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Old 07-28-2019, 12:45 PM   #1
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Black iron fuel tanks

Hello, I am looking at mid 1980 Taiwan built trawlers. Some have black iron diesel fuel tanks. I have no background knowledge about these type of fuel tanks. I would appreciate any comments concerning their reliability and what can be done if they develop problems (i.e. aside from finding a leak is there a way to inspect them, can they be repaired or must they be replaced, for a typical mid 1980 Taiwan trawler is repair/replace as big an undertaking as it would appear?). I realize that that there are many factors to consider for any particular boat, and that answers to board questions will be generalizations. But any information I learn will be helpful. Thanks in advance.
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Old 07-28-2019, 01:21 PM   #2
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Hello, I am looking at mid 1980 Taiwan built trawlers. Some have black iron diesel fuel tanks. I have no background knowledge about these type of fuel tanks. I would appreciate any comments concerning their reliability and what can be done if they develop problems (i.e. aside from finding a leak is there a way to inspect them, can they be repaired or must they be replaced, for a typical mid 1980 Taiwan trawler is repair/replace as big an undertaking as it would appear?). I realize that that there are many factors to consider for any particular boat, and that answers to board questions will be generalizations. But any information I learn will be helpful. Thanks in advance.
There are two types of Taiwan trawlers, those that have had their fuel tanks replaced and those that need them replaced.

These tanks are NOT "black iron, they are mild steel. "Black iron" is a catchy name that some have glommed on to but is completely inaccurate.

Check out this article on Taiwan trawlers. http://onboardislandtime.com/venerab...e_trawlers.pdf
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Old 07-28-2019, 01:57 PM   #3
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from what I've seen the tanks fail in one of the following ways; deck leaks cause the top to rust out which is viable from the engine room or water settles to the bottom of the tank which causes it to rust out. At some point they will fail, but when is the unknown. I wouldn't necessarily avoid all boats with iron tanks if otherwise they checked all the other boxes but I would be concerned of the potential failure problem.
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Old 07-28-2019, 02:54 PM   #4
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I've looked at a lot of older boats with original steel tanks. Before making an offer visualize how involved it will be to get the old tanks out and new ones installed. With one exception the boats all had tanks that were in the engine room outboard of the engine(s). I imagine single engine boats would be far less trouble then twins.

I did see one clever solution on a single engine Hershine with a roomy engine room. The tanks had been replace by two on each side. Full length and full width but half height of the original tanks. Tanks on each side joined by some tight plumbing. The pair of tanks held in place by unistrut. Funky, but it would have worked except for one thing. The deck leaks were never attended to and the tops of all the tanks, 4 now instead of 2, were badly rusted to the point they were leaking.
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Old 07-28-2019, 03:03 PM   #5
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When we were looking we saw a lot of difference in early/mid 80's Taiwan boats vs the late 80's ones. Ours is a 1988 CHB Present - never had screwed down teak decks and all fuel/water/holding tank fills are well founded and sealed to the fiberglass - no leaks (that could be detected. We have two 120 gal fuel tanks on each side outside of the two Lehman 135's. Engines would have to be pulled to remove the tanks. But that is not an impossible feat - we pulled a huge 12.5k Westerbeke Gen out and replaced it with a 9k Kohler - took the guys about 3 hours. They said they have pulled many engines in order to change out tanks on older boats.
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Old 07-28-2019, 05:49 PM   #6
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I have one of mine out now I'll post a few pics if I can find them. mine was rusted through a lower corner from a slow water heater leak. they were rusted badly on top also so I thought it had rusted through from inside out , but that wasn't the case . I am planning on using two plastic tanks in place of it .I will go from 145 gallons down to 100 on that side.
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Old 07-28-2019, 05:53 PM   #7
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Fun times
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Old 07-28-2019, 06:43 PM   #8
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You can use a borescope to check interior of tank and back of tank against hull. Top of tank is visible with mirror and led light. I lightly sanded corrosion with scotchbrite pads, emery cloth, and wire brush. I was careful to not get obsessed with shiny metal. I simply knocked down the rust. Masked everything, sprayed rustoleum primer, then a finish coat. Seems to be holding up, but I do NOT leave my bilge pump on auto.
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Old 07-28-2019, 06:46 PM   #9
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Old 07-28-2019, 07:25 PM   #10
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Gees mate. There's nuthin wrong wif dat tank. Wire brush it, hit wif sum paint, and bob's yer ant.




In all seriousness, I have seen worse tanks have their side or top replaced, coated, and reinstalled. I don't know how they weld through the oily film, but they do it.
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Old 07-28-2019, 08:52 PM   #11
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If long-term memory serves, Ospho was the rust treatment/primer product used with success by fellow cruisers for fuel tanks. Amazon (Prime) sells it for just over half the price of West Marine. Read the Amazon reviews & pay attention to mfr. instructions. I have a shipping container being delivered this week (2nd one), & am considering using it prior to painting. Has anyone tried it?
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Old 07-28-2019, 09:18 PM   #12
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If long-term memory serves, Ospho was the rust treatment/primer product used with success by fellow cruisers for fuel tanks. Amazon (Prime) sells it for just over half the price of West Marine. Read the Amazon reviews & pay attention to mfr. instructions. I have a shipping container being delivered this week (2nd one), & am considering using it prior to painting. Has anyone tried it?



Thank you. That's what I was thinking of but couldn't remember the right name.


Here it is. It's not cheap but a little bit goes a long way. I've used it and it works well on old vehicles.


https://www.amazon.com/SKYBRYTE-Skyc...language=en_US
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Old 07-28-2019, 11:15 PM   #13
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Ours in an 87 with the original fuel tanks. They are enclosed with some sort of insulation so I cannot see much of the tanks. I can see the filler neck area and there is no visible rust there. But I am concerned about them in the long run. I am seriously considering starting this winter in replacing one of the two fuel tanks. I will have to lift the port engine and slide it over above the starboard engine for the replacement. I will also clean and paint that side of the engine room. Probably replace whatever looks questionable, water heater and water pump and clean up the wiring. There are currently no indications of a problem with the fuel tanks but I want to replace them before I get too old to be able to do it, maybe already too old... I am starting to look at my options in building a frame to hold an I beam for the trolly and hoist. I have about 1150 pounds engine and a couple of hundred more for the transmission. Anyone have an idea what size I beam I need to span 8’?
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Old 07-29-2019, 02:20 AM   #14
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Ours in an 87 with the original fuel tanks. They are enclosed with some sort of insulation so I cannot see much of the tanks. I can see the filler neck area and there is no visible rust there. But I am concerned about them in the long run. I am seriously considering starting this winter in replacing one of the two fuel tanks. I will have to lift the port engine and slide it over above the starboard engine for the replacement. I will also clean and paint that side of the engine room. Probably replace whatever looks questionable, water heater and water pump and clean up the wiring. There are currently no indications of a problem with the fuel tanks but I want to replace them before I get too old to be able to do it, maybe already too old... I am starting to look at my options in building a frame to hold an I beam for the trolly and hoist. I have about 1150 pounds engine and a couple of hundred more for the transmission. Anyone have an idea what size I beam I need to span 8’?
Have you considered cutting the old tank out and save the hassle and expense of moving an engine? Put two or three smaller tanks back in and only loose about 10% of your original capacity.
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Old 07-29-2019, 05:43 AM   #15
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Ospho is simple to use. Wire brush the gross rust off, spray with Ospho - let dry overnight, prime/paint, no washing off or neutralization required. Usually a single quart is all you need for a lifetime. Available on the shelf at most ACE hardware stores. If u need huge quantities, buy bulk Phosphoric acid and dilute to 20%.
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Old 07-29-2019, 07:28 AM   #16
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Ospho is simple to use. Wire brush the gross rust off, spray with Ospho - let dry overnight, prime/paint, no washing off or neutralization required. Usually a single quart is all you need for a lifetime. Available on the shelf at most ACE hardware stores. If u need huge quantities, buy bulk Phosphoric acid and dilute to 20%.

Rust converters are commonly used on steel work boats. A combination of phosphoric acid and a water based coating. Two I've used are Conquest Rust Coverter and Corroseal Rust Converter. As with Ospho make a reasonable effort to get the loose stuff off then coat it.
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Old 07-29-2019, 09:06 AM   #17
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IF the tank shows no signs of rusting , it will last "forever " if maintained.

On the outside a good coat of paint , and a check for deck leaks after a heavy rain should do.

On the inside the game is to remove any7all water.

A dip tube and hand pump might work, or fitting a simple plug on the bottom after draining .
Install a fuel rated valve and stick a plug in it when not in use, to discourage MUrphy.

Why go to expense and look for trouble with an OK tank?

NEVER emulsify the fuel in the hope the filters may catch the water.
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Old 07-29-2019, 09:36 AM   #18
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Rust converters are commonly used on steel work boats. A combination of phosphoric acid and a water based coating. Two I've used are Conquest Rust Coverter and Corroseal Rust Converter. As with Ospho make a reasonable effort to get the loose stuff off then coat it.
Ospho works well but leaves a white powder residue. I think of it as an old tech, less refined, product, "since 1947". I feel obligated to clean it before I paint it.

If you google "rust converter" you will hit on a variety of more modern, more refined products. They leave a black, shiny coating that is ready to paint. Extend is another one.

Another type of rust treatment product that I haven't personally tried but will, one brand is Evaporust. There are others of the type. I've heard good feedback, no bad.

There are also electrolytic, galvanic rust treatments that are not easily applicable.

Someday I'll probably try a wet blast type of treatment for the inside of a tank but it will probably be a removable, easily washable tank. A stationary tank if I could get inside it with a water hose and a shop vac.


Surface prep, surface finish provides the resistance to corrosion, oxidation. Even if you don't spray, or brush on a coating, the surface you leave is important to resisting the elements.
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Old 07-29-2019, 10:23 AM   #19
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Have you considered cutting the old tank out and save the hassle and expense of moving an engine? Put two or three smaller tanks back in and only loose about 10% of your original capacity.
I don’t think that I could even get to them well enough to even cut them up much less to put in smaller replacement tanks. It is really tight on the outboard side of the engines.
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Old 07-29-2019, 11:18 AM   #20
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My boat is an 86 with original tanks. They are 4 separate tanks, 2 on each side, 150 gal each. That’s 600 gallons of fuel. My boat burns about 4 gal/hr. That’s way more fuel that I never need onboard. My plan is that if and when one starts leaking, I’ll decommission it. I’ll do the same if another starts to leak. I just hope that I’d be one on each side, not both on the same side, for balance reasons. 300 gallons will be just fine for me.

I’m hoping by the time this starts to happen I’ll have more time/money to deal with it. Most likely I’d use the original tanks as the housing to hold large bladders.
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