'Blind' fixings for a steel inspection cover - ideas wanted

[tinnews]

One of the jobs I need to do on our recently (recently, over a year ago now!) bought boat is to sort out the fixings on an inspection cover in the bathing platform.

The cover is an, approximately, 2ft square steel plate on the top surface of the bathing platform. The bathing platform itself is essentially a 1ft deep (or a little less) box welded onto the back of the boat. The previous owner's intention was to use this as a 'black water' tank though his hasn't been done yet.

Anyway, while I was 'exploring' our new boat I took the cover off, this was an exercise in frustration because the bolts holding it screwed into nuts welded onto the inside of the bathing platform and were badly corroded. About two thirds of them came out, a few sheared and three or four broke the welded nuts off inside the platform and I had to use various crude methods for removing them.

So, I'm after a better (as in less likely to cause similar frustration) method of fixing the cover. It doesn't have to provide great mechanical strength but it does need to be able to pull the cover down tight so that it's watertight, though flooding the bathing platform wouldn't endanger the boat at all.

Welding stuff inside the bathing platform would be very difficult but bolting 'things' of some sort around the hole would be quite possible. Does anyone have any suggestions for either stainless steel fixings of some sort or maybe even plastic ones?

[Harry Bloomfield]

[e-mail] expressed precisely :

To avoid the need to weld the nuts on the inside....

A steel ring with stainless nuts welded to it. Fix that in place, inside the tank, with countersunk screws. The later only need to retain it, long enough to get the main bolts started. Then stainless bolts to fix the cover in place. Hopefully the hole is other than round, to allow the ring to be lowered into the tank?

[Steve Walker]

If it was round, then simply cutting out the section between two bolt holes would let it be rotated or sprung in wouldn't it?

SteveW

[Harry Bloomfield]

That would depend upon how much the sealing plate diameter, over-laps the bolt hole diameter by.

Alternatively, perhaps the ring with the nuts welded to it could be split so it could be 'wound in through the hole'.

[tinnews]

Yes, that would certainly work, I'll need to develop my stainless steel welding skills but that's possible.

[tinnews]

It's not round, it's square, so that's not an issue. :-)

[MuddyMike]

Just cut some short lengths of flat steel stock, drill a hole in the centre, weld a stainless nut over the hole then countersunk screw or rivet the plate on the underside of the fixing point. Its quite easy to mig weld stainless nuts onto steel plate with steel welding wire.

Mike

[Roger Mills]

How about stainless steel Rivnuts - such as

- and stainless steel countersunk setscrews to screw into them and hold the cover on?

[Andrew Mawson]

provide

bathing

possible.

fixings of

If it is used for 'black water' in the future don't underestimate the upwards force on the hatch when the boat pitches and the weight of water is flung upwards onto the hatch.

AWEM

[tinnews]

Yes, they're definitely a possibility, only issue is cost as the tool to insert stainless rivnuts has to be quite a meaty one.

[Andy Dingley]

If you only have a few to do, you can do them without the tool. Use a heavy dolly as a backing bar, and a small ball pein hammer to set them. You can also use a cheap rivnut tool (well worth having) to set them just enough to stop them falling out (or even superglue), then the hammer to finally set them.

Watch out for dissimilar metals though, if it's an electrolytically active environment. Any nearby aluminium could become a problem.

[tinnews]

OK, thanks for the ideas.

It's all steel, and the boat will be in fresh water by the time I do this.