Help me choose the correct prop size please

[genesis78]

Hello all, I am new to boating and just purchased my first boat. It is a 19 foot Wellcraft 190 Classic bowrider. It has a Mercruiser 3.0 135HP. After getting used to the boat for a little bit I went WOT and found that this equates to about 40mph. While this is perfectly fine with me, I found that the engine only reaches 4K RPM. From my research I think the max RPM form my engine at WOT is 4800, so I am not reaching anywhere near the revs I should be. I checked that prop (it needs to be replaced, has a few chips in it) and found it marked "21P" Does that mean it is a 21 pitch prop? If so I think that is why I cant get my engine over 4K.

I think I need a 17P prop based on the information I read stateing that I will gain 200RPM for every inch pitch I drop. If that is correct, will dropping to the right pitch actually slow my boat down?

 

[Haut Medoc]

Re: Help me choose the correct prop size please

Hello all, I am new to boating and just purchased my first boat. It is a 19 foot Wellcraft 190 Classic bowrider. It has a Mercruiser 3.0 135HP. After getting used to the boat for a little bit I went WOT and found that this equates to about 40mph. While this is perfectly fine with me, I found that the engine only reaches 4K RPM. From my research I think the max RPM form my engine at WOT is 4800, so I am not reaching anywhere near the revs I should be. I checked that prop (it needs to be replaced, has a few chips in it) and found it marked "21P" Does that mean it is a 21 pitch prop? If so I think that is why I cant get my engine over 4K.

I think I need a 17P prop based on the information I read stateing that I will gain 200RPM for every inch pitch I drop. If that is correct, will dropping to the right pitch actually slow my boat down?

I would verify the tach, but, yeah a 17 or 19 pitch is more like it....
4800 seems a little high .....
4200-4600 is more like it..........
You will get a better hole shot.....
You really should not lose top end & your engine won't have to work as hard or 'lug'.......
Welcome to iboats, btw......

 

[Chris1956]

Re: Help me choose the correct prop size please

A 19" pitch prop of the same style, should raise the RPM by +400, which I think perfect.

 

[180shabah]

Re: Help me choose the correct prop size please

Verify your tach first.
A prop with chips and dings in it can cut several hundred RPMs off the top if they are bad enough. You may not need to reduce pitch at all. Can you borrow a good prop from someone to test with. If not, your dealer may have a prop exchange program, this will let you try out a few different props and purchase the one you like best.



PS - this should really be in the prop forum.

 

[Don S]

Re: Help me choose the correct prop size please

Moving to Prop Topics and Questions.

 

[genesis78]

Re: Help me choose the correct prop size please

Thanks for the quick response! How do I verify my tach?

 

[Silvertip]

Re: Help me choose the correct prop size please

You verify your tach against another tach -- a shop tach for example or a timing light with a built-in tach.

 

[genesis78]

Re: Help me choose the correct prop size please

Ahh ok, I guess I need to do that first then. Ok thanks for the help. Am I damageing my engine by lugging it with a prop that is to big? (still going to fix the issue just curious as I don't know how long the possibly incorrect prop has been on the boat.)