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How many holes up should a Yamaha F90 outboard be mounted on a 1993 Montauk 17?

The installer [of a Yamaha F90 engine on a 1993 MONTAUK 17] only mounted the engine one-hole-up. I thought [the F90 engine] should be [installed with a mounting height of] two-holes-up. I plan to go back [to the installer] and have [the F90 engine] remounted, but I wanted to make sure I’m correct. I want forum advice.

Thanks

Engine mounting height is not a particularly hard and fast rule for all boats, all engines, and all propellers. As a general rule, starting at one-hole-up engine mounting height is a safe practice. You should evaluate how the boat is running now with the engine mounting height at one-hole-up before raising the engine to a higher mounting.

I recommend you test the 1993 MONTAUK 17 boat with the new Yamaha F90 engine mounted one-hole-up on the water and observed the position of the engine anti-ventilation plate relative to the flow of water around the engine gear case when the boat is on plane and running in the upper speed range. Observing the relationship between the anti-ventilation plate and the flow of water is probably the best in indicator of the engine mounting height being proper.

Another good indicator of engine mounting height is the pressure in the cooling water system.

Do you have a cooling water pressure gauge?

Another method to infer the engine mounting height is to observe the top boat speed possible with various engine mounting heights. An indication of an engine mounting height that is too high will be a reduction in boat speed due to too much propeller SLIP.

Thanks for your input - I’m not much of an Outboard engine person.

I was hoping that some other classic Montauk 17 owners may have been down this road before

Any additional insight will be appreciated

Thanks

Please update your email address in your profile.

Moving up to a two-holes-up mounting might be an improvement over one-hole-up mounting, but without testing the boat as it is now configured at one-hole-up mounting, you won't be able to know if the change was for the better or the worse. That is why I suggest you try the boat as it is set-up now at one-hole-up mounting, get a feel for how it runs, and get get some data about engine speed and boat speed. Then if you want to change to a higher mounting there will be a basis for comparison. Since the boat boat is already to go with one-hole-up mounting height, I don't see anything to lose by trying it.

I personally like [engine mounting height to be] three-holes-up, but I would go at least two-holes-up mounting. You can [change engine mounting height] yourself in about 15 minutes using the tongue jack and a block of wood under the skeg.