Strange Leak

[CaptMick]

Since you have not said that anything was done to the boat since it was built I will suggest one odd thing to look at. Check if the transom flexes at the bottom where it meets the hull. I ran an I/O boat commercially that looked fine at rest in the water and did not take on water but when we were under power the transom flexed and let water in at the bottom of the bilge. You could look in the engine compartment as you throttled up and see the water start to come in.

But I agree with Chuck and Jon as well.