Oz'

Loose from compression?

You're asking the right question. I do believe that is what makes the
bolts on a bolt on keel come loose. I believe that compression on the
fibre glass causes it to take a permanent set (Even if just sitting on
the hard) This set gives the, bolt on, the ability to work (Move)

On my past boats I found this to be true. I installed packing under the
washers before torquing. It gave me a dry hull but was never sure of the
bolts outside the hull and the moisture penetrating the fibre glass on
the drilled holes?

Ole Thom