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Old 11-01-2018, 05:39 AM   #1
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Default Props just to be clear

So, I have a 3 blade 21p prop now, I am looking to slightly improve hole shot and lower plane speed and I donít care about cruising speed as much and I donít care about top speed at all.....saying that, I am thinking that a 4 blade 19 or 20p prop would be ideal. I have no avenue to test before I purchase but I believe I will be happy with the results. Any feedback from you ladies and gentlemen would be appreciated.

I have some time to consider this as it will be 7-8 months before the boat gets wet again.....so sad.


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Old 11-01-2018, 05:42 AM   #2
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Sorry.....

2000 SR2100, 5.7carb, alpha one gen 2. Prop calculator says I have the right prop and I agree the boat has the power and so on to do it but I tow kids on the tube and skis so I want to fine tune my on the water performance to suit my needs.

Thanks!!!


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Old 11-01-2018, 02:48 PM   #3
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Going from 3 to a 4 blade will help you attain these goals.
At the same diameter, dropping 1-2 in in pitch is the rule of thumb.
If you are at the low end of the WOT range, I'd reduce pitch by 2, if you're already maxing out RPM, only reduce by 1.
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Old 11-01-2018, 02:54 PM   #4
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Quote:
Originally Posted by Overboard View Post
I am looking to slightly improve hole shot and lower plane speed and I don’t care about cruising speed as much and I don’t care about top speed at all.....
Do you mean the speed at which the boat is on plane, or the time to get on plane? (I suspect the latter).

The variables you're modifying are at odds with one another.

1) Reducing pitch will decrease the time to plane, increase max rpm and decrease max speed. Increase rpm for cruise speed.

3) Increasing blades is equivalent to adding pitch. It will increase the time to plane, decrease max rpm and decrease rpm for cruise speed.

By adding a blade and dropping pitch, you risk not changing anything.

I would start with what your current max rpm is at WOT and then go from there. It should be between 4400-4800.
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Old 11-01-2018, 05:04 PM   #5
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Decreasing pitch one size down and adding a blade will most likely null each other out and there will be no change in performance.
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Old 11-02-2018, 01:03 AM   #6
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Quote:
Originally Posted by shrew View Post
Do you mean the speed at which the boat is on plane, or the time to get on plane? (I suspect the latter).
Shrew, I’m looking to stay on plane at slower speed as well as get on plane slightly quicker if possible.

From the responses I see I can surmise I should be dropping from 21 to 19 but I will have to consider WOT as right now, propped as I am I hit 4550-4600 which is perfect IMO


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Old 11-02-2018, 02:29 AM   #7
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The boat will plane at the same speed given it has the same load.
Changing the prop will not change the speed (MPH) the boat will plane.
Trim tabs will help get the boat on plane faster and at a bit slower speed.
You are running at the correct RPMs now, the only thing that changing the prop will do is a better hole shot and higher RPMs.
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Old 11-02-2018, 02:23 PM   #8
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Planing is a function of the hull shape combined with speed. The speed required will be dictated by the hull shape. This is why a flat bottom jon boat will plane at much lower speeds than a offshore racer with an agressive V bottom. Changing the prop will not change this.

Trim tabs will be about the only thing that will allow you to stay on plane at lower speeds. The tabs will need to be all the way down and I am doubtful that fuel economy will be achieved because the tabs will introduce so much drag.

If you're at 4550-4600 now, then you could increase max rpm by dropping an inch in pitch. If you add a blade, you'd need to drop 2 inches of pitch. You'd need to make sure that you don't exceed 4800 rpm's.

It would improve the holeshot slightly, but won't change speed at plane.
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Old 11-03-2018, 03:34 AM   #9
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Thanks everyone, I will update in the spring as to what I have done and my findings on the water


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