Crownline 202 LPX merc 5.0 prop & rpm issue?

[agronomyguy]

Help! Bought the boat a couple weeks ago, I'm worried about the rpm's @ WOT. When I brought the boat home, i was running 5200 rpm's... Here are the details:
1.62 gear ratio
2 people on board
1/3 tank of fuel
19 pitch aluminum prop... (Assuming it was stock)
47 mph (on speedo)

From what i can find... I should be after 46-4800 rpm's... First of all, I'm a little worried about shelling the motor or the lower unit... Second, I'm guessing I'm sacraficing som top end speed???

I brought home a Laser 2... 23P (obviously stainless steel)... Picked up 3-4 mph (again on the speedo)... But the rpm's are still running 5200-5300 at WOT...

Anyone have any suggestions... Or am I missing something. Recently moved to the 202BR from my 225CCR... Bravo 1 to the Alpha...

Thanks all!!!

 

[45Auto]

Re: Crownline 202 LPX merc 5.0 prop & rpm issue?

You went from a 19" to 23" pitch prop and RPM didn't change?

I would be double checking the markings on the props to make sure you didn't mis-read them, and verifying that the tach was correct.

 

[craze1cars]

Re: Crownline 202 LPX merc 5.0 prop & rpm issue?

Prop slip calculator says one of your numbers is a lie...you have to figure out which number it is.

When I plug in 1.62 ratio, 23 pitch, 5,200 rpms...your theoretical top speed is 70 mph. So if you're only going about 50, that means you have 29% slip. That's completely unrealistic for that boat.

I suspect most likely your tach is not accurate. Or you've mis-reported one of the other two figures.

Your slip calulation for the 19 pitch prop is somewhat realistic at 19%...that's a lotta slip, but not all that uncommon for a stock aluminum prop on a V8.

After you figure out which of your numbers is wrong and correct it, we can help you select a good prop for your boat.