Prop selection..

[toddc76]

All,

First post but longtime lurker. I like to research my problems and try to solve them from previous posts and not bother you fine folks but I don't see the answer to my question.

I have a '88 Bayliner 2155 (3100# 22' cabin cruiser) powered by a OMC 5.0L (gm 305c/i). Its time for a new prop and I am pretty lost and overwhelmed by the options. It has a 15.5" x 15" 3-blade on there now. Had it out this weekend and it only seemed to be turning 3500 rpm with a lot of hole-shot (which I really don't care about). I like cruising around and saying hi to everyone and maybe the occasional pulling a tube around sorta fun when we have guests. Would a 4-blade be better or stick with a 3?

This boat is a restoration and is new to me. So far I am pretty happy.

Thanks in advance.

-T

 

[steelespike]

Re: Prop selection..

What was the speed at 3,500?
Speaking very basically I think the motor is rated at 4600 rpm.
If the tach is accurate your about 1100 rpm short. The speed will help tell
if the rpm is accurate.You can't make up that much with a prop.
Again reminding if the tach is accurate You need to check out the motor.
Simple to start with are all plug wires hooked up.Does the throttle open all the way at the carb?Is the motor in excellent tune timing set right and advancing as it should?
Does the boat respond to up trim. Check the compression.

 

[reeltime170]

Re: Prop selection..

I was actually wondering about prop selection as well. I bought a used 1989 Larson, 17' with a 3.7 mercruiser, but someone stole the prop before i got it, so I dont know what prop to get, regarding pitch.

 

[reddogg]

Re: Prop selection..

From what I understand a 4 blade is better for holeshot/pulling and not so good for top speed. The pitch is measured in inches per revolution, so a 15 pitch will move the boat 15" in one turn of the prop. The prop should be sized so that when the boat is at wot the rpm's fall within the operating range, i;ve heard it's good to be right in the middle of it.

red

 

[reeltime170]

Re: Prop selection..

Thanks, very helpful info. Anything I can help ya with, feel free to ask

 

[toddc76]

Re: Prop selection..

What was the speed at 3,500?
Speaking very basically I think the motor is rated at 4600 rpm.
If the tach is accurate your about 1100 rpm short. The speed will help tell
if the rpm is accurate.You can't make up that much with a prop.
Again reminding if the tach is accurate You need to check out the motor.
Simple to start with are all plug wires hooked up.Does the throttle open all the way at the carb?Is the motor in excellent tune timing set right and advancing as it should?
Does the boat respond to up trim. Check the compression.

Speed was around 33-35 checked with a GPS.
Engine starts right up but have not checked compression.
Tach IS suspect, its 23 years old. I will borrow a known good tach and check it out.
I did some basic tune-up when I took possession of the boat but have not gone through it soup to nuts.
At that speed the engine sounds good for a V8, hums right along.

I would think that 33mph is pretty decent for a boat of that weight, maybe I should leave good enough alone and just order the same prop.