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Posts: 10
Reply with quote  #1 
Hello, I have another question. Been running my new alumacraft pro 185 with a 115 g2. I raised the motor two holes A few weeks ago so it’s in the second highest position I’m running an RX3 19pitch prop. Motor trimmed up I can run 5800 rpm at 46 mph. Motor trimmed all the way down full throttle is 5000 rpm. I’m noticing as I trim the motor out and get past about 5400 rpms the motor gets quite a bit louder like the exhaust note is changing. Is the motor too high? Should I drop it a hole or I have a 17” prop I can go too. Also with the motor trimmed all the way out my steering becomes very stiff, if I let off the throttle just a tad or trim the motor down the steering comes back, I’m wondering if the trim tab is coming out of the water.My water pressure is around 22 to 23 at full throttle. I just don’t wanna hurt the motor and it seems to me that maybe I’ve got it sitting too high now but wanted everyone else’s opinion, The anti-ventilation plate is approximately 2 inches above the keel of the boat being measured with a straight edge and a level, this is with the motor at neutral trim

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Michael Lewis 


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Posts: 4,097
Reply with quote  #2 

Clear hi res. video of AV plate running on the water on plane above 4000 rpms at the high lift point and trimmed out to optimum trim and speed.

AV plate to keel relationship is only a starting point for beginning tuning.


Posts: 85
Reply with quote  #3 
Ventilation at 5400 rpm is normal for high mount. Ur almost at top speed and max trim. You don't cruise at 5400 all day more like 3000-4500. As u speed up the water has less time to rise up from bottom of hull and feed the propeller. Therefore your prop will be a little out of water. But at cruise speed your AV plate will be JUST touching the water surface. If u want motor to not ventilate at WOT then when you're cruising ur plate will be bugging down. The choice of yours, want the best ride and economy, handling at slow-mid cruise(rise the motor) Or you can choose the ability to go fast in rough without propping out(lower the motor).

Can't have both ;-) but u can have the 'sweet spot'
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