Having seen your photo I would suggest that you talk to Paul thomason about building a wingsail, I recall discussing this sail system with him when he was working on the Isle of Man he was very keen to use the system on a large scale model.
However I do know that he is very ill at the moment but in the meantime have a look at his gallery and forum listings, he also had a piece printed in model boat mag in november showing his trent lifeboat.