After a lot of research with conflicting stories I have a formed opinion but want to offer it as a "straw man"
So, the exam question is if a transom is 23" from bracket height to stern, what length shaft is correct?
I think: the transom is not vertical, the outboard bracket and then the shaft adds distance from the transom. The cav plate is ideally 1" above or below the keel line, or on it. So a 20" long shaft, trimmed right in will be, probably as much as 2" above the keel measured at the cav plate? As you trim out the radius means the cav plate gets lower, i.e it moves to 1" above keel, and then zero and so on before the arc means it starts to rise again?
Am I right to think this?
An xl shaft at 25" while it might feel right as trimmed in will be near perfect, will actually cause drag and maybe produce a rooster tail as you trim out?
After all my research the only think I'm sure about is if it has wheels or a transom there are many opinions and versions of what's right 😄
In an ideal world you would try both shaft lengths and learn from the practical. That's not going to happen this needs a leap of faith so please help
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If you don't like my opinion, I have others.