell in the engine compartment and quarter birth. With a new poly tank no more smell.

Thats probably the cause of the odor in my quarter berth as well. The tank is 40 years old. I think i will coat the botom of the tanks with epoxy and check them every few years. If i can get 20 years out of them, and i dont see why i shouldnt be able to, i will be pretty satisfied.

[gonesail]

my builder actually put the fuel tank into a pan .. diesel can't get to the bilge if it leaks but you will smell it. easy lift out from settee.

[User 09]

Originally Posted by gonesail

my builder actually put the fuel tank into a pan .. diesel can't get to the bilge if it leaks but you will smell it. easy lift out from settee.

I like that idea. I might try and do this if I can make it work.

I will have all my connections at the top of the new tanks because they will let me specify exactly what type of connections i want and where to place them. So hopefully this will mitigate any chance of big leaks.

[scherzoja]

If you're still going to build with aluminum, you might consider designing it so no part of the tank touches non-aluminum structure (i.e. plywood). When I pulled the 40 you aluminum tank it was pitted on the outside where the lower corners and lower 1/3 of all sides were touching the plywood base. Plywood got wet and water never evaporated. The subsequent pitting caused pinhole leaks.

The original tank was held down with galvanized plumbers tape. Although isolated from tank contact with some kind of rubber strips, there was corrosion between those rubber strips and the tank.

I designed the replacement tank with brackets that bolted onto aluminum angle that was bolted to the glassed-in plywood base. Now, aluminum only touches aluminum, the SS bolts and washers are isolated with tef-gel and plastic washers. Additionally, I sloped the tank so the top sheds any water that might find its way in.

[User 09]

Originally Posted by scherzoja

If you're still going to build with aluminum, you might consider designing it so no part of the tank touches non-aluminum structure (i.e. plywood). When I pulled the 40 you aluminum tank it was pitted on the outside where the lower corners and lower 1/3 of all sides were touching the plywood base. Plywood got wet and water never evaporated. The subsequent pitting caused pinhole leaks.

The original tank was held down with galvanized plumbers tape. Although isolated from tank contact with some kind of rubber strips, there was corrosion between those rubber strips and the tank.

I designed the replacement tank with brackets that bolted onto aluminum angle that was bolted to the glassed-in plywood base. Now, aluminum only touches aluminum, the SS bolts and washers are isolated with tef-gel and plastic washers. Additionally, I sloped the tank so the top sheds any water that might find its way in.

Thats a nice design.

My water tanks (which i have easy access to) were installed almost exactly the same way as your original tanks. They also leak and i suspect from similar situation. I cant imagine they installed my diesel tank any different.

I think i will get some quotes for a custom tank before i make a final decision. I can get a drop in replacemet for about $750 plus shipping. If a customm tank is in the ballpark i might do this. I would love to have brackets like that. Currently the tanks are wedged between wooden blocks fiberglassed to the hull and held down by the heavy structure of the settee frames.

[Tin Tin]

In our catamarans over the last 10 years with alloy tanks installed under rear cabin bunks there was no diesel smell at all until pin hole leaks developed. In the first boat they developed in year 7 and in the second boat in year 13. In the first boat the tanks were kept off the base by ribbed rubber straps. The corrosion was not where the straps were it was a seam leak in a floor weld. Replaced the tank with a 50% thicker alloy custom made.

In the second boat the tanks had aluminium tabs bolted to the floor and frame so the tank itself did not touch any surface. However over the years with 3 different owners in remote islands there must have been water/bug development and the bottom of one developed pinholes. Had new floor re-welded in. In the second tank someone in the distant past had done some electrical work and in the process had dropped two stainless screws that fell down the narrow gap and lodged in the air gap under the bottom of the tank, I found these two and the corrosion holes when removing the tank. Repaired with spot welds. I now regularly use a water/bug killer. If these tanks leak again I will replace with stock size diesel rated poly baffled tanks which may carry 10% less fuel due to shape requirements.

[MikeHoncho]

Originally Posted by User 09

Thats probably the cause of the odor in my quarter berth as well. The tank is 40 years old. I think i will coat the botom of the tanks with epoxy and check them every few years. If i can get 20 years out of them, and i dont see why i shouldnt be able to, i will be pretty satisfied.

They oxidize from the inside out.

[jsanton]

I added diesel tankage using flexible tanks. Then, when the added tankage isn’t needed, I can store stuff there. I’ve even considered resting a flexible water tank atop it. Then I have a diesel/water tankage option. Depending on the itinerary, I could take 50g water or diesel.
Just an idea for you…
J