4 blade prop on a 115 merc?

[sim]

Can anybody recommend a 4 blade prop to put on an 89 Predictor with a 115 Merc. What difference could I expect to see between that and a 23 pitch stainless steel which porpoises a lot and a 21 inch aluminum which ventilates really fast when you trim up?

 

[boatman4021]

4 blade props will work! I have a friend who has a 17" bass boat with a 125 merc and he runs a 23" Trophy+. It works very well. The Trophy+ or the Turning Point Classic will work very well. boatman

 

[Mark]

I found the Trophy to be too big for the 4 cylinder motors to turn. My experience has been the intermediate size motors need a smaller prop in order to get out of the hole quick. Because these motors are almost always on smaller boats they do not need big blade area to push them. The best prop I have found has been the Powertech RXB4. It is only 13" in diameter so it will spool up quickly. It will not ventilate at all and has good speed. With only moderate rake it has less bow lift and therefore less porpoising. It looks like a Trophy or TRO4 that your wife shrunk in the wash. I am running a 19" on my Diplomat and turning it to 6000 RPM. Top end is not my first priority since we ski behind this boat. Note: PT props are always a little steep in pitch for what they are stamped. The RXB's are a little tough to find used. Pitstop Marine is probably cheapest new. Here is a complete catalogue of Powertech props...it will stagger the mind how many they make.
http://www.rundquist.com/Naples/PowerTechCatalog.pdf

 

[Mark]

BTW, the SCD4 would probably get rid of all your propoising as it is a stern lifter not a bow lifter like the PTR4. The RXB4 is in between.

 

[sim]

thanks, Mark. A question

Mark- what are you running? Is it a Yamaha, as it appears in your photo?
And whats it's rated top rpm. On my merc it's 4750 t0 5250. With an aluminum 3 blade 21 pitch (13 diam) it's wot at 5000 and 48 mph on the gps.
Stainless steel 23 pitch is about 200 rpm less and 52 on the gps. What's your speed at the 6000 you mentioned and is that the correct rpm.
I don't mind trading some top speed for better bite and lower planing when skiing or tubing the family.

 

[Mark]

It is a 130 yamaha. WOT rated to 6000 RPM. I am seeing 55 MPH.
If you want holeshot you want the least pitched prop that won't over-rev your motor at WOT. Therefore, you should be propping right up to 5250 RPM. I would recommend a 19" SCD4 or RXB4. The lower pitch (than the 21 AL) will raise your RPM 300 but the extra blade will drop it 100. Should get you to 5200 or so.
I own half a dozen PT props. They are miles ahead of everybody in prop R&D.
There is a guy at the Powertech factory called Marcus. If you call him he will spend half an hour on the phone with you and help you find the right prop.