outboard mount height

[tbag]

Well I wanted to share something pretty cool that I did with my boat last week. it is a 89 22' cruiser with a new this summer to me 05 yamaha 90 which I installed myself. I have been very pleased with how easy starting, efficient (~4mpg at 4700 rpm at 25mph) and quite this motor has been and thought that all was good.

I took it into a local shop to give a 300 hr check up and the mechanic asked what my WOT RPM was. It has been 5700 with light boat and 5500 with full boat both doing easily over 30 mph, which I though was just fine and dandy. the mechanic said I should be up near 6000 when I am light and 5700 when I am heavy, and suggested a new prop.

When I bought the motor I also bought a new solas 13.5x15 prop for it and a permatrim on the advice of every one here. So I really did not want to but a new prop. Instead I raised the motor up one hole to bring the top of the AV ~1" above the boat of the hull. just below the bottom of the plug hole.

this last weekend I went out hunting with the boat with two friends just for the day. We had the raft on top of the boat and enough stuff for the day, so I would say a medium load. Conditions where great SE 10knt wind 1-2 foot seas. Well I got ~4.25 mpg at 4800 rpm doing 26 mph going out and same speed but ~4.33 mpgs on the way back. WOT was 5900 doing 34.5 mph!!! and the hole shot and motor spin up was much faster.

This is just one data point and performance may suffer in rougher water but damn that is a great improvement. So everyone check you engine height, it may get 6-9% improvement to your speed and efficiency.

[Chester]

I suspect mine are mounted too low. I can only go up one hole the way the transom was drilled. Might be a good winter project.