3 or 4 blade.. reasons not to

MBAKER

Petty Officer 1st Class
Joined
Jun 9, 2008
Messages
275
Im going to try something different. What im interested in is reasons NOT to go to a 4 blade. There are all kinds of posts praising the 4 blade switch and if I look at pretty much any help section about the 4 blades, they all say the same thing better hole shot, better midrange cruise , better time to plane, smoother, etc etc. the only downside generally mentioned is lower top speed. For most general boating needs, outside of wide open throttle runs, it seems like a 4 blade would be superior, yet I almost always see 3 blades used most of the time. But I also read conflicting posts about whether to use them on sterndrives vs outboards based on drive depth, heavy vs light boats, high vs low HP etc. One local dealer I talk to recomneds 3 blade cause blades are larger, another says 4 blade cause even though its smaller blades its more blade area.

FYI
my application is a 21' bowrider 5.7 Alpha 1, we do mostly watersports and normal cruising aroudn the lakes. The only time we ever even open it up WOT is testing a new prop for a short blast. Otherwise water is usually too rough to run much faster than midrange rpm anyway. I am looking at getting a new prop, but cant get a solid feel on whether a 4 blade would be any solid benefit.
 

Georgesalmon

Lieutenant Commander
Joined
Apr 14, 2012
Messages
1,793
Re: 3 or 4 blade.. reasons not to

Get the 4 blade for the uses you describe. Three blades are the most common because they do give the best WOT performance in most cases and that's what sells a lot of boats. You'll find the four blade is kinda like downshifting in a car. MORE POWER for pulling in watersports but not high speed. Just make sure you are running your engine in the WOT RPM range suggested by the manufacturer.
 

emilsr

Senior Chief Petty Officer
Joined
Dec 16, 2010
Messages
774
Re: 3 or 4 blade.. reasons not to

There's a lot of conflicting info out there, and a lot of misconceptions. I'll take a crack at it anyway. :rolleyes:

The potential benefits....and I say potential because you never really know until you test....are these:

Better holeshot: Part of this is because of the extra blade(s), but part of it is you have to drop an inch or 2 of pitch when you add a blade to keep the revs in the recommended rev range. This is "all other things being equal"....which they almost never are....but a lower pitched prop is as George said; it's like running in a lower gear or with a higher (numerical) gear ratio in the final drive.

Better midrange cruise: This is because the extra blade(s) usually cut down on prop slip, especially in the midrange. Prop slip isn't necessarily a bad thing (your drive will be happier), but it can be managed to improve performance (and not just at WOT). The lower pitch also tends to help with midrange accelleration.

Better time to plane: See holeshot above, but there's another factor involved and that's whether it's a naturally bow lifting, naturally stern lifting or more of a neutral lift prop. This actually has more to do with the rake of the blades, but in many cases the 4-blade props have less rake angle and therefore move the lift back further in the boat. That helps pick the transom up out of the water easier (and faster). It also tends to reduce minimum planing speed (not by a lot, but it's there).

Smoother: Yea....in theory spreading the power pulses over more than 3 blades would make for a smoother running prop, but I honestly think this aspect is overrated. It's certainly more subjective than actual performance measurements.

There's a metric buttload of other factors at play; blade shape, cup, diameter, the boat's center of gravity, the depth of the prop's centerline below the water.....the list can go on and on. The bottom line is all you can really do is go with others' experiences with similar boats and your own preferences. Lots of people really like the benefits of the extra blade, but others don't like them.....so try one out and make your own decision as to which prop you like best.

That's all theory though.....

A few years ago I had a 20' bowrider, 5.0mpi (260hp) with a 1.62 gear ratio. I tested 7 or 8 different props; wound up running a 4-blade Turbo 2+2TH, 22" of pitch (at the recommendation of others with the same boat). Compared to the fastest prop at WOT (a 23p Laser II) I lost about 2mph at WOT, but at anything less than 4500rpm the Turbo was actually faster. It also had all the benefits you've mentioned. For me it was a good fit, but again you'll have to make that determination as you're the one running it.
 

MBAKER

Petty Officer 1st Class
Joined
Jun 9, 2008
Messages
275
Re: 3 or 4 blade.. reasons not to

does a 4 blade act any different at idle speed, handling wise? I though I read one time where they caused the boat to not want to turn one way or the other as easily, making it more difficult to maneuver?
 

emilsr

Senior Chief Petty Officer
Joined
Dec 16, 2010
Messages
774
Re: 3 or 4 blade.. reasons not to

does a 4 blade act any different at idle speed, handling wise? I though I read one time where they caused the boat to not want to turn one way or the other as easily, making it more difficult to maneuver?

That has more to do with rake angle and pitch than how many blades.

Every prop will "feel" a little different around the docks but you get used to the differences.

If you're looking for downsides....

It'll be a little harder on the drive with less slip, and the drunken walk at idle is slightly worse....but just slightly.
 

mpsyamaha

Petty Officer 1st Class
Joined
Jun 8, 2007
Messages
395
Re: 3 or 4 blade.. reasons not to

it has been my experience that four bladed props handle slightly better around the dock on most boats. I feel like they have more grab for tight maneuvering at low speed. This is very evident on a twin outboard powered boat that i drive regularly, handles much better with the four bladers.
 

Ccfbailey

Seaman Apprentice
Joined
Apr 18, 2013
Messages
33
Re: 3 or 4 blade.. reasons not to

I just put a 4 blade on mine and can't believe the difference going through rough water. I use to bounce off the waves with the 3 blade, now it goes through them. MUCH nicer ride and handling.
 

callen369

Petty Officer 3rd Class
Joined
May 16, 2013
Messages
82
Re: 3 or 4 blade.. reasons not to

I just switched to a 4 blade Hustler prop, and the following were my results. Notice I did not change pitch on mine. It seems to be a decent prop. Time will tell.

I purchased the 14x21 4 blade to replace an original 14.5x21 3 blade merc prop on my 19' Sea Ray w/4.3 liter I/O. First off, the reason for a new prop...the old prop was a little worn on the edges from sand and other strikes I suppose, being this boat is new to me, and I felt there was a little more vibration when cruising than I like. I have to say the boat was propped right. It would jump out of the hole and plane in no time, and top speed was 48 at 4800 RPM. As the Turning Point site recommended, I stuck with the same size/pitch. I sacrificed a bit of diameter, and with a more aggressive prop, I figured the hole shot would be the same, maybe better, and maybe a touch more top end.

Well, took it out today, and there is quite a difference....right off the dock the boat handles better. Less left to right swaying at low speed. Just center the wheel and let it go. Nice.

Hole shot....well, not much difference if any. Though mine already had good hole shot so no deal breakers there.

Vibration.....what vibration??? Much better. Very smooth running prop. I guess control and vibration are why a lot of people choose a 4 blade, and I can see why.

Handling...well, my old prop handled great, and this one is no different. I can crank it hard and no cavitation, no slipping, just turns.

Speed....hehehe....well, I was a little concerned at first. My old prop accelerated great and topped out at 48, plenty for a 19' bowrider. So I drop the hammer and it takes off....a bit...and what's the deal???? we're only just past 40??? I should say, with the old prop, I could run 44/45 with the trim all the way down, and up a quarter, came the last couple MPH's. This new prop does not like the trim down. Brought it up a quarter, and wow..that's better, up some more, and there it is 48/49 verified by GPS. Now we're talking nearly all the way trimmed up, as in as far as you take the motor with the thumb switch, not the trailer switch. So I played around for a quarter tank or so, and honestly, this boat came out of the hole and planed just as well even starting off with the trim up almost a quarter. Also, cruising speed dropped a bit too. Before she was more comfortable around 3000 and 27/28 MPH, now she is fine with 2700/2800 at 24. Which for mileage could be a plus.

Finish on the prop looks pretty good/durable. Build looks as thick as the old one at the base, with thinner blades.

Overall I am pretty happy with it. Was a breeze to put on, maybe 15 minutes, and that's with my old prop sticking a bit and requiring a little talking to. SO...switching to a 4 blade smoothed out the vibrations, and may give me a little better economy at cruise, and I didn't sacrifice any hole shot or top end. Think I'll stick with it for a while.
 

callen369

Petty Officer 3rd Class
Joined
May 16, 2013
Messages
82
Re: 3 or 4 blade.. reasons not to

FYI
we do mostly watersports and normal cruising aroudn the lakes. The only time we ever even open it up WOT is testing a new prop for a short blast. Otherwise water is usually too rough to run much faster than midrange rpm anyway. .

That is your reason for not sticking with a 3 blade. 3 Blades will get you a little better top end, which you just said is never used. There are a lot of guys with your setup running a 5 blade.

Don't get a 4 blade if you want to be the fastest....though, when I switched to 4, I gained 1 MPH.....go figure.
 

MBAKER

Petty Officer 1st Class
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Jun 9, 2008
Messages
275
Re: 3 or 4 blade.. reasons not to

So the 4 blade did not like being deep in the water i take it?

Did you notice the hole shot being better at all with the 4? You state that it was as good as your 3 but doesnt seem like it was a great difference if any?

Based on your post would it be safe to say the most difference was in midrange cruising?
 

Ccfbailey

Seaman Apprentice
Joined
Apr 18, 2013
Messages
33
Re: 3 or 4 blade.. reasons not to

Thanks callen!! Was just about to ask for thoughts on Turning Point props. Just heard of them today. Think I'm getting the 19p 4blade Hustler. Priced well!!
 

carey965

Petty Officer 2nd Class
Joined
Jul 25, 2010
Messages
176
Re: 3 or 4 blade.. reasons not to

I just bought my boat and never used it with a 3 blade. Just went stright for the 4 and i will say its pretty nice. Gret holeshot and still managed 46mph in my 19ft br with the 4.3 and 1.81 gears

I might pick up a nice 3 blade ss 23p prop for when i want to go fast save the 4 for skiing and what not
 

rallyart

Lieutenant Junior Grade
Joined
Jun 7, 2008
Messages
1,175
Re: 3 or 4 blade.. reasons not to

Well MBAKER, to answer your first question: the 3 blade costs less, which is good 'cause you'll use more gas getting on plane and the money will be there to help with that; The 3 blade costs less to fix when you back onto the rocks and chew it up; the 3 blade is better if your sterndrive accidentally had a 1:1 drive put it and you need an 12" pitch prop; and... it weighs less so you can go up hills when you trailer, faster. (Maybe)
 

callen369

Petty Officer 3rd Class
Joined
May 16, 2013
Messages
82
Re: 3 or 4 blade.. reasons not to

So the 4 blade did not like being deep in the water i take it?

Did you notice the hole shot being better at all with the 4? You state that it was as good as your 3 but doesnt seem like it was a great difference if any?

Based on your post would it be safe to say the most difference was in midrange cruising?

That would be plenty safe. Along with better control at idle speeds and less/no vibration.

I probably had an extra hundred pounds or so on board when I switched to the 4, but not a noticeable difference. I'm guessing there are a few factors....slightly smaller diameter, the fact that the Hustler prop has to cleaver blades for better speed, and is ventilated....which is supposed to help, but since I already had good hole shot, probably didn't do much.

And no, it does not like trim down. It will take off great trimmed down all the way, but you realize pretty quick that you are lacking speed when planed out. There is a much smaller margin on this prop between porpoising and proper trim.

When selecting size, I went to the HUstler site, and they say that when switching from your original 3 blade, to select the same size and pitch in a 4 blade....or something along those lines.

A lot of guys will tell you to drop a pitch to keep RPM's, which may be the case with some, but I would advise anyone to excercise caution if choosing a Hustler due to the different blade size. Though... I sorta wonder what my results would have been with a 19 pitch....noticeably more hole shot I think and slightly less top end....well at the price point, I may have to try it out later this season.
 

MBAKER

Petty Officer 1st Class
Joined
Jun 9, 2008
Messages
275
Re: 3 or 4 blade.. reasons not to

So do you feel if you left it trimmed down at cruise it noticeably loaded the engine down more? and/lor felt sluggish?

Only reason I ask. most time we are pulling something we dont even mess with trim, just leave it down. If we are cruising sometimes ill mess with it depending on water, usually though its rough enough water I leave it down to ride a little better. Maybe I dont mess with it as much as I should. Whenever I do seems like im constanly back and forth, trimming up to free it up but then starts crashing around or porpoising and I let it back down. So if the 4 blade would drag that much more maybe I personally woudl be better off with a 3.. I dont know.
 

callen369

Petty Officer 3rd Class
Joined
May 16, 2013
Messages
82
Re: 3 or 4 blade.. reasons not to

Honestly, maybe a little at slow cruise, but not a lot. I will say even trimmed out the boat seemed to bounce less when hitting some waves.

As far as taking off...The boat seemed to plane about the same with the trim either down, or trimmed up a quarter. The prop gets up on plane quick, so after a while, I just left it trimmed up a quarter even for takeoff.

Have vacation coming up in another week! Can't wait to get the kids out on the tube and skis for the first time. That'll be the real test for the prop.
 
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