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Just bought a 1978 Montauk 17 that I re-powered with a 2010 Yamaha F90. The Yamaha dealer's certified technician is concerned that the engine is too mounted too high, as the anti-ventilation plate is about 2-3 inches above the bottom of the transom. He has the "upper" bolts in the bottom of the four holes and feels that he can't re-position to one of the higher of the four holes, because the "lower" bolt is right at the bottom of the splash well.

1) Have any of you Montauk owners attempted to mount a Yamaha F90 and come across the same issue?
2) Would you know if the "lower" bolt holes on the Yamaha are elongated, allowing the bolt to slide up or down, as the "upper" bolts are repositioned into different holes?
3) Any recommendations on the prop pitch etc.. for this boat/engine combination? Dealer said he's putting a SS prop on, but I'd love to hear input from guys that know...

(Edit to add photo)

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You will probably need to drill 2 new lower holes in the transom.
You will need to drill the "Green" holes in this diagram.
https://www.whalercentral.com/article...icle_id=82

See this members documentation on our site here.
This is on a 15' hull but the same applies to your boat.
http://www.whalercentral.com/userphot...lbum_id=64

Your technician is right on letting you know his observations.
I think they will see what the outcome is from those diagrams.
The motor these days is more efficient mounted 2 holes Up:
https://www.whalercentral.com/article...cle_id=106

Maybe print those diagrams out and take them to them.

There have been Hundreds fo thousands of motors mounted on Whaler hulls.
Most of the motors only have 4 holes to mount them in from 3/4" apart.
So, if it is mounted all the way down, or all the way up, you only have 2 1/4" of adjustment one way or the other. In the old days, it was all the way down.

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1979 Montauk 90 HP Yamaha 4 stroke.

Engine installed in 2004. It has the bottom hole of the 4 and the second from the top.

2019 Installed new 90 HP 4 stroke Yamaha. Bolts installed same location

X
X bolt installed here
X
X bolt installed here

Prop is stainless steel SOLAS 3 blade 13 1/2 X 15 Dealer stated I could go as high as 17 if I wanted more speed.
I am happy with the 15.

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Thank you Joe. I cannot tell you how valuable it is to have guys like you being willing to share your knowledge with new Whaler owners such as myself.

Sincerely,
-John Lipaj

(Edit to add photos)

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I have mine mounted all the way up and it performs just fine. Try it with a 17" prop.

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The existing holes are not in the standard BIA locations.

What is the exact measurement of the anticavitation plate above the bottom of the keel.

Use a straight edge and measure.

Report back.

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Phil, Will try to get from the dealer. I'll get back to you. Thanks,

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I installed a Yam 90 4S in Feb. with the same top hole shown above. Dealer plugged two existing bottom holes and drilled two new however the bottom engine holes are at the top of the slot on the engine. (Effectively, I can only raise the engine) 1988 17' Montauk. There's approximately 1" between top of transom and engine. I'm running a Powertech SCD3R17PVM90 prop and am very happy with the performance. Let me know if you want a picture.

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Phil et al....that should be fine. That does not look too high. I would try the 17" however. If it slips when nailed like a 6k torque convertor, probably too high ;) When you can see the PTnT motor, now you are getting up there.

Biggie's setup:

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Cubby,
Your motor is mounted all the way up.
Top bolt is in bottom hole of the top bracket.

With your setup you cannot lower or raise the motor.
As biggie mentions, his works fine all the way up, so if your setup works fine then I would leave it the way it is.
However, If you need to lower the motor one hole, then you would need to drill the "Green" holes at 6 1/2" below your top holes as shown in the drawing.

At this point, your lower holes appear to be 5 3/4" below your top holes? and you are stuck there for now, all the way up.

Let us know how you come out.

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And???

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Last night was the first opportunity to test the boat with the engine moved down per Joe and Phil's recommendations. The anti-ventilation plate is now level with the bottom of the transom and we used a 17" aluminum test prop.

With 350 lbs of "people" on board everything felt good and we were hitting 35-37 MPH for brief spurts (Lake Erie has a 3-4 chop last night).

The only issue, is that the boat is leaning to port. The engine is mounted exactly in the center of the transom, so that isn't causing the problem.

The Yamaha dealer is moving the battery from the port transom corner, to the console today and we'll re-test.

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Might need to tweak your trim tab above the prop(zinc anode sometimes).

How did you lower the engine? Why did you lower it too far?

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When the dealer mounted the new engine, the anti-ventilation plate was several inches above the bottom of the transom, which he felt would be a problem. So he folllowed the replies from Joe & Phil (see thread) to re-mount to the right height. Basically, didn't mount a bolt through the single lower bolt hole, and is now using two bolts per side, in the upper four bolt holes.

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Ok...I might have tried it out first but if you are running in 3' chop, an engine that high would not be ideal. I would no try and raise it about 1.5" above keel. If the battery does not improve your list. Adjust the skeg above your prop if it has one. Yamaha usually does.