Propellers 101

[Beefer]

I think a Prop 101 Sticky thread would be helpful, especially for those that are prop-challenged, like myself.

I understand what pitch means, and how it relates to distance traveled per revolution, and how it affects rpms. Not everyone may.

I don't, however, know what affects the diameter of a prop does among props of the same pitch. How does it affect performance, etc.?

Insight into the world of prop hubs could be useful as well.

Benefits/downside to available prop materials (SS, brass, aluminum, etc.).

Just the basics so that when a newbie, or a not-so-newbie is discussing/reading/researching props, we have a better understand of the how/what/why's of what's being said.

Now I excuse myself, and leave this thread to the guru's. Thanks!

 

[Dhadley]

Re: Propellers 101

Diameter itself isn't that much to worry about. What they do or don't do with the extra or less diameter is what counts. There are props made for certian hull designs. Some props have bow lift, some stern lift and some overall lift. Blade area comes into play just like rake, amount of cup and cup placement.

It may help to know what kind of boat you have, the set up and what motor. It would also help to know what props you've tried as that will establish a baseline. It may be that you have a rig someone is familiar with and what props did what on similar rigs.

Very, very generally speaking if you compare similar props of the same manufacturer and one is a larger diameter, it may be possible (but not always) to run that prop higher.

 

[learningasIgo]

Re: Propellers 101

Yes, but a guy like myself doesn't even understand how to measure pitch and how it affects the handly/torque/speed. Can someone take the time to lay out the very basics for those of us who barely qualify to visit the forums and make idiots of ourselves?? It really would be greatly appreciated and would let us feel a little less stupid about something that is obviously very important to boating.

 

[191Seanymphstriper]

Re: Propellers 101

I have a 19 and a half ft aluminum center console running a 1989 90hp mariner (same as merc)! When I purchased the boat it came with 1 aluminum 13x19P prop.


The Max (wide open throttle) (WOT) was 5K rpm at 36MPH With people aboard 4800 etc at 32 to 34MPH. So then my Prop testing began! I purchased a new 13 1/2 x 17P Stainless steel prop and installed it. The Boat did 5800 Rpm (TO HIGH) at 34MPH. The recommended Max Rpm Range at WOT on this motor is 5K to 5500 Rpm Max Rpm is 5800 but not recommended.


Then I purchased a None cupped 13x19 Stainless steel prop which was recommended by a nuckle head and the boat did 5500 rpm at 34MPH but had NO cruise range. It wouldn't plane out until 4600 rpm. Way to high rpm! But the aluminum cuped 13x19 planned good at a lower 3200 rpm.
I then was very frustarited and found this website http://www.mercurymarine.com/propellers/prop-selector/

Now the outboards only date back to like 90 or 95 etc but the bore, stroke and gear ration is the same on ELPTO outboards from 79 to present day. This site also workd for other outboard manufacturers! Not just merc

Anyway after putting in all my gps speeds and rpms and present pitch's etc

The site recommended a 13x18 stainless steel prop!


I coulnt have been happier. Toping out at 41MPH and a WOT rpm of 5350 rpm the site has given me a good outcome. Giving my boat the best planing speed as well as top speed and piece of mind that I am running the right prop...

The bad.... Im stuck with 2 new props that I don't want and are collecting dust. The good I found the rite prop after all!


Hope this post helps someone else as well...
Good luck!

 

[roncoop75]

Re: Propellers 101

Yes, but a guy like myself doesn't even understand how to measure pitch and how it affects the handly/torque/speed. Can someone take the time to lay out the very basics for those of us who barely qualify to visit the forums and make idiots of ourselves?? It really would be greatly appreciated and would let us feel a little less stupid about something that is obviously very important to boating.

Go here:
http://boatpropellers.iboats.com/

About 2/3 the way down the page is the "Propeller Help Guide". LOTS of good starter information there. It brought me up the point where I could at least know the terms used in the forum like cup, rake, ventilation, cavitation ect.

Reading this forum voraciously will fill in the details. You'll be far from an expert but should be able to at least understand the conversations and suggestions given here.

 

[Dhadley]

Re: Propellers 101

Measuring pitch in the field is going to be tricky. Most every prop I know of today has progressive pitch and they don't really publish where they measure it. Most measure around 50%, some don't. There is a way to do it, Jim Booe showed me one day but while it was easy for him I got lost pretty quick.

 

[EricJRW]

Re: Propellers 101

Go here:
http://boatpropellers.iboats.com/

About 2/3 the way down the page is the "Propeller Help Guide". LOTS of good starter information there. It brought me up the point where I could at least know the terms used in the forum like cup, rake, ventilation, cavitation ect.

Reading this forum voraciously will fill in the details. You'll be far from an expert but should be able to at least understand the conversations and suggestions given here.

If you had not mentioned that, I was! That's where I started...

Here's a direct link if interested: http://boatpropellers.iboats.com/propeller-tutorials/how_to_choose_prop

At the bottom of this page is also links for more prop info.

 

[88phantom]

Re: Propellers 101

Try these links to prop information:

Propellors 101 by Turning Point Props

http://www.lake-link.com/boating/props101.cfm

http://www.vicprop.com/propeller101.htm

http://turbo-props.com/prop101.php

Try this Prop Calculator:

Propellor Calculator Page

I'm sure there is more stuff on the web, these come up easy with a google search.

 

[learningasIgo]

Re: Propellers 101

Thanks so much to each of you who posted the links. Looks like I have plenty of studying to do!! I really appreciate those of you on this forum that are so willing to help us "less educated ones" gain the knowledge we desire to become more informed boaters. God bless to each of you. (Remove all potentially mushy hugs!)

 

[WIMUSKY]

Re: Propellers 101

The bad.... Im stuck with 2 new props that I don't want and are collecting dust. The good I found the rite prop after all!

E-bay........

 

[dave4881]

Re: Propellers 101

Yes, but a guy like myself doesn't even understand how to measure pitch and how it affects the handly/torque/speed. Can someone take the time to lay out the very basics for those of us who barely qualify to visit the forums and make idiots of ourselves?? It really would be greatly appreciated and would let us feel a little less stupid about something that is obviously very important to boating.

Pitch on a prop is the theoretical distance in inches that the prop would move forward in one revolution, if slippage were not a factor. The higher the number, the farther the prop will travel in one revolution. Higher pitched props are like a taller gear in a land vehicle. Lower pitched props are like a lower gear and have better pulling power or hole shot.

You don't really measure the pitch. It is stamped on the prop and is usually the last number in the series, i.e., 14 1/2 X 19 would be a 14 1/2" diameter prop with a pitch of 19".

To properly prop a boat, you need to know the maximum operating rpm's of the motor, usually found in the owner's manual. Then, on smooth water, your boat should reach maximum operating rpm's at full throttle. If it falls short of this, you need to "prop down" or get a prop with less pitch. Generally, a change of 2" of pitch will increase engine speed about 200 rpms. If you can easily exceed the engine's maximum operating range, then you should get a prop with more pitch, or be careful about how much throttle you apply at full speed. Hope this helps...