This boarding platform on the transom of a R43 is made from 2" aluminium pipe with an aluminum mesh welded into it. It is pulled up by the lines and tied up on long passages or when berthing in a tight marina.

A truly magnificent job on a fold up boarding platform on Donald's NY46. Able to be lowered and raised by one finger this platform folds flush into the transom. Note the ladder that swings down when the platform is lowered to facilitate easy boarding after swimming and then rests on the transom to allow easy boarding when in the up position..

This boarding platform has been built into the transom of a R310. If your design has a negative sloping transom then you could well consider incorperating this idea into your vessel while in the building stage.