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Old 04-05-2019, 06:06 PM   #1
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Older boats and their fuel tanks

We're searching for out next boat. Our finances dictate we consider only older boats. One of the biggest financial risks I'm trying to get a handle on is the cost to replace fuel tanks should the old tanks start to leak.



Can any of you share the lessons learned on replacing the tanks in a twin engine boat with the tanks outboard of the engines.


Assume:
  • Salon decking is removable for full access to the engines and tanks.
  • Engines will have to come out, they will fit through the salon doors.


Thank you all for the time to respond to this post!
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Old 04-05-2019, 06:32 PM   #2
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You have it right. Cost is mostly labor to remove engines etc, so if you have facilities and friends to assist, and time, then its not that big a deal.

Use primed steel to make new tanks, then a good epoxy paint system when all welding is done. And address the reason the tanks failed initially. It could be poor deck fills, or perhaps ER vents with vertical slats that allow rain to enter, as it was in my case. But it still took 30 years. With epoxy painted steel, and no regular water entry new steel tanks will last a very, very long time.

But, be aware that while the engines and tanks are out it will be the perfect time to replace other stuff 'while we have excellent access'. Scope of work rapidly escalates!
Clean and paint the bilge, new plumbing lines, hydronic heating lines, fuel lines - you name it!

All I would say is that before starting, know that the boat is the right one for your needs for 10 years or so. Costs do add up, and if you only have the boat a few years you won't recover the expenditure. You wont after 10 years either, but you will have had 10 years of worry/cost free, routine maintenance-only boating which is priceless. I've just completed 7 years....
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Old 04-05-2019, 06:32 PM   #3
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I would look carefully at flexible 'bladder' tanks. Use the existing tanks as 'containers' for the bladder tanks. You would cut holes in the existing tanks just large enough to slip in the flexible bladders.


No decking removed, no engines removed, old tanks stay (mostly) in place.


I replaced a freshwater tank in a previous boat. Installed a bladder in it's place. Worked like a charm.


One downside of this is that the existing tanks you are replacing may have baffles inside to prevent sloshing of the fuel -- I don't think there is any way to duplicate these baffles inside a bladder tank.


One upside of this is that the tanks will never have any air space (ullage) in them and this will help you prevent moisture laden air from getting your fuel wet.


Good luck with this.


One question...If I were looking for the absolutely lowest cost option, I would go single-engine versus twins. Depending on how you are going to use the boat, and how much money you are prepared to spend annually maintaining two engines vs. one...a single engine option can actually be more reliable and definitely less expensive.


Maybe this seems counter-intuitive, but most here will tell you that a single engine that is very well maintained can be more reliable than twins that are poorly maintained.


We currently own both a single engine trawler and a twin-engine pilothouse, so I speak from both sides of the fence.


Just a thought.
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Old 04-05-2019, 06:40 PM   #4
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Yes, bladders are an option. But to me they shout: only going to keep the boat for a short time, don't go very far from home port and don't go out very often. All of that is fine.

In my previous post I should also have noted that I cruise a lot, and at times far from home port. In that case doing the job thoroughly made sense.
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Old 04-05-2019, 07:57 PM   #5
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When I replaced my tanks the overwhelming advice was to replace w aluminum tanks. We did about 12 years ago.
Absolutely no indication it was a bad choice.
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Old 04-05-2019, 08:50 PM   #6
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Find a fuel tank cleaning and restoration service, have them inspect the tanks before you buy.


Here is a good article on fuel tank issues written by someone who posts here.


https://stevedmarineconsulting.com/c...g-diesel-tanks
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Old 04-05-2019, 09:42 PM   #7
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I don't know why you would use steel, it would be the last material I would choose.

There are bladders that are foam filled, and do not slosh - better than baffles.
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Old 04-05-2019, 10:55 PM   #8
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My 1942 steel tanks are fine. They appear to have started as 1/4" plate. The trick to not having tank problems is to use a fuel conditioner. A good one makes it easier for the Racor to remove water. W/o water there are no organisms that produce acid in their waste. No acid, no holes in the tank bottom.
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Old 04-05-2019, 11:28 PM   #9
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Different strokes for different boats. I have quite a bit of experience with bladders as we pioneered them in a commercial form for transporting latex, wine etc etc.
When I renovated my single engine Birchwood I removed the old tanks and replaced with a larger mild steel tanks using 1/8th plate, I fitted 2 baffles, an inspection hatch which allowed all 3 sections to be cleaned with a wet/dry vacuum if necessary.
As Insequent correctly states this is the perfect time to upgrade all systems within the engine room so don't be surprised if you go a tad over budget. I took the opportunity to paint the bilges and insulated down to the water line. I also insulated the tanks to reduce condensation but also to reduce engine noise via the 'echo' effect from half empty tanks. Others may have different views, all I can say is its still a good job some years later.
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Old 04-06-2019, 05:36 AM   #10
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Seems the well installed and maintained (no leaks above) (internal water removed) tanks can last the vessels lifetime.

Knowledge of a possible repair/methods is great insurance , a careful inspection before purchase might be even better.

Sure its expensive , but Monel would still seem to be the superior tank material.
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Old 04-06-2019, 07:41 AM   #11
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About $20K. engines may be moved instead of taken out all depends on the salon floor construction.
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Old 04-06-2019, 09:07 AM   #12
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One of the reasons we only looked at boats with fiberglass fuel tanks when we were picking out our current boat.
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Old 04-06-2019, 11:08 AM   #13
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Fuel tank replacement

Ok, I just finished replacing a fuel tank. My boat has two tanks. 265 gallon under the master bed and a 400 gallon in the lazarette. Both tanks are/were 1/4" aluminum. The 265 started leaking so I assumed both 30 year old tanks would need replacing. Quote to remove and replace with new multiple aluminum tanks (so they can fit) was $14,500. All fuel in the 265 was moved to the non leaking 400. The bed was removed, the water tanks were removed then the old tank was cut out in sections and removed. During this process it became clear that the inside of the tanks looked beautiful, even the bottom of the V as she sits center line running bow and stern for all of 150". Then when cleaning the inside of each section we would see a stained look on the bottom. After removing the section, we turn it over and you can see the corrosion on the bottom working in. So here are some facts and assumptions. When the boat (1991 Californian 55 CPMY) was built the bilge area in which the tank sat was completely enclosed. No escape or incursion of water from other parts of the bilges. It was designed to be dry. Then I assume the water tank above leaked and was replaced with out proper removal of water from the tank bilge. So it sat in water for years. Having seen this I now know that my aft tank is still good because it is well elevated above the bilges. $7,000 then was the negotiated cost for replacing the one 265 with four aluminum tanks tied together. Not sure of the current tank volume. I did move and polish the old fuel from the 400 tank back into the new tank. Then had inspection ports in stalled and the 400 cleaned. There is my story, sad but true. I was worried about old fuel tanks when I bought the boat last year but neither were leaking then and the fact that they were aluminum gave me false confidence. I discussed the tanks with my surveyor and he said tanks almost always corrode from the outside in. There was no way to know that there was water in that bilge as the only access was below the head board and I keep a dinghy on the foredeck making it bow heavy. Any water pooled forward where there was no inspection port.
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Old 04-06-2019, 12:26 PM   #14
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We replaced our tanks 3 years ago. We have a single engine which came out so we could get the old tanks out and the new tanks in. Our tanks are not square boxes so the fabrication costs were high. If you took out the engine rebuild and focused just on the tank replacement, we probably could have done the project for $20-$25K. Hereís the thread for project.

Krogen 42 Fuel Tank Replacement
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Old 04-06-2019, 01:33 PM   #15
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I agree, ideally, look for a boat with fiberglass tanks.
May take some time to find the right boat, but maybe worth it.
Also, negotiating the price of a boat with steel tanks may provide you with the money to replace them.
Location of the steel tanks is the critical part!
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Old 04-07-2019, 06:13 AM   #16
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"One of the reasons we only looked at boats with fiberglass fuel tanks when we were picking out our current boat."

GRP fuel tanks were sometimes destroyed by the Ethanol demanded in gasoline.

Now that its hard to escaped diesel with at least 5% bio gunk , I would check the fuel filters for glass strands.

Only time will tell weather new diesel is destructive.
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Old 04-12-2019, 01:04 PM   #17
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Research bladders. They work. Aircraft use them. You can mimic baffles by putting several small bladders plumbed together inside your old tank. I had a Bayfield 32 Cutter that had part of its fuel tank top cut out to stuff a bladder into and never had a problem
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Old 04-12-2019, 01:19 PM   #18
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Quote:
Originally Posted by Boat View Post
Find a fuel tank cleaning and restoration service, have them inspect the tanks before you buy.


Here is a good article on fuel tank issues written by someone who posts here.


https://stevedmarineconsulting.com/c...g-diesel-tanks
Thanks, here's one on tank design as well. Valuable if you are going to have a tank fabricated. http://stevedmarineconsulting.com/wp...TankDesign.pdf

And another on tank installation https://stevedmarineconsulting.com/f...-installation/

Among other things tank tops should be sloped inboard to shed water that leaks from decks or vents. A well or sump built into the bottom is a very nice feature, along with inspection ports for each baffled chamber. Adding these features when a tank is built is not very costly. No hygroscopic materials should make contact with metallic tanks, and that includes non-hygroscopic materials such as Starboard that can trap water against a tank surface. Threaded tank fittings should use welding bosses, rather than pipe couplings.

I would strongly recommend against a bladder for dealing with a failing tank, you'd have to cut a portion of the tank top out, and cut out the baffles if you are placing it inside the tank, and leave no sharp edges, and a very thorough cleaning of the tank interior to eliminate odors, a considerable job to say the least. Getting the plumbing properly oriented and looking right is very difficult. They are pretty much impossible to clean or drain water from. I could go on. As another member noted, it would also be a huge red flag at the time of sale.

Most custom fab'd tanks today are made from 5000 series aluminum (I prefer un-coated).

Fiberglass, as some have noted, is an excellent material for diesel fuel tanks, it's my tank material of choice. Ideally they should be VE resin or epoxy, and fire retardant, although many are made from PE resin with no issues. Nordhavns, Flemings, Hamptons, and a number of other vessels use FRP for fuel and in some cases every tank. Thus far I have encountered no problems with bio-diesel and FRP tanks in these vessels. Hatteras has used FRP for fuel tanks for over 30 years, plain old PE resin too. I've cleaned out some of these tanks, shoveling out the crud and hot water pressure washing the interior and the tanks look like new inside afterward, something that can't often be said of steel and aluminum tanks of that age.

Every gas filling station's tanks in the US are fiberglass, albeit a proprietary formula made by Xerxes (I called them to ask what it was but they wouldn't tell me), and some are used for 70% ethanol.
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Old 04-12-2019, 11:00 PM   #19
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I assisted in replacing tanks outboard of twin engines in a 37-foot trawler. We pulled one engine at a time using come-alongs and a timber frame set up in the salon over the removed engine room hatches. We stacked the pulled engine on 4X4 timbers over top of the other engine. Then we cut up and removed the old tanks (one 250 gallon tank per side) and replaced them with two aluminum tanks before swapping sides.
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Old 04-13-2019, 01:59 AM   #20
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Originally Posted by Riverguy View Post
I would look carefully at flexible 'bladder' tanks. Use the existing tanks as 'containers' for the bladder tanks. You would cut holes in the existing tanks just large enough to slip in the flexible bladders.

One downside of this is that the existing tanks you are replacing may have baffles inside to prevent sloshing of the fuel -- I don't think there is any way to duplicate these baffles inside a bladder tank.


One upside of this is that the tanks will never have any air space (ullage) in them and this will help you prevent moisture laden air from getting your...
If I were looking for the absolutely lowest cost option, I would go single-engine versus twins. Depending on how you are going to use the boat, and how much money you are prepared to spend annually maintaining two engines vs. one...a single engine option can actually be more reliable and definitely less expensive.


Maybe this seems counter-intuitive, but most here will tell you that a single engine that is very well maintained can be more reliable than twins that are poorly maintained.

.
I get the idea of bladders in old tanks, but will the baffles be good to the bladders. Protrusions, sharp edges etc. My tanks are tall and relatively narrow, how are the bladders supported, what happens as they empty,do they collapse to the base of the old tank and fold over, I`m not sure how it works in practice.

If a single engine set up is more reliable than twins, it follows that no engines at all would be even more reliable. Certainly no chance of engine failure.
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