will this prop work for my boat

rsimmons42

Petty Officer 2nd Class
Joined
Aug 25, 2008
Messages
194
I am looking at a Stainless Steel Prop 13/21 13 spline. I have a 1977 70hp Johnson. I have it mounted on my 16' Sunbird. What is this prop designed for. I have not figured out the pitch, and how it relates to the boat. Will this one effect RPM? Any infor would be appreciated.
 

Kenny1970

Seaman
Joined
Sep 21, 2007
Messages
60
Re: will this prop work for my boat

I think it is made for speed and any prop that has a different pitch will effect your rpm.
 

rsimmons42

Petty Officer 2nd Class
Joined
Aug 25, 2008
Messages
194
Re: will this prop work for my boat

do other people concur that this is built for speed, if a prop is built for speed, does that mean that it will increase my normal WOT RPM? And will this one fit my boat.
 

Kenny1970

Seaman
Joined
Sep 21, 2007
Messages
60
Re: will this prop work for my boat

do other people concur that this is built for speed, if a prop is built for speed, does that mean that it will increase my normal WOT RPM? And will this one fit my boat.

Here is what happen to me.16 foot trihull with 120 chrysler.
13X17 6500Rpm at WOT 33 MPH
13X19 5900RPM at WOT 37 MPH
13X21 Cuped stainless 5300Rpm at WOT 36MPH

The higher the pitch the lower the rpm.
What prop do you have now and what is the Rpm at WOT?
 

Kenny1970

Seaman
Joined
Sep 21, 2007
Messages
60
Re: will this prop work for my boat

13x15 WOT 5500 speed 32


I would stay with what you have.
A 21 pitch will drop your rpm about 600 to 800,Your hole shot will suck and you will more than likely loose 3 to 5 MPH
 

rsimmons42

Petty Officer 2nd Class
Joined
Aug 25, 2008
Messages
194
Re: will this prop work for my boat

What does it mean that your hole shot will suck? I just rebuilt the carbs and am taking it in to have a complete link and sink done. I can tell the throttle plates are not paralle. So i am taking it in to get it tuned, which should increase WOT RPM's, which I would believe would off set the two. My timing is off a bit as well. any sugestions, prop is only $70 and is SS, so I think it might be worth it. let me know what you think
 

Kenny1970

Seaman
Joined
Sep 21, 2007
Messages
60
Re: will this prop work for my boat

If you are not getting your max RPM at WOT it will take longer to get on plain/Hole shot.
If there is to much pitch it will just strain the engine and go slower after you get on top of the water.
After you get it tuned check you rpms and see where they are at.
I like to be able to go 100 to 200 over the Max RPM
 

Silvertip

Supreme Mariner
Joined
Sep 22, 2003
Messages
28,771
Re: will this prop work for my boat

You seem hell-bent on putting a 23P prop on an engine that cannot handle that much pitch. You are wasting your money and in the end will be looking for help determining why your engine burned a piston.
 

rsimmons42

Petty Officer 2nd Class
Joined
Aug 25, 2008
Messages
194
Re: will this prop work for my boat

thanks everyone for your advice. I am backing out of the buy of the prop. I am new to this boating thing. And I don't want to burn up my engine. Thanks for all of your advice. What is the Max prop pitch that I should be shoping for if I want to buy a SS prop?
 

Kenny1970

Seaman
Joined
Sep 21, 2007
Messages
60
Re: will this prop work for my boat

17 pitch only if you are still doing 5500Rpm with the 15 pitch that you have now after they sink and tune your carbs
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: will this prop work for my boat

do other people concur that this is built for speed, if a prop is built for speed, does that mean that it will increase my normal WOT RPM? And will this one fit my boat.

Not built for speed specifically but increasing pitch will improve speed
if the motor can turn it up to proper rpm.Selecting a prop is like selecting one gear in a car to do everything.incresaing pitch= higher gear decreasing pitch = lower gear.General use you need the prop that produces best speed without killing the hole shot.(acceleration).Sometimes you need a second lower pitch to use specifically for skiing and such.
 

jamieat

Seaman Apprentice
Joined
Sep 4, 2007
Messages
40
Re: will this prop work for my boat

Propeller pitch is the theoretical forward movement of a propeller for one revolution, assuming that there is no prop slip. For example, a 21 pitch propeller will theoretically move 21 inches for every revolution. Propeller slip occurs with every propeller, but the amount of slip varies depending on propeller design. More aggressively and efficiently designed propellers will slip less.

When selecting a propeller pitch for your boat, it is important that the propeller runs at the upper end of your engines wide-open-throttle RPM range. If you want your RPM's to increase, go down in pitch. To decrease RPM's, go up in pitch. As a general guide, for every 2" of pitch, RPM's will change approximately 400 RPM's.

For water sports or extra people on board, you should generally drop 2" of pitch to help compensate for the added weight and drag on your boat. It makes a noticeable difference in your boat's hole shot, fuel efficiency, RPM's, and overall performance. You should ALWAYS carry a spare propeller on board, and if you're into water sports or occasionally load the boat with extra people, a spare prop with a lesser pitch is a good idea. When thinking a propeller pitch, compare it to a gear on car - lower gear, higher RPM's.

The same pitch from different manufacturers will run slightly different RPM's due to a difference in blade design. Speed differences among the same pitch from various manufacturers will vary even more. For example a 17 pitch from one brand could run up to 7 mph faster than a 17 pitch from another brand.

Pitch is the 2nd two digits that are listed in a propeller item description (14-1/4 x 19, 19 is the pitch, 14-1/4 is the diameter)
 
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