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Author Topic:   E-TEC efficiency with Viper vs. Rebel props

seahorse posted 02-24-2006 09:00 AM ET (US)
You can see the differences in mid-range fuel economy just by a prop style change.
Here is a comparison of the 19" Rebel and the Viper series of propellers. Notice the better speeds and lower fuel consumption figures on the twin 250 E-TEC's on a 30' SeaCraft.
The inefficiency of the Viper at mid speeds is one of the reasons that the magazine test reports show that the E-TEC is not always as economical as other engines at cruise.

19" Rebel - 3 blade
RPM MPH GPH MPG
500 2.2 0.36 6.0
1000 5.7 1.46 3.9
1500 7.9 2.97 2.6
2000 9.0 5.98 1.5
2500 14.7 12.22 1.2
3000 21.4 14.20 1.5
3500 29.0 17.19 1.7
4000 35.3 20.70 1.7
4500 41.0 24.45 1.7
5000 46.2 31.59 1.5
5400 48.7 37.84 1.3
Viper 19" 3 blade
RPM MPH GPH MPG
500 2.3 0.36 6.3
1000 5.4 1.49 3.6
1500 7.4 3.08 2.4
2000 8.8 7.41 1.2
2500 9.8 12.30 0.8
3000 16.5 14.63 1.1
3500 22.8 17.58 1.3
4000 31.2 23.03 1.4
4500 37.3 26.94 1.4
5000 42.9 35.52 1.2
5500 47.8 41.44 1.2
5700 48.9 44.80 1.1

jimh posted 02-24-2006 09:09 AM ET (US)
Those results are very interesting. Changing the propeller gives a significant change in fuel economy.
At 3,500-RPM the fuel economy improves to 1.7-MPG from 1.3-MPG. That is a 30-percent increase. Wow! The new propeller will pay for itself in reduced fuel burn.
The Judge posted 02-24-2006 09:18 AM ET (US)
Certain things do not make sense though...how can the engines burn 7gph more at WOT with the Viper? WOT is WOT and no matter what prop you are running. When the hammer is on the table, she is WOT.
seahorse posted 02-24-2006 09:47 AM ET (US)
Jim,
Could I impose on you to "clean up" the charts? They were pasted from an Excel spreadsheet and looked good on preview.
thanks
fourdfish posted 02-24-2006 10:15 AM ET (US)
So much for the magazine shootout test Larry!
fourdfish posted 02-24-2006 10:21 AM ET (US)
Seahorse-I was thinking, this change would affect all of the test results of the magazine shootout. The conclusion at the end of the test was that differences were not significant anyway and some people chose to ignore that statement. Kind of blows a hole in the Merc new ad campaign which was based on that test.
NewportMe posted 02-24-2006 11:14 AM ET (US)
Could the extra 300 rpm at wot account for the increased fuel burn Bigs....er Judge I have no Idea I'm just asking.
Peter posted 02-24-2006 11:25 AM ET (US)
I discovered the lower efficiency of the Viper design at cruising speeds 2 years ago. The 225 Fichts on my 27 Whaler were equipped with Vipers and I was finding the Vipers had a hard time maintaining grip at cruising speeds causing me to experiment with a number of different propellers. I was also having a difficult time docking the boat with the Vipers as well as most of the other three blade propellers I tried.
On the other hand, of all the propellers I tested, the Vipers produced the fasted top speed by 1 to 2 MPH as I recall.
The Judge posted 02-24-2006 12:08 PM ET (US)
Nope! That is what I mean, engine does not care if it is turning 4000rpm pushing a barge @ 12mph or 80mph at 6k on a bass boat. Hammer down is hammer down.
fourdfish posted 02-24-2006 12:14 PM ET (US)
What?????
sraab928 posted 02-24-2006 01:41 PM ET (US)
I also find it interesting that at 3500 RPM you get better GPH fuel consumption and also you are cruising 6.2 MPH faster - what a difference.
Peter posted 02-24-2006 01:57 PM ET (US)
The Rebel is doing a much better job of getting the boat over the "hump" at 3500 RPM. With any of the 3 blade propellers I tried, the boat would start to fall off plane at 3500 RPM, just like it looks like its doing on the Seacraft. The Mirage was the best of the 3-blades but still was no match for the 4-blades on holding a low speed plane.
SIM posted 02-24-2006 02:16 PM ET (US)
Isn't the most important consideration when choosing a propeller that the engine (what ever brand) see's its rated WOT rpm under a normal load?
Andy
fourdfish posted 02-24-2006 03:02 PM ET (US)
Andy, As I know well that you have far more experience than I in this area, isn't it also true that prop selection and design is not exact science given all the variables. I in fact have tried 3 different props this year with different conditions and have noticed some real differences in RPMs at WOT. I then kept 2 of them with different pitchs. I still am not sure which one I want to run for trolling.
This test was with 2- 19" props(same pitch) and the results were different enough to explain some of the differences in that so called scientific magazine test being touted around here by some! The mag test even said as much in thier conclusion.
SIM posted 02-25-2006 10:51 AM ET (US)
Fourdfish,
I aggree with you 100%. I run across it all the time(big differences) when comparing similar diameter\pitch props of different brands. I will say this that the Yamaha SW series and the Merc Mirages of similar dia and pitch give very close to the same WOT rpm numbers on the same boat\engine combo. But the WOT speed is slightly better with the Merc's. I think Merc really shines head and shoulders above all the other prop companies in prop design and quality.
I don't want to derail this thread, but customers will ask "I want to turn such and such a rpm at this given speed range" and try to prop there engine accordingly. I firmly believe (and I would bet that most engine manufactuers would as well) that the single most important first consideration when proping a engine is that the engine see's the upper end of its rated RPM range at WOT. Example: 4-stroke Yamaha's.......Ideally when loaded normally(gear,fuel,persons) that is see 5800 rpms trimmed up at WOT.
I did not read the above mentioned article, but I have read so much mis-information over the years in boating magazines and Power Boat Reports that I am skeptical of most of there info. PBR does do some adequate electronics tests and boat gizmo testing though.
Andy
Peter posted 02-25-2006 11:20 AM ET (US)
Andy -- I think you are really referring to getting the pitch of any given propeller right for a selected propeller type. Getting the pitch right so that the engine turns in the proper range at WOT would be the main universal concern of the engine manufacturers.
However, there are really two considerations in prop selection: (1) what the user wants out of the propeller (cruise efficiency, good seakeeping, and/or top speed), we'll call this propeller type, and (2) then once propeller type is selected, getting the pitch of selected propeller type right so that the motor is not running over loaded.
My understanding is that the Yamaha SW series was not designed as a speed propeller according to Yamaha, but rather a propeller designed to provide an efficient mid-range cruise and provide a good hold on the water offshore. That was generally my experience with that propeller when I had one on my single powered 22 Revenge. The Mirage, on the other hand, seems not to be that great the cruising department (poor hold in offshore conditions at cruise) but seems to provide good top speed performance. For Yamahas, if one's propeller selection priority was top speed, I would recommend trying the Mirage and if cruising, offshore hold ability, I would recommend the Yamaha SWS. While one could bracket where to start with propeller pitch for either of these propellers, actual proper pitch really needs to be determine on a trial and error basis as every motor/boat combination even within the same family of motor and boat combinations can be different.
seahorse posted 02-25-2006 02:15 PM ET (US)
Great post, Peter,
Also there is the boat used for water skiing, towing, etc.
Those types will require a different style of prop and will be propped to the absolute top rpm range so they have plenty of acceleration and thrust at lower speeds where the power is needed. In some applicaitons, they may even be underpropped meaning the boat operator has to watch the engine rpms if he is running without much load at high speeds.
SIM posted 02-25-2006 05:53 PM ET (US)
Pete,
I did not meant to imply that Merc Mirage and Yamaha SW were the greatest props out there. I was just trying to say that I feel that they perform similarly......same boat...same engine ect and the better overall prop being the Mirage. At least in my experiences.
Your second paragraph I agree. They both have a direct effect on each other. Lets not get into prop slip.......OK? :^) jk
After reading what I posted maybe I come off a little gruff about the WOT rpm thing, but I still believe that.
Andy
Peter posted 02-25-2006 07:10 PM ET (US)
Andy -- I didn't read your post at all with the implication you suggested. I think the SWS and Mirage are good propellers and similar in some respects but different in others based on my experience. If you look at them side by side, as I'm sure you have, they are differently shaped and accordingly one should expect different results. I think that the SWS, with its more cleaver like shape, probably does better running lower in the water and provides an efficient cruise. The Mirage is meant to run higher in the water to achieve speeds but gives up some mid-range based on my experience. As is always the case in boating, everything is a compromise of one sort or another.
I agree with the slip comment. Comparing slip from one propeller brand or even type to another is meaningless unless they all use exactly the same standards to designate pitch, which they don't. When determining which was the best set of propellers for my current rig, I didn't use calculated slip but instead used my Navman 3100's readout for instant MPG at various boat/motor speeds (making sure to be in the upper end of the WOT engine speed range) to find the best propeller for my needs. Turned out that the 4-blade Rev 4 edged out the the 4-blade Renegade of the same designated pitch. The Renegade I tried didn't have enough pitch. It seems to me that a 19P designation for an OMC propeller is about the equal of a 17P on Mercury's scale. Jim's experience seems to confirm my own experience. See the boat speed vs. engine speed plots continuouswave.com/whaler/reference/propellerWDSingle.html
Your principal concern regarding reaching proper WOT engine speeds is dead-on, universal and independent of propeller brand or type.

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Author	Topic: E-TEC efficiency with Viper vs. Rebel props
seahorse	posted 02-24-2006 09:00 AM ET (US) You can see the differences in mid-range fuel economy just by a prop style change. Here is a comparison of the 19" Rebel and the Viper series of propellers. Notice the better speeds and lower fuel consumption figures on the twin 250 E-TEC's on a 30' SeaCraft. The inefficiency of the Viper at mid speeds is one of the reasons that the magazine test reports show that the E-TEC is not always as economical as other engines at cruise. 19" Rebel - 3 blade RPM MPH GPH MPG 500 2.2 0.36 6.0 1000 5.7 1.46 3.9 1500 7.9 2.97 2.6 2000 9.0 5.98 1.5 2500 14.7 12.22 1.2 3000 21.4 14.20 1.5 3500 29.0 17.19 1.7 4000 35.3 20.70 1.7 4500 41.0 24.45 1.7 5000 46.2 31.59 1.5 5400 48.7 37.84 1.3 Viper 19" 3 blade RPM MPH GPH MPG 500 2.3 0.36 6.3 1000 5.4 1.49 3.6 1500 7.4 3.08 2.4 2000 8.8 7.41 1.2 2500 9.8 12.30 0.8 3000 16.5 14.63 1.1 3500 22.8 17.58 1.3 4000 31.2 23.03 1.4 4500 37.3 26.94 1.4 5000 42.9 35.52 1.2 5500 47.8 41.44 1.2 5700 48.9 44.80 1.1
jimh	posted 02-24-2006 09:09 AM ET (US) Those results are very interesting. Changing the propeller gives a significant change in fuel economy. At 3,500-RPM the fuel economy improves to 1.7-MPG from 1.3-MPG. That is a 30-percent increase. Wow! The new propeller will pay for itself in reduced fuel burn.
The Judge	posted 02-24-2006 09:18 AM ET (US) Certain things do not make sense though...how can the engines burn 7gph more at WOT with the Viper? WOT is WOT and no matter what prop you are running. When the hammer is on the table, she is WOT.
seahorse	posted 02-24-2006 09:47 AM ET (US) Jim, Could I impose on you to "clean up" the charts? They were pasted from an Excel spreadsheet and looked good on preview. thanks
fourdfish	posted 02-24-2006 10:15 AM ET (US) So much for the magazine shootout test Larry!
fourdfish	posted 02-24-2006 10:21 AM ET (US) Seahorse-I was thinking, this change would affect all of the test results of the magazine shootout. The conclusion at the end of the test was that differences were not significant anyway and some people chose to ignore that statement. Kind of blows a hole in the Merc new ad campaign which was based on that test.
NewportMe	posted 02-24-2006 11:14 AM ET (US) Could the extra 300 rpm at wot account for the increased fuel burn Bigs....er Judge I have no Idea I'm just asking.
Peter	posted 02-24-2006 11:25 AM ET (US) I discovered the lower efficiency of the Viper design at cruising speeds 2 years ago. The 225 Fichts on my 27 Whaler were equipped with Vipers and I was finding the Vipers had a hard time maintaining grip at cruising speeds causing me to experiment with a number of different propellers. I was also having a difficult time docking the boat with the Vipers as well as most of the other three blade propellers I tried. On the other hand, of all the propellers I tested, the Vipers produced the fasted top speed by 1 to 2 MPH as I recall.
The Judge	posted 02-24-2006 12:08 PM ET (US) Nope! That is what I mean, engine does not care if it is turning 4000rpm pushing a barge @ 12mph or 80mph at 6k on a bass boat. Hammer down is hammer down.
fourdfish	posted 02-24-2006 12:14 PM ET (US) What?????
sraab928	posted 02-24-2006 01:41 PM ET (US) I also find it interesting that at 3500 RPM you get better GPH fuel consumption and also you are cruising 6.2 MPH faster - what a difference.
Peter	posted 02-24-2006 01:57 PM ET (US) The Rebel is doing a much better job of getting the boat over the "hump" at 3500 RPM. With any of the 3 blade propellers I tried, the boat would start to fall off plane at 3500 RPM, just like it looks like its doing on the Seacraft. The Mirage was the best of the 3-blades but still was no match for the 4-blades on holding a low speed plane.
SIM	posted 02-24-2006 02:16 PM ET (US) Isn't the most important consideration when choosing a propeller that the engine (what ever brand) see's its rated WOT rpm under a normal load? Andy
fourdfish	posted 02-24-2006 03:02 PM ET (US) Andy, As I know well that you have far more experience than I in this area, isn't it also true that prop selection and design is not exact science given all the variables. I in fact have tried 3 different props this year with different conditions and have noticed some real differences in RPMs at WOT. I then kept 2 of them with different pitchs. I still am not sure which one I want to run for trolling. This test was with 2- 19" props(same pitch) and the results were different enough to explain some of the differences in that so called scientific magazine test being touted around here by some! The mag test even said as much in thier conclusion.
SIM	posted 02-25-2006 10:51 AM ET (US) Fourdfish, I aggree with you 100%. I run across it all the time(big differences) when comparing similar diameter\pitch props of different brands. I will say this that the Yamaha SW series and the Merc Mirages of similar dia and pitch give very close to the same WOT rpm numbers on the same boat\engine combo. But the WOT speed is slightly better with the Merc's. I think Merc really shines head and shoulders above all the other prop companies in prop design and quality. I don't want to derail this thread, but customers will ask "I want to turn such and such a rpm at this given speed range" and try to prop there engine accordingly. I firmly believe (and I would bet that most engine manufactuers would as well) that the single most important first consideration when proping a engine is that the engine see's the upper end of its rated RPM range at WOT. Example: 4-stroke Yamaha's.......Ideally when loaded normally(gear,fuel,persons) that is see 5800 rpms trimmed up at WOT. I did not read the above mentioned article, but I have read so much mis-information over the years in boating magazines and Power Boat Reports that I am skeptical of most of there info. PBR does do some adequate electronics tests and boat gizmo testing though. Andy
Peter	posted 02-25-2006 11:20 AM ET (US) Andy -- I think you are really referring to getting the pitch of any given propeller right for a selected propeller type. Getting the pitch right so that the engine turns in the proper range at WOT would be the main universal concern of the engine manufacturers. However, there are really two considerations in prop selection: (1) what the user wants out of the propeller (cruise efficiency, good seakeeping, and/or top speed), we'll call this propeller type, and (2) then once propeller type is selected, getting the pitch of selected propeller type right so that the motor is not running over loaded. My understanding is that the Yamaha SW series was not designed as a speed propeller according to Yamaha, but rather a propeller designed to provide an efficient mid-range cruise and provide a good hold on the water offshore. That was generally my experience with that propeller when I had one on my single powered 22 Revenge. The Mirage, on the other hand, seems not to be that great the cruising department (poor hold in offshore conditions at cruise) but seems to provide good top speed performance. For Yamahas, if one's propeller selection priority was top speed, I would recommend trying the Mirage and if cruising, offshore hold ability, I would recommend the Yamaha SWS. While one could bracket where to start with propeller pitch for either of these propellers, actual proper pitch really needs to be determine on a trial and error basis as every motor/boat combination even within the same family of motor and boat combinations can be different.
seahorse	posted 02-25-2006 02:15 PM ET (US) Great post, Peter, Also there is the boat used for water skiing, towing, etc. Those types will require a different style of prop and will be propped to the absolute top rpm range so they have plenty of acceleration and thrust at lower speeds where the power is needed. In some applicaitons, they may even be underpropped meaning the boat operator has to watch the engine rpms if he is running without much load at high speeds.
SIM	posted 02-25-2006 05:53 PM ET (US) Pete, I did not meant to imply that Merc Mirage and Yamaha SW were the greatest props out there. I was just trying to say that I feel that they perform similarly......same boat...same engine ect and the better overall prop being the Mirage. At least in my experiences. Your second paragraph I agree. They both have a direct effect on each other. Lets not get into prop slip.......OK? :^) jk After reading what I posted maybe I come off a little gruff about the WOT rpm thing, but I still believe that. Andy
Peter	posted 02-25-2006 07:10 PM ET (US) Andy -- I didn't read your post at all with the implication you suggested. I think the SWS and Mirage are good propellers and similar in some respects but different in others based on my experience. If you look at them side by side, as I'm sure you have, they are differently shaped and accordingly one should expect different results. I think that the SWS, with its more cleaver like shape, probably does better running lower in the water and provides an efficient cruise. The Mirage is meant to run higher in the water to achieve speeds but gives up some mid-range based on my experience. As is always the case in boating, everything is a compromise of one sort or another. I agree with the slip comment. Comparing slip from one propeller brand or even type to another is meaningless unless they all use exactly the same standards to designate pitch, which they don't. When determining which was the best set of propellers for my current rig, I didn't use calculated slip but instead used my Navman 3100's readout for instant MPG at various boat/motor speeds (making sure to be in the upper end of the WOT engine speed range) to find the best propeller for my needs. Turned out that the 4-blade Rev 4 edged out the the 4-blade Renegade of the same designated pitch. The Renegade I tried didn't have enough pitch. It seems to me that a 19P designation for an OMC propeller is about the equal of a 17P on Mercury's scale. Jim's experience seems to confirm my own experience. See the boat speed vs. engine speed plots continuouswave.com/whaler/reference/propellerWDSingle.html Your principal concern regarding reaching proper WOT engine speeds is dead-on, universal and independent of propeller brand or type.