Waaaaaaay wrong prop?

J

Joe SixPack

Cadet
Joined
May 13, 2004
Messages
13
I just purchased a Bayliner 185BR at an auction. It has a 3.0 Mercruiser Stern drive and (2) 14.25x21 props. At WOT she is turning 3000rpms at a speedometer speed of 42mph. Shouldn't it be between 44-4800rpm? Why would these props be so far off?
 
A

americaneagler77

Petty Officer 1st Class
Joined
Jun 15, 2011
Messages
231
Re: Waaaaaaay wrong prop?

42mph seems pretty close to top speed with a 3.0. rpm should be higher but im wondering if your tach is off?
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Waaaaaaay wrong prop?

depending on the year,everyone seems to want to keep that a secret,.lol
If its a 1.98 gear ratio and the speedo is accurate the rpm should be around 4600.
The tach may just be set wrong or the selector on the back is dirty.note the position
and rotate it a few times and try it out Not sure if the numbers match the number of cylinders but give it a try.Only way to be sure of the speed is a gps.
 
Don S

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
Re: Waaaaaaay wrong prop?

You don't have a prop problem, but you may have the wrong gear ratio. Check the gear ratio stamped into the upper gear case near the serial number.
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Waaaaaaay wrong prop?

If my figures are right in order to get 42 out of 3000 rpm the ratio would have to be .14.
 
B

bnicov

Petty Officer 1st Class
Joined
May 25, 2009
Messages
348
Re: Waaaaaaay wrong prop?

An 18.5ft boat with a 3.0 running 42mph, that's about right for your top speed. I'd be looking at the tach to make sure it is functioning correctly. Check the settings on the back and verify that it is set to 4cyl. If it is, then have it verified against a shop tach. Don't think you will see 50mph with that boat/motor setup you have. Now depending on the manufacturer of the tach, it may have a lifetime warranty. I know Faria guages do, for a nominal fee, they will rebuild/replace the guage for you (the fee covers shipping charges).
 
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