Help with Prop "lingo"

I have been lurking and learning on here for a month. Just bought a used 06 Stingray 200LX and believe I need a 4 blade 19 or 21 degree pitch for tubing and getting on plane quicker... Maybe later in the sumer.

Question is when one says go down a size are you referring to going from a 21 pitch to a 19 pitch or going down as in 14 1/2 diameter to a 14' diameter? Seems many use " when referring to pitch I thought " meant inches.

I use to run a 21 foot 86 ranger bass boat went to a 19 pitch and planed quick but slowed almost 10 mph went back to a 21 pitch raker with cavitation holes and ran 67 mph.

I know the basics"sorta" just confused in terms and uses.

PS Seems to be some really knowledgable people on here and great place for info

Re: Help with Prop "lingo"

wtx said:

I have been lurking and learning on here for a month. Just bought a used 06 Stingray 200LX and believe I need a 4 blade 19 or 21 degree pitch for tubing and getting on plane quicker... Maybe later in the sumer.

Question is when one says go down a size are you referring to going from a 21 pitch to a 19 pitch or going down as in 14 1/2 diameter to a 14' diameter? Seems many use " when referring to pitch I thought " meant inches.

I use to run a 21 foot 86 ranger bass boat went to a 19 pitch and planed quick but slowed almost 10 mph went back to a 21 pitch raker with cavitation holes and ran 67 mph.

I know the basics"sorta" just confused in terms and uses.

PS Seems to be some really knowledgable people on here and great place for info

Click to expand...

Ayuh,... Part of your problem is, Degrees has absolutely Nothing to do with any of it....

Pitch is the Inches of travel in 1 revolution....
Inches of Diameter has Everything to do with Blade Design, 'n shouldn't be used for shopping Pitch...

Shop for a prop Designed for the Uses you expect to need...
Then buy the Inches of Pitch needed to put yer motor at it's optimum rpms at Wot...
The Diameter will work itself out, 'n you needn't be to concerned with it at All...
The Designing Engineer already took care of that for you...

Re: Help with Prop "lingo"

Thanks

I knew about the inches of travel. Confused on diameter. I assume a 14 1/2 19 pitch prop may have a little more cup (1/4 inch) than a 14 1/4 19 pitch. I assume the 14 1/4 " could" spool up" RPM just a little faster and may get you maybe 100-200 rpm closer to your max RPM.

Re: Help with Prop "lingo"

wtx said:

Thanks

I knew about the inches of travel. Confused on diameter. I assume a 14 1/2 19 pitch prop may have a little more cup (1/4 inch) than a 14 1/4 19 pitch. I assume the 14 1/4 " could" spool up" RPM just a little faster and may get you maybe 100-200 rpm closer to your max RPM.

Click to expand...

Generally diameter is a secondary consideration mostly to just be sure it will fit.Diameter in the extreme around an inch different could effect rpm But is generally not used except in specific
problem applicatioms.To my experience diameter has no bearing on cup.Some props have a lot of cup others next to none and again diameter is a secondary consideration.

Re: Help with Prop "lingo"

Thanks

Re: Help with Prop "lingo"

Understanding how pitch affects diameter requires that you look at three props from the same manufacturer and the same series. Look at the diameters for a 15, 17 and 19 pitch for example. You will generally see an increase in diameter as you go down in pitch (say from 17 to 15). You will see a slight decrease in diameter as you go up in pitch. The amount of change is a function of prop design and DOES NOT apply if you are comparing props from different manufacturers and different series, or for that matter, props from the same manufacturer but a different series. In some cases there is zero difference in diameter as pitch moves up or down. As was pointed out, you start by buying a prop designed for your engine, then select the pitch you need and then diameter works itself out. Unless you make some test runs at WOT with what you consider an average load, noting maximum RPM, you may already have the best prop for your application.