Hi, I am planning to replace the all metal swim platform on my boat with composites ones to save weight.
The current solution is as below from a project point of view, I am asking if it does make sense to build the "C" shaped support in fiberglass (as the rest of the swim platform) glued to the plane VS building it in SS and bolting it to the plane.
The tube connecting the transom and the swim platform is just for adding strength and load balancing and it is not intended to move or shake (even if some vibration can be forecasted).
Thanks

Make sense from what perspective? Cost? Weight saving? Ease of building? Strength? Could be a yes or a no depending on what your priorities are. 

Strength wise, mechanically fastening to composites is never ideal, unless you have designed for it. Simply drilling a hole and putting a bolt and nut through a fibreglass laminate will put stress on the laminate and be a weak point over time. So for me, bonding is better - whether that means bonding the U-section or bonding in a fastener to the fibreglass to facilitate bolting. You could simply bond a SS U-section to the fibreglass using an appropriate adhesive, it wouldn't have to be fibreglass.