Aluminum Alloys

[skipmac]

Well, cut a 20 cm piece out of the bottom of one tank and found more or less what I was expecting; many isolated spots on the inside of the tank where the metal was eaten away and one pin hole where it was eaten all the way through.

What I didn't expect was that most of the metal looked perfect, the corroded spots were small (largest 3-4 mm across) isolated and randomly distributed. I was expecting to see the corrosion over most of the bottom and not so spotty.

In a piece 10 X 20 cm there were 4 large spots and about a dozen down to about 0.5 mm. With a strong magnifier I could see a lot more down to the limits of the lens, but still in isolated areas. Lots of areas were completely clear of any visible corrosion. Next step, see how far it extends up the bottom of the tank.

[s/v Jedi]

Starts to sound like contamination with copper or something....

[skipmac]

Originally Posted by s/v Jedi

Starts to sound like contamination with copper or something....

Copper? Where, in the alloy of the Al, the fuel?

My theory is the corrosion is caused by a low pH sludge composed of the breakdown products from the fuel, asphaltenes, polymerized oil, miscellaneous solids. Cause of the breakdown could have been just old fuel left in the tanks possibly exacerbated by water and bacterial growth.

[cal40john]

Originally Posted by skipmac

Not sure what limits on vessels subject to the regs. Thanks to Delmarrey for posting the original information. Here's a link to the original regs.


46 CFR 58 : MAIN AND AUXILIARY MACHINERY AND RELATED SYSTEMS [ 46 CFR 58 ] : (SHIPPING [ 46 CFR ])

Fuel tanks are section 58.50. I glanced through briefly but didn't see anything about where this applies but I think it was for any vessel. Maybe you have the patience to read through the pages to see.

33 CFR 183 is for non commercial boats. Note they use the word boat instead of vessel, and they define what they mean by boat. in 183.3

33 CFR 183 : BOATS AND ASSOCIATED EQUIPMENT [ 33 CFR 183 ] : (NAVIGATION AND NAVIGABLE WATERS [ 33 CFR ])

33 CFR 183.1

This part prescribes standards and regulations for boats and associated equipment to which 46 U.S.C. Chapter 43 applies and to which certification requirements in Part 181 of this subchapter apply

33 CFR 183.3

Boat means any vessel—

(1) Manufactured or used primarily for noncommercial use;

(2) Leased, rented, or chartered to another for the latter's noncommercial use; or

(3) Operated as an uninspected passenger vessel subject to the requirements of 46 CFR chapter I, subchapter C.


subpart J is about fuel systems. 183.501 (a) says subpart J applies to boats with gasoline engines

As far as I've found there are no federal regulations about fuel system installation on diesel boats.

Many would insist that you need to follow ABYC standards.

(Probably not current as it seems ABYC makes you pay for the standards)
https://law.resource.org/pub/us/cfr/....H-33.1989.pdf

Diesel Fuel Tank Design

[Jim Cate]

Originally Posted by bobconnie

Ive patched a couple of tanks with edge leaks with alminum angle iron welded along the edges, worked well and it was all I could find where we were at the time! just a thought

Bob, this may be heresy, but I have patched corner leaks in alloy fuel tanks by epoxying (Marinetex) some light gage alloy sheet bent into a 90 degree angle over the affected area. Still tight 15+ years later!

The good thing about this method is one can do it in situ, no worries about welding on a fuel container and it is very inexpensive.

What's not to like?

Cheers,

Jim

[skipmac]

Originally Posted by Jim Cate

Bob, this may be heresy, but I have patched corner leaks in alloy fuel tanks by epoxying (Marinetex) some light gage alloy sheet bent into a 90 degree angle over the affected area. Still tight 15+ years later!

The good thing about this method is one can do it in situ, no worries about welding on a fuel container and it is very inexpensive.

What's not to like?

Cheers,

Jim

Did the same on an old car but didn't even cover the damage with a piece of sheet metal. Bumped a rock sticking up in a parking lot and poked a hole in the gas tank. Did a "temporary" repair with Marine Tex by just brushing the dirt and rust off the outside and mashing a blob of epoxy over the hole. Years later when I sold the car the patch was still holding.

Now would not patch a gas tank on a boat like that due to the risks but would certainly give it a go with a diesel tank.

[David M]

I use both grades on my aluminum boat. They are welded to each other in many places. Additionally, the USCG approves this for inspected vessels which says a lot.

[delmarrey]

Originally Posted by cal40john

33 CFR 183 is for non commercial boats. Note they use the word boat instead of vessel, and they define what they mean by boat. in 183.3

33 CFR 183 : BOATS AND ASSOCIATED EQUIPMENT [ 33 CFR 183 ] : (NAVIGATION AND NAVIGABLE WATERS [ 33 CFR ])

33 CFR 183.1

This part prescribes standards and regulations for boats and associated equipment to which 46 U.S.C. Chapter 43 applies and to which certification requirements in Part 181 of this subchapter apply

33 CFR 183.3

Boat means any vessel—

(1) Manufactured or used primarily for noncommercial use;

(2) Leased, rented, or chartered to another for the latter's noncommercial use; or

(3) Operated as an uninspected passenger vessel subject to the requirements of 46 CFR chapter I, subchapter C.


subpart J is about fuel systems. 183.501 (a) says subpart J applies to boats with gasoline engines

As far as I've found there are no federal regulations about fuel system installation on diesel boats.

Many would insist that you need to follow ABYC standards.

(Probably not current as it seems ABYC makes you pay for the standards)
https://law.resource.org/pub/us/cfr/....H-33.1989.pdf

Diesel Fuel Tank Design

This is why I designated the 46 CFR, since gasoline was the basis for 33. I would think it would be better to go with the commercial standard then the unknown.

I think I'll write to the USCG and request a clarification on the matter. This has come up before in previous threads.