Steel fuel tank age survey

angus99 said:

Is it possible to completely inspect a KK42's tanks externally?

(Great thread, BTW)

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Only the tops can you easily see by looking from the back. You may get a better view in areas with an endoscope.

Also, our tanks are coated on the outside.

"black iron" is a broker term. It means plain old mild steel, just like any other steel tank, some thinner some thicker. !0 gauge is not unusuall. 3/16 is normall, 1/4 inch is considered heavy for a boat less than 65 feet and non commercial. I know there are lots of steel tanks out there getting the job done, and aluminum for that matter, But on my boat, unless its monel, its coming out for a look see. I dont trust them and will not patch a fuel tank. Water yes, fuel no. If you buy a boat I have owned it will have new tanks or photo evidence of the removal and replacement of the originals with close up detailed pics. Unless, as on a previous post by CP, I can inspect visually every inch of the tank, inside and out. Like I said, I'm a little paranoid. My dad taught me as a boy to do it right the first time or I could do it right the second time, my choice.

Thanks to everyone who participated. TF members rock when it comes to sharing knowledge, experience and opinions.

I need to replace fuel tanks. Any suggestions on suppliers and cost I plan to cut up the tanks in place and replace with 4 smaller 80 gal tanks made of aluminum or poly. Currently has 2 175 gal tanks.

Inca Molded Products | Custom Rotational Plastic Molding

Kracor Incorporation Rotational Molders - Marine Industry

How about tanks leaking from the inside because of water and sludge? Most of our tanks are not designed with a sump. I know of 3 tanks that leaked from the inside. Two were repaired successfully in place. The owner of the third replaced his. Just saying. __________________


This is mostly a problem for a dock queen.

Motion , if the boat is operated , will usually mix the water with the fuel where the filter catches it.

Of course a leaking fill fitting might add enough water to be a problem over the years too.

51 years and they all look fine inside and what I can see on the outside.

Could it be said that no diesel fuel tanks used in boats have a better track record than steel - IF - water inside and out is kept at bay?

FF said:

Motion , if the boat is operated , will usually mix the water with the fuel where the filter catches it.

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I wouldn't be so sure. the whole point of tank baffles is to keep fuel from moving around. I would think unless the boat is in very rough and/or choppy water and the fuel levels are low, there is not much if any real mixing going on.

If you put fuel and water in a glass jar and just roll it around not much mixing goes on. You have to shake it up for it to really start to mix together.

So Far I have checked out:

Duracast - They dont do fuel tanks
Inca - busy signal all day, sent e-mail
Kracor - Stock tanks, biggest is 80 gal would have to stack two to get to present volume
Moller- They have one saddle model, 83 Gal which is the closest, lowering capacity from 175 x 2 to 83 x 2.

A drawback to plastic seems to be, stuck with available designs and no inspection ports. They say they cant be installed in a plastic tank. How to you get the sludge out? Looks like Aluminium custom will be what I look into next.

sunchaser said:

Could it be said that no diesel fuel tanks used in boats have a better track record than steel - IF - water inside and out is kept at bay?

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IMO yes. I'd only add they have the same stellar track record in gasoline applications with the same proviso. One more example of design and maintenance standards trumping material choice.

Could it be said that no diesel fuel tanks used in boats have a better track record than steel - IF - water inside and out is kept at bay?

Unquestionably NOT.

Monel is unsurpassed , weather full of water or diesel or both .If not Forever , at least till Dooms Day.

It just takes rudimentary skills and MONEY , as monel is not as cheap as steel.

Easy tho in monel to make a genuine useful fuel tank , rather than just a box of fuel.

Monel - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Monel‎Wikipedia


Monel is a trademark of Special Metals Corporation for a series of nickel alloys, primarily composed of nickel (up to 67%) and copper, with some iron and other ...‎

The Eagle tanks are 36 years old. Every year I add additive that absorb water back into the fuel, keep the exterior of the tank bone dry as the engine room kept between 55 to 70+ degrees. I try to use/turn the fuel every year, and polish the fuel through out the year.

When we bought the Eagle the middle tank did leak, so cut a 18” X 18” hole, crawled into the tank and found were the weld seam had broken. The tanks was in good shape no rust so had a welder weld the seam and closed up the tank. So if a tank does leak, will again cut a hole in it and see if it can be repaired/welded. If not then several smaller tanks will be installed inside the old tank.

Greatlaker221 said:

A drawback to plastic seems to be, stuck with available designs and no inspection ports. They say they cant be installed in a plastic tank. How to you get the sludge out? Looks like Aluminium custom will be what I look into next.

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Replacing 2 tanks with 4 is pretty common. Can you get 2 full sized tanks back into your engine area without cutting the sides or bottom out of the boat or moving your engine/s?

FF said:

Monel is unsurpassed , weather full of water or diesel or both .If not Forever , at least till Dooms Day.

It just takes rudimentary skills and MONEY , as monel is not as cheap as steel.

Easy tho in monel to make a genuine useful fuel tank , rather than just a box of fuel.

‎

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What are the weld characteristics of Monel? When it's welded is it as susceptible to having porous seams as stainless steel? I've seen a number of stainless steel tanks that started leaking fuel at their welded seems after being installed and used for a while. I've also seen SS water tanks develop leaks where the baffles were welded to the tank tops. SS is a bit tricky to weld when it comes to getting a fuel tight seam. Where as "black iron" is very easy to work with.

Bill11 - Not without removing the engine. I have been researching non integral FRP tanks. With out moving the engine, They can be built in place to almost the same size and with the right resin should hold up to even Bio diesel. Cost will be lower as well. I can add bottom drain an sump. I have built small boats using cold molding before so I feel comfortable with that material. Sound reasonable?

Greatlaker221 said:

Sound reasonable?

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Yes it does. Just make sure they are baffled properly and that you can brace them properly as well to prevent them from oil canning.

Monel is normally constructed with out welding.

100 years ago it would be braised or silver soldered .

Today I assume its the same.

I have used tanks I am guessing were from the 1920 era (from the boat they were removed from) with zero problems.

Many from the post war 1950 wooden boat boom era , again no problem.

Monel can be welded with special monel rods.

FF said:

Monel is normally constructed with out welding.

100 years ago it would be braised or silver soldered .

Today I assume its the same.

I have used tanks I am guessing were from the 1920 era (from the boat they were removed from) with zero problems.

Many from the post war 1950 wooden boat boom era , again no problem.

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I was using "welded" in a generic way. While it would seem Monel can develop pin hole leaks at it's seams like SS, if braised carefully it's not likely to.

Now if there was only a way to get the price down.

Monel is not a magic metal, it is one of many used for corrosive liquids that have been tinkered with and improved upon over the last century. Monel was "devised" by INCO one hundred years ago to bolster their nickel business. Monel is about 65% Ni with a high copper content - think cupro nickel too. It has one very bad trait for the marine environment, it is quite prone to electrolysis and must be isolated from any steel, so don't use it with a steel hull unless you know what you are doing.

In the industrial world unless a metal can be cost effectively welded and fabricated it will see little if any application. This is Monel's Achilles heel. Various alloys of Monel have been improved upon over the years so that it's weldability is improved and fabrication then more cost effective.

Each liquid and slurry has a specific tank material that is suitable for it. For diesel fuel, mild steel is one of many that can be economically used. If properly installed and taken care of it may well outlast the vessel.

Here is a factoid, mild steel works just fine with 95% Baume sulfuric acid but dilute the H2SO4 with water to 65% and the steel goes kapoot - not unlike diesel and water. All the H2SO4 tankers you see driving down the road are mild steel.

>In the industrial world unless a metal can be cost effectively welded and fabricated it will see little if any application. This is Monel's Achilles heel. Various alloys of Monel have been improved upon over the years so that it's weldability is improved and fabrication then more cost effective.<

Industry is seldom willing to pay extra for extra for Piece of Mind , years away.

Yachtie$ are different.

For a person purchasing a 1/2 or Million dollar toy , increasing the purchase price .01% for a properly constructed , easily maintained fuel system is a no brainer.

The labor cost would be less than steel (easier to cut and shape) only the material is more costly.

It has amazed me for decades that the first purchaser does not DEMAND a proper fuel tank and system , rather than accepting a box of fuel and a batch of filters.

>For diesel fuel, mild steel is one of many that can be economically used. If properly installed and taken care of it may well outlast the vessel.<

Its the > properly cared for< , no water contact, that can NOT be counted on over the decades, and variety of owners.

Fuel tank leak

I started this thread a year ago due to all the stories I have heard about tank leaks. Well it finally happened to me. We took on fuel just prior to going into the lift slings for a prop repair. The next day I found fuel in the bilge. It was coming from the port tank. The boat was sitting in the slings on blocks with the bow up a few degrees and a port list. I got the yard to level the boat and the leak stopped. The tank has a 8"x12" rust spot around the fill and vent. The rust flaked off in sheets when I cleaned and degreased it. The area around it is clean, solid and painted. I spent a day degreasing and wire brushing the area. The next day I put a half quart of Marine Tex on for the repair. The holes have probably been there for years and were never challenged due to tank level.
I am having my remote inspection camera shipped to the yard so I can inspect my repair and take a good hard look at both tanks. My repair should do the trick but I will start planning for a tank replacement.
Most of the work was done by feel. I only found the holes by sticking a camera inside the space and taking pictures. You can only see a small area with your eyes.
Timing was good because we are sitting in Brewerton NY for a week waiting on the Erie Canal to re-open.
In the picture is the vent. the shot was taken about 3" from the tank. I think the vent is about 1/2"

We repaired leaking tanks on our 30 year old boat in 2013. Just could not afford to replace the tanks. For the details read:

@ TheOffice: A little bit of Diesel makes a big mess

The fact the boat set up for 7 years most likely caused the internal rusting. No problems so far.

Although I’m a firm believer in the marine usability of Monel material in not just tanks… I can't help but wonder why a thicker aluminum material can't simply be used… with a high tech inner resin coating affixed to all surfaces (or not). Tank weight should remain reasonable. As long as mounted correctly for exterior surfaces' air-flow/condensation-evaporation purposes and kept dry in general the aluminum tank should virtually last forever. ??? Correct ???

We have two 100 gal aluminum tanks that seem to still be in good condition. I believe they are original 1977’s. Being that we are 2nd owner and the Original Owner seems to have been fastidious in boat/engine/tank care it shows via camera review on all accessible areas that these tanks have not been abused by standing water against their bottom, top or sides. 90 + yr old OO passed away before we purchased. Our Tolly was thereafter well tended by the OO’s decade long marine assistant. That said... the original tank installation does leave much to be desired regarding tank bottom elevated slightly off the plywood base for air-flow and vapor evaporation. I place water and bio remover additive (Soltron) into each refill. For general area cruises and near marina anchor outs I keep tanks approx 50% full then use down to the 10% level… refill to 50% so new gas consistently replaces the old. When taking longer cruise we fill em both up and replace with new as needed.

If you keep water from collecting in the bottom of aluminum tanks they do pretty well...


In a perfect world...I love the poly tanks but once they get too big, I would go fiberglass.


That's what gas stations use for their storage tanks underground at least around here...(out of sight in a rough environment...kinda like many boat tanks)

Replaced tanks after 28 years in 2013. One was leaking and the other had a hidden dangerous rust area. Tank split open as we removed plywood covering panel.

"The rust was from outside in, tank sides that were against the hull and on bottom."

That it in a nutshell.

If the boat assembler knew and followed proper techniques ,,,and the owner will be kind enough to stop deck leaks ,,few will ever have a problem.

The rare tank with constant standing water inside will usually leak at a seam, an easy patch from outside.

Iron Fuel Tanks, If a frog had wings! Leaking Tanks Story

You have identified the cause and effect of leaking BUT some one built a boat around the tank, installed engines with in inches of them! You can not always patch the outside and getting to the inside is a chore. I know many will have this problem if not today then soon as tanks get near the 30+ year mark. Ours started leaking at the stringers hold the tanks level and the corrosion was on the inside that gave the iron a pocked moonscape look from the acid breakdown of the fuel. Some sainted boaters will dodge this bullet because they burn copious amounts of fuel, but dock queens will suffer.
Our fix or patch if you will cost less than one boat buck at the time we did it.

@ TheOffice: September 2013

FF said:

"The rust was from outside in, tank sides that were against the hull and on bottom."

That it in a nutshell.

If the boat assembler knew and followed proper techniques ,,,and the owner will be kind enough to stop deck leaks ,,few will ever have a problem.

The rare tank with constant standing water inside will usually leak at a seam, an easy patch from outside.

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"Some sainted boaters will dodge this bullet because they burn copious amounts of fuel, but dock queens will suffer."

Any boat with a proper fuel tank , not a box of fuel can last almost indefiniatly.

The difference between a uel tank and a fuel box id weather it has a servicible sump.