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  1984 Outrage 25: Maximum Mounting Height for Twin Engines

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Author Topic:   1984 Outrage 25: Maximum Mounting Height for Twin Engines
russellbailey posted 03-28-2014 12:39 PM ET (US)   Profile for russellbailey   Send Email to russellbailey  
My 1984 Outrage 25 has twin 25" Optimax 150s (2006) on the original 20" transom. The prior owner had Cook jackplates installed and the motors were mounted as high as possible on them, but likely still a bit low looking at the motor plates when running - I've never come close to loosing grip with the Rev4 propellers.

Largely for fun and to experiment, I've replaced the Cook jack plates with some high rise jackplates from Hydrodynamics. These jackplates already have a built in 5.375" verticlal offset in them, and 4.5" of travel available above that. They also are easy to adjust from the boat. See http://www.hydrodynamics-usa.com/ . These are not custom for my boat but were a leftover pair that Steve had from a production order. They are 10" setback and powder-coated.

So now I can really play with how high the motors can go. I am familiar with comments by Tom Clark that at least on a single engine Boston Whaler, that you will loose grip well before you have any concerns about adequate cooling water. And I've seen comments from Larry Goltz that a twin engine boat cannot take as high a mounting as a single engine.

Tom, does your guidance about loosing grip before cooling problems still hold for a twin engine setup? [I've confirmed it does on my Striper 15 setup playing with height]

Any guesses for how high above the bottom of the hull at the motor centerline is appropriate?

I'm not aiming for max speed, but instead appreciate shallow draft and the ability to be able to do more adjustment of the motor trim angle than I can now (I get porpoising fairly easily with only a small amount of trim).

Teak Oil posted 03-28-2014 01:38 PM ET (US)     Profile for Teak Oil  Send Email to Teak Oil     
If you are porpoising you are most likely too low. Since Tom gets close to 50mph at top end with his twin 150 OUTRAGE you should be getting close to the same.

If you are nervous about raising the motors too high just go in small increments you will not hurt anything. It will start to ventilate in tight turns and rough water well before you lose cooling pressure

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