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post #1 of 11 (permalink) Old 05-27-2014, 04:00 PM Thread Starter
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Prop ?

I have a 20hp 4-stroke Tohotsu on my 1548 grizzly. I cant get on plane with 3/people. Would I be better off switching to a smaller pitch high thrust prop. I tried a whale tail and lost top end and still could not get up. The boat does 20-25mph and goes on plane at 15mph with 1-2 people with 3 11mph.
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post #2 of 11 (permalink) Old 05-27-2014, 04:31 PM
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Re: Prop ?

At what RPM are you running with the present prop. Getting on plane has to do with many factors. Balancing your load, angle of your motor in reference to the transom, weight of the boat and all equipment, including personnel are just to name a few.

Does your motor allow for angle adjustment and is it properly set up for your boat? Is the anti-ventilation plate of the motor within an inch of the hull (bottom of the boat)?

Pitch of the prop ensures that the motor is running in its optimum rpm range, it has nothing to do with getting on plane.
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post #3 of 11 (permalink) Old 05-27-2014, 04:48 PM
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Re: Prop ?

Not sure what you want. You said it gets on plane at 15mph with 1-2 people and with 3 people at 11mph. assuming you have those numbers switched you are getting on plane. if you have too much weight forward it will affect getting up and as ststes, the angle of the moter has an effect as well. Before I messed with the prop I would trim the motor differently and see what happens.




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post #4 of 11 (permalink) Old 05-27-2014, 04:58 PM Thread Starter
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Re: Prop ?

It doesn't get on plane with 3 at all and my goal is to get to plane with 3 if possible. I would give up top end 20-25mph 1-2 people if I could get 15mph with 3 by switching to higher thrust prop with the added weight.
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post #5 of 11 (permalink) Old 05-27-2014, 06:20 PM
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Re: Prop ?

Well, you will lose top end speed with more weight. Where do you usually sit the third person? If this person is sitting near to the bow of the boat it probably doesn't have the power to plane where the individual is sitting. Try moving the passenger closer to the stern of the boat. This will shift center of gravity and allow the boat to rise on plane.
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post #6 of 11 (permalink) Old 05-28-2014, 04:35 PM
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Re: Prop ?

Quote:
Originally Posted by scottm2012
Well, you will lose top end speed with more weight. Where do you usually sit the third person? If this person is sitting near to the bow of the boat it probably doesn't have the power to plane where the individual is sitting. Try moving the passenger closer to the stern of the boat. This will shift center of gravity and allow the boat to rise on plane.
I'm sorry scott, but that's entirely wrong. The more weight you put in the stern of the boat the harder it is to plane out. If you want to plane out easier/faster put as much of the weight in the front of the boat. I'll give you an example. I had a 21' Starcraft center console that I used on Pymy a few times. With the 9.9 pushing it I could only get 5mph out of it with two people sitting behind the console. If I had my buddy sit on the deck up by the bow I could eek 7.5mph out of it.

First thing you will need to do is find out the RPM's of the motor with both 2 and 3 people in it. Problem is if you just drop the pitch you might be fine with 3 people in the boat, but with 2 you might over-rev the motor. Trouble you have is you're trying to do too much with a limited amount of horse power. You might have to sacrifice something. First thing to do is find a tachometer so you can read the RPM's. There used to be some cheap ones online for like $20.

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post #7 of 11 (permalink) Old 05-28-2014, 05:33 PM
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Re: Prop ?

Trapjaw, you're talking top-end speed after planing. I'm talking about getting the boat to plane. Shifting center of gravity is key. I stated,
Quote:
"Where do you usually sit the third person? If this person is sitting near to the bow of the boat it probably doesn't have the power to plane where the individual is sitting.
You would insist moving that person more forward? If the boat is plowing, moving the weight more forward would just make the boat plow even more. I intend for him to move the weight further aft to get the bow to rise.
I'll agree he has limited horsepower, but on my Wagemaker Wolverine, with a properly configured 18 hp motor, I can get the boat to plane with three individuals and their fishing equipment and top out at 12 mph with center of gravity slightly aft.
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post #8 of 11 (permalink) Old 05-29-2014, 03:20 AM Thread Starter
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Re: Prop ?

My factory prop is a 3 blade 9.25" x 9 pitch. I smacked it up on the Ohio river and tried a 4 blade 9.25 x 10 Solas for more speed and better hole-shot. I don't think it helped much on low or top end. I tried a whale tail to try and help out and lost too much top end and still not a good start off. I understand now how important rpm at full throttle is but don't have a tester. I have read that I might need to have different props for varied situations.
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post #9 of 11 (permalink) Old 05-29-2014, 11:36 AM
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Re: Prop ?

Sorry man but I believe you're just reaching the outer limits of your boats capabilities with 3 people onboard. Switching props is not going to give you the performance you desire. The only way to acheive that is more HP.

3 people, a four stroke outboard, and all your other gear has to be pushing the weight capacity of that model boat. I have a 1648 Grizzly and it would be close on mine, and your boat is shorter.
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post #10 of 11 (permalink) Old 05-29-2014, 02:16 PM
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Re: Prop ?

There is some good information here.

Your motor should be able to handle (at least get on plane) three people.

In regards to your four blade prop. If the 9.25 x 9 is the proper prop for your motor, when going to a four blade you should have decreased the pitch to a 7 or 8, not increase. Tohatsu suggests a 10 x 7 4 bladed prop for a heavy loaded boat (which I would agree your boat is heavy).
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