Cutting aluminium diesel fuel tank on board

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Boater On Thames

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I am going to cut a big hole 50cm X 90cm on top of the 200-gallon aluminium diesel fuel tank on board. Is it dangerous to do so? It's empty, but not wash yet because it's very big with only a small hole for the fuel level sender. A bit of grease inside but not too much, and very little diesel on the bottom far corner can't pump out completely. I have a circular saw and a jigsaw. I am planning to put a vacuum cleaner to suck air from the fuel level sender hole while the outside fule inlet open. Any advice to keep safe to avoid fire or explosion? Many thank!
 
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Depending what you are cutting it with ?
An angle grinder with cutting disc?
I wouldn't introduce air by sucking with a vacuum cleaner, better a steam cleaner or possibly a pressure washer running while you cut.
With aluminium little chance of sparks anyway.
 
Before you cut into your fuel tank have you investigated having a liner made by a specialist so avoiding the need to disturb the interior of the boat. I also have 2 aluminium fuel tanks of 150 gallons that are 23 years old and realise there is a likelihood of them leaking. There was a company mentioned on a thread here recently that seems to sort this problem although no costs were mentioned. If cutting aluminium a jigsaw would be best.
 
My tank is under the bathroom and closet in the master bedroom. I am going to cut the floor of the closet to gain access to do the job. So except for the closest floor, no other interior will be impacted.
 
drill a 8mm hole (or whatever the jigsaw blade will fit in) and use the jigsaw, no way of introducing sparks there, not to mention that diesel is not that easy to set off...
more concerned with the shavings that are going to end up at the bottom of the tank and following that to the filters.
Are you sure there's no baffle where you are cutting, not that it will affect things much tbh.
Resealing is not a v. easy job. How are you going to hold the nuts on the underside of the hole for the bolts to go through? or are you going to go selftapers?
you'll most likely introduce different metals in there, not ideal but being on top and just occasionally splashed with diesel should be fine.
 
There are some baffles in it. I am planning to remove all baffles and put several small fuel tanks into them. Because the big tank is leaking a bit and I don't think I can fix the leakage due to the access is very limited and with those baffles blocked the way. I also don't want to cut a huge hole on the hull from the sideway to replace the big tank. So that's why I am going to try to install small tanks instead.
 
OK,
what are the small tanks going to be made of?
how are you going to interconnect them to suck the diesel out?
if on the bottom (where you should I guess...) it's going to create a series of new issues with tanks moving a bit, connections stressed and possibly leaking again

sorry for asking all these Qs, but I've got a few friends with similar issues one ended up removing engines to reach and remove the wing tanks and eventually built new ones smaller and now putting the whole lot together. Maybe one flex tank if surfaces are smooth and safe for it?
 
Lucas Gan said:
There are some baffles in it. I am planning to remove all baffles and put several small fuel tanks into them. Because the big tank is leaking a bit and I don't think I can fix the leakage due to the access is very limited and with those baffles blocked the way. I also don't want to cut a huge hole on the hull from the sideway to replace the big tank. So that's why I am going to try to install small tanks instead.
Click to expand...
Why not fill it nearly full then cut of water
 
I thought about it. Just don't know where to dump those 200-gallon of oily water afterwards.

I still have about 40-gallon oily bilge water storage in my drum barrel which haven't dump yet. The boatyard people tell me to dump it at the nearby recycling centre but I haven't been yet.
 
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just to give you a different view, another mate cut with an angle grinder a mild steel tank on the side fairly low and there was still a bit of diesel left at the bottom that couldnt be sucked out.
he's still alive (and the boat) :)
Not suggesting to anyone this approach just to stress that diesel seems not to be that flammable
 
Okay. Here is my plan:

I am thinking to buy or custom made 3 to 4 plastic or aluminium small tanks. Connecting each other between the very bottom, and also near the top with fule pipe so they can keep the same fuel level and same air pressure. All inlet, outlet, level sender and vent holes will be on the very outside-accessible one under the closet floor. Each small tank will be heavily glued from the bottom attached to the old aluminium tank so they won't move.

I know this is not perfect. I don't know if this is a good idea or not. But this is the only way I think I could recover some of the capacity of the tank to use. Hopefully recover 60-70% say around 120-140 gallon after done.
 
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Sorry to ask but how can u connect them unless they are open at the top , have you not though about fiberglassing
 
I cut an access hole into an (almost) empty steel tank with a jigsaw. This was done to install an access hatch. The fact is that diesel is not all that volatile. Steel does (can) create sparks when cut whereas aluminium does not.
 
They now do thin discs for angle grinders that are OK for aluminium. Likely the easiest way to cut into the tank. Just put a couple of inches of water in the tank to keep things cool .
 
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Glad you ask. Here is how in my mind:

Assumed three small tanks. Each tank in trapezoid shape approximately size (WxLxH) 60cm X 40cm X 70cm. So, each gap between tanks is around 20cm when all three small tanks inside the big tank. Because the old big tank cut open will be 90cm long, so it will have 20cm extra room for me to put my hands in to the gap to secure the pipe and fittings.

So the procedure is put in the first tank, slide into the empty big old tank, then put the second tank in, secure pipe and fittings, sild two tanks into the empty big old tank, then put the third tank in, secure the pipe and fittings, done. The two 20cm gaps between the three tanks will have a hard object put in them to stop the movement. It could be a piece of hard foam or plastic. I will also pour some glue to the whole bottom of the big old tank beforehand. So that should make it more secure when dried.

I will have to make three tanks prototype by using the cardboard box to verify this idea.
 
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sounds fine in theory but if one of your joints leak and you have stuck everything in you may be regretting this idea and if your pouring the glue before hand wont it be difficult to place your foam and tanks.
 
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