LM27 new fuel tank Jul 14, 2020 19:03:03 GMT
Post by oceandancer on Jul 14, 2020 19:03:03 GMT
I said I would write this up for general information and now I have, I just hope you will not need it!
I first realised that I had a leak when I began to run down the fuel level in order to clean my old tank. I had been having trouble with diesel bug, a nasty black gunge that collects in the bottom of the tank and threatens to get sucked up and into the first fuel filter - not good. One day after I had run the level well down it became obvious that I had a leak I still don't know when it started or how much fuel was lost. I don't even know where it went!
I now believe that the bug and my subsequent leak were probably caused by the use of DERV or diesel engine road fuel or white diesel. I had been using this as a convenience, just buying a can full every so often and filling up alongside - easy but the problem with DERV is the level of bio fuel in it, currently up to 12%. Bio fuel is the main source of diesel bug and over 150 different organisims have been identified. I have, of course, only found this out with expensive hindsight and internet research. In the USA they have no choice but to use white diesel and there is quite a lot on their forums about diesel bug and GRP fuel tank leaks. It seems that the bio fuel rots the GRP and causes microscopic holes.
After consulting several engineers I determined that the best replacement is a plastic tank made of HDPE ( High Density Poly Ethylene). but how to get the old one out?
I first cut the locker floor just inside the removable FWD locker front that I have fitted, (you wouldn't make this cut if you did not have the locker fronts fitted , it just made it easier in my case ). There is at least 2 inches between the floor and the tank.
I then cut the cockpit floor across the end of the aft locker, across to the engine hatch. I removed the narrow panel created complete with the little hatch.
I then removed the locker floor with a bit a of persuassion and a good dictionary of swear words!
The old tank was then revealed, but how to remove it?
It turns out that the tank is filleted to the hull on the outboard side and on the AFT side. It's almost impossible to get to these areas so I decided to cut the top off the old tank and fit the new one inside. This was quite easily done with an angle grinder. The result you can see in pic 1. It's enormous- like the captain's bathtub!
I could easily sit inside it. Once the top was removed I could, by prising the sides, see that the tank was sitting in about 3 in of fuel which I removed with an oil sucker, where the rest went I do not know! The compartment seems to be sealed all round. I could not see any hole in the old tank.
Now. I don't do great expeditions in my boat and I find it difficult to fill the tank for the winter as you are supposed to do so I decided to have a smaller tank, exactly half the size, or 58Lt. At 5knts my Beta 28hp uses just over 1 Lt/hr so this tank would be enough for at least 2 full days of motoring or about 240 nm.
I had a tank made by TEK TANK Ltd. I had to make plywood templates complete with details of the fittings required.
You can see the new tank inside the old in pic2, not a bad fit, about 12mm space all round which I filled with builders foam and wood fillets. You also need a 18mm wooden floor for it to sit on. The floor also sits on a layer of foam as the hull is curved.
I then built some framing across the aft end to really keep it in place. The result can be seen in Pic3 which also shows it connected up. You can also just see some of the builders foam, You need a new level gauge as the TEK TANK level sender will not talk to the old VDO gauge. Oddly my old tank did not have a separate fuel return connection but instead I have a T into the breather pipe- it seems to work. The new tank has an access hatch and so the locker floor is removable. You need to add an extra bearer at the end of the locker to support the floor. I also cut the floor in half and the unused space is now a locker whiich will accept a 10 Lt jerry can.
It's all now complete and filled with Marine Fuel 100 which is RED and guaranteed to contain less than 1% of bio fuel - I just won't be able to go to Belgium!
Pic 1 The old tank with the lid cut off - the captain's bath tub!
Pic 2 The new tank inside the old one - not a bad fit- notice the unused space aft and the round access hatch in the new tank.
Pic 3 The new tank connected up with bracing. I cut the floor at the cross bearer and the aft section is a locker lid for the unused space