MFF US Northwest > Wyoming

Prop question

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fish/hunt4ever:
On the new boat it has a 13x24 prop and gets me out of the hole quick, just seems like the 175 does not hit the speeds I am thinking it should.  Just wondering what everyone else thinks of the prop that is installed on the boat.  Thanks for all and any help.

Mac Attack:
Need to look at RPM of the engine at full speed.
Compare that for the manufactured published allowable rpm specs of your motor.
There’s a rule of thumb often used that says each inch of pitch is generally worth 150 – 200 rpm.
Lowering the pitch increases rpm and vice versa.
So, for instance, if you were to lower from a 23-pitch to a 21-pitch propeller, you’ll increase engine RPM by about 400 revolutions.

4 blade props give you a better hole shot but you sacrifice top end.
Stainless props are stiffer than aluminum, so they resist flexing.
A thinner stainless steel prop spins up quicker and will attain a higher rpm vs an aluminum because of this.
So a stainless steel prop will out-perform an aluminum prop both out of the hole and at top end.
However, there's tons of guys that won't use a stainless prop for fear of damaging the lower unit or motor if they hit something with the prop.
All things to consider.

Good luck

Dorado:

--- Quote from: Mac Attack on May 15, 2023, 01:25 PM ---Need to look at RPM of the engine at full speed.
Compare that for the manufactured published allowable rpm specs of your motor.
There’s a rule of thumb often used that says each inch of pitch is generally worth 150 – 200 rpm.
Lowering the pitch increases rpm and vice versa.
So, for instance, if you were to lower from a 23-pitch to a 21-pitch propeller, you’ll increase engine RPM by about 400 revolutions.

4 blade props give you a better hole shot but you sacrifice top end.
Stainless props are stiffer than aluminum, so they resist flexing.
A thinner stainless steel prop spins up quicker and will attain a higher rpm vs an aluminum because of this.
So a stainless steel prop will out-perform an aluminum prop both out of the hole and at top end.
However, there's tons of guys that won't use a stainless prop for fear of damaging the lower unit or motor if they hit something with the prop.
All things to consider.

Good luck

--- End quote ---

Great advice.  I have found that here in WY, you need to go down several sizes in the pitch of the propellers that come on boats set up to run at lower elevations than we typically have here.  Boysen is around 4,800 feet.  The lakes I go on the most range from 6,400-8,000, you really notice that difference! 

I would go out with your boat loaded as you typically use it (not empty of people, gear and gas) and note your maximum RPM at full throttle.  You want to be able to achieve close to max RPM at full throttle.  Your manual you got with the new boat should tell you what the max RPM is, looks like 5,500-6,000 RPM.  I would guess you are going to want a 21" pitch, but you won't know until you get out and test it. 

I am in the process of doing the same thing on my new (to me) boat.  It has a 19" x14.5" and I am thinking I will need to go with a 15".  Your hole shot will noticeably improve with the correct prop!  Plus, as I have read, it is better on the engine to not overload it with a too large propellor that does not allow max RPM...

fish/hunt4ever:
RPM on the motor when I trim it out, fully loaded with 5 people and my gear and dog, I get the 6000 rpm that they say I should be getting. The boat gets on plane right now, pushes you back in the seat. Just seems like everyone I talked to said they usually get about 45 mph out of their boats, I know not mine, but figured it was worth a question, plus I always learn something new from these types of questions.

As I am one of those guys that tend to stay away from stainless props but now understand the reason that some really like to run them, I just seem to hit things from time to time and would hate to kill my lower unit and then have to pay to repair it, but I guess hitting something might do that anyways.

TT:
What is your speed at 6000rpm loaded?

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