I have a 1973 Steury very very solid and clean boat that is missing a motor it is rated for a 100HP I have a 115 Evinrude 4 cylinder that runs great about the smae year. If I put it on this boat will I break the transom most likely or will the boat most likely survive whatever size weight difference their might be and the extra 15 ponies. I am between it or trading it off for something a bit smaller my boat is a 16 footer thanks for any help
BUT - and there's always a BUT - keep in mind that having more power than the boat is rated for can invalidate any insurance you may have on the boat and may make you liable in the event of an accident.
Also, your boat is nearly 40 years old and although you describe it as solid, be VERY sure it is structurally sound. The weight of the 115 may be similar to that of a 100, but it puts a bit more torque on the transom.
AND, depending on the state where you live, can be an issue with DNR Enforcement Officers. If your outboard exceeds the BIA plaque, Georgia gets an instant attitude! (I've heard they'll impound your boat as being "unsafe"!)