Motor height

[Dullboy]

After reading http://macgregorsailors.com/phpBB/viewtopic.php?t=3237 and others, It seems the recommended distance from the anti-cavitation plate (top? Bottom?) is approx 1". I used a straight edge and measured mine and it is mounted 1 3/4" below the boat bottom and the top of the anti-cav plate.

Each hole in the mounting measures 3/4" on centers, so I am looking at moving the engine up by one hole. Does this all sound accurate?

In another series of posts, you guys also got me looking at the engines trim angle. I usually just put the power trim all the way down. In looking at the motor height I did notice the trim brought the foot past vertical parallel. I would think this would be desireable at low speed, but parallel would be more desireable at higher speeds. Does this make sense?

Dave

[ALX357]

It was my understanding that the anti-ventilation/anti-cavitation plate was best mounted level with the bottom of the transom/hull corner of the boat. And after moving my motor to that height it finally acheived a highest speed of 17 mph at 4500 RPM, with my 50hp Merc Classic. That was about 2.5 miles an hour faster than at 2" below the transom corner.

[ALX357]

It was my understanding that the anti-ventilation/anti-cavitation plate was best mounted level with the bottom of the transom/hull corner of the boat. And after moving my motor to that height it finally acheived a highest speed of 17 mph at 4500 RPM, with my 50hp Merc Classic. That was about 2.5 miles an hour faster than at 2" below the transom corner.
As for the trim, i just go by the sound of the motor, at any given speed.
If it sounds better, i figure it is doing better. Lotsa factors here, including the immediate balance of the boat, weight aft, or in the cabin, etc. and as crew/passengers move back and forth, plus the height of the motor, plus the prop, etc.

[ALX357]

It's great to have that analysis, and the reasons for those motor height choices. Under the inland lake conditions i usually have, the level placement of the vent/cav plate works fine, but maybe in large swells on coastal waters, or rough conditions, that extra inch of depth would be a factor.
I also assumed ( a** out of you and me, i know, ) that the motor sounds best when it is straining the least, and is running the best ; but that might require more sensory ability than some folks have, to hear and feel the best performance of an outboard. There is a noticable difference in just one or two degrees, and my GPS has confirmed the higher speed when the motor sounds "best".

[Chip Hindes]

that might require more sensory ability than some folks have,

Actually it's fairly easy to detect a motor pitch difference of only a few RPM. Just blip the trim up and down for highet RPM at a given throttle setting.

[Catigale]

Moe - thanks for sharing your expertise on this aspect of motoring

I have never been able to see much difference on trimming the motor (2002 Mercury BF EFI 50 on a ) but I rarely exceed 10 kts on the river

At 10 kts or below, Im guessing I am not on plane, just lifting bow a bit, and so trim adjustments are not that important

Does that gybe with you??

[Moe]

I suspect trimming up at that speed or below is conterproductive and RPM doesn't rise, maybe even falls as the bow rises. It's easy enough to check out though.