Tank hatch for uneven surface

[mullet]

My stainless diesel tank has no inspection hatch. I’d like to add two but the top surface of the tank is not particularly flat (it’s is quite small - around 40l - so I assume this is due to stresses when it was welded).

Any suggestions for a hatch design that will seal well, even though it wouldn’t be on a totally flat surface? Would a neoprene gasket be a bad idea with diesel? Try to hammer a steel plate to match the unevenness of the tank top, then bolt it down?

It’s on a sailing boat so the fuel will wash around the hatches when heeling with a fullish tank, hence the need for a perfect seal. I bought some Wema hatches but I don’t think their gasket is big enough or flexible enough to conform to such an uneven surface (and I’m hesitant to cut into the tank until I have a hatch/solution I’m confident will work). Also a bit concerned that the uneven surface might change shape when I cut holes in it…

 

[Plum]

My stainless diesel tank has no inspection hatch. I’d like to add two but the top surface of the tank is not particularly flat (it’s is quite small - around 40l - so I assume this is due to stresses when it was welded).

Any suggestions for a hatch design that will seal well, even though it wouldn’t be on a totally flat surface? Would a neoprene gasket be a bad idea with diesel? Try to hammer a steel plate to match the unevenness of the tank top, then bolt it down?

It’s on a sailing boat so the fuel will wash around the hatches when heeling with a fullish tank, hence the need for a perfect seal. I bought some Wema hatches but I don’t think their gasket is big enough or flexible enough to conform to such an uneven surface (and I’m hesitant to cut into the tank until I have a hatch/solution I’m confident will work). Also a bit concerned that the uneven surface might change shape when I cut holes in it…

this type of hatch seals against the edge of the opening rather than the top surface so less critical of a flat top Inspection port Ø120 mm- universal post for diesel and wastewater tanks

www.solocoastalsailing.co.uk

 

[PCUK]

Fit 5mm steel rings onto the tank and then fit your hatches onto those.

 

[mullet]

this type of hatch seals against the edge of the opening rather than the top surface so less critical of a flat top Inspection port Ø120 mm- universal post for diesel and wastewater tanks

www.solocoastalsailing.co.uk

Thanks for the suggestion. I might be misunderstanding how it works, but I can't see how the bit that sandwiches the inside/outside of the tank would make a good seal on an uneven mounting surface. Does it have a lot of flex, or a thick compressible gasket, or would it rely on using lots of sealant?

 

[Plum]

Thanks for the suggestion. I might be misunderstanding how it works, but I can't see how the bit that sandwiches the inside/outside of the tank would make a good seal on an uneven mounting surface. Does it have a lot of flex, or a thick compressible gasket, or would it rely on using lots of sealant?

As the two parts of the collar are clamped together a rubber sleeve expands outwards sealing against the cut edge of the hole without sealant.

 

[mullet]

Gotcha, thanks for explaining.

 

[mullet]

Update in case anyone cares(!): I cut the hole in the tank and it released some tension and the whole top of the tank ”popped” back into shape and evened out to near enough flat - so the Wema hatch did the trick. Many thanks @Plum and @PCUK for taking the time to reply with your advice all the same.

 

[PCUK]

Serendipity - A happy accident. Perfect.