Bravo III Props 3 blade to 4?

[ss3964spd]

My 2004MY 24 foot cuddy has the 350 MAG MPI and 2:1 B3 combination, with the original 24P 3 blade B3 prop set.

Does anyone have any experience with running the 3 blade set against the newer 4 blade set? Merc's prop selector, using "overall good performance" and "current boat performance" (24P, WOT = 4800, current top speed = 48 MPH) as a criteria, suggests an impressive increase in top end without (I assume) any loss in hole shot with their new 24P 4 blade prop set. But running the calculator and substituting current boat performance for "current boat length" (24') it recommends the same prop set but no increase in top end.

Just looking for anyone who has made the switch and can share their observations.

 

[alldodge]

Howdy

Your at your optimum rpm at WOT. Going from a 3 to 4 blade prop gives you more lift, and lift can be good and bad, all depends on the boat.

IMO going from 24 3x3 to 24 4x4 would drop your rpm at WOT to around 4400 rpm. If you used a 24 4x3 you would drop around 4500 rpm.

The rule of thumb is go down 2 inch of pitch going from 3x3 to 4x4, so you would be in the 22 for Hill Marine props or 23 for Merc XR. I am currently working with 24 4x4 and 26 3x3 on my Formula. My boat is much heavier then yours, but at WOT my trim is real touchy, takes next to nothing to go from proposing to plowing with the 4x4. To achieve 1 mph more then what you have at max rpm you need more HP.

 

[ss3964spd]

Thanks for the feedback AD. Yes, I do know the general rules of thumb when it comes to props.

​What I found interesting was that Merc's online prop selector did not recommend a 3 blade prop set no matter how I changed the input parameters. Each recommendation was a 4 blade set, but some with different pitches and diameters, but still all 4 blade sets.

And another site, Hill Marine, has this to say about their 4 blade set: "The Signature Four By 4 Propellers were designed to run at the same RPM range as the OME three blade propellers. It is not necessary to drop pitch sizes when going to the four blade combination unless an increase or decrease in RPM is desired. All mounting hardware remains the same , no additional hardware is required." http://www.hillmarine.net/Bravo-3-4-blade-propellers-p/tpl4ds-hpr4cs.htm

Anyway, still looking for any direct experience from anyone who's made the switch.

 

[alldodge]

I had a long talk with John Hill prior to buying my set. I was using a 26 3x3 set and was reaching 5200 rpm WOT. He recommended the 24 4x4 to replace the 26. I still achieve the 5200 rpm but no fast. John is good to talk with, give them a call and if available he will talk to you, and his son is also good (family business)

 

[ss3964spd]

Thanks AD, your feed back is appreciated.

​Dan