Fuel tank idea - comments?

[Chinookie]

Hi, thought I would run an idea by the forum for comment. I need new fuel tanks for my 228. The main tank is shot and the aux is running on borrowed time. The original drawings show .125 is to be used for the 92 gallon main tank, and .09 is to be used for the aux. My understanding is that when pinholes appear, they will be bottom and/or top of the tank. Is that a true statement? if so, does it make sense to specify using a thicker material like 3/16ths on the top and bottom skins only? There would be no point of using 3/16 for the tank sides and baffling because they wont develop pinholes and that will save tank build costs.

 

[seasick]

The reason for the pin holes is corrosion from galvanic activity that is generated when the aluminum comes in contact with another conductive material in the presence of moisture (mainly sea water) as an electrolyte.
Often the tanks sit on structural supports, bulkheads or stringers in addition to whatever is used to hold the tank in place like topside straps, or tank brackets. Moisture often gets trapped between the supports and the tank surface. Depending on what materials were used an mounting surfaces and/or insulators, corrosion can occur.
In summary, the methods and materials used to mount the tank and protect the tank coffin from trapping moisture are more important that the tank thickness, Yes, thicker material will take longer for the corrosion to go through the tank wall but it won't stop it.

 

[DennisG01]

To add onto what Seasick said... another common cause for corrosion in this area is when water is allowed to sit on the aluminum. Or, more specifically, when aluminum does not have contact with the air. When Al has good oxygen, it will self protect itself.

So, the solution, as noted above, is to build a mouse trap than Grady did. You can epoxy coat the tank... you can ensure the installation doesn't allow any gaps/cracks where water will sit or where the AL won't have air movement around it.

 

[Hookup1]

Take a look at my thread below. My advise is to have quality tanks made at a certified tank builder. SP Tanks is too far away from you. I'm sure there are West Coast builders.

Use 0.125 aluminum. Have the tank epoxy primed. Install nitril strips with 3M4000 to insulate the tank. Corrosion will occur where water is trapped against the tank. Install new deck ports with 3m4000, clear grease on o-rings and consider caulking them with silicone. This will keep water off the top of the tank. Make sure you deck is solid (not full of water) and screws are properly caulked.

Thread '268 Islander Fuel Tank Replacement'

Jul 10, 2023

Decided that this is the year to replace my 25 yo fuel tanks. No leaks. I plan to keep the boat. I'll document the process here.

Pulled the hatch. This hatch was rebuilt a few years ago with Coosa board. Looks good and feels solid. Hatch was set with 3M 4000 - kept everything sealed. Some difficulty cutting with blade to get it up. Not sure what it will go down with. Deck ports were caulked in from the underside as well. Kept the tanks dry.



I also put plastic over the fill, sending unit and pickup. This deflects any water away from the busy area of the tank.

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• Hookup1
• Replies: 70
• Forum: Tips, Modifications and Electronics

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[Sardinia306Canyon]

All good pints above, nothing to add.
I wrote it already in other treads, if the top of the fuel tank would be slightly curved with a flat spot for fuel sender plate then the water dropping from the pie plate above to sender unit would still drip there, but not poodle there as it would run away to the sides and away from fueltank top.

I am still thinking about how to make a "gutter" below pie plate to deviate the water.

However coal tar the tank seems the best way to preserve a aluminum fuel tank for longest time, even if no coating at all would be best if fuel tank would be 100% dry.

Chris