Installing an Inspection Plate in an Aluminum Fuel Tank

[MPB]

Hello everyone,

Contrary to all of you who are out on their boats having the time of their lives, sailing or tackling new projects, I am 5,000 miles away from my boat, which sits melancholy at its dock in San Pedro, California.

But even far away, I do get to undertake projects - just don't get my hands cut up and bruised.

Enough of the nostalgia -
After a sailing trip this summer, our engine went into a coma - clogged fuel filters ! The aluminum tank was a haven for a huge colony of microbes. We replaced the primary and secondary filters, and all was fine again.

But the problem is not solved.
I need to open up an inspection port to get the sludge out. Then, I want to install an independent on-board fuel polishing system - the kind you make yourself with a Walbro pump and Racor 500ma filter.

My question concerns the access plate - It will serve as an access port as well as base for the feed and return lines for the re-circulating system.
Originally, I was going to use a1/4" aluminum 6061 plate (6" X 6"). Tap 2 holes into the center for the fuel fittings, tap and screw into place. But then, I began reading about the incompatibilities of bronze, copper, stainless, and aluminum.

So, instead - what about using Rigid a High-Density Polyethylene sheet (maybe 3/8" thick) ? It would solve the galvanic incompatibilities. I can still tap threads into it for the fittings, goop them up to seal properly, and I can even attach a back nut to ensure a better fit.

Hope this is not a dumb question ?
Thanks to all.

[chiropaul]

check out this website for proper tank inspection plates. Fuel Tank Access Plate
Seabuilt - Access Plate Systems

[S/V Illusion]

Either use compatible hardware or dielectric grease which will inhibit corrosion somewhat. More important, do you know if there are internal baffles in the tank which would necessitate multiple cleanouts?

[MPB]

I don't know if there are baffles yet. Good point.
Re. the Rigid High-Density Polyethylene sheet vs aluminum - any comments before I start the project ?
Thanks

[S/V Illusion]

The corrosion issue might be of concern with the fasteners more so than the plate material. Regardless, since the cover plate isn't in constant direct contact with the fuel, either should work although aluminum doesn't break or crack easily.

[David M]

I run an aluminum boat with tanks integral to the hull with two aluminum inspection ports that are large enough to allow me to crawl inside the tanks. What I am saying is there are lots of bolts with plenty of places to potentially leak.

About seven years ago it became necessary to open the tanks to clean them. Upon inspecting the tank, I found no corrosion whatsoever, even where the stainless steel bolts make direct contact with the aluminum. This is on an aluminum boat that was built in 1975.


The way to do your aluminum tank is to go ahead and use stainless steel fasteners. Don't worry about electrolysis...it wont happen in that environment. If you are still concerned about the external bolts and nuts then coat them in Permatex. The internal side of the fasteners are not going to cause electrolysis sitting in a diesel environment. If they were sitting in salt water, you can bet there would be electrolysis. Remember, diesel does not conduct electrons as salt water does.

I used N-butyl rubber as the gasket material which I coated on both sides with Aviation Grade Permatex sealant.

A plastic gasket may be to rigid to create a good seal if the two surfaces which need to mate are not perfectly flat. I would sandwich in some Permatex anyway just to be safe with that seal.

http://www.permatex.com/products/aut..._Sealant_a.htm

[MPB]

David and S/V

Thank you.

I never considered the cracking aspect of polyethylene. OK will go with the aluminum, propbably 3/8" to get a decent thread for the fittings.

Will be using the Nitrile N-Buna as a gasket - I guessed 1/8" would be good.

Will use the permatex idea - good.

Now that we are on this - what material would you use for the fuel fittings - bronze ?

Re. the pick-up tube, I read that some people are using Nitrile type tubes, instead of copper. I guess it might have to do with the easy to slip these on to the fitting - any thoughts ?

Thanks for the great indications !

[David M]

No, not bronze. Bronze is more reactive with aluminum than is stainless. Not that electrolysis will happen, but why take a greater chance of it happening? Stainless is also less likely to shear off than bronze given it's a softer metal.