What Pitch do I need?

GunnerSC

Cadet
Joined
Jul 1, 2009
Messages
24
I have a 1996 Mariner 150 Mag III 2.5 litter outboard. It is on a 1996 procraft bass boat. The boat is 18 feet. The motor has a 15 pitch SS on it now, but I think that I may need a higher pitch prop. It is on a jack plate also. When I start off at full throttle it's like it slipps or something? If the rpm gauge is right it turns above 6500 to 7000 rpms at start. Just woundering what everyone else thought? By the speedometer at WOT and trimmed up it will run around 57 mph.
 
Last edited:

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: What Pitch do I need?

What is the wot rpm @ 57? 15" prop seems really small to me.
 

GunnerSC

Cadet
Joined
Jul 1, 2009
Messages
24
Re: What Pitch do I need?

To answer your question the RPM at 57 mph is around 6400. The problem is that I took it out this past weekend and pulled my daughter on a tube. I normally used it for fishing, but I was doing the family thing on this day. So I ran maybe a little over a quarter of a tank of gas out and stopped to swim. About 30 min we got back in and rode down the lake not pulling anyone just riding and let them off at the ramp. I was waiting for them to back the trailor in and an alarm went off. BEEEEEEEEEP!! The beep was solid and didn't stop. The first thing I thought was over heating, because the oil injection has been disconnected.(I Premix) I shut it down right then cause I was skeered. I started it back up and pulled it on the trailor and it started beeeeeeeep again. I have read a lot of different things on here about that issue and will try some of that stuff, but I was thinking if I had to small of prop that the high rpms would cause it to overheat when trying to pull someone. Thank you so much for your help.
 

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: What Pitch do I need?

The max rpm rating is 5,600 Some might run at 6,000 but don't take my word for it.
Bass boats are usually pretty fast so require more pitch I would think your boat would normally run at least a 21" prop.Just a seat of the pants estimate.
A 15" prop would be on something really heavy and hard to push like a pontoon boat. Usually if you had damage from overreving you would hear it.Hopefully you jusy have a spontanious failure of the thermostat or impeller.
Don't exceed that 5,600 rating if you run with the 15" prop.
 

GunnerSC

Cadet
Joined
Jul 1, 2009
Messages
24
Re: What Pitch do I need?

Ok Thanks so much for your help!! What would I hear if something screwed up? When I heard that alarm I shut it off right then.
 

GunnerSC

Cadet
Joined
Jul 1, 2009
Messages
24
Re: What Pitch do I need?

Ok, I took temps of the engine heads while the motor was running at 1000 rmps for 20 mins. The drivers side top cylinder was the hottest @ 17o degrees. The other never got above 165. Is this ok temp? Thanks again.
 

GunnerSC

Cadet
Joined
Jul 1, 2009
Messages
24
Re: What Pitch do I need?

Update

Went to deal where I bought the boat and exchanged my 15 pitch ss for a lazer II ss 21 pitch.
Results

Wounderfull!!! At WOT I'm running at 4500 - 5000 rpm and 63 MPH!!

No more heat issues.
Thanks so much!
 
Top