Leaking Diesel fuel tank; what to do

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obthomas

obthomas

Guru
Joined
May 16, 2013
Messages
560
Location
USA
Vessel Name
TheVenture
Vessel Make
1985 Bestway Labelle Sundeck 40ft
Alas I have a center Diesel belly tank that leaks into the bilge. The tank is now abandoned in place and my boat is arranged to run from the port and starboard side tanks.

I have removed the top inspection hole cover and what is left is maybe 1/4 inch of diesel and sludge. I want to start cutting the tank out and eventually replace it with a HDPE one. The tank is long and slender dead center the boat and is between the center engine rails. It held about 130 gallons. The boat builders sandwiched the tank in place with a covering of fiberglass across the top from rail to rail.

I would appreciate advice on the following:

1. The tank and this fiberglass covering tend to be a box; and so I wonder if it provides a strength to the hull that I would not want to eliminate?

2. If I put some water in the tank and floated the diesel remnants would it be safe to pump it out to a bucket skimming the top with a bilge pump?

3. At what point is it safe to use an electric sawzall?
 
Suck out all the remaining diesel. Wipe it dry inside if you can by snaking a bunch of oil absorbent pads into the far ends. Drop about 5 pounds of dry ice in the tank and allow the air to vent out the top. When you get a good dose of CO2 out the tank vent, have at it with the sawzall.

Cut a small panel out of the end opposite the inspection cover and then use a vacuum cleaner or a blower to keep a good circulation of air through the tank while cutting the rest of it apart. Once most of the top is gone you are good to go.

The chance of that FG cover having a structural function is slim to nil. If it is not at least 1/4 inch thick and well tabbed in to the stringers it is just to keep feet off the tank top.
 
Yup What Mr Rick B said.
I'd say he's right on.

I have also seen a air chisel used to cut the tank. A little less sparks.

SD
 
I just cut out my tanks with a sawzall...no sparks...not much heat and all I did was have a small fan blowing into the inspection port on top...as soon as the saw blade made contact with the inside airflow was out the cut...once a bigger hole was made...plenty of airflow and no fume problem.

The CO2 dry ice is probably a good idea but so many have said that the tiniest amount of airflow is all you need.
 
This is what I did when I had leaking tanks.

LEAKING FUEL TANKS

The bane of the Taiwan trawler style.
CC RIDER is a 1981 CHB that I purchased in 1985. Since I do all of my own maintenance, she and I are intimately acquainted, probably in the Biblical sense! I digress. Knowing well the proclivities of these boats I have babied the tanks over the years, to little avail. Noting however that there was no rust on the top of the tanks from deck leaks. This spring the two port side tanks sprang minute leaks in their bottoms. To remedy this I took the following steps:

1. Pumped all fuel from the tanks.
2. Opened the inspection hatch that is located on the side and wiped out any residual fuel with paper towels after scooping all the crud out with the bottom half of a 2 liter bottle.
3. Liberally splashed the tanks with liquid detergent and washed the tank with water that was then pumped to a barrel on the dock. This requires surprisingly little water. This was done three times to make sure that all scum and fuel residue was removed. You must get to the far side of the baffle!
4. Any oil in the water in the barrel may be skimmed and the water dumped.
5. I then placed an electric fan to blow into the tank to remove any fumes, this was done overnight.
6. The tanks were then cut loose from their mount and raised about four inches, which was the maximum room available. This was done using a crow bar and a number of small blocks of wood cut for the purpose.
7. On one tank I could see the source of the leak and used my 4.5-inch De Walt grinder with a wire brush wheel to get rid of the rust and paint. This was done to all accessible seams and wherever there was rust. With the tank exposed I filled it with water and looked for any additional leaks. Since there were only two and both were readily accessible to the welder he merely welded them.
8. To protect the bottom of the boat from the heat of the welding I merely placed a piece of plywood right under where he was welding. Of course a water hose was kept at the ready and was used to cool the tank as the paint burned and caused smoke. The water kept the smoke down to a manageable level, which was blown outside using several fans.
9. The other tank was a different story. This one required a 14 inch square manhole be cut in the side, the baffle be cut out and then all seams welded from the inside of the tank. Depending on space constraints, possibly two holes may be required.
10. A 3/8 steel flange was welded inside the tank around the manhole. I then fabricated an aluminum cover and drilled and tapped it to match. This was the most tedious work.
11. The tanks were then primed, painted and dropped back into place.
12. End of Portside side story.
13. The starboard side presented a different set of problems. Of all things on the first trip subsequent to the foregoing repairs the starboard tanks
sprang leaks, go figure!
14. The forward tank was not accessible for any type of work on it. These like the others measured 64 inches long and about 24 inches deep by 28 high. They would not come out the available hatch without moving the generator set so it was necessary to cut 24 inches off of the length of each tank. The same procedure was followed as above as to cleaning and cutting.
15. Upon removal they were easy to repair by welding any pinholes and scabbing in steel plate where necessary. A number of places were patched like this. New ends were welded on, fill pipes moved and the like. Three tanks were made of the two with some loss of capacity. They were sandblasted coated and painted prior to reinstallation. The "3rd " tank was "sistered" to one of the others so as to not require a separate deck fill, though it has its own vent and does not rely on the vent for its mate.

This or these methods are not touted as cure alls but they did work for me. Of course new aluminum tanks could have been built or plastic ones purchased. I found that only 55- gallon plastic are readily available.
If you desire additional information I may be reached: charlesculotta@gmail.com This e-mail address is being protected from spambots. You need JavaScript enabled to view it

In closing I was surprised at the amount of scum in the aft tanks as compared to the forward ones. I attribute this to the fact that it is my custom to
run the aft tanks dry first and then the forward ones. This leaves them low on fuel for extended periods for as soon as the forward tanks are low I refuel. Thus we have more condensation and the result is more water and scum formation. I am scrupulous about always using a biocide and changing filters every 200 hours. I have never had a filter clog following this regimen.
 
I would open the top only large enough to clean the tank and then install a custom made bladder tank.

All are custom built so the cost is not excessive.

IF you later decide to cruise inshore a second bladder tank that is OK for drinking water could be installed.

Our 90/90 uses two (one diesel , one water) in her tank areas and the choice is nice to have.

200G of extra fuel OR 200G of fresh water.
 
Astral Blue said:
Try using this tool for tight spots or areas where your saw is not viable:
Click to expand...

That'll take about 65 years and as many tools. A mini-grinder with cut-off wheels or even standard grinding wheels will make short (if messy) work of SS sheet metal.

You will burn through a fortune in Sawzall blades cutting that stuff. I recommend the mini-grinder route.
 
My tank is about 20 gage black steel. I have both a sawsall and an angle grinder with a 4 inch cut off blade. I think there will be no problem with the actual cutting.
 
I went through maybe 10 or so 6" (2 packs at $17/pack) Milwaukee TORCH blades on my 2-200 gallon tanks....

It depends on how many cuts you have to make getting them out...I would say mine came out in about 7-10 pieces each. It would have been much less had I had the room to lift or shift them while cutting.

I found a little cutting oil kept things cool and the blades lasted longer...I used the little one handed sawzall from Rigid (Home Depot Brand) and did wait about 5 minutes for every 5-10 cutting to let it cool. The whole cutting and removal job took about 10 days of maybe cutting 2-3 hrs per day but that included setup/cleanup as we are living aboard.

I just didn't trust the sparks of a cutting wheel though I would have preferred one...I didn't know how volatile the thick coat of residue on the tank innards was...and after a little cutting with the one handed sawzall...wasn't so bad I was cursing the chore everyday. Plus the mess the cutting tool would have made might have been a bigger PIA to clean than just using the saw.
 
Last edited:
I would not cut up take out the tanks until they are inspected. I cut an 18” X 18” hole big enough for me to climb inside the tank which I clean up and had a weld climb into the tank and weld the tank up. that was about 15 years ago and still holding.

If the tanks could not be repaired I would not take out the tanks, but use them as a frame work for smaller multi smaller plastic tanks that fit inside and manifold together.
 
I couldn't really inspect mine until they were cut up and out...I might have cared more about inspecting in place if I didn't really just want to stop carrying so much fuel and really wanted the now very nice additional storage area in my engine room.
 
Phil Fill said:
I cut an 18” X 18” hole big enough for me to climb inside the tank which I clean up and had a weld climb into the tank and weld the tank up. that was about 15 years ago and still holding.
Click to expand...

That should have caused some filter clogging ... not to mention some really nasty smelling fuel.
 
RickB said:
That should have caused some filter clogging ... not to mention some really nasty smelling fuel.
Click to expand...

Oh! I forgot, I had the welder climb out before I closed up the tank.:D

I cut the hole in the side of the tank, not the top as only the side was accessible. Had a hatch/cover made with studs welded to the cover that bolted thru the tank with a gasket seal around it. 15 years and has not leaked. I also want smaller tanks as each tank is 400 gallons so having several smaller tanks would be better. I am not sure I want to significant reduce the total fuel capacity? But dealing with one or two smaller tanks would be less of a concern than one big tank.

Because the tanks are so old I fill 1/2 full so it one tank does leak there is room in the other two tanks. Anyway that is the plan! :confused:
 
mini or even 4 inch cut off wheels make a lot of sparks, sawzall is a safer alterative if possible:)
 
This subject scares the hell out of me, I have 4 massive 200gal tanks and 2 100gal tanks. They are steel encased in fiberglass so there would be no way to weld inside or outside without starting fires. Cutting them out would be near impossible without removing the engines.

Would not a steel epoxy like JB weld work for leaks?

Psneeld, Out of curiosity what are you replacing your tanks with?
 
We replaced the 2 350 gallon mild steel tanks on Bay Pelican during the summer (off season) of 2011. We used both sawzalls and grinding wheels depending on the location we were cutting. To avoid moving the main engine we replaced the two large tanks with 4 smaller ones with only 60% of the original capacity.

The tanks were flushed out with water before the cutting began.

Marty
 
Greetings,
Mr. Rick B. I think someone might be fearing...

captain-america.gif
 
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