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I just repowered with a 2016 Suzuki df90a, stainless propeller 14"x18", motor was mounted on the first hole. I am half way through the break in period and I am starting to question the position hole that the dealer selected. At WOT 5900 rpm I am seeing 32 mph with a moderate chop and a following sea. With a head sea an a moderate chop the boat planes fine however at cruise 4000 rpms, the rpms will start to gradually drop. The cavitation plate is under water while the boat is planing. Any advice ?

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The first hole doesn't tell us the whole story.
1st hole from the top or from the bottom?

See this FAQ:
http://www.whalercentral.com/articles...cle_id=106

Your motor is mounted too low.
2 holes up is more of a standard starting place these days.
All the way down is like dragging and anchor.

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Joe thanks for the quick reply. They mounted the motor first hole from the top .

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OK.
So from the link I gave you, the motor is mounted all the way down.

The motor needs to be raised up.

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Go two up and test!
TP

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I will tell the dealer when I see him next week , thanks.

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Lolas -

Warning: The dealer will often tell you "this is the way we mount the motor, we have been doing this for years. etc.

This is WRONG.

Each boat brand and hull is unique and engine mounting can be different.

The member based recommendation for Boston Whaler hulls is mount the motor 2 or 3 holes up. If unsure, start at 2 holes up.
E-TEC's are unique and they should be mounted all the way up.

Top bracket holes

0 - Bolt here is "all the way down, motor resting on transom
0 - 1 hole up
0 - 2 holes up
0 - 3 holes up

Once the engine height is properly set, the proper propeller can be set.

In reading your performance report I can see that the current prop is not appropriate. Have no fear. We can help you.

Fix the engine height and report back.

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I have the same motor an prop on my Montauk.
One hole up and close to 40mph and 6200rpm if I remenber correct.
I think I could raise it one more hole.
3 holes up is too much I think.
See last pictures in my personal page.

It's a question of how much distance between anti cavitation plate and the bottom of the keel when parallel.
1-1,5 inch I think is best.

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When suggesting engine mounting heights on a Forum such as this, it is important to remember that not all engines, even within the same brand, have the same vertical dimension between the top bolt hole and the anti-ventilation plate. in spite of all being labeled 20", 25" or 30". Even centerline dimensions between the prop shaft and anti-vent plate can vary in gear case design between brands.

There seems to be enough experience here with the Evinrude 90 E-tec installed on a classic Montauk that the mounting height can pretty well be indicated. it appears that Evnirude uses a longer gear case, requiring more installation height. But with other brands, actual experimentation and visual sighting is the best method. Even gearcase design matters.

For many years of outboard history, Mercurys have always been recognized as the fastest engines. I believe one of the way they accomplished this was by intentionally making "shorter" mid-section designs, thereby automatically raising the engine prop center over what the competition bolt hole pattern would indicate, and hence reducing gearcase drag. As an example, I have noticed that my classic in-line 6 engines have a "short" mid-section length. Hence a lesser hole mounting height still gives a surface piercing prop location. On these older Mercs, mounted on a Montauk, the third (middle of five) set of holes is all the propeller will tolerate, even with a performance prop like a Laser II. Yet all of the time we are hearing here that an E-tec 90 has to be up all the way. The Evinrude evidently has a "deeper" mid section dimension.

The other thing I have noticed is that the so called "Big Foot" gearcases are about an 1" longer than the regular gearcases. Hence Bigfoot engines need to be mounted higher.

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Edit: I think I must have 40mph + at WOT as I had 41mph with the aluprop.

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I too have a 1996 Montauk and just bought a new Suzuki DF 90. I am curious to see what the outcome is when he talks to his dealer on Thursday. Would like to get this resolved before I bring the boat in for engine install. Right now I'm leaning toward the 2 holes up.

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I was thinking of raising my engine this spring.
I think there are some differences in the transom on Montauk models. I have a 1988 with an ETEC 90. Is there a visual way to eye up the prop hub or cavitation plate in reference to the keel to judge the correct height (although I will not be near my boat for a few more months).
A photo of an ETEC lower unit on a Montauk model similar to mine might be a help.

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@LolasG Please let us know how it worked out if you test to raise the motor.

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You want the cav plate about 1" above the keel of the boat.

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I'll get back to the boat next month. an old photo I have looks like the plate is higher but hard to tell because the motor is tilted some.

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https://www.dropbox.com/s/i9b9cqsfdf9...2.jpg?dl=0

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Action- The motor appears to be one hole up. You should go up at least 2, if not 3, since it is an E-TEC.