Cleaning an integral keel diesel tank

[stillbuilding]

I have 25 yo 18m steel long-keeled steel yacht with a single diesel (70cm x 50cm x 6m) integral tank on top of the sealed keel ballast. There is no inspection hatch and to make things more difficult there are two integral water tanks on top of the forward half of the fuel tank and the motor is aft of this leaving 1 m of tank top exposed aft. The 50mm fuel fill is forward, 20mm pick-up, return and breather are aft.

In an unhappy saga the fuel tank was completely flooded with water for several months at least. I have removed the water, cleaned several times with water + detergent, alcohol and diesel. Initially I did not get any black algae but in a seaway the 20mm pick-up blocked with large clumps of black solids and the newly filled diesel is black-green. I reckon if there is enough crud to block the pickup, the cleaning of the tank is incomplete to say the least and probably past the stage of cleaning with fuel polishing systems (would be delighted to hear otherwise). I expect the entire tank is covered in closely-attached black goo.

I am considering cutting an inspection hatch in the aft section and cleaning the tank with a high pressure cat-pump based system but using diesel instead of water. Or maybe just use water pressure and remove the water later)

I suspect I am at the stage of radical measures as above or just calling it quits and using one of the two large integral water tanks for fuel and writing off the keel tank.

Has anyone tried cleaning a tank as above or care to comment. I suspect this is past the fuel polishing scenario but would be delighted to hear otherwise.

Thanks for any input.

[JPA Cate]

FWIW,

I saw a similar job done, where they opened the hull on the outside to get at and clean up everything, then welded it up when they were done. Made a nice, tidy fix, but was lots of hours of work.

[lorenzo b]

Increase the size of the fuel line leaving the tank of go directly to a large Racor 900 fuel filter. You can even put in a t fitting with a blow out nozzle. Lots of large ships flood their fuel tanks with sea water to maintain ballast when at sea and just filter the fuel as they need it.

[Cheechako]

Is it easier to cut the top off the tank, degoo it and install a plastic tank slightly smaller?

[rw58ph]

I would also post on TrawlerForum as that is a power/trawler forum which have large tanks and diesel fuel is a common problem. So how much fuel is on the tank? Does the tank have a valve/opening at the bottom for a sight tube has you could use instead of the pick up tube? The Eagles tanks have sight tubes that could be used to pump the fuel out of the tank, or used to transfer/equalize the tanks.

It sounds what you have is tarring, not algae bugs. Tarring is when old fuel separates into a back goo that would turn the diesel black/green. cleaning the tanks with water/soap probable did not touch the stuff. Having a good primary filter/polishing system might be able to clean up the fuel and the tanks.

[gjordan]

If it is as serious as it seems, going in from the side would be the most effective method. Talk to a yard that does work boats and they will probably have experiance doing this. Pump tank as dry as possible, fill tank with CO2 or some other inert gas, cut nice big inspection hole in the side of the keel. Sandblast the inside of the tank, and coat with whatever is recommended for steel tanks. Weld up the hole and it is good for another 30 years. The only spot without the new coating will be the welds, but if you dont get water intrusion, they will last decades. From your description it doesnt seem like you have enough access from the top to do a good job, and sandblasting from the inside would be very difficult, let alone the probability of getting sand all over the inside of your boat. If you decide to clean with pressure diesel, be aware that while diesel fumes are not as dangerous as petrel fumes, they can still be ignited and make a huge explosion. This type of repair (from the outside) is one of the advantages of owning a steel boat. Try cutting into the keel of a GRP boat and having it come out as strong after finishing. I hope this helps. ____Grant.

[stillbuilding]

Originally Posted by Cheechako

Is it easier to cut the top off the tank, degoo it and install a plastic tank slightly smaller?

Not really accessible. Can cut hatch 50 x 80 in aft section but have to reach 3 m forward - hence thinking of high pressure extension.

[stillbuilding]

Originally Posted by Ann T. Cate

FWIW, I saw a similar job done, where they opened the hull on the outside to get at and clean up everything, then welded it up when they were done. Made a nice, tidy fix, but was lots of hours of work.

Know someone who did same and left it as bolt-on hatch to facilitate future access. Maybe an option when i get steel work done in Malaysia next year but not now.

[stillbuilding]

Originally Posted by lorenzo b

Increase the size of the fuel line leaving the tank of go directly to a large Racor 900 fuel filter. You can even put in a t fitting with a blow out nozzle. Lots of large ships flood their fuel tanks with sea water to maintain ballast when at sea and just filter the fuel as they need it.

I have two Racor 1000's but wonder if just cleaning will be enough. Blockage always seems to be in a gale, on a lee shore, or 3 am - or all three. Really do not want to risk this on continuing basis so want to do an initial really good scour so future cleaning is routine filters. Already running 12mm pickup line.

[stillbuilding]

Originally Posted by rw58ph

I would also post on TrawlerForum as that is a power/trawler forum which have large tanks and diesel fuel is a common problem. So how much fuel is on the tank? Does the tank have a valve/opening at the bottom for a sight tube has you could use instead of the pick up tube? The Eagles tanks have sight tubes that could be used to pump the fuel out of the tank, or used to transfer/equalize the tanks. It sounds what you have is tarring, not algae bugs. Tarring is when old fuel separates into a back goo that would turn the diesel black/green. cleaning the tanks with water/soap probable did not touch the stuff. Having a good primary filter/polishing system might be able to clean up the fuel and the tanks.

I would say the tank has never been cleaned so 25 years of crud plus flooded for months. Presumably the entire tank is covered in this tar. You think just filters will be enough? Not worried about water but black crud that blocks a 10mm pickup sounds more serious to me.

[stillbuilding]

Originally Posted by gjordan

If it is as serious as it seems, going in from the side would be the most effective method. Talk to a yard that does work boats and they will probably have experiance doing this. Pump tank as dry as possible, fill tank with CO2 or some other inert gas, cut nice big inspection hole in the side of the keel. Sandblast the inside of the tank, and coat with whatever is recommended for steel tanks. Weld up the hole and it is good for another 30 years. The only spot without the new coating will be the welds, but if you dont get water intrusion, they will last decades. From your description it doesnt seem like you have enough access from the top to do a good job, and sandblasting from the inside would be very difficult, let alone the probability of getting sand all over the inside of your boat. If you decide to clean with pressure diesel, be aware that while diesel fumes are not as dangerous as petrel fumes, they can still be ignited and make a huge explosion. This type of repair (from the outside) is one of the advantages of owning a steel boat. Try cutting into the keel of a GRP boat and having it come out as strong after finishing. I hope this helps. ____Grant.

Maybe an option next year. Maybe just have to use a flexible tank as alternatve till then. Or use one of the huge water tanks for fuel.

[stillbuilding]

Originally Posted by gjordan

If it is as serious as it seems, going in from the side would be the most effective method. Talk to a yard that does work boats and they will probably have experiance doing this. Pump tank as dry as possible, fill tank with CO2 or some other inert gas, cut nice big inspection hole in the side of the keel. Sandblast the inside of the tank, and coat with whatever is recommended for steel tanks. Weld up the hole and it is good for another 30 years. The only spot without the new coating will be the welds, but if you dont get water intrusion, they will last decades. From your description it doesnt seem like you have enough access from the top to do a good job, and sandblasting from the inside would be very difficult, let alone the probability of getting sand all over the inside of your boat. If you decide to clean with pressure diesel, be aware that while diesel fumes are not as dangerous as petrel fumes, they can still be ignited and make a huge explosion. This type of repair (from the outside) is one of the advantages of owning a steel boat. Try cutting into the keel of a GRP boat and having it come out as strong after finishing. I hope this helps. ____Grant.

Understand the risk if ignition so maybe just high pressure water and clean that out after the crud is dislodged

[gjordan]

You mention steel work next year. To put off the problem for a year, you might install a day tank that feeds your engine, and pump from the bilge tank through good filters into the day tank. That way if you have plugged filters, you are still running on clean fuel while you change them out. I would make the day tank big enough for about 24 hours of running, and make it a habit of not running it down to less than half. That gives you hours of running time even after your filters from the bilge tank need changing. The advantages to this system are NO DEAD ENGINE from plugged filters, change out plugged filters without shutting down engine or having to bleed it. If you have not let the day tank get too low, you will have time to maybe get some sleep before filter changing, or wait to do it in daylight. I would go to some great lengths before I would contaminate a water tank.______ Just a few more thoughts.______Grant.

[rw58ph]

Originally Posted by stillbuilding

Know someone who did same and left it as bolt-on hatch to facilitate future access. Maybe an option when i get steel work done in Malaysia next year but not now.

The mid 400 gallon tank side weld cracked, so cut a 18” X 18” square hole in the tank big enough for me to climb in. I had a bolt in place hatch cover made that held for 10+ years. The tanks was not in that bad of shape except the weld seam cracked. I would not go through the hull if you can access and cut a hole in the tank.

[stillbuilding]

[QUOTE="gjordan;1368024"]You mention steel work next year. To put off the problem for a year, you might install a day tank that feeds your engine, and pump from the bilge tank through good filters into the day tank. That way if you have plugged filters, you are still running on clean fuel while you change them out. I would make the day tank big enough for about 24 hours of running, and make it a habit of not running it down to less than half. That gives you hours of running time even after your filters from the bilge tank need changing. The advantages to this system are NO DEAD ENGINE from plugged filters, change out plugged filters without shutting down engine or having to bleed it. If you have not let the day tank get too low, you will have time to maybe get some sleep before filter changing, or wait to do it in daylight. I would go to some great lengths before I would contaminate a water tank.______ Just a few more thoughts.______Grant.[/QUOTE

This may be best option for the moment.
Still have to clean later but easier then.