new to boating, not sure which prop to get

[delacruz845]

Hello everyone, I just bought a 2002 celebrity bowrider with a 3.0 mercruiser I/O last weekend. I plan on cruising around but also maybe some tubing and skiing. Right now there is a 3 blade prop on there, not sure what the pitch is, any suggestions on a 3 blade or 4 blade and pitch? Any other tips for a newbie would be greatly appreciated, thanks everyone

 

[Sea Rider]

Welcome to Iboats,

Need max rpm wot numbers achieved with lightly loaded boat on flat calm waters to start with...

Happy Boating

 

[Chris1956]

As was said, load the boat normally, and run it wide open, with trim enough to give her light steering. Note the RPM, an post back.

 

[steelespike]

Welcome If you read the stickys at the top of the prop forum and get us as much info as possible it will help us.
Your prop size should appear near the base of the blades or under the prop nut.Your prop size and present lightly loaded wot rpm and gps speed will help.
Prop size is written diameter X pitch. Pitch is the key number.Very basically Low pitch(low number) gives more power less speed ,higher pitch
gives more speed less power. Boat needs to have a pitch that allows the motor to reach its rated wot (wide open throttle) rpm.
probably 4800 for your motor.Of course yopu can opertatye the boat at what ever speed you require.
Typically a 3.0 will end up with a 17,19 or 21" pitch.Depending on the typical load, activities and boat size and weight.

 

[delacruz845]

Thank you all very much, I have to replace the shift cable today or else I would be out on the water testing it. I'll record everything next weekend and get you guys all the info you need. Thanks again

 

[delacruz845]

So I was finally able to get it out on the river and open it up. With 3 guys in the boat I was able to cruise at 30mph and the rpm was at 3900-4000 rpm. The boat seems very sluggish and slow off the start, not sure if changing the prop will help. Also just a little more info, I rebuilt the carb, new spark plugs, new fuel pump, amd a new ignition coil.

 

[steelespike]

We need your prop size should be near the based of the blades or under the prop nut.

 

[steelespike]

rpm and speed was at wot? Is speed by gps?
We need your prop size should be near the base of the blades or under the prop nut.

 

[delacruz845]

Yes the speed was by gps and I was at wot and the tach was right at 3900rpm, give me a few and I will get the prop size

 

[delacruz845]

88 78120A10819P that is the only numbers I can find on my prop, it looks like it was painted before

 

[jestor68]

Interestingly, that boat most likely came originally equipped with a 21 pitch prop(confirmed by the Mercury prop selector based on the boats weight,etc.). And would have been able to turn around 4600 rpm when new.

The fact that it has a 19 pitch demonstrates how over time, it had to be re propped to maintain decent performance as the motor lost some of it's getty up.

Now it can't pull a 19 pitch anymore, and needs to be re propped again down to a 17 pitch in order to get the rpm back up within the proper range(barely).

Your motor is pretty well worn out, and really needs to be rebuilt/replaced. The 3.0L motors are usually abused( lots of full throttle time) and don't last as long as the larger motor that doesn't have to go wide open to go 40 mph.

The only other choice is to keep re propping til you find that pitch that gets the rpm back up where it should be.

Realistically, you need to go down to a 15 X 15 in order get back up near the top of the rpm range. You likely won't lose any top speed; probably will go faster

 

[steelespike]

While Jestor is probably right on the nose but it is possible something simple is going on Perhaps the throttle isn't opening all the way?
Perhaps an issue with the ignition/timing.
You did replace the shift cable perhaps the throttle cable got messed up in the process.

 

[Starcraft5834]

Agree with Jestor.......take a look at Solas 14.75 x15p 4 blade props...........that would likely give you the punch you need and get you back around recommended rpm range...

 

[bspeth]

A prop is cheaper than an engine,just sayin

 

[gddavid]

Interestingly, that boat most likely came originally equipped with a 21 pitch prop(confirmed by the Mercury prop selector based on the boats weight,etc.). And would have been able to turn around 4600 rpm when new.
The fact that it has a 19 pitch demonstrates how over time, it had to be re propped to maintain decent performance as the motor lost some of it's getty up.
Now it can't pull a 19 pitch anymore, and needs to be re propped again down to a 17 pitch in order to get the rpm back up within the proper range(barely).
Your motor is pretty well worn out, and really needs to be rebuilt/replaced. The 3.0L motors are usually abused( lots of full throttle time) and don't last as long as the larger motor that doesn't have to go wide open to go 40 mph.
The only other choice is to keep re propping til you find that pitch that gets the rpm back up where it should be.
Realistically, you need to go down to a 15 X 15 in order get back up near the top of the rpm range. You likely won't lose any top speed; probably will go faster

I believe the OP stated the boat was cruising at 30 mph @ 3900-4000 rpm not wide open throttle. I would be willing to wager the boat came with a 19" prop and it is still operating as it should. The 3.0L is a pretty tough little beast and seldom does the average boater put enough hours on them to wear them out. I believe your jumping to conclusions that his motor is worn out is a bit premature.

 

[steelespike]

He did say speed was by gps and at wot, further down the thread.

 

[delacruz845]

Thank you all for your input. I'm almost positive the throttle is opening all the way, I will try to make a few more adjustments on the carb but in the meantime I will look into getting a new prop and see how that goes

 

[midcarolina]

So I was finally able to get it out on the river and open it up. With 3 guys in the boat I was able to cruise at 30mph and the rpm was at 3900-4000 rpm. The boat seems very sluggish and slow off the start, not sure if changing the prop will help. Also just a little more info, I rebuilt the carb, new spark plugs, new fuel pump, amd a new ignition coil.

IMO......There is no way anyone can make the determination of a tired motor based on the very limited information in this thread, one can guess, but it is just as likely that the boat's flotation under floor is water logged, or the timing is off, or there is a fuel delivery problem, or the carb butterflies are not opening all the way.......And that is just a few of the possible issue's

If you think it may be a tired motor, it is very easy to do a compression test to confirm or rule out.

 

[steelespike]

Most of your suggestions have already been made I overlooked absorbed water and at 12 years old anything is possible.

 

[steelespike]

While prop selection can help get part of the performance back. If the motor is tired you end up with a a motor turning wot rpm but at 3/4 of normal speed.
IMO further aggravating the motors condition.