Swap from 3 Blade prop 19P to 4 blade prop

[Franco_boater]

Hello, in Mercruiser section I’ve found discussion about running engine lean when swap from 3blade to 4 blade prop . So here’s my question
Now I am using 3 blade 19P black diamond in alpha one gen 2, got 4 blade 19P Nemesis in good price, can I expect better hole shot and handling??

 

[alldodge]

can I expect better hole shot and handling??

Not necessarily. Everything has trade offs. 4B-19 is like a 3B-21, so using a 4B your going to loose RPM at WOT. The 4B bites better and therefore has less slip, but depending on the boat (heavier) a 3B will get you up quicker because RPM's will come up faster and put the motor higher in its torque curve

This is my opinion and others will be along shortly tell ya the opposite

 

[Franco_boater]

Ehhh so I screwed up.. wanted to get on plane faster, I’m towing with family I’m not running at WOT ….
It’s 19 footer bow rider

 

[alldodge]

If you went to a 4B-17 that might do it, or going to a 3B-17 will jump out good.

I use to use a 3B-19 when pulling skiiers and tubes and go back to 3B-21 when just cruising. Could over Rev with the 19, but it would sure get the boat up fast

 

[Franco_boater]

now I’m using 3B-19p and I was generally happy even for top speed and hole but just wanted to experience something new… so here we are with wrong prop…
Do you think it’s “safe” to use this 4B-19 during this season? Or I can stress gear /engine

 

[mbaker812]

Hello, in Mercruiser section I’ve found discussion about running engine lean when swap from 3blade to 4 blade prop . So here’s my question
Now I am using 3 blade 19P black diamond in alpha one gen 2, got 4 blade 19P Nemesis in good price, can I expect better hole shot and handling??

I just made this swap but went from a 14.25-21 three blade to a 14-21 four blade. tried it this weekend and better bite and handling for sure with the 4 blade especially at lower speeds. stayed planed all the way down to 15 mph. 3 blade would come off plane at 18 mph. docking and trailering was smoother in my opinion. both props were turning point props and new 4 blade is the TP Hustler.
I have a sea ray 210 sundeck. heavy boat with a 5.7 mercruiser EFI TBI

 

[alldodge]

now I’m using 3B-19p and I was generally happy even for top speed and hole but just wanted to experience something new… so here we are with wrong prop…
Do you think it’s “safe” to use this 4B-19 during this season? Or I can stress gear /engine

Won't hurt a thing short term. Your probably not going to reach WOT RPM as you did before, so a bit of lugging but probably not enough to worry with now

 

[Scott06]

I think it depends on the 4B prop. The Nemesis is not that big bladed prop and doesn't have too much bite so you may not loose too many rpm. Either way you want prop pitch to be such that you can get to the upper part of the WOT RPM range.

I have run several 4 blade props - 21" Vensura, 21" Revolution4, and a 23" Spitfire (merc name of Quicksilver branded nemesis).

The 23" Spitfire/nemesis has same WOT RPM as the Rev4.
The Vensura had best hole shot but also had 20% slip at WOT - this is what AD had mentioned it allowed the engine to spin up a little faster as the blades didn't have as much bite as the Rev4
I settled on using the Revolution 4, with vent plugs opened had slightly worse hole shot than the Vensura, but top speed bested even a 3 B Enteria because it bit well enough I could fully trim out.

So bottom line some experimentation is in order between pitch and blade design. For how I use my boat (loaded watersports) I think a 4B really performs nicely

 

[Texasmark]

My Turning Point Hustler 4 blade aluminum props are ported....holes under the leading edge of the blade. As "alldodge" mentioned, getting the RPMs up fast gets the HP up fast and HP twists the prop shaft. The 4 blade has more bite but you need HP to drive that bite if you expect a fast HS. The ports allow exhaust gasses to flow across the blades at low speeds which reduces the density of the water which allows the engine to rev faster which gets up up and going faster. Once up to speed, the new water flowing past the prop seals off the ports and they no longer affect performance.

So if you are getting a faster shot with the 4 blade with nothing else changed other than the prop, the ports are giving it to you.