Props, 3 blade vs 4 blade

R

rcwass

New member
I operate in high current waters. My 22' cruiser is all over the place in this current. I currently have a 1990 70HP Johnson but will be re-powering in the early spring. Most boaters I know have 3 blade props. My current prop is a 3 blade. I'm told that a 4 blade prop would give me more control. Does anyone have knowledge of what a 4 blade prop would give me over a 3 blade prop? Thanks for your help.
Dick
 
This has been talked about before here at the site. try a search. also the whole compsite over alum or steel prop. I have run a comprop and now have a 4 blade alum one and I really like it.
 
Here's a couple of links from elsewhere on the site

http://www.c-brats.com/viewtopic.php?t= ... rop++blade
http://www.c-brats.com/viewtopic.php?t= ... rop++blade

You could
1) Look at these links - which discuss it a lot w/o really coming to a conclusion
2) Do your own search to find even more links which also discuss it without really coming to a conclusion
3) Do whatever feels right to you or
4) Wait for DoD or BC to reply since there's nothing they like better than talking about props :lol: (and then do 3)...

Roger on the SeaDNA
 
When I bought a spare propeller for my 16 Cruiser/Honda 50 the dealer recommended the 4 blade version. I installed it to test and haven't taken it off, the original 3 blade is the spare. No scientific test data but the 4 blade wheel seems to provide a bit more control in rough condidions (for some reason).

-- Chuck
 
OK, here is a comparison, including MPH and MPG of two identical CD25s, both with Honda BF150s. Pat (Daydream) is running a 4 blade ProPulse and David (Anna Leigh) MUST be running the stock 3 blade stainless, based on reported speeds (I was getting exactly the same speeds when I ran the 3 blade). If anything, Daydream is loaded heavier (sorry I can't do real tables here - is there a way?).

RPM MPH..............MPG
.......Pat.David....Pat.David
2500 8.3 6.2.......5.5 4.8
3000 10.3 8.0.....3.0 3.5
3500 13.5 9.6.....3.1 2.5
4000 17.0 12.5....3.2 3.1
4500 20.7 15.5....3.6 3.2
5000 23.8 19..... 3.5 3.1

I am sure we will both do a lot more checking with the Navmans (Navmen?) but one thing you can see right off the bat is the 4 blade is giving higher speeds at lower RPMs, which I presume would translate into less engine wear - but it seems like we both have our "sweet spot" for fuel economy somewhere around 4500 RPMs, and 4 blade is giving a little bit better fuel economy.
 
Pat here is you helping hand....Prop Chart.



PropChart1.jpg
 
Pat-

Pretty interesting!

Assuming David's 3-blade is the same 15 inch pitch as yours, it would seem that the results support my theory that heavy boats like the C-Dory benefit more from the extra area of a 4 -blade prop than they can from the speed accomodation of a three-blade.

Lighter boats can often make better use of three blade props, which have a greater range of speed accomodation with their lesser surface area and other design differences in rake, cup, etc.

Big boats need more bite to efficiently transfer energy from the propshaft into forward thrust.

Joe.
 
OK, I've plotted them, as usual. And I hope they appear below. Either that or they're posted on the Journey On album.

I assume that both props are pitched at 15" My 4 blade is pitched at 16", and I'll try to get a RPM curve this weekend. The flowmeter comes later (much later, according to Judy.)

Note that the 4 blade runs slower (lower RPMs at same speed,geared lower) that the 3 blade. The fuel difference at a 15 mph cruise isn't so great, but once you go off 4000 rpm the 4 blade does give better mileage. And the CompProp is half the price of the !@#$ stainless 3 blade.

C_25_MPG_0.jpg
C_25_RPM_0.jpg

Boris
 
I didn't see any speed changes on my 22 between a 3 bladed 15 pitch and a 4 bladed 15 pitch. What I did see was better acceleration. With the 4 blade I could feel myself being pushed back in the seat but never felt that with the 3 blade.
 
OK, we finally did run her up to WOT - 5600 RPM, about 26 mph, and probably climbing - we just wanted to see where the RPMs would go...





Sea Skipper":kt2xzixo said:
Pat, what is your maximum Wide Open Throttle (WOT) with the Pro Pulse prop set @ 15" pitch?

Hank (Sea Skipper)
Click to expand...
 
I've spent some time collecting performance data for the Suzuki 90 with a ProPulse (4-blade) prop set at 17P. I'm fairly satisfied with the ProPulse, (atleast performance seems somewhat better than with the factory 14x17P 3-blade).

Piranha Prop ( www.piranha.com ), another composite prop manufacturer, has a hub/blade configuration that is 14" diameter x 18P (whereas the ProPulse is only 13.5 diameter) that may be my next experiment. (Still trying to get up a reliable 4mpg at 4000-4200rpm cruise.)

With the ProPulse (17P) I got 5600@WOT which is high for the Suzuki (WOT: 4500-5500rpm). I figure the Piranha's greater diameter + 18P may bring WOT down to about 4800 with greater thrust (and hopefully increased MPG). We'll see.

The sea trials are kind of fun, but challenging since you'd got to keep test parameters reasonably standardized. Oh well, when I get the Piranha prop, I guess we'll just have to go back to the Keys for more testing. ...a guys gotta do, what a guys gotta do!

I'd post the Excel spreadsheet data, but can't figure-out how to do it here(...even read the instructions for doing Attachments!). Oh Well. If anyone want's a copy of the spreadsheet, email me. (I know how to do that!)

Casey
C-Dory Naknek
lorencasebeer@aol.com
 
OK, here's what I found out today in San Diego.

First, Daydream, I assume when you said MPH, you meant MPH, not Knots?
That's a question.

For Journey On, two data points:

3500 RPM 16.0 MPH (13.9 Knts)
4000 RPM 19.6 MPH (17.0 Knts)

Fast enough for Judy, and the boat was loaded for the week end. CompProp at 16 in.

Boris
 
Yes, it is mph not knots. When you say 16 in., I assume you mean 16 pitch. I have my ProPulse at 15 pitch. The big question at 16 pitch is whether at WOT you can hit the bottom of the full-throttle range, which on the BF150 is 5000 - 6000 RPM (page 104 of the manual). I originally had it set at 16 pitch and couldn't exceed 4500 RPMs, so I ratched it back to 15 pitch, which is as low as it goes. I did run it up to 5000 RPM just to check that I could get there, and that was nearly 24 mph, but did not keep going to see what RPM or speed WOT might ultimately reach - I am guessing maybe 5500 RPM. For me, the 4500 RPM speed of 20+ mph is about as fast as I am likely to go anyway.


journey on":12oslb6u said:
First, Daydream, I assume when you said MPH, you meant MPH, not Knots?
That's a question.

For Journey On, two data points:

3500 RPM 16.0 MPH (13.9 Knts)
4000 RPM 19.6 MPH (17.0 Knts)

CompProp at 16 in.

Boris
Click to expand...
 
I went to my local marine service and asked about the purchase of a 4 blade prop for my 1990 70HP Johnson 2 Stroke. The service manager told me not to put a 4 blade on this motor. He said a 2 stroke needs to run a higher RPM's and a 4 blade would run at lower RPM's and bog the motor down eventually doing damage to the motor. He said 4 blade props are great for 4 stroke outboards or in/out drives but not 2 stroke outboards.
Any comments on this?
Thanks,
Dick
 
Your engine is rated (and recommended) to run to 6000 rpms. As long as the prop lets the engine do this, then you'll be fine.

You may have to drop down in pitch to accommodate the 4 blade. The added blade does put more load on the prop(for the same pitch)

Also, the 3 blade will be more efficient, but you may not notice it.
 
dick i ran a 4 blade compprop on my 70 hp johnson on my old boat, a 20 starcraft. I really loved it. I was able to cruise on plan at lower rpm. my top end was higher and the boat was firmer in the water. it did not slide out on tight turns. trolled in a straighter line and trolled slower to. also if you are boating in colder water and troll with your main you can thin your oil mix just a little to get the motor to idle at trolling speed all day. to mush oil and they will not troll at all. that was a great motor and I got a lot of use out of it.
 
Another thing I should mention is I went to Michigan Wheel Corps, a prop manufacturer, website and went to thier "Propellor Search", searching for a replacement 4 blade prop. I supplied the following data: Outboard, Johnson, 70HP, 3 Cylinder, 1990, 22' boat, aluminum prop, thru hub exhaust. My current prop is a 3 blade, 13 1/4 x 17. Michigan Wheels website suggested a 14 x 12, 4 blade prop. That's a huge change in pitch. I say the Michigan Wheel brand on the Boat US website and don't know of other brands. This pitch change seems quite drastic. Any comments?
 
I run a 4 blade Solas the same pitch as my 3 blade stock prop on an ETEC 90. The difference in RPM was less than 100 WOT (5100 vs 5200). The difference in performance was more pronounced. When accelerating from 3800 rpm up to 4600, you can actually feel the thrust (push back in the seat) whereas on the 3 blade, I didn't feel anything. All in all I'm pleased with the 4 blade.
 
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