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 Post subject: A Prop Pitch Question
PostPosted: 20 Oct 2016, 15:52 

Joined: 22 Aug 2014, 08:22
Posts: 31
Location: North Fork, Long Island N.Y.
My 16' Lund is a semi V hull, with a 30hp e tec. With me & cargo I guess about 750 to 800lbs. The prop on the motor now is a 10.3X11, & I have no tac. Boat is used for salt water fishing in L.I. Sound, & runs fine, I'm not looking for more speed. I guess my question is in general as the pitch numbers go up from 10.3X11, to 10.3X12, & 10.3X13 what happens? I would be happy with a little quicker "get up on plane" & mid range power.
Thanks
John



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2008 16' Lund WC, 2015, tiller, 30hp E Tec
1980 14' Mirrorcraft 1977, tiller, 25hp Johnson
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 Post subject: A Prop Pitch Question
PostPosted: 20 Oct 2016, 17:45 

Joined: 13 Nov 2014, 08:01
Posts: 736
You want to go down in pitch to get better holeshot. If you have a prop shop near you, they may be able to repitch it 1 step down for not much $.


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 Post subject: A Prop Pitch Question
PostPosted: 21 Oct 2016, 11:17 

Joined: 16 May 2009, 18:57
Posts: 6
If you are familiar with rear end ratios in cars, there is a good analogy that explains prop pitch. Changing prop pitch is like changing a car's rear end ratio.

Let's say you are looking for a good ratio for 1/4 mile drag racing. You might choose a 4.56 or a 5.14 to one ratio for better / quicker acceleration. This is like reducing a prop's pitch - like going from a 10 X 13 to a 10 X 12 or 10 X 11.

On the flip side, let's say you are headed to the Bonneville Salt Flats where acceleration is not the prime desire, but rather ultimate top speed is. Here you might use a 2.73 or 3.08 to one ratio for your car. This give you a higher top speed that the 4.56 above, but it will take longer to reach that top speed. This is like increasing your prop's pitch from a 10 X13 to a 10 X 17 or 10 X 19.


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 Post subject: A Prop Pitch Question
PostPosted: 21 Oct 2016, 16:26 

Joined: 22 Aug 2014, 08:22
Posts: 31
Location: North Fork, Long Island N.Y.
NewportNewsMike wrote:
If you are familiar with rear end ratios in cars, there is a good analogy that explains prop pitch. Changing prop pitch is like changing a car's rear end ratio.

Let's say you are looking for a good ratio for 1/4 mile drag racing. You might choose a 4.56 or a 5.14 to one ratio for better / quicker acceleration. This is like reducing a prop's pitch - like going from a 10 X 13 to a 10 X 12 or 10 X 11.

On the flip side, let's say you are headed to the Bonneville Salt Flats where acceleration is not the prime desire, but rather ultimate top speed is. Here you might use a 2.73 or 3.08 to one ratio for your car. This give you a higher top speed that the 4.56 above, but it will take longer to reach that top speed. This is like increasing your prop's pitch from a 10 X13 to a 10 X 17 or 10 X 19.


That I understand.
Johm



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2008 16' Lund WC, 2015, tiller, 30hp E Tec
1980 14' Mirrorcraft 1977, tiller, 25hp Johnson
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 Post subject: A Prop Pitch Question
PostPosted: 21 Oct 2016, 17:59 
Donor
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Joined: 12 Dec 2014, 14:32
Posts: 2051
Location: Eastern Mass
Without a tach you are guessing ... I wouldn't accept a prop that wouldn't allow the motor to turn up to no LESS than 100-200 RPMs off the stated maximum RPMs for that motor when running it with typical gear, 1/2 fuel and 1 person. However, you could try the prop calculator here and if all the data is good, then you could find the right pitch prop for your rig and use. See: http://forum.tinboats.net/viewtopic.php?f=4&t=37433

If you run TOO steep a prop, you can lug the motor ... which is like running in too tall a gear. I've seen this firsthand on bigger motors (V4s, V6s, etc.) and it can kill the motor in a number of years.

Less not adding oil to the crankcase of a 4-stroke or into the mix or mix tank for a 2-stroke, I know of no surer way to kill a motor than wearing a too steep/tall a pitch prop.



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#1) 1st tin rebuild, 18' Lund viewtopic.php?f=21&t=36583
#2) 25' Parker refurb from EMPTY hull http://www.classicparker.com/phpBB3/vie ... p?f=15&t=6
#3) 16' V-tin rebuild viewtopic.php?f=21&t=36465
#4 Procraft SV14
#5) 16' Starcraft entirely NEW Transom Skins viewtopic.php?f=3&t=37548
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 Post subject: A Prop Pitch Question
PostPosted: 22 Oct 2016, 19:38 

Joined: 24 Dec 2011, 22:06
Posts: 974
Location: 72032
DaleH wrote:
Without a tach you are guessing
Less not adding oil to the crankcase of a 4-stroke or into the mix or mix tank for a 2-stroke, I know of no surer way [color=#FF0000]to kill a motor
than wearing a too steep/tall a pitch prop.



Well said.


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 Post subject: A Prop Pitch Question
PostPosted: 23 Oct 2016, 06:49 
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Joined: 08 Jul 2015, 08:37
Posts: 97
Location: Greenfield, Indiana
DaleH wrote:
Without a tach you are guessing ... I wouldn't accept a prop that wouldn't allow the motor to turn up to no LESS than 100-200 RPMs off the stated maximum RPMs for that motor when running it with typical gear, 1/2 fuel and 1 person. However, you could try the prop calculator here and if all the data is good, then you could find the right pitch prop for your rig and use. See: http://forum.tinboats.net/viewtopic.php?f=4&t=37433

If you run TOO steep a prop, you can lug the motor ... which is like running in too tall a gear. I've seen this firsthand on bigger motors (V4s, V6s, etc.) and it can kill the motor in a number of years.

Less not adding oil to the crankcase of a 4-stroke or into the mix or mix tank for a 2-stroke, I know of no surer way to kill a motor than wearing a too steep/tall a pitch prop.


I agree a tach is a must have when you are setting up a boat. I tried to set my motor up without one it was a huge guessing game. I wish I would have spent the money for a tiny tach before messing with my set up. It would have been 20 dollars well spent and saved me money on buying several props. In the end I bought one to get my set up right.


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 Post subject: A Prop Pitch Question
PostPosted: 24 Oct 2016, 06:33 

Joined: 29 Dec 2011, 17:29
Posts: 650
The more pitch the more load you put on your motor and the results is lower rpms and higher fuel usage. You want the lowest pitch to give you the max rpms when unloaded. That way when you load the boat normally it should be fine. If your load range varies significantly then you might want to consider a second prop with lower pitch for heavy load conditions.


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