Sika has a special goo for that. Read the instructions carefully. Both surfaces need to be prepared and primed with the right Sika Primer. Seal failure here is in most cases do to not preparing properly and/or not priming.
I note that in places there is a gap betwean the hull and my iron keel. Should this be filled/made watertight. I guess that sea water could affect the junction of the stainless bolts and the iron??