Hi Mart
Garry may have been referring to an existing boat kitted out with submerged drive, and just interested in experimenting with prop/engine combinations with that set up.
In respect of surface drive versus submerged drive, I don't think it is quite as cut and dry as to which set up is best. Arguably a hull designed for surface drive and set up properly should have significant advantages on oval type courses where sharp turns are not the key requirement.
However consider the BMPRS Championship tables for 2013 and 2014. In the smaller AA and A classes, what boats won the championships for two years on the trot? They were boats designed for and fitted with submerge drive prop shafts. So that perhaps puts a different angle on things.
Danny suggested a couple of potential advantages with submerged drive set ups and I would like to suggest a couple more:
1) For beginners, the lack of the big rooster tail of prop wash makes the boat easier to see when developing one's driving skills.
2) Durability and maintenance: The solid prop shaft in my submerged drive Crusader 3, has never been removed from its tube in two years of regular racing. All I do is apply a little bit of grease through the ball race housing hole, prior to each new run. It doesn't get more maintenance free than that.
All in all though I accept that it is down to personal preference and of course the choice of propulsion may well be dictated to, by what the hull is designed for.
Finally I am interested to know what Garry is really doing with a potential modification....is he trying to up the speed of his B-Class challenger with a bigger engine??
Craig