Rusting fuel tanks

We just finished the survey and sea trial of our new to us 1987 Jefferson 42.
Other than some clamps needing to be replaced and a non functioning float switch the survey went well.
However the biggest issue was rust on the iron fuel tanks. We found some top and bottom. We cant tell the severity as they are enclosed behind sound barrier walls and only open at the site tube valves.
They may not be a problem now however they are not going to het any better during my ownership and will become a potential issue for the next owner.
What is this groups familiarity with changing out the tanks as far as process and potential cost? As well as difficulty.

Do a search...there are MANY posts on that very subject.

Good luck

I recently spent 3 days, 25 cut-off wheels and 5 sawzall blades to get one tank out. I'll have to wait a few weeks for the back pain to subside before tackling the other tank/

If the idiot builder had built them 2" lower, they would have slipped out of the cockpit hatch.

Only one tank was leaking in an inaccessible area so it figures the other won't be long to follow. We're changing both and they will be 2" lower so we can slide the new ones in.

PS. They are steel. No pleasure craft are built with iron tanks ( in the last century ).

I have a 1986 Marine Trader...basically the same thing. I have 4 separate 150 gallon tanks. If one starts to leak, I’ll decommission it. I figure when I get to 2 tanks remaining, I’ll deal with it then.

That’s my situation. The only thing I’d suggest is to have the fuel polished (cleaned) and topped off by the seller. If all is well then I’d be ok with rolling the dice.

I just went through the same thing with the survey on our '79 CHB 41; it had a new port tank and the starboard had been "inspected" and found to be fine when the port side was replaced. My surveyor found some rust on the top.

What I did was to get a quote on a fuel tank replacement ($10k for the one side) and split the difference with the seller (knocked $5k off agreed price) which I felt was fair since the tank was serviceable and I knew it wasn't new and would likely eventually need replacement when I made the original offer.

I might have played hardball and tried to get more but I felt like in general the boat was fairly priced. But I am really glad I learned about it before taking possession! You should def get a quote - some of them are harder than others, and it could easily be a $20k job. Moreover if it needs to be done now (e.g. holes/leaks), the yards around here are booked through September so you could be looking at missing the summer season.

I have 1942 steel tanks. If you keep paint on the outside and keep water out of the fuel, steel tanks last a very long time.

Lepke said:

I have 1942 steel tanks. If you keep paint on the outside and keep water out of the fuel, steel tanks last a very long time.

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Certainly true!

But how do you know if you can’t inspect the whole tank and there’s already evidence of rust?

Better to hear this from someone who has done it, but you may be able to view inside the tank with a borescope. Try searching "borescope in fuel tank", see what comes up.
As a boatowner/seller I could not persuade myself to replace tanks which were not leaking but one might(or would).
You could cost replacement and seek a proportion as a deduction.

1970 Willard 36. Just replaced two steel 225 gallon saddle tanks with four fiberglass tanks and maybe lost 10 gallons of capacity. Tough to say on final cost as I had other work done but around $10k all in. Boat is in Mexico so US around $20k is about right. I agree with the comment about splitting difference with seller on a tank that is serviceable but suspect. Old boat, not reasonable to expect new/full replacement.

Peter

BruceK said:

Better to hear this from someone who has done it, but you may be able to view inside the tank with a borescope. Try searching "borescope in fuel tank", see what comes up.
As a boatowner/seller I could not persuade myself to replace tanks which were not leaking but one might(or would).
You could cost replacement and seek a proportion as a deduction.

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Easier said than done - the search function on this forum really sucks.

Having lurked here for a long time I have come across many references to the potential disaster of buying an older Taiwanese trawler with rusted out fuel tanks. Now that I am actively searching here in the Great Lakes about half the boats I have researched have had tank replacements. Amongst those that haven't the response upon enquiry runs something like "It's not a problem - the boat has spent it's entire life in fresh water." Is that a valid argument; or is a fresh water boat just as likely as a salt water boat to have a rusted out tank? It does seem reasonable to think that a boat that spends only 50% of the year floating about in cool fresh water is less likely to have rust/corrosion problems that one that sits year round in a Florida salt bath, but after 40 years is there going to be a toll in either case?

R. Bush said:

Easier said than done - the search function on this forum really sucks.

Having lurked here for a long time I have come across many references to the potential disaster of buying an older Taiwanese trawler with rusted out fuel tanks. Now that I am actively searching here in the Great Lakes about half the boats I have researched have had tank replacements. Amongst those that haven't the response upon enquiry runs something like "It's not a problem - the boat has spent it's entire life in fresh water." Is that a valid argument; or is a fresh water boat just as likely as a salt water boat to have a rusted out tank? It does seem reasonable to think that a boat that spends only 50% of the year floating about in cool fresh water is less likely to have rust/corrosion problems that one that sits year round in a Florida salt bath, but after 40 years is there going to be a toll in either case?

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Here is one of the 17yr old rusted tanks that I cut out this year in Whitby.
This boat spent 2 winters in Bahamas after I had sealed all leaks on to the tanks. The (fresh water) corrosion was well established before we took her south

BEWARE!!!

New tanks will run in the neighborhood of $20,000

pete

R. Bush said:

Easier said than done - the search function on this forum really sucks.

Having lurked here for a long time I have come across many references to the potential disaster of buying an older Taiwanese trawler with rusted out fuel tanks. Now that I am actively searching here in the Great Lakes about half the boats I have researched have had tank replacements. Amongst those that haven't the response upon enquiry runs something like "It's not a problem - the boat has spent it's entire life in fresh water." Is that a valid argument; or is a fresh water boat just as likely as a salt water boat to have a rusted out tank? It does seem reasonable to think that a boat that spends only 50% of the year floating about in cool fresh water is less likely to have rust/corrosion problems that one that sits year round in a Florida salt bath, but after 40 years is there going to be a toll in either case?

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Not much less likely, the rust often comes from water making its way through degraded leaking decks, affecting the tank tops. Which leads us to deck repairs..If you find one you like with replaced tanks it`s a big plus. Decks renovated too is even better.Good luck with the search.

R. Bush said:

Amongst those that haven't the response upon enquiry runs something like "It's not a problem - the boat has spent it's entire life in fresh water." Is that a valid argument; or is a fresh water boat just as likely as a salt water boat to have a rusted out tank?

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Most tanks rust-out due to water intrusion through the deck-fills or deteriorated fasteners in teak side-decks. Rain water is the main culprit, not seawater.

Freshwater boats have their benefits. They are used less, and often in colder climates with less direct sun and sometimes even stored in covered/heated spaces over the winter. They retain their youthful glow well into middle age - sort of a "Christi Brinkley" of the boat world. But for fuel tanks, while saltwater leak-down would cause more corrosion than fresh, over time the constant drip of rainwater is going to be the issue.

Peter

Rusty tanks are hit or miss..

The tank could be in great shape and have a pinhole in a seam weld.....or be trashed inside or out and needing replacement. Rust can come from fresh or salt water....my vote is yes, salt water is worse.

In my single engine with good access, I cut my tanks out in less than a week and installed much smaller poly tanks for well under $1000. Messy job, but not all that bad or that difficult.

So it depends somewhat on the boat and somewhat on how you want to proceed and how much you are willing to do and what the final product will be.

I am always amazed that many folks replace rusty tanks with new tanks that will also rust.

Plastic , GRP or Monel might be better choices?

Sure would slow down the problems when the boat is sold.

Almost all engine room wing fuel tanks that I’ve seem rust out for two reasons; (1) stuffing box slinging SW or (2) more common is fuel fill deck fitting leaking and water running down hose laying atop tanks. The later has ruined quite a few GB sales. The leakage or spray fixes are pretty straight forward in fact you almost never see stuffing boxes attacking tanks anymore.

Stainless steel diesel tanks is rarely the answer as most are improperly welded causing too much heat and weld decay in way of the seams. 1000° heat burns or migrates the carbon and chrome apart creating galvanic potential and pin leakage. Most Asian tanks are 304 and not 316

Many if not most Asian builders cannot or will not build a 100% fiberglass tank so they lay up the base and sides then cap the top with plywood glassed on both sides. Imagine diesel migration into the plywood in way of the fuel fill, vent, and return line penetrations. This was quite common well into the late 90’s. Don’t tell me the penetrations won’t eventually leak.

Steel tanks are mild steel plate and not ‘ black iron ‘ as brokers and brochures tout. Properly built they can outlast the hull and certainly the machinery.

Good tanks need the following features for reliability and use.

I prefer 12 ga plate though most are 14 ga
Full baffles with transverse 25-35” centers and centerline full welds & limbers
Removable inspection clean out plates and working clearance to utilize
Tank tops sloped to drain
Good paint or coating systems exterior only
Full clearance and air ventilation space all sides
Supported by tank bearer frames with rubber chafe protection
Fill hoses accessible for inspection and replacement
Vertical retaining frames from stringers to deckhead
Water traps with drains bottom of tank can be fitted with evacuation tubes
Vent lines at least 25% of fill pipe size

Lots of older commercial vessels with properly build fuel tanks and no problems. In fact I’ve known several fisherman who bought old scrap tanks from wrecks for new installs.

Lepke said:

I have 1942 steel tanks. If you keep paint on the outside and keep water out of the fuel, steel tanks last a very long time.

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Great maintenance info for anyone with a newer boat or new steel tanks.

R. Bush said:

Easier said than done - the search function on this forum really sucks.

Having lurked here for a long time I have come across many references to the potential disaster of buying an older Taiwanese trawler with rusted out fuel tanks. Now that I am actively searching here in the Great Lakes about half the boats I have researched have had tank replacements. Amongst those that haven't the response upon enquiry runs something like "It's not a problem - the boat has spent it's entire life in fresh water." Is that a valid argument; or is a fresh water boat just as likely as a salt water boat to have a rusted out tank? It does seem reasonable to think that a boat that spends only 50% of the year floating about in cool fresh water is less likely to have rust/corrosion problems that one that sits year round in a Florida salt bath, but after 40 years is there going to be a toll in either case?

Click to expand...

Many forums suffer from poor search engines. Here's how I work around that for any forum. Google: "your subject terms" with 'trawlerforum" OR "trawler forum" in the search box. This way google looks in forum for threads. Hope you find this helpful.

Swfla said:

Many forums suffer from poor search engines. Here's how I work around that for any forum. Google: "your subject terms" with 'trawlerforum" OR "trawler forum" in the search box. This way google looks in forum for threads. Hope you find this helpful.

Click to expand...

Even better:

Type the following into Google, replacing your search for the brackets:
[search terms] site:trawlerforum.com

Even better!!

In reading this thread I can’t help but say it’s too bad your surveyor was not equipped to audio-gauge ( ultrasonic inspection) the tank walls. Whenever possible I offered this service to customers however there was always an additional charge. The limiting factor to engine room wing tanks is access. Rarely can one reach much of the bottom, most of the outboard wall and with Grand Banks limited access to tops. But overall a visual inspection and probe contact in accessible areas will give the buyer a good representative evaluation of % of wastage. With thin 14 ga or less steel tanks I would probably condem on 25-35% wastage. I’ve punctured several GB tank tops but I’m real gentle on suspect tank sides and bottoms. A couple hundred gallons of fuel oil in the bilge is sleep disturbing.

garbler said:

In reading this thread I can’t help but say it’s too bad your surveyor was not equipped to audio-gauge ( ultrasonic inspection) the tank walls. Whenever possible I offered this service to customers however there was always an additional charge. The limiting factor to engine room wing tanks is access. Rarely can one reach much of the bottom, most of the outboard wall and with Grand Banks limited access to tops. But overall a visual inspection and probe contact in accessible areas will give the buyer a good representative evaluation of % of wastage. With thin 14 ga or less steel tanks I would probably condem on 25-35% wastage. I’ve punctured several GB tank tops but I’m real gentle on suspect tank sides and bottoms. A couple hundred gallons of fuel oil in the bilge is sleep disturbing.

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I am normally one of the first to jump on the surveyor however ..... the way these tanks are installed and covered up, there is rarely access to the areas that typically corrode. Audio gauging simply wouldn't help in the vast majority of cases particularly with TT's.

If these areas had proper access, drainage and ventilation in the first place this thread would not exist.

boatpoker said:

I am normally one of the first to jump on the surveyor however ..... the way these tanks are installed and covered up, there is rarely access to the areas that typically corrode. Audio gauging simply wouldn't help in the vast majority of cases particularly with TT's.

If these areas had proper access, drainage and ventilation in the first place this thread would not exist.

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I agree and it’s unfortunate. I only added this to the thread because every now and then there is a decent tank installation that provides Just maybe enough access to make an informed opinion. I’ve shot a few that showed enough wastage to condemn based on the limited readings. But very few.