I recently decided to add a jack plate on my 2006 HP170 with a 90 HP 2 stroke Yamaha. I have only been getting about 37-38 MPH GPS and 4400 RPM with the motor mounted on the lowest holes. When I get to about 2/3 or 3/4 trim, I start to porpoise really bad. Rather than just raising the motor, I thought I would go ahead and get the jack plate. My prop is a 3 blade SS with 19-K engraved on it, but I don't know who its made by. I am assuming I should be getting closer to 43-45 MPH, but could be wrong.
I recently purchased a CMC manual jack plate with a 6" set back. When I received it and looked closer, I realized that I may not be able to install it because of the existing screws that go through the transom. Two screws on each side would get covered by the jack plate. Anyone have any suggestions? Anyone else with a similar boat with a jack plate, and if so what kind?
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Thanks,
Ed