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I am repowering my 1978 17 Montauk with a Yamaha 90HP 4-Stroke and need a Jack Plate for mounting. Mechanic is having problems locating a suitable jack plate that will not require major modifications. Looking for the best match.

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Given the added weight of the 4 stroke, adding a jackplate is not necessarily wise.

Most likely the prior motor was mounted using the blind holes and not the BIA pattern.

Print out this article and give it to the installer. Note you should mount the engine at least 2 holes UP.

Mounting:

http://www.whalercentral.com/articles...icle_id=82

Engine Height:
http://www.whalercentral.com/articles...cle_id=106

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I use jackplates, and I believe the very best one you can buy is by Sea Star Solutions, who bought out the the previous Detwiler brand. These are made from black and silver ANODIZED aluminum, which is important in eliminating the aluminum corrosion problems with most other brands. They are also very nice looking and simple to adjust height.

I have a 1979 Montauk with the same transom configuration as yours. I use the 6" setback, but my in-line 6 Merc engine only weighs 305#, The boat handles this combination beautifully, and with a Mercury Laser II prop, will blow the doors off almost any other Montauk on the water!

I used this particular jackplate in Manual version because it has two sets of mounting holes, 1" apart. This means the two inner holes (vertically) are only 7" apart, and allow the plate to be mounted on the shallow Montauk transom without modification. You can see my installation here:

http://photobucket.com/gallery/user/l...Gc=/?ref=1 the bottom bolts don't show in the photo, but they DO come into the splashwell. See other photos in the album also.

Here is the jackplate, showing the hole pattern:

http://www.seastarsolutions.com/produ...mechanical

With the heavier engine, I would use the 4" setback model only.

However, Phil makes a good point on the heavier engine, and by using the hole pattern indicated, you can save the $400 expense of the jackplate. The engine will automatically be mounted up 2 holes, which should be OK and give good performance. In either case I would use one of those transom stiffener bars across the top holes.

So take your pick as to what you want to do. Here is a close up of the jackplate installation on my Outrage 19, also with a shallow transom configuration:

http://photobucket.com/gallery/user/l...jc=/?ref=1