same pitch different speed?

[georgiaboy]

I have a 2005 Triton 176 ( aluminum) with a Johnson 90 hp. It came with a 14" prop with a 19" pitch. I have to change it so I got a 13 1/4" prop with a 19" pitch. the old prop would turn 5400 rpm and the new one will only turn 4800 both trimed out the same. What's the difference?

 

[junior1113]

Re: same pitch different speed?

that 13.25 dia. is more than likely a prop that needs to be closer to the surface can the motor go up . setup means everything

 

[QC]

Re: same pitch different speed?

the old prop would turn 5400 rpm and the new one will only turn 4800 both trimed out the same. What's the difference?

600 RPM . . .

Sorry, couldn't help it. The new one may be cupped which can act like more pitch. How much time between testing the two different props? Do you have the other one? Can you still get 5400 with it? The point is that it is possible that there is some other issue that is causing loss of WOT RPM . . . IS the new one Stainless? They flex less and usually cause a loss of RPM. But 600 is a lot, for the same pitch. Same # of blades?

 

[steelespike]

Re: same pitch different speed?

Why did you have to change it?We could tell better whats goingn on if we had speed and rpm.Was the old prop dinged up?
It appears to me that while a 19 should be a little too much prop for that setup it performed like it was a 17" I have to wonder if someone reworked it at some point.A prop shop can measure the pitch for you.

 

[georgiaboy]

Re: same pitch different speed?

Boat came equiped with the 14" prop. I changed it because I hit a rock. Both are cast aluminum. Put new one on the next day-hardly time for engine to change its ability to turn up rpms. I am going to have the old prop rebuilt but i think the question will remain- what happened to my rpms. The boat would run about 54 mph and now 48 mpg is all I can get.

 

[QC]

Re: same pitch different speed?

If you get your speed back after the rebuild, you have your answer. The new prop is a POS . . .