3 Blade to 4 Bladed Prop

Suzook

So, I'm looking at changing props from a 3 blade SS Yamaha 17-M 14.25 x 17 to a 4 bladed Aluminum unit.  My sticking point right now is keeping the same diameter and pitch or changing one or the other.  However, I've done so much research I'm more confused than when I started, thoughts anyone?

Ernest_T

I think pitch is more important than diameter.  I went from a Yamaha 17p ss prop to a Powertech 15p ss prop on my boat.  The goal in prop selection is to maintain you maximal rpms with the new prop.  For my Yamaha 150 four stroke, I was hitting very close to the max of 6000 rpms with the Yamaha prop that came on the boat, which is optimal for performance.  I wanted the 4 blade prop for better hole shot for towing skiers.  I contacted Powertech, and their tech. suggested prop choices that would get me close to optimal rpms.  Most prop manufacturers can suggest a 4 blade prop for your boat, but prop selection is always a crap shoot.  It helps if you get a prop that can be returned if it doesn't work out.  When I switched to the 15p prop my max rpms dropped to 5800, which was pretty close to optimal, and the tech told me he doubted we could get any closer to 6000 rpms with any other 4 bladed prop.  

The first step is to know what your max. rpms are, and what you are getting with your current prop.  I can just about guarantee you that if you go from a 17p 3 blade prop to a 17p 4 blade prop you will be very disappointed in the performance.  You almost always have to drop in pitch from 3 to 4 blades.

nprcoolcop380

I have a stainless steel "Vengeance" prop on my Hurricane. Yamaha 150. Max RPM's and have had no complaints.

Suzook

Thank you for the replies. Ernest T, I actually started my research based on your posts and TNrivers.   My requirements basically mimic ya'lls, in that, my wife doesn't appreciate the glory of WOT (LOL), and we mostly tow water toys and fish.  Anyhow, one of the concerns made by some had to do with the increased loads of a 4-bladed prop on the lower unit, and or to the transom itself.  As I'm still fairly new to boating I probably am making more of this than it needs to be, but I appreciate any advice/comments on the topic.  As it is right now I think the best thing to do is to go out and make some WOT runs to make a better decision.  Coming out of winter I still have a full fuel load can I continue on with tests or get closer to a 1/2 tank?

Ernest_T

I think you can run it as is to get an idea of where you are at now.  I don't think there would be any worry about damage to your lower unit or transom from switching props.  

Here is a link for Yamaha's prop selector:  http://www.yamahapropselector.com/propSelector/web/
And here is Mercury's selector: https://www.mercurymarine.com/en/us/propellers/selector/#/step-one

You can use these as guides to help get you in the ballpark.