Joe:
The swim platform should be mounted where it will remain above the water when under sail or power. The stern wave on an IP 35 (ie. the black grease line) is your line you should be above. This turns out to be just over the exhaust. That is the place to mount it on an IP 35. I have seen many mounted in different ways. Some with support braces under the platform some with them above. It is all up to your welder.
If I were to ever add one, it would much narrower than most that I see. It would also have top support bars that run down to the outer corners. This way when you lower the dinghy these bars allow it to slide down and past the platform.
So, keep it narrow, maybe 12"-18: wide, just enough to sit on or stand on. Run outer supports to guide the dinghy down from the davits. Make the platform out of fake teak. That's what I would do, if I wanted a platform.
I board from the side, it is lower, easier, and more calm.
Hayden...on IP 35-165 in Stuart Fl heading to Caribbean Sea
