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Props, 3 blade vs 4 blade
- Thread starter rcwass
- Start date
I was able to put my boat in the water for the first time last Friday. With all the heavy rains there has been loads of debris in the river so I've waited for the waters to clear. I ran my 22' C-Dory Cruiser, 70HP 2 Stroke 1990 Johnson at WOT. I got 4700 RPM and after playing with the trim the best I got was 5000 RPM. I still have the original prop on my boat, a 13.25 X 17 Prop. I'm using a lot of gas. I'm told that I should switch to a 13 pitch prop, a 13.75 X 13 to be exact. i normally run my motor at 4000 RPM which means with a 4700 RPM WOT I'm running that motor hard and using more gas. Is this right and is this change a good change?
Thanks for all of your responses.
Dick
Thanks for all of your responses.
Dick
rcwass-
You'll never really know until you try it!
However, since you're contemplating going from a 17 inch prop to a 13, and each inch of pitch ='s approximately 200 rpm (oversimplified rule of thumb). 4 inches of prop pitch should equal 800 rpm, and 4700 + 800 ='s 5500, which is about right, since your motor is rated for a max rpm range of 5000-6000 rpm.
As pitch comes down, diameter is raised to get more bite, because the lower pitched props are used for heavier boats and/or loads. A 1/2 inch increase in diameter seems reasonable and is in the stanbdard range for a 13 inch diameter prop.
Sooner or later you're going to have to put it to the test and see how it performs.
No one can exactly predict what will work and exactly what will be the best or ideal solution. Too many variables exist between motors, boats, loading, atmospheric performance conditions, and even your own preferences between top speed, hole shot, cruising speed and mileage importance.
And you'll never really know if there just isn't another slightly different prop that might be just a bit better.
But go ahead and give it a try!
If it performs well to your satisfaction, you're good to go.
If you want to find the perfect prop, find a dealer with a big inventory of alternative props on the shelf that will let you try them out and make extensive measurements until you're satisfied.
Good Luck!
Joe.
You'll never really know until you try it!
However, since you're contemplating going from a 17 inch prop to a 13, and each inch of pitch ='s approximately 200 rpm (oversimplified rule of thumb). 4 inches of prop pitch should equal 800 rpm, and 4700 + 800 ='s 5500, which is about right, since your motor is rated for a max rpm range of 5000-6000 rpm.
As pitch comes down, diameter is raised to get more bite, because the lower pitched props are used for heavier boats and/or loads. A 1/2 inch increase in diameter seems reasonable and is in the stanbdard range for a 13 inch diameter prop.
Sooner or later you're going to have to put it to the test and see how it performs.
No one can exactly predict what will work and exactly what will be the best or ideal solution. Too many variables exist between motors, boats, loading, atmospheric performance conditions, and even your own preferences between top speed, hole shot, cruising speed and mileage importance.
And you'll never really know if there just isn't another slightly different prop that might be just a bit better.
But go ahead and give it a try!
If it performs well to your satisfaction, you're good to go.
If you want to find the perfect prop, find a dealer with a big inventory of alternative props on the shelf that will let you try them out and make extensive measurements until you're satisfied.
Good Luck!
Joe.
Hi Dick, I've got an '89 22' Cruiser w/ Johnson 70. My motor was supplied with a 13.25 x 17 also. I went to a 13.75 x 15 and got my rpms up to 5600 or so. As time passed I carried more and more stuff and my rpms dropped so I finally went to a 14 x 13 and am propped for about 5700. I recently picked up a Michigan 4 blade 14 x 10 (link) I'm getting about the same 5700 rpms with it. It was on sale cheap and I'm hoping it will eliminate the occasional "ventilation" I get in rough, frothy water such as the Columbia River Bar. Go here (link) and do a search and you'll find that the resident experts agree that our motors need to be propped for 5500-6000. The closer to 6000 the better, in their collective opinion. You're overpropped and your motor is being lugged with a max of only 5000.
Anyone install a Piranha 4 Blade Prop on a Suzuki? The instructions say to not use the Thrust Washer, just the flatwasher. Well the prop assembly has 4 different washer types, none called a Thrust washer in the service manual. From the prop nut i have a washer, spacer, propeller, stopper, and another spacer. Anyone know which one is the Thrust Washer?
If I ever get the prop installed, I bought a 16 and 18 pitch, I llet you know the results. I'm now running a 3x14x17.
Thanks Jim
If I ever get the prop installed, I bought a 16 and 18 pitch, I llet you know the results. I'm now running a 3x14x17.
Thanks Jim
petemos":35l67pn0 said:Anyone install a Piranha 4 Blade Prop on a Suzuki? The instructions say to not use the Thrust Washer, just the flatwasher. Well the prop assembly has 4 different washer types, none called a Thrust washer in the service manual. From the prop nut i have a washer, spacer, propeller, stopper, and another spacer. Anyone know which one is the Thrust Washer?
If I ever get the prop installed, I bought a 16 and 18 pitch, I llet you know the results. I'm now running a 3x14x17.
Thanks Jim
Jim-
The thrust washer is designed to take the forward thrust from the propeller and deliver it to the shaft of the drive unit where it's then transferred to the bearings inside the hub. Otherwise, the prop would slide forward on the shaft until it met up against the hub housing, and friction between the two would destroy them both.
Therefore, the thrust washer, when put on the shaft will slide forward only so far, then remain stationary, holding the prop back a safe distance from the hub.
Many thrust washers are splined to fit the shaft, sliding only up as far as l the splines go, but not all are splined. Sometimes the shaft has a diameter change that stops the forward movement.
From your description, I can't tell which of the washers is the thrust washer, but from my description of their function, maybe you can.
If the instructions say not to use it, then the hub of the Piranha must be designed to function as a thrust washer.
Once you decide you've got the right arrangement, be sure there's no possibility of contact between the prop and the lower unit housing, and that the rearward parts fit properly.
That's the best I can do under the circumstances.
Joe. :teeth :thup