Bertram props

Curious why you are only running at 1700 rpm? Are you not making rated rpm at WOT? Isn’t an 80% cruise on your 892’s more in the 1900-1950 rpm range?

Do you know the diameter and pitch of the wheels?

One of the most over looked issues on old boats is the old props that come installed.
No history, no data, no idea if correct or knot.

During the 80s, I remember two purchases of old boats and was not happy with either's performance. Come to find out the props were so old and fixed so many times, the blades were thin and a lot of the diameter was missing. Fresher props, same pitch, thicker blades, more diameter, suddenly better performance.

Then on a friends boat he purchased the props were over pitched. The PO thought it would help on slower RPM cruising. Removed the pitch, then speed, RPM, economy then increased and engine-exhaust noise went aweigh.

Sadly, Factory support is gone to help ensure your running the correct wheels to start with. You can try the next best thing by contacting https://www.hightidemarine.cc/index.htm if they have any factory data.

More blades do not always increase performance. Working with a real propeller shop may help guide you in this matter.

A good, well respected prop shop will get you real close. How clean is the bottom? On my old boat I blasted years of old paint off and gained noticeable speed. Along with new wheels I was able to pull back 300 rpm and cruse at the same speed and Not opening the secondary's on gas engines. It took a couple of tweeks on the cup but was able to nail the WOT. At 750 hp you shouldn't have a problem cruising at 21,22.