Boat transom length question

[milenine]

I measured it just like in the link you posted and I get just over 17 inches. My prop is much further down from the cavitation plate than in the picture in the link, which is why the prop ends up below the bottom of a 20in transom. I read that the cavitation plate should be nearly level with the bottom of the transom, but could vary 2 inches in either direction. I definately don't want to ruin the motor, but if this motor will work for trolling around this summer I would be happy. It isn't going to go fast anyway, it is just a 5hp on a pretty large boat. 1-5MPH is what I am looking for.
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