Biffer has very kindly been repairing the knees on Exodus, my Tohatsu 7.1
Not sure exactly when/why/how the cracks appeared, see here for pics - post 17 http://rib.net/forum/showthread.php?t=33109&page=2
My view was that although the cracks were small they weren't going to get any smaller and I really didn't want to loose the transom and engine into the oggin. They were spotted after a run out across Poole Bay, there were 6 of us on board but it was a calm day. Probably the accumulation of damage over many trips and one too many hard landings.
Biffer described how the original build process (read cost management) probably contributed to the inevitability of this sort of damage. Principally that the knees are a seperate piece of wood from the stringers. This leaves a join which would be inherently weaker than if made from a single piece, but much cheaper to build.
The solution Biff came up with was to remove the GRP on the knees all the way down to the hull, past the stringers, double up the knee, but connecting it directly to the stringer. The only problem seems to have been that one of the knees was wet.
Looks like he's nearly finished an excellent job and I might get to see the fireworks at Cowes this week, weather permitting.