Slow to plane and not reaching WOT

[ehenry]

Gentlemen, I have a 14' Monark flat bottom aluminum boat (sorry I dont know the weight) powerd by 2003 Mercury 25 horse classic two stroke engine. The problem I'm having is the boat is slow to plane and will not reach WOT which I've read in these forums is anywhere between 5500 and 6000 rpm's.

With just me in the boat and a 6 gallon tank of fuel, its slow to plane and will only reach about 4500 4800 rpms. I've moved the trimi bar to its lowest setting and theres not much change. Lord help me if I put a standard size (185 lb) friend in the boat along with a 50+ lb cooler.

The prop thats currently on the boat is a Mchigan Wheel. The specs on the prop are: DIA=10 3/8 PITCH=13 . Its a 3 blade prop. I would like for the boat to plane quickly, run with a 300 to 500 + lb. load and reach WOT or somewhere close to WOT.

Also, I understand if I want to stay with an aluminum prop or go with a stainless prop pitch and size may differ. Stainless recomendations will be welcomed.

Thanks for your help.

 

[hwsiii]

Re: Slow to plane and not reaching WOT

Henry, all of my calculations show you should be running a 13" Pitch prop just like you have. Either you have a motor that has a problem or you may have the motor too far down on the transom or both. The anti ventilation plate should at least be even with the bottom of the boat, not below it. If you can borrow a prop of the same size from someone try it too, you didn't mention any problems with it, but something is wrong somewhere.
You need to find the problem before you get a new prop.
I show your motor to have a WOT of 5,000 to 6,000 RPM with a gear ratio of 2.25 to 1, if this is wrong my calculations are wrong so please chek them.
You should be getting full RPM easily, as your boat, motor and you weigh less than 650 pounds. Have the motor tuned up and check timing, as well as when you turn the throttle wide open the butterfly in the carburetor should be exactly level in the opening. Check this and get back with us Henry, and we will be glad to help.
Prop Picker

Prop Change 10"

H

 

[ehenry]

Re: Slow to plane and not reaching WOT

HWSiii, I appreciate your reply. I looked down the throat of carburetor yesterday afternoon and found that the throttle plate was not opening all the way when the tiller grip was turned to WOT. I haven't been able to put the boat in the water since I made the adjustment to fix this so I'll let you know how it turns out.

 

[hwsiii]

Re: Slow to plane and not reaching WOT

PLease do ehenry.

H

 

[ehenry]

Re: Slow to plane and not reaching WOT

Made a bayou run to my hunting camp saturday to prepare my camp house for a flood.

According to the Tiny Tach I have installed I was turning 5180 rpms @ WOT. The boat did get up on plane a good bit quicker than it had been. On the return trip I had probably an extra 130 to 150 lbs of weight in the boat and still got 5130 rpm's @ WOT. Would you drop a notch in pitch to get the 5500 - 6000 rpm WOT or leave it alone?

 

[steelespike]

Re: Slow to plane and not reaching WOT

Check out the Turning point Rascal in 11".Close to stainless performance at aluminum prices.Should give you across the board improvement.

 

[ehenry]

Re: Slow to plane and not reaching WOT

SteelSpike, you say check out a Turning Point Rascal in an 11" prop but ya dont say what pitch.

 

[hwsiii]

Re: Slow to plane and not reaching WOT

Henry, steele is recommending an 11" Pitch prop. But I still find a problem with the numbers. Look at the capacity plate on the boat and tell me the reommended HP as well as weight of the boat and recommended load capacity. Also put a straight board under and parallel to the keel and measure the height of the anti cavitation plate from the top of the board. Something is still wrong and I don't know what. Do this please and get back with me before you purhase a different prop. Also please check the gear ratio of your motor.

H

 

[ehenry]

Re: Slow to plane and not reaching WOT

The Cavitation plate is dead even with the bottom on the boat. The first thing I had to do when I got the boat was raise the engine almost two inches. The gear ratio is 2:25 to 1. I cant tell you what the boat weighs. The spec plate was missing off the boat when I bought it.

 

[hwsiii]

Re: Slow to plane and not reaching WOT

Henry, go with steele's recommendation of the 11" Turning Point.

H

 

[ehenry]

Re: Slow to plane and not reaching WOT

If I choose to go with a stainless prop, what diameter and pitch should I go with ?

 

[hwsiii]

Re: Slow to plane and not reaching WOT

I would go with an 11" pith and dont worry about diameter.

H