Motor Height

[jherchel]

I have a 98 crestliner 1750 tournament pro with a 115 merc the prop is 9 inches below pad does anyone know how far below pad I should be running.
I am only getting around 4600 RPM's. Top speed is 40 MPH. Prop is aluminum and 23 pitch. I can only raise the motor about another 1.5 inches.Should i get a jackplate.

Jim

 

[steelespike]

Re: Motor Height

You measure motor height by the antivent(cavitation) plate just above the prop.Even with the bottom (pad?) is considered a starting point.
Correct height is with the least motor in the water without venting (cavitation) problems.Be sure it pumps water.23 is too much prop I think you need to be around 19" that should put you at about 5,400.Check out the Turning Point Hustler props ,stainless performance at aluminum prices.

 

[11rufus11]

Re: Motor Height

One of your problems is you are over propped. A 19 pitch stainless prop would probably be the optimum prop and a good starting point anyway. A 17 pitch may even work out best. You will get a better hole shot and less stress on the motor. I believe that Merc should run at least 5500-5600 rpm at WOT for the best performance. But first get the height of your motor correct and get the motor and carbs tuned before you worry about that.

 

[hwsiii]

Re: Motor Height

If I knew your lower gear ratio and the WOT manufacturer recommended RPM, I could be more helpful.

H

 

[jherchel]

Re: Motor Height

If I knew your lower gear ratio and the WOT manufacturer recommended RPM, I could be more helpful.

H

My lower end gear ratio is 2.07:1 and Max RPM is 4750 -5250.

 

[hwsiii]

Re: Motor Height

jherchel, Steele and rufus are giving you very good advice. I find your slip is at 17% and normally with aluminum should be about 11%.

I agree with them you should be running a 19" pitch prop. If you buy the same model prop you have now, you should have a speed increase of about 4 MPH and RPM about 5300 and much better acceleration to higher speeds.

Hope this helps.

H

 

[Sandhammaren05]

Re: Motor Height

4600 RPM is too low. How high is the cavitation plate above the bottom of the boat, and how much offset is built into the transom? With a good enough power/weight ratio and a bottom with little or no hook, the more offset the higher the motor should be set on the transom.

I have a 98 crestliner 1750 tournament pro with a 115 merc the prop is 9 inches below pad does anyone know how far below pad I should be running.
I am only getting around 4600 RPM's. Top speed is 40 MPH. Prop is aluminum and 23 pitch. I can only raise the motor about another 1.5 inches.Should i get a jackplate.

Jim