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Old 08-06-2017, 01:09 AM   #1
City: Adelaide
Country: Australia
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Fuel Tank Check

I am looking to purchase a 1981 36ft trawler that has sat completely idle for over 5 years. She requires engine work but I am interested in how I can check the fuel tanks for internal and external corrosion as renewing them would be a major (deal breaker) job.

She has twin 600 litre yanks that seem to be built in under the side decks. I believe the decks to be sound. The tanks are steel but very much hidden behind sound deadening material.

I am a newbie here so thanks in advance for your collective wisdom.

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Old 08-06-2017, 02:50 AM   #2
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IF the filler neck is pretty straight, jam a stick clear down to the bottom of the tank, withdraw and inspect.
Does it have vacuum guage?
Easy to install one inline, even temporary.
Pull a primary fuel filter, if its a spin-on, cut it open and inspect.
I wouldn't think fuel tanks would be a deal breaker, the boat is old and needs engine work anyway, so your offer should be quite low.

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Old 08-06-2017, 06:04 AM   #3
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If it is a Taiwanese Tub and has teak decks, I would assume it needs new fuel tanks and deck repair. More importantly, you really should have the boat surveyed.
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Old 08-06-2017, 06:15 AM   #4
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I would insist that the tanks be emptied, if they are not already, and use a scope to go insidethrough the filler neck to inspect them. Unfortunately the inside may look fine but the outside could have major corrosion. As noted in prior posts, if the decks are leaking, you may have to consider that the tanks will need to be replaced. A project boat may look like a good opportunity to get into boating but the dollars you end up spending may be much more than you had anticipated. As me how I know!
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Old 08-06-2017, 08:21 AM   #5
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Been there, almost done with that.

Our TT had fiberglass coated steel tanks behind a sound deadening enclosure. Had the boat for a year before the port tank dumped major amounts of fuel into the bilge. When cut out, the exterior of the tank looked new. The interior of the tank looked new, too, except along the bottom where there was lots of sludge and some corrosion. Most of the corrosion appeared very minor and I never did find the actual leak. We cut the starboard tank out too; it appeared to be seeping from the steel into the fiberglass covering, so removal was a good decision.

Our TT had the large side access ports. The 6' long tanks had a single baffle so no one could really clean or inspect the whole of the tank.

Without the ability to inspect the tanks, either from the outside (for rusting through the top due to deck leaks) or from inside the bottom; it's a crapshoot that will be lost eventually.
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Old 08-07-2017, 09:03 PM   #6
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This is what mine looked like after I cut them out. In the middle you can see one of the pieces with really thick rust on the corner seam. The rust started on the top of the tanks and flowed over the front edge and down the face.

It was amazing that they never leaked but it was only a matter of time before they would have. There were plenty of chunks of steel missing on the inside surface from corrosion. There was also a 2"+ thick layer of dead bugs laying on the bottom of them. Nasty stuff.

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Old 08-07-2017, 11:49 PM   #7
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Apprentice, what is it?
My 1981 decks needed an overhaul but (touch wood) the steel fuel and water tanks are original. I had rust treated on top of the fuel tanks, but elsewhere (firmly grasping wood), nothing alarming.
Go on what you and any surveyor find, don`t make a lot of expensive wallet churning assumptions. If survey etc suggests corrosion maybe you need to look inside, but once you feel that, you probably have tank issues.
You say the decks are sound.Teak? Check for cupped planks, failing caulk, missing screw plugs, signs of water penetration or wicking below. They could be sound,again it`s step by step,don`t write anything off without investigation.
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Old 08-08-2017, 01:02 AM   #8
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Welcome Apprentice!

Good to have another Adelaide member on here.

Tank inspections are always a bit tricky. The tanks looked good on my boat during the survey inspection but they were externally corroded from the bottom. It is sometimes hard to tell. Looking at how the tank is designed and mounted often gives a few hints about where it may be corroded..
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Old 08-12-2017, 02:03 AM   #9
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Thanks for your collective support and advice. Spent some more time crawling around inside this week with the surveyor and didn't find anything too scary. She has teak over glass on the decks with some leakage around the starboard fuel filler which is offset to the tank. Looking again they probably wouldn't be a deal breaker. Removal while being a major pain in the %$#^ could happen as there is quite a bit of space below. The tanks have a small 10-15mm dip stick ports on both sides which revealed they are about 30% full.


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