Charlie:
I mounted Kato Marine davits on our IP27 and sailed them for 8 years. I next moved these same davits to out IP35 and we have sailed these since 2001. Mounting these are easy. I, unlike many other IP owners, simply use large screws an d screw the davit bases into the teak cap rail. I do not see the need for through bolting these and for a backing plate because the forces on the davit bases are fore and aft, NOT lifting up, so screwing down works well. Backing plates and through bolts would be needed if the forces are pulling UP, but that is not the case with a davit base, the forces are fore and aft due to leverage and the pivot point of the top stern rail. That is how I mounted our davits and this has worked for over 20+ years.
As for the top stern rail, the davit supplier will have a top rail clamping fitting and this simply goes around your top stern rail.
The real issue with IPs and davits is that on the older IPs the top stern rail is more aft than then teak cap rail where the davit base will mount. You can see this if you take a boat hook and simply hold it vertical where you want to mount the davit. Now make the bottom touch the middle of the teak cap at the deck. You will see your boat hook will be leaning aft. This is a problem. Now, move your boat hook towards the outside keeping it vertical and you will see the lean is less. What you are looking for is the most vertical position you can find. It may still lean aft, but the more vertical the better. The davits will have more of a less than 90 degree shape and the less the better because of this situation with the top stern rail leaning aft.
One more topic is, extended base plates. Kato Marine makes a davit base plate that will move the bottom of the davit arm aft helping with the vertical issue. If these are needed, then these need to be through bolted and with backing plates because these will loft off.
So, check you stern rail and see where you can mount your davits.
Hayden
