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Propeller Tests: Whaler Drive Single Engine
|Author||Topic: Propeller Tests: Whaler Drive Single Engine|
posted 11-21-2004 10:48 AM ET (US)
Over the course of the summer I tried eight different propellers in combination with my Boston Whaler REVENGE 22 WT WD and Evinrude 225-HP engine. The results are presented in:
The weather became too cold for testing of the ninth propeller available, a MiragePlus 17-inch. We will resume testing in the spring, as I don' t feel I have found the optimum propeller.
One factor of which I became more aware during the course of the testing, but unfortunately I did not keep good records for, was the affect on the hull trim of the propeller, especially in terms of stern lift. Some propellers had much better stern lift, lifting the boat out of the water and, it seemed, creating a smaller wake. I will take more careful notes on this aspect in future testing, and I recommend its observance to others.
Please use this message thread for any comments or questions about the tests.
Even if you are not particularly interested in my results, the article does provide a comprehensive example of how to evaluate and test your boat. The appendix on boat weight is also a good example of how to calculate your boat weight. It comes as no surprise that the boat often weighs more than anticipated.
posted 11-21-2004 11:11 AM ET (US)
I also invite comments on the results shown, particularly with any possible insight into what might be a good candidate for a propeller on this boat. I think the ultimate solution is to change to twin engines, but I do not anticipate doing that in the next year. Thus a great help would be to find a propeller that gives good performance with the current engine set up. Note that the engine is mounted as low as possible, so any propeller recommended has to be one that can tolerate a rather high mounting height.
Among the propellers tested already, what looks good?
posted 11-21-2004 11:17 AM ET (US)
Thank you Jim for yet another informative and well written article.
I'm hoping to move up to a 22ft Outrage Cuddy with WD so I'll definitely be referring to the article again.
posted 11-21-2004 12:33 PM ET (US)
Based on my experience with Dougherty's 15, 18, 22 and now 27 foot hulls, I think using the 180 hull constant provides the most accurate prediction of performance. Using an average of 4600 lbs as fully loaded, your predicted WOT top speed should be about 40 MPH, which is what your data tends to show with the better of the different propellers.
The best propellers in my opinion appear to be No. 6, the Mirage 15P and No. 5, the Viper 17P. This is because they both allow the motor to reach higher RPM while achieving nearly the same top speed. The Mirage seems to do better in the mid-range which is where you would likely run your boat most of the time and so that is why I rank it higher than the Viper. I think that the better mid-range peformance of the Mirage is simply the fact that the Mirage has more blade surface area and gets a better hold than the Viper does to carry the load due to its 3/4 inch greater diameter and blade shape.
Finding the optimum propeller is difficult without a fuel flow gauge. I have found different propellers producing what appears to be similar results via the tachometer, produce different results via the fuel flow meter.
Choosing the optimum propeller is a matter of trade offs like everything in boating. For example, the most efficient cruising propeller (30 to 34 MPH) I've run so far on my boat are 17P Mirage propellers. These propellers work well for most conditions that I encounter except when the seas become greater than 3 to 4 feet where boat speed is limited to less than 25 MPH. At speeds less than 25 MPH, they do not get a very good grip on the water and make running the boat in a heavy sea quite a chore. It's my belief that this is simply a function of not having enough blade surface area to carry the heavy load of my boat in the low speed plane range 15 to 25 MPH even with trim tabs down. Other three bladed propellers I've tried also have the same difficulties at these lower on-plane speeds.
In an attempt to improve upon low speed control, I've tried a pair of Revolution 17P propellers. These propellers have much, much better grip at low speed but they are not very fuel efficient (about 17 percent less fuel efficient than the Mirage 17P and about 12 percent less fuel efficient than the Viper 19P) at the optimum cruising speed of 33 MPH. They are also slower at WOT. It may be that if I had an inch of pitch taken out of the Revolutions that they might become a little more efficient for my boat. Thus, here's the tradeoff -- everything else being equal, propellers with more blades seem to be less efficient due to increased drag and weight but seem to provide better grip at low on-plane speeds. If I know I'm going off shore and its likely that I'll encounter big seas, the 4-bladers are the better choice at the cost of lower fuel economy.
It will be interesting to see how the 17P Mirage compares to the 15P Mirage and the 17P Viper. It would be worth your while to compare these with a fuel flow meter measuring fuel consumption in addition to engine speed. Having looked at the 8 propellers you've tested so far, I'm guessing that the 15P Mirage will be the best all around propeller for your boat.
posted 11-22-2004 01:45 AM ET (US)
Nice article. Your observations closely follow my experiences with my '89 Revenge 22 WT WD with its 225 Optimax. I run a 17p Mirage Plus (new model with the pvs vents, all plugged). Note that in the Mirage line, as pitch increases, diameter decreases--the 17p is 15.5" diameter while the 19p is 15.25" diameter. So most definitely try out the 17p Mirage Plus!
posted 11-22-2004 11:33 PM ET (US)
What amazes me about this, is you found a dealer that had let you demo 8 different props without buying anything. What dealer are you going through? Also, you say you haven't found the optimum prop yet. What do you consider optimum?
posted 11-23-2004 11:53 AM ET (US)
One thing to make sure to keep note of is the environmental conditions under which the tests are run. A humid 90 degree day can produce quite different results than a crisp 45 degree fall day -- by far the fastest speeds I've ever seen on several of my boats were in the latter conditions.
posted 11-29-2004 09:22 AM ET (US)
Testing in consistent temperature--good point. The last boating we did this year was in quite crisp conditions, and I did notice the boat seemed to be running quite nicely in that cold water and cold air. Both were in the 50-degree range. Our summer boating is normally done when both water and air are 20-degrees warmer.
posted 11-30-2004 07:27 AM ET (US)
Another excellent article Jim. I went through the same process this season, running six or seven different propellers. The difference was very noticable. It is worth going through the process because it can make a big difference in the way the boat handles, rides and performs.
The propeller I am very happy with now was the one that was recommended initially when I asked for advice on this forum.
The propeller I ended up with has the boat running at the low end of the max rpm range but the ride and fuel economy improvements were dramatic.
The 17 pitch Mirage was the worse prop I tested on my boat. Vented like crazy, rough ride. The 19 pitch has the boat handling great, no ventilation in the rough stuff and excellent fuel economy for my motor.
A move up in two inches of pitch in the same style propeller did not only make a difference in max rpms but in the way the boat handles, especially the ride- no more pounding.
Thanks for a great analysis. The material and advice offered on this site really helped me prop the boat.
posted 11-30-2004 05:46 PM ET (US)
Can you refresh our memory (well mine anyways) on the following:
1. Which boat you are talking about?
posted 11-30-2004 08:34 PM ET (US)
It is a 1997 21 Outrage with a 2003 Mercury 250EFI mounted "one hole up". I wound up with the Mirage Plus 19 pitch propeller. Vent holes plugged, hole shot and up on plane is excellent, around 2800 rpms. Max rpms are 5300-5400, dirty bottom and a big t-top hard top with enclosure.
Fuel economy went up from around 2 mpg to 2.5 mpg at cruise speed (25-30 mph, 3500-3800rpm, 10 to 12 or so gallons per hour).
Top speed around 46 mph.
The best result of all is the confidence I have in the boat now with this propeller. I've been playing alot now in the ocean and it is now fun- I have great control of the boat.
I think I am going to wind up running at the lower end of the recommended range but she seems real happy where it is now.
I will probably try a couple more. It was fun testing the various propellers. Everyone thought I was nuts for going through the process. It does pay off to try as many as you can.
posted 11-30-2004 08:38 PM ET (US)
My current plan is to purchase a fuel flow meter (like a NAVMAN Fuel 3100) and re-do several of the propeller tests, this time collecting information about fuel consumption.
I think there can be significant variation in fuel economy, as Rich has shown. And with the price of marine fuel (in Canada for sure) heading above $3/gallon, fuel economy will be much appreciated.
posted 05-15-2005 11:07 PM ET (US)
Update: MAY 2005
I installed a NAVMAN 3100 fuel flow meter. I also tested two more propellers.
posted 05-16-2005 09:38 AM ET (US)
Jim - Interesting results in the update. My fuel economy results running both the 17P SST and the 17P Mirage (in pairs, however) are reversed relative to your results. The Mirages produced slightly better fuel economy. I too found that the SSTs don't have the low plane speed holding power of the Mirage. They would blow out easier than the Mirage. I think the differences could be related to motor mounting height and the need for more blade surface area to carry the load of my boat, something that the Mirages provide. Also, with twin engines, the propellers are not aligned with the keel and so the boat's tendency to roll from port to starboard or starboard to port in some conditions tends to pry one the propellers loose when the rolling is significant causing blow out (heard as over reving and seen as over reving on the tachometer). This is something I never experienced with a single outboard with the propeller aligned with the keel such that roll has little influence on propeller bite.
With respect to theoretical slip, I think your Navman data shows that it may not be too meaningful to compare the theoretical slip results from one propeller brand to another. A comparison of calculated theoretical slip number must assume that all propellers that are nominally designated as having a 17 inch pitch, for example, use the same measuring/assessing techniques for such designation.
Comparing your various propeller data across the board, I see a trend that the performance of a 17P designation for a Mercury propeller more closely matches the 19P designation OMC propeller than it does for a 17P OMC propeller. If we were able to actually determine the pitch of the SST and Mirage using the same method for measuring or assessing pitch, I think we would find that the SST would have a lower pitch than the Mirage and therefore it's actual "slip" would be lower than the calculated theoretical. In short, it would appear that OMC has a tendency to round its pitch up to the nearest whole and and Mercury tends to round down.
Also, with respect to slip, the fact that the SST gets higher fuel economy (2.3 mpg) at a given engine speed while at the same time having a higher theoretical slip would almost seem to suggest less actual slip from the SST than the Mirage. Since I've installed my Navman, I have not worried about calculated theoretical propeller slip as the Navman fuel consumption data provides a better indication of actual efficency and overcomes manufacturer's pitch assessment variances.
posted 05-17-2005 09:42 PM ET (US)
[Added three new photographs to article. Most interesting is the last one which shows the blade area of the SST propeller compared to the blade area of the MIRAGE PLUS propeller.]
posted 05-18-2005 01:13 PM ET (US)
Jim - In looking at your figures, and seeing that the conventional "elephant ear" OMC SST props seem to perform well, it occurred to me that this actually makes sense.
As I have mentioned on another post, Mercury indicates that for boats that run 40 MPH or so top end, the conventional props should be used, for best performance and fuel economy. This is what you are finding also. The high tech, performance series of props, usually not made in lower pitch ranges, are not recommended for a boat that runs about 40.
The prop you really should try is highly polished Mercury 15" Venegeance, #48-16312A45, a series of SS props that give surprisingly good performance and holding up to 45-50 MPH speeds. If you remember, the Marine Max 240 Outrage that we rode in at Stuart last year was running a pair of these in 19" pitch, and Robert Moore commented to me that he was quite surprised at the 51 MPH these props gave on the twin 150 Optimax engines. With 14-1/2" diameter in 15" pitch, this is the prop you want to try. It should get the engine up to 6000 rpm. 15" is the lowest pitch available on a Vengeance.
As I have also said, the prop manufacturers tend to reveal what prop line is appropriate by the pitches offered. In 15" pitch for the 4-3/4" gearcase, Mercury only makes 3 props, the aluminum Black Max, the Vengeance and the Mirage.
When you mention that the conventional OMC SS props make a smaller wake, that is because they do not give bow lift, or looking at it in other terms, because they do not PUSH DOWN on the stern like the Mirage does, even though it, too, is not known for much bow lift. Expect the same from a Vengeanc
posted 05-19-2005 09:58 PM ET (US)
I stopped by Lockeman's Boat and Hardware to return the 17-inch pitch SST, and Dave handed me another propeller. Said he'd read the results on line, and he dug up a nice 15 x 15 SST for me to try. The weather forecast is decent this weekend, so you know what Chris and I will be doing.
I also thought of a 17-inch pitch Vengeance. Its diameter is a bit small. All of the small diameter propellers seem to have trouble getting the boat on plane, and they also show high SLIP around 3500 RPM. That is the RPM we're looking at for cruise.
This latest round of testing has been with the boat really stripped and very light weight. If we were leaving the dock for a weekend of cruising, we would probably have at least 750 pounds of additional weight aboard. Much of that would be fuel--70 gallons at 6-pounds-per-gallon--and gear. Because of this, I want to see test results where the engine can really wind to maximum RPM with this light load. That means 5700-6000 RPM.
The 15-inch Mirage is a good propeller, but too much diameter.
posted 05-20-2005 12:20 PM ET (US)
I would also look at a 15" Michigan Wheel "Rapture". I hear they are pretty decent props, with good holding and bow lift.
posted 05-24-2005 07:01 AM ET (US)
Propeller No. 11 has been tested. We got some interesting results from another SST three-blade, this time a 15-inch pitch. We could wind this propeller all the way to red-line at 5,900 RPM.
posted 05-24-2005 08:29 AM ET (US)
I'm still convinced that Propellor Test #12 - with my 17 pitch Offshore/VenSura will be the last one you will ever have to make...whenever we get together again!
posted 05-24-2005 04:49 PM ET (US)
Here again we see what the Mercury technical rep had told me at Stuart, that the same pitch Mirage will run 400 RPM less than a standard prop, becasue of it's greater efficiency (less slip). When Jim tested the Mirage 15, he achieved 5500 RPM vs the 5900 of the SST elephant ear. I note that the 17" Mirage gave an average RPM of 5200, also about right.
Steve, although I think the Offshore/Vensura would be excellent for the boat, the question will be whether the engine can turn it. Running through the Evinrude's 1.87 gear ratio, the 17" is a 45 MPH prop, a speed I don't think it can attain. If they made a 15" Vensura, it would probably be perfect.
With a boat that runs right around 40, it also appears that what they have been saying holds true - you gain nothing in performance or economy over a regular SS prop, like the SS or Vengeance, by going to a performance model, which is why the Vensura & Revolution-4 are not made below 17" pitch, and 19" for the Laser II and Tempest props.
posted 05-27-2005 03:35 PM ET (US)
Jim I have another post in this forum. I was wondering if you or the other esteemed posters to this thread coould be of any help?
posted 05-28-2005 07:36 PM ET (US)
The more I read Jim's test results the happier I become with my 15 1/4 X 15 Yamaha SWS prop. My prop has matched the Mirage and SST's best numbers for this application and although my engine is only 2.6 litres, it still winds up to 5600 RPM (RPM range of 4800 -5800) at mid trim with a heavy load. I don't know if a Yamaha prop will work on an Evinrude but I don't think there is a better prop for this boat/motor setup.
posted 05-29-2005 10:03 AM ET (US)
Regarding the Yamaha SWS propeller: that same thought had occurred to me!
The Mercury propeller catalogue has many choices for propellers in higher pitch, and these imply much higher speeds than I will ever see (or want to see) on my REVENGE.
The Mercury Performance Venting System (PVS) is a good idea for very light boats that have very high power. In that situation the PVS vents can help make a very high pitch propeller, that can obtain very high ultimate speeds, become more useful at lower speeds and during acceleration. But I cannot see any application for them in my situation.
It is not like I could turn a 23-inch or 25-inch pitch propeller to 6,000-RPM, if I could just get the engine spooled up. Maybe if I had 500-HP on the transom. But with a single 225-HP and a fairly heavily loaded boat, I am turning 15-17 inch pitch propellers, and they are no problem for the engine to spool up to speed. Therefore the PVS vent is not of much advantage that I can see. For most Boston Whaler boats, I wonder if there is a need for the Mercury PVS propellers. I think they're targeted at boats with a much higher speed potential ( above 50-MPH) than most Boston Whalers (which are 40-MPH boats typically).
Propeller performance is not all about final speed. Other characteristics are important. How well the propeller stays connected in rough water is a concern. How much fuel consumption the propeller needs is another. Also, the affect of the propeller on the boat's ride is important. Does it have stern lift? Bow lift?
posted 05-29-2005 11:06 AM ET (US)
Unless the gear ratio of a drive is down well below 1.5:1, the PVS venting system on a 17P or a 15P propeller really doesn't make much sense to me. You've got bigger problems to solve if your motor can't turn either of these propellers well right from the start.
I've got Mercury Mirage and Rev 4 propellers with the PVS system and I have all the vents plugged. The 3.3L Evinrudes have no problem braking these propellers loose if I lean on the throttle too hard on start up. Open vents would just make that problem worse. I never had a hole shot problem with the ventless 17P SWS propeller connected to the Yamaha Ox66 225 hanging on my 22 Revenge's transom.
The 150 Johnson on my 18 Outrage was turning a 20 or 21P OMC Raker that had vent holes. When I leaned on the throttle hard, the boat would drag for perhaps 3 feet before it would be on plane. It took off as if someone "dropped the clutch". There was no way to plug the vent holes to determine whether they made much of a difference.
It used to be rare to see vent holes on props below the 20P range. I think they may appear on the lower pitch Mercury "performance line" propellers (Mirage, Rev 4s) for several reasons: (1) gives something for the Mercury marketing department to talk about as well as the perception that they are higher peformance than the actually are; (2) makes the Mercury marketing department's life easier by reducing or eliminating questions like "why do some props have the vent holes and some don't in the same line-up"; and (3) no significant variations in the manufacturing process for all of the various pitch propellers in the line-up -- all of the hub castings are the same.
I've been running the Rev 4s lately and they seem to do well for my heavy load. They enable me to slow my boat down while maintaining plane and reasonable fuel economy! With the Mirages, I had to run about 4250 RPM to 4500 RPM and 32 to 34 MPH for good fuel economy. Sometimes that is just a little too fast for conditions. With the extra blade surface on the Rev 4s, I can run below 4000 RPM and 30 MPH while getting about the same fuel economy. Engine synchronization seems to be more critical for getting the best fuel economy with twin engines and the 4 blade props.
Based on Jim's report, I just bought a pair of OMC Renegade Offshore 4 blade propellers in the same pitch. I'll make a comparative report later this season after I've had some time running with each pair. Based on Jim's report, I expect that the Renegade 4s might have a faster WOT speed.
posted 06-06-2005 08:42 AM ET (US)
Update: Finally bought a propeller! Actually, I bought two. They are both Evinrude SST three-blade stainless steel. Both are used--well used, too. I bought both a 15-inch pitch and a 17-inch pitch.
With the boat still very light, we took the new 17-inch-pitch propeller out for a test drive. I added the results to test No. 10 in the reference article. This propeller had very similar numbers to its twin-brother we tested earlier. This time we were out in bigger water where we could see how the boat ran in wind and waves. We put about 35 miles on the propeller, in all sorts of conditions. It seemed to perform quite well. This propeller needs a little cosmetic work, but the blades seem to be in good shape, no obvious dings or dents apparent.
I checked the blade pitch for consistency by spinning the propeller on the prop shaft and carefully setting a reference for the position of each blade tip as it passed the anti-ventilation plate and trim tab . One blade tip seems to pass at a point slightly different than the other two, perhaps a 1/16 of an inch off. I didn't notice any vibration with this propeller. As I said, it is a used propeller. And the price was very attractive. I am satisfied.
Prior to this test I reset the spark plug gap on the Champion QL77JC4 plugs to 0.030-inches. The plug gap had been over 0.040. We also added a 12-oz. can of BPR Fuel System Cleaner to about 40-gallons of gasoline.
In one stretch of calm water running upstream in the Middle Channel of St. Clair flats delta, we wound the engine up to 5500-RPM at wide open. Then I gave the engine some more trim up, and watched the engine speed climb quickly to 6,000-RPM. The engine seemed to really have no trouble spinning up there to 6,000, which is faster than I like to see its 13-year-old pistons and crankshaft turn. I had to get off the throttle quickly, so I did not get
We'll try the 15-inch propeller when we get the boat heavily loaded with fuel and gear for cruising. That will probably be the propeller of choice for long trips like that.
posted 07-06-2005 08:33 AM ET (US)
We ran the boat for five days of cruising with the 15 X 15 three-blade SST propeller. The boat was heavily loaded with cruising gear, fuel, and two people. The propeller worked very well for us.
There were no problems with ventilation or loss of bite in heavy conditions. We experienced quite a range of seas. We motored across the Straits of Mackinac in 6-8 foot seas with no problems. We also punched into some really nasty steep faced 2-foot waves (strong wind against strong current) without the propeller coming loose.
Even with the heavy load, in a stretch of calm water and no current, we could still wind the engine up to 5500-5600 RPM and 37.2 MPH.
posted 12-23-2005 09:17 PM ET (US)
Graphs plotting the boat speed as a function of engine speed were added.
posted 12-24-2005 10:50 AM ET (US)
Jim -- I think it would be interesting to also have a plot comparing the different makes/models but same nominal pitch.
posted 08-01-2006 10:43 PM ET (US)
Recently we had a chance to run the boat with a heavy load, seven people on board. The results were still very good. Running with the 15-inch propeller, about half-tank of fuel, and light canvas (just the flying top), we were able to hit 5,650-RPM and about 38-MPH. This calculates to about 12-percent SLIP, which is a bit higher than previously observed around this speed (about 10-percent SLIP).
This test was run in significantly warmer water (72-degrees versus 48-degrees). There was a slight tail wind and perhaps a bit of favorable current. I attribute the higher slip to the heavier load.
What impressed me was the ability of the engine to still spin up near the red-line value. This reaffirmed the choice of the 15-inch propeller. There was absolutely no problem to get the boat up on plane with this big load. Also, with three or four people sitting in the stern seat, the hull draft was increased at the stern. The propeller was running a bit deeper than normal, and I believe this helped, too. My feeling has always been that the propeller shaft height is a bit on the high side for this rig; the deeper draft seemed to be no handicap and perhaps a bit of a boost.
I also plan to re-test the Mercury MIRAGEplus three-blade 17-inch pitch propeller sometime in the near future. We will test with medium vent plugs in the PVS vents. Stay tuned for more data.
|Tom W Clark||
posted 08-02-2006 02:36 PM ET (US)
If you test any Mercury propeller with the PVS system, I suggest you use solid plugs. There is no advantage to a vented propeller on a boat like yours (or mine).
posted 09-15-2007 10:37 AM ET (US)
Update September 2007: I retested the 17-inch-pitch Mercury MIRAGEplus propeller and added the results to the article. I also made some measurements of the Whaler Drive and engine dimensions regarding the position of the anti-ventilation plate and the propeller centerline relative to the hull keel and transom.
The latest MIRAGEplus results were rather odd. The propeller showed a lot of SLIP. I think this might be due to the rather warm water. I am heading up north in a couple of weeks and should be able to test again in some colder water. The higher SLIP may also be due to the propeller having been run with the engine trimmed out farther than in prior tests. When I installed this propeller I tightened the propeller nut to the recommended 55-ft-lbs of torque. It still "clunks" when you shift, but it didn't seem as bad as in the past. Maybe I am just getting used to it. As Tom suggested, I left the full plugs in the PVS holes.
The dimensions of the Whaler Drive mounting for the single engine are now seen in one of the photographs which I just revised. The angle of the photo distorts some of the relationships. The end of the Whaler Drive appears to be closer to the keel in the picture than it actually is. The end of the Whaler Drive is about 2.25-inches above the keel centerline. In other words, the AV plate is just slightly above the end of the Whaler Drive (about 0.25-inch higher).
You would think after three seasons with the boat and testing 11 propellers that I would have found the perfect one, but I am still chasing that elusive device. At one point I owned five propellers for the boat, but I have cut that down to just four. I still have the original aluminum 19-inch three-blade which I now carry on-board when cruising as a spare. It is the lightest of the propellers so that is why I carry it for a spare--saves weight. For most of the past season I was in relatively calm water and ran with the 17 SST. Then I changed back to the 15 SST for a couple of trips out on the Great Lakes and bigger water. The MIRAGEplus had been sitting in the box for a year so I decided to try it again.
My inclination regarding the optimum propeller is now leaning toward a four-blade. I think the larger blade area will help the propeller when it has to run in airy water. As one of the pictures shows, the propeller thrust and boat wake are very airy and have lots of foam. And that is a picture in freshwater, too. My experience is that saltwater seems to be more foamy than freshwater, and therefore that picture of the foamy wake in freshwater is telling.
posted 09-15-2007 11:59 AM ET (US)
Interesting, I'm currently using the same propeller with the Johnson 150 on my 18 Outrage and I am calculating almost no slip at all for a variety of boat and engine speeds. The Johnson has the same or nearly the same gear ratio as your 225 but it has the larger Magnum gearcase.
The only odd thing that I find with the Mirage on the 18 Outrage is at throttle up it seems to do a fair amount of ventilating at first and then seems to shed the air almost all at once like a engaging a clutch on a car as long as I don't have too much throttle advance. If I advance the throttle too fast, the propeller just seems to spin up a froth until I back off, just like it did on my 27 Whaler WD.
While it is probably true for all propellers, it seems that Mirage is quite sensitive to aerated water. The Rev 4, on the other hand, is much less so based on my experience on the 27 Whaler WD. I think that the 15 inch Rev 4 may be just the propeller you've been searching for.
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