4 Blade vs 3 blade props

B

Baxter

New member
This may start a controversy. I have a Venture 23 with twin Honda 50's and have been running Honda brand propsC4x10.5x13 4 blade props based on information that it provides more torque. Also the information says helps boats that are stern heavy which mine is with two motors, 60 gal. of fuel, two 12VDC batteries and
other stuff that seems to collect back there.

I have been told I would be able to run engines at high RPMs which most outboards are designed to do., 5500 rpm range.

Seems lots of up grades being done is people want more speed. I have found we usually go 15 knots as it has the boat on plane and we are our there to enjoy the
scenery not go 30 mph. As a practical matter waves often prohibit conformable
ride at high speeds. So can't often even do the 15 knots.

We have cruised Chesapeake Bay to Pudget Sound and lots of lakes and rivers in-between. North to Canada and the touque sure seems to help us move through some very high currents on way to Campbell River and Desolation Sound.

WE average 4 gallons/hour depending and wind and current conditions.

Would welcome any thoughts. I also run aluminum props. we hit to many things on rivers and anywhere as there is always something lurking floating below the waters. I have run stainless on other boats they will take more abuse but my theory is rather bend alum. that save the prop but stress the drive train.

All thoughts appreciated. Baxter
 
As long as you can get over 5500 RPM with the props you have, you are good to go. What is their pitch and diameter?
What is the RPM at 15 knots?

(The Honda 50 range of Wide open throttle is 5500 to 6000 RPM.). If less than 5500, then you are tending to lug the motors, which is not particularly good for them.
 
On my past 22, I preferred to run a 4 blade prop as opposed to a 3 blade. Just seemed to give me better performance. I believe they say to go down one in pitch when going to a 4 blade from a 3 blade. I have not tried a 4 blade on my 25 yet, simply because I have not found the right size yet. Regarding my 25, running a Yamaha 150, it came with a 15.25 x 15 3 blade aluminum. I was too shy of spec's at WOT, so I went to a 15 3/8 x 13. That put me up where I needed to be with RPM's, however I also noticed a slight drop in top speed and in fuel efficiency. I've decided to stay with the 15 pitch for now when doing mostly slow cruising, and run the 13 pitch when I'm boating at higher altitudes or running faster. (Less work for the outboard!) Like you, I prefer aluminum over SS to save the drive shaft. Also, on a prior Searay 288 Sundancer, I really didn't notice any difference in Aluminum vs. SS. Colby
 
I really don't think it can matter all that much with this boat design. In theory, and everything else being equal, a 4 blade prop should allow you to plane at a slower speed with a cost of a slightly slower top end. With the right boat, maybe. I suspect permatrims will generate far more stern lift if that is what you are really after.

I'm with Bob, if you can get 5.5 - 6 thousand rpms out of them, it's about right. Mine will go a bit over 6k for some reason - not even sure the tach is accurate, but I don't ever really run over 80% throttle since it just burns lots of gas and accelerates wear dramatically. I'm pretty sure I'm in the running for the oldest outboards right now with 1994s.....you guys and your new stuff :-)
 
When I had my 16 and 19 starcrafts I changed over from 3 to 4 bladed props and the difference on those light boats was night and day. On plane faster, could plane slower, cornered better, better mpg. It was just better all the way around. The 19 with a 70hp 2 stroke would just jump up on plane. Because of that I have always ran 4 blades on my22 and now on my 27. Nothing but good results on both. I do run stainless steel because of the weight of the boats. I do know that SS will not bend and warp while accelerating the way alum will and cause slipping. As far at hitting things.. SS just chews up the little stuff that would dent or bend alum and If you do hit something big that is what the hub rubber is for. You should not do any damage to your lower unit. I think that idea is left over from days gone by when many out boards did not have a sacrificial hub. I just do not see it as a problem with floating wood and debris. Now if you are running at speed and hit the rocks you got other problems that make a new prop look minor.
 
Tom, I’m totally in agreement with your analysis of the aluminum vs stainless props. My experience with 4 blade vs 3 blade differs. On our CD22 we have tried the four blade twice with the 3 blade being superior both times. The below is a performance comparison on Yellowstone lake, where due to elevation the twin Honda 60’s put out 92 hp instead of 120 hp. The 4 blade was 10.5 inch x 13 pitch & the three blade 11.1 inch x 14 pitch & both same make Solas aluminum. Along with no advantage in speed at varying rpm, I also didn’t observe any of the other advantages mentioned from you & others with the 4 blade over three blade. This was my experience & not saying with other prop & boat configurations that a four Blade isn’t beneficial.


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Jay
 
Interesting but your chart only shows the difference in rpm to mph. None of that reflects speed needed to plane or mpg. The biggest benefit was in my 19 start craft with a 2 stroke 70 1976 model. With a 4 blade the boat would just hop on to plane and stay there at 14 mph or push the throttle forward and run in the high 20 low 30's? . Its been 20 years now so. But that was a very light boat for its size.

On the 22 we had the same effect but not as pronounced. We did have to change pitch more then one size but I don't recall what it was. That was 10 plus years ago.

On the 19 we had a composite 4 blade prop . We did try that on the 22 but it was big mistake. On the heavier boat the prop would disform and slip really bad unless you very slowly advanced the throttle. So we when to a SS and loved it. The 27 came with the 4 and has been flawless but maybe I should not say better as its the only on I have had on there. I have been thinking of trying other props but SS is to expensive for that. Maybe a alum one to find the right size then go SS in that size.

My new dream is for Suzuki to bring their dual prop out board motor to the 200 to 250 range of motors. a friend has a 26 Sea sport with 350 dual prop and loves it. mpg is right at 4 mpg. that is almost double the same boat with a single prop out board. I am at 2.25 mpg on the 27 all the way up to 30 mph. If I could get that to 3.5 or 4 I would be thrilled. With 100 gallon tanks it adds 100 miles between stops. That is a game changer if we go to Alaska.
 
I'm with Tom.

I've had both 3 blade and 4 blade props on my CD25. With the 200hp engine, I get plenty of speed (can easily get to 35mph+ on smooth water), and I am all in for trading some speed for more torque. A lower pitched prop gives me a lot of that (indeed, I'd go even lower if a new SS didn't cost me $500), but that's not so true at lower RPMs. That's where I notice the 4 blade: more purchase (bite, if you will) at low RPMs.......especially from a stand still. Does it cost me speed? Yep, but so what, I don't like to go much above 24mph or even 20mph anyway, and with our NW chop I often don't go more than hull speed.
 
What Sandy & Tom are saying about added torque at low end with some normally not used high end speed reduction along with much reading on others having the same results is what convinced me to spend the $ to try again the 4 blade. As the chart shows my results were just the opposite of what I was expecting. No reduction in high end speed or increase in noticeable torque. If anything it was slower to come on plane than with the 3 blade. If the results had been as expected, I had planned on going with the 4 blade SS. It could be the brand or manufacture defect giving my results, but I’m done testing for myself & very satisfied with my 3 blade 11.1 inch x 15 pitch stainless Honda Solas Amita. The 13 pitch 4 blade aluminum & 3 blade 14 pitch aluminum for spares for sea level to Yellowstone Lake. The pair of 3 blade stainless 13 pitch for Yellowstone Lake when running extremely heavy & the stainless 3 blade 10 pitch for single engine running on plane if needed.

Jay
 
Not sure it would make a big difference in bite with twins on the back? Already two props in the water digging. I would bet that it would make a bigger difference with a single. I need a new prop, the stock prop on my 115 yamaha has a little corrosion where it makes contact with the thrust washer? Just did a full service on the outboards(boat new to me) full tune, oil changes and zinc inside and out. She is happy now. May do some research here to see what 4 blade works well on a 23' with the 115 Yami?

I will take down some numbers and give my seat of the pants review after.
 
crazy4salmon":7wn4qang said:
Not sure it would make a big difference in bite with twins on the back? Already two props in the water digging. I would bet that it would make a bigger difference with a single. I need a new prop, the stock prop on my 115 yamaha has a little corrosion where it makes contact with the thrust washer? Just did a full service on the outboards(boat new to me) full tune, oil changes and zinc inside and out. She is happy now. May do some research here to see what 4 blade works well on a 23' with the 115 Yami?

I will take down some numbers and give my seat of the pants review after.
Click to expand...

I think you may have hit the nail on the head on the difference with the twins already having more bite & most likely less slip already with the 3 blade over the single, so maybe less torque improvement too. I did read there is more surface area on the combined twin props then the larger single prop, when I was researching 3 blade vs 4.
 
a friend has a 26 Sea sport with 350 dual prop and loves it. mpg is right at 4 mpg.
Click to expand...

Tom, you sure about those #'s? I've been stalking Sea Sports as a possible upgrade for a while and their site shows the best performance with twins and no where close to those numbers. https://seasportboats.com/boat/kenai-2600/.

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If those are actual #'s my boat may be for sale when she's done.

R/
John
Scallywag[/url]
 
Nice chart - it's pretty much what I expected. I'm pretty sure the most fuel efficient 26-27 foot Seasport ever put on the water is the 2700 pilot with the volvo KAD series diesel and it didn't get 4 mpg. It does/did get 3 mpg through, which is really good for a boat in that class. It is also rather slow, but the cruise is a very tolerable 18-22 mph. I'd love to have one and I'm not sure why there are not offered with the D4 320 hp or a D6 375 hp diesel. It's probably economics - Volvo diesels are very expensive.

Back to props...As somebody that used to have other boats and do water sports, I know props make a difference. In that application I got what I felt was my best performance with a 4 blade. But remember, this is "felt" better. Was it really? I am convinced it was, but it was not that dramatic a change where I felt I was driving a different boat.

Maybe looking at it like this will help.....lol....You can put all different kinds of tooth counts on your circular saw and each one of the them cuts wood just fine. Some tooth counts are better for some applications, just like some props are better than others in specific applications. A three blade works really well though and that is why they are on the back of so many boats.
 
Well thats the thing only one or two boats have been rigged that way. The place that sells them is a honda / yamaha (?) dealer so I think they want to not show other motors. I talked to the boat dealer ( not my favorite so not mentioning names) and they will order and rig it any way I want but they are really pushing the twin 225 hondas. Which in the motor on my current cdory 27. Its a good but heavy motor. I think one 400 or 350 is a better what to go even with out the counter rotating props. Not all dealer motor choices are made for you benefit.

The dealer has to cater to a lot of hard core fisherman the want to go fast first and mpg be dammed. Well thats not me, no really. I am willing to go slower, not 50 but 35, if it gets me better mpg. A lot of other people will not be the first to buy a new tech. I had to listen to one blow hard last week going on and on about how the new 600hp mercury was untested. Yeah they sell untested motors for 60k each. That motor has been in testing for 10 years.
 
Having spent a great deal of time, money and effort in trying to get a half a knot more from a sailboat - I have found that changing lots of little things in the mix is often less expensive, easier and more effective than dropping the big bucks on the big change. Just a few thoughts:
#1 Bottom paint or not and should you fair the hull - speed paints
#2 Twins, their spacing on the transom (in all directions) and counter rotating props
#3 Windage, especially high and facing forward
#4 Weights - location and amount (stay low - stop pitching moments)
#5 Motor tune, fuel choices, and engine control chips
#6 Lubrication choices, frequency of changes, and temp control
#7 Trim devices and need vs "FARKLE SHINE"
#8 Driver Ed - how to run trim and throttle
#9 etc etc etc etc
Bob Jarrard
 
Number 8 is a big one.

A unnamed father in law of mine was complaining about his new 17 ft out board fishing boat not planning well and being slow. So we went for a ride. Yep it was not planning well and was slower then it should be. He was talking about taking it back to the dealer and maybe opting for a bigger motor. I leaned over and pushed the " trim tilt " button on the throttle. As the boats bow raised up out of the water and the boat gained 10 mph over its bow down plow position my father inlaws eyes lite up. He had the boat for two month and did not know how to do that. And no one at the dealer even mentioned it. Here we are 25 years later and now I own that boat, he gave it to me, and it still runs just fine, if not a little under powered with just a 50hp on it. took my son James fishing just this weekend.

So yes learn to trim a boat for best performance and do not assume everyone else knows how.
 
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