Does this make sense - Need some validation

[dmanmtl]

Boat is a 2003 Bayliner 175, 135HP, Alpha 1. Current prop is the stock 14.25/21pitch. I would like to have a backup prop on board, just in case...

I would also like to try a 4 blade. The local Marina suggest I got with a 14/19 Pitch. My current WOT is about 5000RPM (too high) and about 43-44 MPH (GPS verified).

I don't mind losing some top end as I rarely drive that fast but would liek a faster plane time for tube pulling etc.

Does the 14inch/19Pitch prop sound like it will help me get what I need (it is an aluminum prop).

DM

 

[MikDee]

That sounds perfect, given the info you posted! You will think you have 2 different boats, and really appreciate it.

 

[Starcraft5834]

I agree with Mik...you will find the proper 4 blade application to be a overall better choice.. advantages far outweigh negatives when it comes to comparing 4 to 3 blade props

 

[eavega]

I agree with the 4-blade being what you really want, if you are looking to trade top end for better planing. HOWEVER, if you are already turning a 21P prop at 5K rpm, then you need to think about having a higher pitch on the 4-blade than 19. I have a similar boat to you (Stingray 176 with the Mercruiser 3.0), and I have been running a 20P SST 3-blade prop. My motor could turn that prop at 4200 RPM WOT, which was slightly low. I needed to drop pitch to increase RPM. I put a 4-blade 17P Solas Amita Aluminum on there, and now my WOT RPM comes in right at 4500.
Lets first assume that the right prop for your application is a 23P 3-blade (should get your RPMs in the 4600 RPM range), then if you go to a 4-blade step that down one for a 22P. I would definitely NOT drop pitch, as that would cause your motor to increase RPM and get further out of your recommended max RPM range.

Rgds
Eric

 

[jestor68]

A test of your boat on the Mercury site resulted in a top speed of 43.6 mph @ 4800 rpm; representing a 9% slip(good).

I believe your tach is a little off, reading 5K at the same speed.

The general recommendation is to drop one inch of pitch to maintain rpm. So it sounds like a 20 pitch 4 blade would be the prudent choice.

Mercury's Alpha 4 comes in 16,18, and 20 pitches. I think Michigan makes a 20 pitch 4 blade also. Solas offers that pitch in SS 4 blade props.

 

[Moose_25_2500]

I have a very similar boat...2002 Bayliner 1950 capri classic with same engine. Just switched from the stock 14.25 x 21p 3 blade to an Alpha 4 18p 4 blade. It planes so much faster 4-5 secs and can pull tubes and skiers a lot easier. I am hitting 36 mph as my top speed but cannot give you an accurate tach reading. having issues with it right now. Love the 4 blade prop. My top end before was no more that 40 mph before the switch. You are getting more out of your engine than me so I would not go below 20p