32 mitchell cove wheel size

unclefish

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Does anybody have a knowledge on what size wheel should a 32 MC w/a 225 john Deere with 2 to 1 gear in it. It has a 24 x 22 lh wheel on it now. I was told it does 15 knts at 2200 rpm. The wheel just looks small to what could be on there. Thanks for help.
 

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If the engine reaches max rpm then the wheel is the proper size
If the engine revs over its rated rpm then the wheel is undersized
If the engine fails to reach its rated rpm then the wheel is oversized

What is the engine rpm, wide open throttle in neutral compared to wide open throttle in gear?
 

unclefish

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I guess I will have to wait till April to answer those questions when she returns to the water. Wasn't sure if anybody else had one with those combos in one.
 

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I'll poke through the archives and see what I can find.
We did a 36 with a 225 JD which did 27 mph, I do not recall the ratio off the top of my head, I am thinking it was a ZF280A 1.77:1 though swinging a 26x26 LH
 

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BillD

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around 100 more give or take
if your engine is rated for 2100 it should do 2200 in neutral
Neutral WOT/no load @ the dock can be engine specific @ least with mechanical engines.
For example, my CPL 2008 Cummins 6BTA 370s reach 3325 WOT in neutral @ the dock.
The engines are rated @ 3000 rpm WOT.

I have the engines propped to 3100-3150 WOT in gear with a full load.
 

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Neutral WOT/no load @ the dock can be engine specific @ least with mechanical engines.
For example, my CPL 2008 Cummins 6BTA 370s reach 3325 WOT in neutral @ the dock.
The engines are rated @ 3000 rpm WOT.

I have the engines propped to 3100-3150 WOT in gear with a full load.
Absolutely
I just tossed out a rule of thumb
My own engine is rated at 2100
But no-loads at 2800
 

Downeaster

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Does anybody have a knowledge on what size wheel should a 32 MC w/a 225 john Deere with 2 to 1 gear in it. It has a 24 x 22 lh wheel on it now. I was told it does 15 knts at 2200 rpm. The wheel just looks small to what could be on there. Thanks for help.
You should have tip clearance equal to 17% of the diameter of the wheel (Gerr). In the example that you cite, you should have 4.08" between the wheel tip and the hull at their closest point. The reason your wheel looks small is that most boat builders or owners ignore this rule.

Gerr's propeller book is a slow read but it is loaded with data that many of the world's NAs cite. Here is a snippet of it.
 

unclefish

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downeaster I beleive somebody told me 2 inches was the closest you wanted to be. but I don't know myself. so if 24 is the biggest i can go how do you adjust with pitch .
higher the number does what ????
lower the number does what ????
 
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Pitch is how far in inches the propeller would travel in one rotation with no slippage. Higher number means that the propeller would travel further, lower number means that the propeller would not travel as far.

Example: 26x32 = 26 inch diameter, 32 inches of pitch (boat would move 32 inches/revolution)

26x34 = 26 inch diameter, 34 inches of pitch (boat would move 34 inches/revolution)

In practice this takes the test vessel from 32 mph to 38 mph, same rpm range.

Without enough torque however, one might not be able to wind in additional pitch willy nilly and the boat ends up going slower since it cannot spin fast enough.
 

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Another couple of "rules of thumb"

An inch of pitch is good for 100 rpm (more pitch = less rpm/less pitch = more rpm)

An inch of diameter is good for 2 inches of pitch (if you have a 24x24 and change it to a 25x24 it would be akin to projected performance to a 24x26)

Again, these are "rules of thumb" and not laws. Every vessel is different. Slow turning engines will benefit from pitch/diameter better than high rpm engines. And as always, gear ratio is very important.
 

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downeaster I beleive somebody told me 2 inches was the closest you wanted to be. but I don't myself. so if 24 is the biggest i can go how do you adjust with pitch .
higher the number does what ????
lower the number does what ????
2" tip clearance is not enough on a 24" diameter prop in my opinion. The closest tip clearance I have ran on my boats was 11% on my 34' Calvin Beal. The 11% was by accident, not on purpose (my dad set the shaft tube and didn't check with me until it was too late). It had a 26" prop and tip clearance was 2.875". Fortunately, everything ran quite smooth at sea trial and all was good, but I would have preferred a 3.5" tip clearance which would have been about 13.5%.

So if your current tip clearance with the 24" prop is 4.5" or higher, you probably have enough room to fit a 26" prop. A 26" prop will reduce tip clearance on the hull by 1". A 26" prop will put more strain on the shaft, so make sure your shaft is adequate for a 26" prop if you decide to jump up in diameter.

The more pitch you add to a prop, the more load it puts on your engine. You should pitch your prop to where you have about 95-97% load on your engine at full throttle.
 

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Tip clearance is important on wooden vessels more so than fiberglass because the cavitation from the blade spinning around won't peel the softer wood from the planks. I've seen a half inch stainless steel propeller with "worm holes" through it due to the cavitation from the bronze propeller in front of it (the propeller was perfect, no signs of cavitation on the blade surface or edge). Even so if the tip clearance is too small on fiberglass hulls you can develop a "rumble" which is just the propwash being flung up from the blade, hitting the hull and bouncing back down, just to be hammered into again over and over.
 

unclefish

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i measured it and it was 4 " the wheel looks to be pretty shot. Anybody have any 24 x 22 lh wheels they want to sell 2" shaft thanks for help.
 
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