posted 04-18-2005 06:08 PM ET (US)            

The extra weight of four-blade propellers can affect how the outboard motor shifts. A heavier propeller has more momentum when turning and more inertia when not turning, so it often causes the shift from neutral to forward (or vice versa) to have more gear clash. (Techically I guess you should say the clash is in the clutch dog. Let's just say more "clunk" in and out of gear.)

As for "resistance" here I assume you mean drag. Yes, dragging the propeller itself through the water becomes one of the major loads on the engine as boat speed increases. This is one of the reasons why most people will generally describe a four-blade propeller as having lower speed potential compared to a three blade propeller--there is just more drag from having more propeller to pull through the water.

But I don't think that either "mass" (weight) or "resistance" (drag) are the real factors which will affect how a four-blade propeller will behave compared to a three-blade propeller. From what very little I know about propeller science, the four-blade propeller will have greater blade area, and this should cause it to have a better "bite" (for lack of a more technical descriptor) than a three blade. As a result, it may be more difficult to turn a four-blade propeller than a three-blade propeller of the same diameter and pitch. Again, this is not due to an increase in "mass" (weight) or "resistance" (drag) but from a better grip on the water (for lack of a better explanation).

Mercury describes their REVOLUTION4 propellers in term that suggest using the same pitch as a three blade propeller from the MIRAGE PLUS series if the WOT engine speed is near the maximum of the recommended range. From this I infer that they mean the engine will slow down slightly with the four-blade, but not so much as to necessitate a change in pitch. They also say to change to a lower pitch if the engine is operating near the lower end of the recommended range. And again, this seems to mean you can anticipate that a four-blade propeller of same diamter, pitch, and blade design as a three-blade will be more difficult to turn and affect the engine by increasing the load. This will probably be seen as a reduction in Wide-Open Throttle (WOT) engine speed, and in turn dictate a decrease in propeller pitch (or diameter) when going to a four-blade.

If you mix and match diameters and blade designs, there is no sure fire way to determine how the four-blade will play compared to a different design in a three-blade. You just have to try it.

One thing I have observed is that at slow speeds there is a different vibration from a four-blade, and in some situations this may be more resonant with other vibrations in the boat. Of course, changing to a four-blade could reduce sympathetic vibrations, too.

posted 04-18-2005 09:34 PM ET (US)            

There are so many different designs and manufacturers.

I asked a propeller manufacturer the same question. They make a propeller of the same diameter in a three blade and a four blade. Very similar blade design. I was told the four blade would run 100 to 200 rpms less, or around one inch of pitch.

According to Mercury the REV4 will run 200-300 rpms less, one to two inches of pitch, than a similar pitch Mirage Plus propeller, which is a large diameter three blade prop. (Over 15 inch, depending on pitch)

The REV4 diameter for a 17 pitch propeller is 14 5/8 inches. The Mirage Plus 17 pitch propeller is a 15 1/2 inch diameter. Very different blade designs and diameter.

My Mirage Plus 19 pitch/15 1/4 diameter three blade propeller runs 200 rpms less than my LaserII 19 pitch/14 diameter three blade.

One to two inches of pitch difference (less for the four blade) would be a good starting point. It will depend on how the props you are running compare to the design of the four blades you are considering.

Rich

posted 04-19-2005 08:01 AM ET (US)            

http://continuouswave.com/whaler/reference/propellerWDSingle.html

posted 04-19-2005 02:56 PM ET (US)            

The Mercury prop calculator (I plugged in weight rather than length) recommends a Revolution 4, but with a 21 pitch; an 6 inch pitch difference and an estimated top speed of 49 mph. I can't see these engines pulling that pitch given their current props and performance.

posted 04-20-2005 09:42 AM ET (US)            

As a result, I think Mercury has effectively marginalized the value of their Propeller Calculator, and for my own case, I find it of no value at all.

posted 04-20-2005 10:49 AM ET (US)            

The prop calculator on the Merc site, as inaccurate as it is, is a JAVA applet. The logo appears to be Sun flavored Java. Have you tried a different browser?

posted 04-20-2005 12:27 PM ET (US)            

I switched to a 19 pitch Mirage, no more ventilation. The 17 pitch Mirage ventilated like crazy, it was the worst of all the propellers I tested. My 19 pitch LaserII will not ventilate either.

With the 19 pitch Mirage, I am now running smack in the middle of the recommended wide open throttle rpm range.

All the propellers I tested were brand new out of the box, so I really can't contribute the ventilation to a "worn" or out of spec propeller.

Increased propeller pitch solved my problem.

When I described the ventilation problem to manufacturers and propeller shops, they suggested adding a little bit of cup to the tip or edge of the propeller blades. I was told sometimes propellers will lose a bit of that cup after a while or there just is not enough there. Might be worth looking into.

I had a propeller shop add a bit of cup to one of my four blades, but did not run it on the boat to see if that resolved the problem. The pitch is just too low for my boat. I think they charged me about fifty dollars, not very expensive to do.

Rich

posted 04-20-2005 03:21 PM ET (US)         

"4-Bade propeller facts:

If you're upgrading (a telling term) from a three blade to a four blade propeller, remember that a 4 blade propeller generally truns 50 to 100 RPM less than a three blade with same pitch.

4-blade props:

* plane the boat faster than 3 blade props
* keep boat on plane at lower speed
* give improved mid-range speed at same RPM as a 3-blade
* provide quicker acceleration than most 3 blades
* run smoother than 3 blades
* have better hodling power in rough conditions
* are less likely to ventilate in sharp turns
* provide better low speed and reverse handling
* are not quite as fast on the top end"

Mercury does say that that the Revolution-4 is usually as fast as the Mirage Plus, however. In my own experience, on my own Whaler, the Rev-4's are 4 mph faster than the Mirage Plus, and hang on like glue at elevated mounting heights. I think they are an amazing propeller.

posted 04-20-2005 08:05 PM ET (US)            

2500 rpm = 13.5mph with motors tucked in and tabs down, not fully on plane
2800 rpm=18 mph, tabs down, motor trimmed up slightly, planing
3000 rpm = 22mph
3200 rpm=24mph and most econmical cruise at 8gph both motors
3500 rpm=28mph
4000 rpm=32
4500 rpm=37
5600 rpm=45

posted 04-23-2005 12:44 PM ET (US)            

I think the Offshore/VenSura props would be a better match for your 135HP engines than the Revolution 4. The Revolution's are substantially heavier with much thicker blades than the Offshore and I believe they are generally recommended for 200HP + engines.

The Revolutions, due to their greater mass, may produce unwelcome clunking when shifting gears as jimh noted above.

posted 04-24-2005 09:27 PM ET (US)            

All the Mercury propellers I've run on the 225s are "clunkier" (not terribly so) when shifting than an OMC/BRP or other brand propeller. I believe the reason for this is that the change-in-direction "clunks" are not cushioned by a rubber hub between the propeller shaft and the propeller hub as is found on the OMC/BRP or other brand propellers. Rather, the changes-in-direction "clunks" are directly transmitted through a semi-rigid plastic Flo-Torq sleeve positioned between the propeller shaft and the propeller hub. In some respects, the Flo-Torq propellers act more like solid hub propellers.

The reason this is noticible to Jim on an OMC V6 outboard is because the OMC/BRP V6 design gearcase is much, much smoother/quieter when shifting than either Yamaha or Mercury. In other words, on an OMC (or BRP) gearcase there is typically no gearcase "clunk" like there is on a Merc or Yamaha (almost a trademark if you ask me) to mask any propeller related "clunks".

Last year the quietness of the OMC/BRP V6 gearcase design came in quite handy for me the first time out with a pair of Mirages. I had just put the Mirages on and took the boat out for a run to see how they performed. When backing into the slip I heard an unusual Mercury/Yamaha like shifting "clunk" when shifting into reverse. Upon examination I found that the Mirage on the port motor was a little loose even though I had torqued it down just as much as the Starboard prop. It turns out that after I ran the propeller that first time, the Flo-Torq decided to seat a little further into the propeller hub (perhaps with some water lubrication) and that caused a little axial play on the propeller shaft and a noticible "clunk" which I'm not sure would have been noticed on a Mercury or Yamaha gearcase.

posted 04-28-2005 08:17 AM ET (US)            

I am surprised at your unfavorable conclusion on the 4-blade props. Were these Revolution 4's? Were you running them without vent plugs?

I installed an Offshore/VenSura 17 pitch last summer on my 21' Walkaround (200HP Yamaha) and it is, by far, the finest prop I have run on this boat. Acceleration and holding are amazing...it's like a new boat! I am running the medium sized vent plugs (available from your Mercury dealer for $.95/each) which allows the prop to bite quicker when it initally spools up (slips) than the non-vented prop. I am also running my engine elevated quite a bit on the transom with a 10" set-back bracket.

IMO, the vent plugs are mandatory for this prop as well as proper engine heigth.

Steve

posted 04-28-2005 03:30 PM ET (US)         

They DO make even number ALUMINUM 4-bladed props, 16, 18 & 20, and they are dogs, I believe.

posted 04-28-2005 06:46 PM ET (US)         

As I have said, I agree those 4 blade aluminum's are a waste of money. JimH tried one in his prop report article, and came up with the same bad performance.

posted 05-04-2005 09:23 PM ET (US)         

The Mercury Mirage Plus is probably the best and most widely used High HP offshore prop in the world. 1000's of users can't be wrong, both outboards and sterndrives.
Sounds like you need a new prop shop too. Homemade vented 4 blade aluminum Alpha 4 props? What a joke. And they tell you they're selling that lousy prop like hot cakes? Yikes. What a bunch of suckers their customers must be.

Stay with those teflon props if you're going to keep those engines. Then people here won't waste their time anymore with your Merc prop trolls.

posted 05-05-2005 11:05 AM ET (US)            

   "the whaler drive begs for stern lift"

posted 05-05-2005 08:08 PM ET (US)         

Cleaver props are your true stern lifting props, but are generally not offered in less than 26" pitch for high speed tunnel type hulls, where the bow lift is produced aeordynamically and do not need the propeller to assist in this function. I can't imagine one of those would run well for you. They are wide-open all out props, not for cruising.

posted 08-21-2006 09:12 PM ET (US)            

In researching to improve performance on my 23 Conquest with twin 135s, I came up upon this post.

Can you provide an update on your 4 blade prop test?

Thanks,

posted 08-27-2006 05:19 AM ET (US)         

I swapped this may motors and propellers:

Before: 2 Yamaha 150 HPDI
2 Yamaha 19'' x 13 3/4 3 Blade black SS props

Now: 2 Yamaha 150 4-Stroke
2 Solas Titan HR4 4 blade 17'' x 14 1/4 ss props

Gains: manoverability at low speeds
Bite in rough water
Same plane speed as with 2 stroke/3 blade props

Losses: Max 5300 rpm instead of 6000
I can't reach more than 38 (-5) knot at wot 5300 rpm
more expensive than 3 blade props
slight vibrations on minimum rpm 600/700

I think that 4 blade props will perform even better on carbed outboards due to their higher low end torque, but i'm still happy with them.

Before switching to 4 blade props, consider that usualy you have to use at least 2'' less pitch to have the same rpm's at wot.

Find a good prop shop and test different 4-blade props on your boat and notify the difference between them.

best regards

posted 08-28-2006 02:39 PM ET (US)            

When I originally created this thread, I was new to my Conquest and twins. I had experienced occasional ventilation in the choppy waters of SF Bay. At that time, I was more familiar with handling my Outrage 17 and its single engine performance and behavior, than dealing with twins. Twins can be more susceptible to ventilation as the props are placed asymmetrically relative to the hull bottom (the outboard side more likely to be at or near the surface on plane).

Since that time, I have learned to:

a) re-trim the engines fully down after stop and
b) re-orient the boat properly to the seas before throttling up.

posted 09-06-2006 12:51 AM ET (US)            

prm1177, your method of dealing with your 23 Conquest is exactly what I do too. For the most part it is not a big deal with the two adjustments mentioned but I still haven't found a way to deal with falling off plane when running in snotty seas. You want to go fast enough to keep on plane but slow enough so it doesn't pound.

I just received my LH 4-blade Merc Revolution and the prop is HUGE! It's way beefier than my current Mirage Plus. Total shipping weight of the prop and hub kit is 24 lbs. I think I'll sell this and just want for the Vensura. I think that's the better prop to get.