What gear ratio and wheel size to use on a 30 young brothers?

shawn1

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I am currently repowering my 30 YB with a 225 6068 deere and don't have a gear. I am either thinking a zf 2:1 or 1.5:1. I need a new wheel so that would be in consideration as well. I was wondering if anyone has this boat with a similar set up and would recommend a ratio and size wheel?

Thanks -Shawn
 

WoundUpMarine

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PatriciaLynn

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There is a real cheap zf68a in 2:1 available. Was a pair, I am picking up one next week. If you want, I will pick it up for you and deliver anywhere from Maine to VA for a fee.
 

P18Flirt

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WoundUpMarine

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hardcore1

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Figure out the largest wheel you can fit and then you can figure the gear. I would imagine 2/1, 2.25/1
 

Powderpro

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Figure out the largest wheel you can fit and then you can figure the gear. I would imagine 2/1, 2.25/1
Great advice- figure out the max diameter prop you want to run and get back with us. 2:1 is always a safe bet in most applications, unless you can only fit a small prop, then you may have to drop to 1.77 or 1.5.
 

MikesMarine22

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I have a 33 Yb and am in this same predicament, kind of. I have a 300 HP. cummins and need a transmission. The largest prop I would be able to fit is probably around a 20. Theres only 23 or 24 inches of clearance. Not to derail the thread but I have heard many different opinions on gear ratio and I have seen anything from 1.5:1 to 2:1.
 

eyecatcher

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You will want the largest prop turning the lowest shaft RPM (1300-1500) ideal within the saftey factor and min clearances.

Be good to know the size of shaft, and the room your have from center line shaft taper to hull top and centerline to skeg bottom to reverse engineer it.
 

Brooksie

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Eyectcher is 100%, start with engine RPM, select ratio to keep shaft RPM around 1300, select largest 4blade prop diameter that has proper clearance (15% above 10% below) then select pitch using prop calculator.
 

eyecatcher

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Lots of variables. With the 2600RPM at 225hp engine 2.25 - 2:1 is good starting point but you may need to go 1.75-1.77 if you can't support a big enough prop. You also want a shaft safety factor of at least 3 which may effect the gear selection, depending on shaft material. Also, the diameter of the prop to shaft comes into play. A 1.5" diameter shaft may be adequate for your application to about 22" prop. If you can swing a larger wheel than that you would also want to increase the shaft to keep the stress down or for other reasons to support a higher HP engine in the future.
 

shawn1

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Thanks for all the support! I did some measuring and came up with this:

Shaft diameter 1.5 inches
The current wheel 19.5 inches (counter rotating why I need to switch anyways)
Bottom of the wheel to skeg 2 inches of clearance
Top of wheel to bottom of boat >2 inches
 

Brooksie

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Seems like your propeller may be as large as it can get w/o hull mods. What was the old gear type & ratio?
Guessing at a few things about your boat and running them through my calculator, it seems that 1.5:1 ratio would be good for a 19-20" prop with 15-16" pitch and you might be cruising at 16K @ 2400.
Please don't use these numbers w/o more information. But they do show that a higher ratio would call for a propeller larger than you have room for. Your shaft diameter is OK unless it is bronze.
 
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