Whilst in my lateral thinking mode, I was pondering on the common problem most of us are experiencing with the plastic seat plugs slipping out whilst we are using our boats.
It occured to me that Mr. Windsurfer had a similar problem when they brought out their first batch of windsurfers in the early 70's. The mast was retained in position on the deck with the means a plastic plug attached to the end of the mast which inserted into a slot in the board. Worked ok but used to slip out from time to time. Solution..
Windsurfer produced the next batch of plugs out of timber being teak I believe. Soon as they got wet they swelled slightly providing a neat firm fit with no more unwanted releases. The windsurfer skins were a plastic and just as slippery as polyethelyne so why arn't we doing the same.
The dimensions of the existing plastic plugs are 17mm diameter by 29mm in length. Not sure if common hardwood dowel comes in 17mm but am going to check tomorrow. If so, drill a hole down the centre and attach using same hardware and problem solved. Could be an idea to do the fix on the hull inserts to beef them up a bit at the same time to ensure the plug holes can take any extra pressure but I have already previously done mine .....Pirate