Mick, I don't see a reason why it wouldn't work on a shaft drive boat if you can find clean water to site it in. If it were me I would be looking to fit it inside the boat somewhere away from the prop. You can fit a transom mount inside the boat to shoot through the hull by using something like plumbers mate initially to see where it works best. When a good place is found you can then fix permanently with a pack glue or in a bath of cheep cooking oil. The most important things when fitting are: clean water, no air between the transducer and the hull, and fixing the transducer upright.
Others will probably have more ideas on how to fix internally
Martin