Another steel fuel tank issue

While doing some maintenance under my cockpit this weekend, I crawled back to my single diesel fuel tank. Unfortunately, I saw 4 small spots of what appears to be rust on the back of the tank (facing astern) in the middle about 1" in diameter. I cannot tell if it is the tank itself, or a cover around the tank, as it appears almost like fiberglass. However, my suspicion is the tank at those areas is rotting away at 30 years of age.

Below the cockpit sole is a very large area, about 3.5 feet tall and 10 foot by 10 foot. The fuel tank is forward at the salon bulkhead. It measures about 8 feet across, almost 3 feet tall and 1.5 feet deep. Rearwards of this (astern) there was once a huge steel water tank, about 4.5 foot wide and 5 feet deep, towards the front of the boat. Inside this are 2 newer 45 gallon freshwater tanks.

What I am considering is draining the old tank, leaving it in place, moving the freshwater tanks forward to butt against the old fuel tank, and having a custom steel or plastic fuel tank made to fit the inside diameter of the old water tank. I will have to open the cockpit center floor to create an opening, but this would also facilitate ease of access to all tanks in the future. Then, just extend the original fuel lines to the new fuel tank.

As the old water tank was in this same space. I don't see an issue with weight distribution.

Does any one see anything I am missing?

I should note that the boat is 38 foot, 12 foot beam with a 3.5" draft, so much like a trawler and built as a sportfisher for the original buyer to his specs by GoldenStar Yachts. The only one my surveyor has ever seen or could find anywhere. Kind of glad the cockpit is so large!

First, I don't know if I'd do anything until I could use day a fiber optic camera to look at the potential rust spots. And even then unless they are real bad I'd still perhaps wait till they leak before going to all that trouble. Unless I could prove they were nothing more than surface rust.

If you have to replace the old tank could you cut it open, remove the baffles and slide in a new slightly smaller tank?

Post some pics of what you are looking at. It does not sound like you have a real problem. A little surface rust on the outside of a tank is nothing to worry about.

I may be jumping the gun a bit, but it seems to be a fact that these Taiwanese steel tanks do fail and at 30 years of age, about time. However, as I don't travel far, if I ran at 1/3 tank, probably ok for a while.

I could possibly try sand some of the lightly rusted spots and see what I find underneath. Where the tank is there is no water hitting the tank sides and the top is dry and dusty.

Had another thought and I will climb back down there soon. The cockpit has a large rectangular bait tank and storage box that appears to sit over a raised lip. It may also be possible to remove this box to gain access to pull the tank. I have to pull the stairs to the flybridge to do this though and then find new SS rivets to reinstall later.

There would be no other way to place a new tank into the old one, unless the bait tank removal shows an opening, or, chain a few tanks together that will fit through the current opening.

READY2GO, sorry, missed your post. Do these steel tanks tend to start to fail inside out, or outside in? Or, both? Next time I can get down there I will take and post a picture.

Goldenstar38 said:

READY2GO, sorry, missed your post. Do these steel tanks tend to start to fail inside out, or outside in? Or, both? Next time I can get down there I will take and post a picture.

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They usually fail from the outside in. I have read several stories where people cut up the tanks only to find out that they were not as bad as they looked from the outside but once the sawzal hits it, it is too late to turn back. My tanks have quite abit of exterior rust (38 years old) but still show no signs of leaking.

Good previous comments dont bring on trouble before its due, if you get a leak deal with it, we just repaired a fiberglass tank today that had an issue and it was a 2008 model.

There are many more options today than years gone by if an issue develops such as painting the inside of the tank with a protective coating.

At least on my boat there is always more to do than borrow trouble

If you can see it a patch can be welded over it. But, mostly what I've seen is steel tanks rusting thru from the inside. I to think you are inventing problems. If it looks rusty its not leaking. If it looked "oily" you may have the makings of a rust pin hole. At the very worst, and replacement is neccessary, bite the bullet and do it right. Replace the tank with the same size. 5086 aluminum would be my choice but steel (properly coated) would be as good.

Attached is a picture of the spots I referred to, 6 total. They are all in the top 1/2 of the tank and the size of, or smaller than, a quarter. I don't know if you can enlarge this picture, but this is not the tank itself, but rather some type of skin over it. It looks up close like a chopped mat material.

My concern now is that if this is rust between this skin and the tank, what must it look like between the 2?

There are no leaks currently, so I think I will just leave it alone and perhaps not fill the tank above 1/2. I have actually been trying to run as much fuel out as I can and replace the filters when low, before refilling.

Grind the coating off and look.
Then seal it up again w something compatable w the original coating.

Chop strand mat on a steel tank is a very bad omen.

Klas44,
Sounds nuts but I have a beautiful picture of a big blue boat that is steel but sheathed in FG. Don't know if it was using polyester or something else but it sure looks good and the owner says no problems.

I for one wouldn't think that the plastic would adhere. Related to that is that it would be unlikely that expansion would be the same for both materials. Think cold hull at night and then bright sun on the hull in the am would bring heavy sheer loads between the two materials.

But it worked for this guy.

Not sure why the mat sheet in front of the tank, other than cosmetic? There is nothing in that area of the hull subject to water splash or impact and the tank is raised. I may cut a bit of it off around one area and see what it looks like. Really afraid of what I will find though. Keep you posted.

Goldenstar38 said:

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Below the cockpit sole is a very large area, about 3.5 feet tall and 10 foot by 10 foot. The fuel tank is forward at the salon bulkhead. It measures about 8 feet across, almost 3 feet tall and 1.5 feet deep. Rearwards of this (astern) there was once a huge steel water tank, about 4.5 foot wide and 5 feet deep, towards the front of the boat. Inside this are 2 newer 45 gallon freshwater tanks.

Does any one see anything I am missing?

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I'm still just trying to get may head around how exactly these tanks are placed, and where..? You start off saying the fuel tanks is up against the for'd bulkhead in the lazaret, then aft of that an old water tank, then throw in a spanner by saying this is towards the front of the boat. How could it be if the fuel tank is for'd of that, then you totally confuse the issue by saying there are two smaller newer water tanks inside that.

Is the old water tank still there, if so are the newer smaller tanks fitted inside that, or in between that and the old fuel tank, or somewhere else, and where is that somewhere else that does not defy the laws of physics. Are they inside the engine room for'd of the lazaret bulkhead, because as described you have three lots of tanks all occupying the same space.

However, whatever the arrangement, I would suggest going with the others who have recommended a cheap quick repair of the rusted areas first, maybe as simple as some epoxy type quick-setting goo. Those look pretty unimpressive rust spots to me.

Peter B, Sorry, I know what I am seeing and perhaps it did not translate properly in my text and in rereading, I can see why your confusion. The fuel tank (1-singular) is not in the engine room, but on the other side of the bulkhead under the rear cockpit up against the bulkhead. The 2 plastic water tanks were placed inside the base of the old steel water tank which was cut out long ago. The water tank is astern of the fuel tank. I hope this helps.

No, they do not look bad, but the stories about steel tanks in Taiwanese boats got me initially quite nervous and fearful of the time and expense to replace. I have since calmed down now and not so stressed. I will continue to enjoy my boat and deal with whatever this issue is as necessary. When time permits, I will remove a small piece of the mat shell and let you know how it looks.

Goldenstar38 said:

Peter B, Sorry, I know what I am seeing and perhaps it did not translate properly in my text and in rereading, I can see why your confusion. The fuel tank (1-singular) is not in the engine room, but on the other side of the bulkhead under the rear cockpit up against the bulkhead. The 2 plastic water tanks were placed inside the base of the old steel water tank which was cut out long ago. The water tank is astern of the fuel tank. I hope this helps.

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Thanks for clarifying that, I thought that's what you were saying, until you got to..."Rearwards of this (astern) there was once a huge steel water tank, about 4.5 foot wide and 5 feet deep, towards the front of the boat", that threw me a bit. All good now, and best of luck. I does sound like your tanks are not too bad at all for their age.

Goldenstar38 said:

No, they do not look bad, but the stories about steel tanks in Taiwanese boats

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Don't respond to stories. You may have a problem one day, but you don't appear to have a major, unmanageable issue today.

I'm going back down there this weekend and spend a little more time checking into cutting off a small piece of the mat tank cover and see what I find. Guess I may have over reacted prematurely.

Good news today though, was I fixed my hydraulic steering. Since I purchased the boat 2 years ago, there was an issue with the flybridge helm wheel (no lower station), it would lightly "click" and "bind" but not to where it would not turn, just annoying. Turns out the box in the rear of the cockpit (storage?) that drops into a cutout in the cockpit was ever so slightly hitting a hydraulic hose. I never suspected that it was enough to cause this, but turns out it was. I went to the flybridge taking a break and turned the wheel for no particular reason and to my surprise, it was smooth as glass! Reset the storage box and bind/click again. Repositioned the hose and Fixed! Always feels good, no matter how simple!

Goldenstar38 said:

I'm going back down there this weekend and spend a little more time checking into cutting off a small piece of the mat tank cover and see what I find. Guess I may have over reacted prematurely.

!

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You have photos. Take more in six months. Compare. If you feel meanwhile you must do something, don't start cutting things off or doing anything destructive, just put a layer of something over and then follow it by sight.

This morning (Merry Christmas!) I went down and cut out a piece of the glass mat cover around two of the small spots to have a look underneath them. To my surprise, the mat was apparently glued at some point to the tank. The tank, when tapped with my finder and a small screwdriver, is actually in great shape! No dullness or thud and no smell of diesel at all. My cut was done with a box cutter, so not straight, but the cover came right off. A picture of the pieces is attached. It looks like rust, but appears to be only the glue used to attach to the tank.

Good, you can now put away the Tums or Rolaids, whatever, and relax.
Repairing your cutouts will be minor (and good therapy).

Ted

I'd go ahead and replace the tanks - just to be sure.

Goldenstar38 said:

...The fuel tank (1-singular) is not in the engine room, but on the other side of the bulkhead under the rear cockpit up against the bulkhead.... .

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The location is the good news, often tanks are either side of the engine(s), which may have to come out, or a hole gets cut in the hull , yours is easily accessed if needs be. I don`t think it looks too bad, I`d be tempted to leave well alone, who knows what might happen when you start grinding back to take a look....

alormaria said:

I'd go ahead and replace the tanks - just to be sure.

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alormaria said:

I'd go ahead and replace the tanks - just to be sure.

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And you'd be prepared to pay for that really cheap option for him would you..?

Mmm, I think (hope) Alormaria was being ironic.

Glad the 'issue' is under control. When you get large flakes of rust is early enough to think of tank replacement. The pic shows what fell off the tank onto the hull. And there were only some pinhole leaks.

"The location is the good news, often tanks are either side of the engine(s), which may have to come out, or a hole gets cut in the hull , yours is easily accessed if needs be."

This is the aluminum or steel boat option.

A GRP boat a proper repair would cost as much as a new hull, IF it could be done.

FF said:

"The location is the good news, often tanks are either side of the engine(s), which may have to come out, or a hole gets cut in the hull , yours is easily accessed if needs be."

This is the aluminum or steel boat option.

A GRP boat a proper repair would cost as much as a new hull, IF it could be done.

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No it's a GRP option as well. And while not cheap, it doesn't cost as much as a new hull.