Hi Martin,
We had the same problem with our boarding ladder.
When we bought Blythe Spirit our Marine Surveyor said it was not compliant with the latest recommendations for rescue and recovery.
We looked around and could find nothing that fitted existing holes, fittings etc.
Our local Marine fabricators came up trumps using half our existing ladder and fabricating an extension piece.
It is great for getting on and off of the stern especially swimming.
Taylor Engineering is based at Emsworth Marina.
It looks like factory spec!
http://www.marine-stainless.co.uk
Various people have seen it and commented!
Most fabricators could do this mod easily!
I can email some pictures to you when I'm on the boat next. She is still out of the water!
Kind regards
David
Blythe Spirit 285 HS