Three vs four blade?

[harringtondav]

I have a 14X21P 3 blade alum that needs repair. The shop is very good, but I expect to pay $80-$90. I can replace it with a Solas Amita 3 E series for $112. But I can also buy a Solas Amita 4 14X21P 4 blade for $11 more.

The 21P 3 blade is my best all around prop. Excellent hole shot and tubing beefy young men. Gotta use the right hand rev limiter though, since it will over rev @ 5200 rpm. Not an issue since I rarely go over 35-40 mph. I've got plenty of power to WOT a 23P 3 blade at 4800, but I don't like the engine loading at 3000 rpm cruising.

I also have a Stiletto 22 P 4 blade SS. Seems the best of both worlds, but I shy away from it due to common river trash an prop shaft risk.

What differences in WOT, max speed and hole shot would I see with the 4 blade 21P prop?
Any advantages?

 

[TunaFish389]

On mine the four has less bow rise-slower plane speed. No other advantages.

 

[harringtondav]

AllDodge . Your thoughts? I liked your insight into TunaFish389's questions, but I couldn't quite translate your advice to my question.

 

[TunaFish389]

You can get the four blade $90 out the door and iboats have a price match, hint waterfun30 item 315253. The three blade <$85 otd item 315248.

 

[alldodge]

A 4B prop takes more power to turn then a 3B, and also provides more lift. Lift can be good and bad but all depends on the boat and its load out. A 4B also has more drag then a prop with less blades, its all trade offs.

I've got plenty of power to WOT a 23P 3 blade at 4800, but I don't like the engine loading at 3000 rpm cruising.

This is your best prop if your speed is also the best, and you shouldn't be loading/lugging the motor, unless with this prop your bow is to high to see, as in pulling toys. If we had numbers for each of you props listed, this can be calculated.

The rule of thumb is 2 pitch down when going from 3 to 4B prop (19P3B = 17P4B), and the other way when going from 4 to 3B. So if a 4B is installed and rpm's stay the same, there is something else going on

So many automatically go to more blades without doing due diligence first. Its all good, but when another buys their boat and they wind up here asking why a boat is doing this with a 4 or 5B prop. Have a set of 4B props (Bravo 3) for my cruiser, and they did work pretty well, but the added lift required less trim (drive tucked in more) and was a bit touchy with proposing. There no longer installed because now I over rev after removing bottom paint

 

[harringtondav]

This is your best prop if . If we had numbers for each of you props listed, this can be calculated.

There no longer installed because now I over rev after removing bottom paint

All numbers are dash speedo and tach: 21P = 5200 rpm @ 48 mph, 3200 rpm at 30 mph. 23P = 4800 rpm at 52 mph. 3000 rpm at 30 mph. Follows the 200 rpm change per inch of pitch rule perfectly. ...don't spend much time at 52 mph. Not much hull in the water, and if someone scratches their nose it wants to start chine walking. I also notice the engine temp is slightly higher and oil pressure slightly lower at 3000 rpm with the 23P. Thus my concern about lugging at cruise.

Also interesting about your bottom paint. Don't use the stuff in fresh water on a lift. I've heard stories how it drags you down. Your story verifies this.

 

[alldodge]

Using your numbers and a 1.81 ratio drive
23P = 10% WOT and 17% cruise
21P = 16% WOT and 15% cruise

The 4B has more lift less bite. The WOT and cruise numbers should show higher slip with both props at WOT when compared to cruise. Can get an app for the phone to measure speed to see how close the boat speed-o is. In most cases they are close in on area but not in another

I also notice the engine temp is slightly higher and oil pressure slightly lower at 3000 rpm with the 23P.

Oil pressure slightly lower with 200 less rpm might happen, but would be so small might not notice. This is also an electrical gauge so variations in components I would suspect first. Would verify with mechanical gauge, and if it is enough to notice I would think something with the motor and/or oil pump.

Same with temp

 

[Starcraft5834]

Heavier boats benefit most by 4 blade.. more bite- meaning thrust.... quicker hole shot, get on plane faster at slower speeds. if your not a speed junkie... id recommend a 4 over 3

 

[BillP]

Both types can be pretty well matched in perfomance by diameter and pitch changes. In my area of Florida 3 blades rule for most boats and 4 blades are used for flats boats with jack plates. 4 blade props let you jack up to the hub center and keep 2 blades in the water.

 

[harringtondav]

Heavier boats benefit most by 4 blade.. more bite- meaning thrust.... quicker hole shot, get on plane faster at slower speeds. if your not a speed junkie... id recommend a 4 over 3

Thanks. My '17 Larson isn't terribly heavy. +-2500#, and the 4.3 LX provides plenty of power. Thinking I'll go with the 4 blade. I have another good 3 blade 21P, but I always carry a spare. Whichever 3 or 4 blade works best, the other goes under the bow seat.

 

[alldodge]

Heavier really?
Rinker 4800 and tried 4 and will stick with 3
Formula 10,000 and would like to try a 4 again to see the difference, but did not like the way the trim was so touchy

All boats are different and so are opinions, just like mine

 

[QBhoy]

I’d say if you don’t need a 4 blade for a reason in particular always try and stay with a 3 blade (for general boats and terms). Much more efficient usually.
I wouldn’t worry about your boat loading at 3000 rpm cruising. That’s probably a good rpm to be cruising at. My boat will cruise at 2200-2400 without loading or lugging.
If you can turn a 23” to max rpm range and it cruises at 3000 rpm. I’d suggest that’s the perfect prop for you ?

 

[Scott06]

Thanks. My '17 Larson isn't terribly heavy. +-2500#, and the 4.3 LX provides plenty of power. Thinking I'll go with the 4 blade. I have another good 3 blade 21P, but I always carry a spare. Whichever 3 or 4 blade works best, the other goes under the bow seat.

ive used 4 blades on my last two boats, but i think it really depends on how you use your boat. The fours I've used Michigan vortex, vensura, and Revolution 4) have provided better stern lift, holeshot, and slower planing speed than the three blades I've used (black max, enertia). 90% of my use is my kids , their friends, water skiing/tubing/wakeboarding... 6-8 people and towing. So for how I use it 4 blade is better in every way except top speed, which I rarely do.

Cueenrt boat is 21 ft Sea Ray sport, beamy and a bit heavy, best top end is with a rev 4, best holeshot with vensura. If you like aluminum and wot is ok with a 21" three blade I'd suggest the Michigan vortex 4 blade, 20". Pretty cheap, good holeshot

 

[porscheguy]

I’ve actually met Scott06 and own his old 22p enertia, which mostly sits on my shelf. I too have a rev4. It does give stern lift which is helpful on mine. It slips a lot when you first hit the throttle, and then it bites down hard and takes off. Minimum Planing speed is about the same as my mirage. Top end is 1mph slower.

 

[harringtondav]

Thanks to all. I pulled the "Place Order" trigger on the 4 blade last night. As I stated before I keep two 21P on the boat. One on the drive, one under the bow cushion as a spare. Now I have the choice of 3 or 4 blade to keep on the drive. I'll report back my numbers with both. Sometime in late July with the Miss river still 8' over my launch level.

Still have the 3 blade 23 P which hits WOT rev when I'm hurry to get somewhere, and the 22P 4 blade SS for whenever. - Mostly bottomless, hazzardless lake boating. I'm pretty well covered.