Stainless inserts

[Ruffles]

Hiya
Got the old dinghy in the garage for a little tlc. Am replacing the steel strip attached to the keel that lets me motor up concrete slipways and pebble beaches

It was 5mm x 15mm galvanised steel. It's been there for 20 years so not much left. So planning on replacing with 3mm x 15mm stainless. And Sikaflex. However all is not as it seems! How unusual!

What I thought were screws into the GF turn out to be 30mm countersunk SS bolts. About 4.6mm diameter but not M5. Thread pitch around 1.1mm. Proper job. Academic though as the inserts they were screwed into seem to have been brass. And largely dissolved.

The holes in the GF are 10mm diameter but open into a damp void. I reckon the GF was laid over a wood keel with brass inserts set into it. The wood has gone. But the GF is a good 10mm thick minimum.
Can I buy stainless inserts to fit a hole that size? They would need to go in the hole not on the surface. Presumably M5 bolts.

 

[Ian_Edwards]

Yes, you can get SS inserts, basically two types, one with a course tread designed to be crewed into wood, but could be use on GRP. The second has fine thread and I normally tap the hole, so they are good for metal and GRP. If the holes are 10mm then you could tap them with an M12 tread and fit an insert, for an M8 setscrew. Which might be too big for what you want.
Try searching for threaded inserts.
eg
https://shop4fasteners.co.uk/fasteners/threaded-inserts.html

 

[lw395]

I think I'd just fill the holes with a glass/epoxy mash and use self tappers?
If you're running up pebble beaches, consider putting a wooden rubbing strake on the keel, then adding your stainless strip to that, it will raise the GRP bottom away from the pebbles and save a lot of wear.