GRP Diesel Tank

[cagey]

Fed up with weld seams weeping on mild steel diesel tank.
Thinking of fabricating new one in GRP, can any body point me in the right direction for guidance,tips and materials. It is fairly complex shape with a variety of pipes of various dias ,guage senders ( 1 electric, 1 mechanical), inspection (cleaning hatch), and fixing points. It is only 120 litres in volume but the only place it will go precludes an off the shelf replacement. The fitting of internal baffles is"baffling" me cant work out how to fix in place.
Remember article in mag ages ago about polystyrene former and building from inside out and then dissolving poly but cant find article,this would seem a solution but don't know the chemistry or risks.
Thanks for any help
Keith

 

[pappaecho]

Had the same problem with a stainless exhaust pot - 28 years old and irreplaceable.
Solution is to use the old item as a patten - I simply glassed the unit. You could do exactly the same with the old tank, using it and essentially encapsulating it

 

[ableseaman]

The fibreglass expert at our yard considers polyester resin to be acceptable for making diesel tanks, evidently they used to be made of polyester resin. I am making a polyester holding tank and will be coating it with several layers of epoxy resin inside and out. You can use the existing space as a mould or make one from 4mm ply and a hot glue gun. Make it in sections and be sure they release from the mould. Baffles glassed in before sealing the top on. New fittings if necessary should seal on. However don't know if Silkaflex can be used with diesel to help seal the tank flanges. Try Silkaflex makers for that info.

 

[macd]

I made a 150 litre GRP tank two years ago. Nigel Calder reckons GRP the second best tank material after polyprop but ahead of stainless steel.

On advice of local GRP expert, it was laid up in polyester, but with an epoxy inner laminate (quite a fine weave, almost like shirt material!), then a flow-coat of epoxy on top of that. Shape wasn't all that complex, but fit was critical, so pattern made in situ, then copied in workshop. The largest face was the curved one inside the hull. I laid this up in situ to mimic the curve, then glassed it to the rest in the workshop. This might work for your unusual shape, but might not. One obvious suggestion: tack the patterns together into the tank's finished shape, then see if you can actually get it where it wants to go.

Baffles: don't use polystyrene -- it dissolves. Your GRP supplier will be able to sell you a suitable foam, or you could simply glass over a piece of plywood cut to shape. The GRP, not the ply, takes the load. On mine, I glassed the top on last, so there was easy access to glass in the baffle. Unless the tank is unusually long, you should only need one baffle for a 120 litre tank. Glass it in under some of the main laminate rather than simply trying to glue it on top.

I fitted a cover from Tek-Tanks for the breather and fuel in and out. This was actually the trickiest bit, because you not only have to create a true face for it to mate to, but also bond in fasteners. I also added another line to the bottom of the tank for pumping out sludge should it ever be needed. The main fuel feed should be located a little above the floor of the tank, and 'point' upwards so it's less likely to scavenge muck or water.

I'm very pleased with the finished job. It has never leaked and should last as long as the boat.

Happy to pass on more info if you wish to PM me.

 

[cagey]

Neat answer thanks everyone
Keith

 

[smb]

Think I remember the article. Didn't the guy make a former out of polystyrene bound together with packing tape or somesuch, glassed up around it and when cured cut an inspection hatch and dissolved the poly out with petrol?

Steve