Boat transom length question

[milenine]

I am likely going to be purchasing a boat this weekend that has a 20in transom. I have measured my motor and it seems to be somewhere between a short and long shaft.... If I measure from the inside of the mounting bracket (where it contacts the top of the transom), to the bottom of the cavitation plate I get 17 inches. The way I understand it a short should be 15 and a long should be 20 when measuring this way. My estimation is that when mounted on a 20 inch transom 95% of the prop will be below the bottom of the transom (bottom of the boat). The motor I am using is under powered for the boat I am putting it on and so I don't think I will even reach "plane" at high speed... the water intakes should be submerged at all times if I am estimating correctly. This motor is also, only a temporary solution until I purchase a bigger motor later in the year. I read on a transom guide that you could be about 2 inches long or two inches short and be fine.

Can any boat experts give me some feed back?
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