Do I really need a 13P prop??

[kjboggs]

Ok, I recently purchased a 1995 sea ray 175 and took it out for the first time this weekend. Has a 21p stainless stiletto prop on the 125 mercury outboard.

This boat is definitely heavier than my 92 dynatrak fish and ski I had previously, which was overpropped when I got it as well. I could get up to about 42 mph in my new sea ray, but no hole shot and WOT was only around 3100 RPM's.

I feel the motor is running great, 140 psi on all cylindars, runs great or would not got it up to 42 mph??, but could tell by the tach and the sound of the engine since I had one very similar before it was no where near the 4800-5200 the manual states.

Main purpose is a little fishing and pulling tubes with the family. Was going to go to a 4 blade prop, and if my calculations are correct Im looking at going from a 21 p to a 13 or 14 pitch 4 blade prop to pull tubes with and get my rpm's where they need to be.

I previously went from a 22 p to a 17 p on my dynatrak and mercury 115, and was right on. But this boat is definitely heavier????

 

[steelespike]

Re: Do I really need a 13P prop??

Either your speed is off or your tach is off.You can't go 42 at 3100 rpm. Is your speed by gps?
using 2.07 gear ratio and 12% slip I get 4900 rpm at 42 mph. w a 21" prop.
Your slow hole shot is probably the 21" prop.
It would seem a 19 would solve your problem and put you at the top of your rpm.
You probably should get a working tach before making any changes.

 

[kjboggs]

Re: Do I really need a 13P prop??

Thanks, I'm not sure which is off? The tach was recently replaced with a new one. And I know the speedo is not that accurate. Will try and check both and see what's off?

 

[Starcraft5834]

Re: Do I really need a 13P prop??

kj.. dont know if this helps, I have a 20ft cuddy, prob 2500lb+,with 3.0 mercruiser 140hp,, put a 4 blade 15p on,, Im at 4600 rpm, and maybe squeeze out 34mph with a tail wind... I had a 3 blade that came with the boat, took for ever to get on top of water with that,, the 4 blade was the answer for me...

 

[dan02gt]

Re: Do I really need a 13P prop??

Your tach is way off.

A friend of mine has a 95 Sea Ray 160 with a 115 Mercury on it. He turns a 21 Stiletto Advantage I (probably the same prop you have). He typically sees 5000-5200 RPMs at between 46-47MPH.

The previous owner used a 17P Solas for water sports (slalom skiing). It has a great hole shot with the 17P but was limited to around 35MPH.

Based on that for general use I would recommend a 19P to get your RPMs up and improve hole shot, and a 17P for serious water sports.

 

[smokeonthewater]

Re: Do I really need a 13P prop??

when the new tach was installed was it set up properly for the engine" they generally have a switch on the back that needs to be set when installing 2, 3, 4, 12, or something like that