Advice on drilling into gelcoat to attach cup holders

My guess is that the OP has bought this type of cup holder, and I doubt that velcro would be very successful...

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Interesting similar to the ones I made several years ago. I made then removable so can be positioned at several different locations.

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This is a triple for the forward end of my binnacle.

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Do you have a link for those cup holders
 
I have always agreed with Hugo du Plessey that self tappers and GRP do not go together, self tappers cause a degree of delamination, but they seem to have become standard.
If at all possible I drill through a use machine screws and nuts.
That's what I was going to say. If you can get a piece of wood in behind, then you can get a machine screw. Both for belt-and-braces.
 
I agree with all those above who don't like self tappers, imho a pilot hole is essential but it's very hard to get it exactly right so that the gelcoat doesn't crack when the screw is inserted or too big and the screw doesn't hold well. When I can't get to the back of the panel to through bolt something, I generally drill and tap a thread and use machine screws. This works very well unless the panel is really thin. The result is a neat job, doesn't cause cracks in the gelcoat and holds just as well if not better than self tappers and is not much more trouble to go to.
 
I agree with all those above who don't like self tappers, imho a pilot hole is essential but it's very hard to get it exactly right so that the gelcoat doesn't crack when the screw is inserted or too big and the screw doesn't hold well. When I can't get to the back of the panel to through bolt something, I generally drill and tap a thread and use machine screws. This works very well unless the panel is really thin. The result is a neat job, doesn't cause cracks in the gelcoat and holds just as well if not better than self tappers and is not much more trouble to go to.

My stanchions were machine bolts into GRP thread .... lasted about 20yrs ... then started working loose as the threads gave out. Drilled out and fitted brass thread inserts ..... they expand as the bolt goes in.

But TBH - for a cup holder ????

Someone said plastic fail and need replacing often ... well mine have been there for many years and still fold, hold a beer ... been out there in sun, snow, rain, -30C freezing weather .... double sided tape.
 
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