Posts: 3508
Location: Elk River, Minnesota | Hiya,
I have a 4" manual set-back that is adjustable on my 2005 Alumacraft Navigator. I have it up so it sits about an inch or so above the highest bolt hole if the motor was mounted on the transom.
What I saw in doing this was the bow did not jump up as much when trimmed under on hole shot, since the weight of the motor is further back, the center of gravity moves rear ward, making the bow easier to trim. And...with the increased height off the transom, I saw an increase in RPM as well, along with better grip on the water...to a point. The higher you go, the more air that is potentially capable of reaching the prop, increasing prop slip. With the right prop, you will feel like your whole boat is lifted higher out of the water as well...which equates to efficiency and speed.
If you do decide to go with a jack plate, be sure to install a water pressure gauge. Go too high and you could burn up your engine as you lose water pressure the higher you go. My rig runs right about 15 - 16 psi on the gauge where I am at, and have tried higher where it dropped to about 12. I did it one summer and found when air temps and water temps were high, that pressure would drop a tad more...to about 10 and that is starting to run risky. Moved it down a half inch and have not moved it since.
Most boat manufacturers don't carry their warranty to a motor mounted on a jack plate as the further back you move the motor, the weight of the motor puts more stress on the transom. I made sure when I did mine, I considered the largest motor HP it could handle, then found the heaviest motor made in that HP, then did some calculations about how my motor would weigh as compared, being another 4 inches back. I wanted to make sure I was still close to the parameters of the heaviest motor.
Overall, I think they are a nice addition and worthwhile if you like to maximize what your rig can potentially do without going inside the motor.
Install is not too bad if you have an engine hoist and a hoist ring above the flywheel of the motor.
Steve
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