Outboard prop & Performance question

[fishnbuddy]

We're thinking of getting a new prop, and I was wondering what would happen if we changed the pitch. Right now we are using 14 X 13. No one has ever explained to me how more or less pitch in the prop affects performance...so I thought I'd ask. How does increasing or decreasing prop pitch affect over all performance?

Boat info...14' tri-hull (Da Hoop'D), 60hp Evinrude
...fishnbuddy

[FishAbility]

14x13 are the prop dimentions. there should be a number with a "P" after it. 15P, 17P, 21P, etc... the pitch is measured in inches and basically means that for one rotation of the prop, the forward movement is 21" (in a zero drag environment) if you have a 21p prop. SO: with a more drastic pitch prop, you will move farther per rotation, BUT you will lose RPM due to increased drag. with a lesser pitch prop you will INCREASE RPM. so it depends on what engine you have and what the manual says your rated RPM under power should be. for a rule of thumb every 1" of pitch will change your RPM by 200. there are other factors involved as well, shape of the prop, material used, (stainless, aluminum, etc.) rake and cup... there is a whole science behind it... whats your boat running RPM wise now?

[fishnbuddy]

Mick I have no clue what the rpm is. We bought the motor, mounted it and I had to do all the carb work myself. I basically did it by ear till it sounded good. I'm no professional, but it runs good.
...fishnbuddy

[jpineda]

you need to find a manual that would give your engines rpm range

[scuba e]

You must get max rpm out of the engine with a fully loaded boat or you will hurt the engine. So, with gear, buddies, food, etc. at wide open throttle you need to be able to get full rpm. If you get there at partial throttle or plain out really fast and the boat "feels" like it could use more prop then you can step up. You may want to get a pro involved or get a tach. You can also use a photo-tach but it may just be cheaper to get a pro as the photo tach may never get used again.
Good luck.

[Deno]

Junior call Joe he’s in Cabo till Wednesday just call and bug the guy, he loves it.

Originally Posted by FishAbility

14x13 are the prop dimentions. there should be a number with a "P" after it. 15P, 17P, 21P, etc... the pitch is measured in inches and basically means that for one rotation of the prop, the forward movement is 21" (in a zero drag environment) if you have a 21p prop. SO: with a more drastic pitch prop, you will move farther per rotation, BUT you will lose RPM due to increased drag. with a lesser pitch prop you will INCREASE RPM. so it depends on what engine you have and what the manual says your rated RPM under power should be. for a rule of thumb every 1" of pitch will change your RPM by 200. there are other factors involved as well, shape of the prop, material used, (stainless, aluminum, etc.) rake and cup... there is a whole science behind it... whats your boat running RPM wise now?

[sandiegosteve]

RPM is key.

If you are running to high, increase the pitch. Too low, then lower the pitch. Too high or too low is based on what the manufacturer says the max RPM range should be at WOT.

Think of pitch like gears in your car. A low pitch, like 12" is like 1st gear, where 17" is more like 3rd or 4th (for an example). You can't shift gears, so you need one that will combine a good hole shot with good cruise and good max speed. So, where you fit in the max RPM range is your area of play.

[joedirt_oef04]

Thanks for all the info. We have to hook up a tach to see where our WOT rpm is at. The boat jumps on plane, but its only 14'.

[Doug V]

Outboard horsepower is usually expressed as "X" horsepower at 5500 to 6500 (whatever the manufacturer spec is) rpm, WOT. If you test the boat/motor/prop combination fully loaded, you would want to be at the lower end of the WOT RPM range. If the combination is tested lightly loaded, you would want to be at the top of the WOT RPM range.

No xspurt here, just what I have read. It made sense to me.

Doug