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Author Topic:   Real World Repower MPG
rehenderson posted 02-01-2004 03:03 PM ET (US)   Profile for rehenderson   Send Email to rehenderson  
I am in the process of evaluating repower options for my 22' Revenge Cuddy (rated for 230 HP and powered for twenty years by a 200 HP Johnson). I am more interested in reliability and mileage than "hole shots" and top speed-here's my question. In looking over engine manufacturer's web page information regarding the performance data for particular boat/engine combinations (especially as to boats most similar to my Revenge) I have been surprised to find that the claimed efficiency of four strokes (or even the high end two strokes) doesn't seem to show up in the actual performance numbers- all the 22-23' V-hulls, no matter how they are powered, seem to end up with a maximum efficiency (speed/mpg) rating hovering around 3.25 to 3.5 mpg. What am I missing?
jimp posted 02-01-2004 04:12 PM ET (US)     Profile for jimp  Send Email to jimp     
Not sure of what the manufacturers are saying, but I repowered my 1990 Revenge 22 WT with a 2003 Merc Optimax. I replaced a carbed 1989 Johnson 225.

The Johnson gave about 2 nautical mpg at 24 kts with a stainless prop (top at about 39+ knots). The Merc Optimax gives about 3.15 nmpg at 27.7 knots, 3700 rpm and a 19" aluminum prop (top at about 39+ knots).


rehenderson posted 02-01-2004 11:09 PM ET (US)     Profile for rehenderson  Send Email to rehenderson     
Thanks for the response. My old Johnson gets about the same 2 mpg you experienced. My confusion is that all the modern motors seem to yield about the same 3.25 or so mpg maximum efficiency, irrespective of technology. That's obviously a big improvement over my motor, but I'm surprised that I'm not seeing more efficiency from the high tech motors vs the "low tech" carb motors.
jimh posted 02-02-2004 09:01 AM ET (US)     Profile for jimh  Send Email to jimh     
In vehicle applications, manufacturers were able to improve fuel economy in impressive ways by providing the consumer with:

--smaller vehicles
--lighter vehicles
--more aerodynamic vehicles
--better tires
--lighter engines
--lower displacement engines
--lower power engines
--more fuel efficient engines

When a boat is re-powered with a new engine, the only thing that changes is the engine efficiency and the total weight. Unfortunately, the total weight usually increases, which immediately has a negative impact on fuel efficiency. Everything else stays the same. The net change in fuel economy thus comes solely from the increased engine efficiency, which is often not as dramatic as the improvements seen in vehicles.

In addition, the newer "more fuel efficient" engine often has larger displacement than the engine it replaces. Again, this tends to have a negative impact on fuel economy.

Even in advertising claims, most engine makers can only find certain operating speeds at which the new engine will provide the claimed "40-percent" improvement in fuel economy.

In addition, in vehicles the move to a more fuel efficient vehicle also tends to affect the driving style of the operator. Faced with less horsepower, less acceleration, and a smaller, lighter vehicle, the manner in which the vehicle is operated often changes. The new driving style may be in itself more fuel efficient, adding to the perception of improved fuel economy.

On a boat, the opposite is often true. A new engine brings new confidence, and the effect may be to modify the operation of the boat in such a way as to tend to increase fuel consumption. Long runs at higher speeds may be more common with a new engine than with an old one. These factors again may have a negative impact on the fuel economy.

And a new engine on a boat may also prompt greater overall usage.

The net effect of all of this is to lessen the effects of improved fuel economy seen when re-powering a boat. Heck, your total fuel bills might even increase!

rehenderson posted 02-02-2004 11:38 AM ET (US)     Profile for rehenderson  Send Email to rehenderson     
Thanks for your thoughtful response, Jim. I think your comment that the efficiencies are achieved only "at certain speeds" is the "X" factor here. This all certainly suggests that the new technologies are not in all respects as they are represented- and that the lower prices on the lower tech engines may be a more rational decision in terms of mpg.
jimh posted 02-03-2004 09:09 AM ET (US)     Profile for jimh  Send Email to jimh     
The principal requirement driving the design of current outboard engines is to meet the recently imposed federal and state (California) requirements for exhaust gas emissions. A reduction in emissions of something like 80-percent was required. It was well known that in a conventional 2-stroke outboard motor that some of the fuel was being thrown out the exhaust post without being burned. This was a problem for both emissions and fuel economy. It was acceptable for decades because it engendered the otherwise very simple design of the 2-stroke outboard motor.

In re-designing the outboard motor to meet exhaust emission standards, the unburned fuel being thrown away was the main target. By recovering this fuel and burning it, exhaust emissions would be improved and at the same time a bonus of better fuel economy would be obtained.

Even if 100-percent of the unburned fuel was recovered and applied to combustion, the fuel economy would not increase in fantastic proportion, because the unburned fuel was only a small portion of the total fuel being provided to the combustion chamber.

If an outboard was throwing one-third of its fuel out the exhaust port without burning it, then for each gallon of fuel it consumed it only used two-thirds for combustion. Recovering all of the wasted fuel and using it for combustion would result in a 50-percent increase in fuel economy. I think this is about the limit of improvement.

Depending on the operating speed, in a conventional 2-stroke there were probably situations where the amount of fuel being wasted was less than a third. Let's say only 20-percent was being unburned. If that is recovered and used for combustion, then the improvement in fuel economy would only be 25-percent.

In order to produce an engine which will not waste the unburned fuel, some designers turned to 4-stroke engines. This added a great deal of complexity to the engine. It now had valves, camshafts, lifters, gears, belts, etc. Turning all of this additional mass at engine speed consumed some horsepower in itself, and that reduced the fuel efficiency.

Increases in combustion chamber efficiency could also contribute to better fuel economy. I am not an engine designer, so you'll have to ask one how much gain was unrealized in the conventional 2-stroke engines.

Better fuel economy from newer engines is a nice plus, but according to surveys and my own general sampling, it seems that owners of these newer engines are more impressed with how quietly they idle, how reliably they start, and how vibration-free they operate. Among owners who had very large twin engines, say V-6 engines over 200 HP, the fuel economy has been cited as being very noticeable. Of course, these owners were using a large quantity of fuel to begin with, so a 30-40 percent reduction for them might mean 30-40 gallons a day--and that is a very noticeable reduction!

For a guy with a 70-HP conventional 2-stroke engine, the fuel savings will be proportionately fewer gallons, and it may take a long time--perhaps the lifetime of the engine--before the savings from reduced fuel consumption makes up for the added cost of the new engine.

Bigshot posted 02-03-2004 11:03 AM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Reread this post and you will find your answer. You state that you are disappointed in their claims of 40% better mileage.....well 2mpg to 3mpg is a 50% improvement last time I checked. If you do a lot of trolling it will REALLY pay off. Most DFI and 4strokes burn about 1/5 a conventional engine burns at trolling speeds. Wide open they burn about the same. Reason being is 225hp is still 225hp no matter how it is generated. Most reports show about 8gph at cruise where my 225 Carbed Johnson burns about 12-13 at the same speed. If you do 100 hours a year you will burn roughly $500 less in fuel which over 5-10 years is substantial.

With smaller engines I am utterly amazed unlike some who think it is too costly. My 70 Suzuki burns about 2.5gph at cruise compared to about 6gph with my old 90 OMC or about 4.5-5gph with my 90 Yamaha 2 stroke. Neat thing is at 1000 rpms I burn less than a qt and hour. I can run all day on a 6 gal tank which is amazing. My average usage with my 27 pate tank is about 1.5gph per tank compared to about 3.5 with the 2 strokes. Now it will take years to make up the difference in gas but the increased range, no smoke, no noise, etc are SOOOOOO worth it.

rehenderson posted 02-03-2004 02:45 PM ET (US)     Profile for rehenderson  Send Email to rehenderson     
My comparison isn't between older and new motors- I am well aware that that any motor currently in production is a dramatic improvement in efficiency over my 20 year old motor (in my particular circumstances, this improvement should represent an additional cruising range of more than 70 miles!). It is surprising, however, that there is no similar superiority achieved by going from a current carb 2 stroke motor to a current injected 4 stroke motor. In other words, if one is looking for improved cruising range (without throwing another tank on board!), there seems to be little gained from selecting a "high tech" engine. As you suggest, there are other very good- maybe even compelling reasons- to go high tech....cruising efficiency just isn't one of them. Agree?
lhg posted 02-03-2004 03:02 PM ET (US)     Profile for lhg    
Mercury's 2003 & 2004 catalogs address this exact question with the Yamaha built 225 4-stroke vs the Mercury built 225 Optimax. Unfortunately, they don't make a third comparison, the 225 EFI, my guess being because of it's superior performance and not-so-hot economy.

But anyway, since the original post involves a 22 Revenge, which would most likely need a 225, this data is relevant here. Here are their "side by side" results comparing the 4-stroke to the Optimax: (the 4-stroke is about 80 lbs heavier than the Optimax) (they don't indicate kind of boat)

Top speed: Optimax 40.8 mph, 4-stroke 38.7 mph

Acceleration 0-20mph: Optimax 4.7 sec, 4-stroke 6.3 sec

Acceleration 0-30mph: Optimax 8.3 sec, 4-stroke 12.2 sec

In performance, the Optimax is much better.

Cruising Fuel Economy: Optimax 2.44 MPG, 4-stroke 2.72 MPG

Full throttle economy: Optimax 1.82 MPG, 4-stroke 1.99MPG

4-stroke gives about 10% better overall economy.

So we each have to decide which makes the most sense for us. Looking at these figures, this test boat seems more like the size of a 25 Outrage rather than a 22 outrage.

rehenderson posted 02-03-2004 03:51 PM ET (US)     Profile for rehenderson  Send Email to rehenderson     
That's really interesting data. I wonder if anyone has ever created a comprehensive chart incorporating all of the major manufacturers....
lhg posted 02-03-2004 04:47 PM ET (US)     Profile for lhg    
If they did they wouldn't have any advertisers. It seems the boating mags go to great length to avoid these comparisons. When they do publish tests, I'm always amazed at how incredibly close the results are, and they ALWAYS find something good to say about each (advertiser). This is not my real world experience. I think differences in same HP engines can be often be considerable.

In my estimation, Mercury probably did the comparison because they have nothing to lose from it. The 4-stroke is bought from a partner/competitor, and it's out of their line (except for leftovers) now that Project X is out. And they probably know the Project X will outperform it too. I think they picked a somewhat heavy boat to minimize the differences and probably not antagonize Yamaha too much. On a lighter boat, the performance differences would have been greater. I have yet to see a 225 4-stroke on a bass or go-fast boat, but Optimax & EFI's abound. So that tells you something.

Bigshot posted 02-04-2004 02:58 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
rehenderson.....confused at your last post. You are stating that a 2004 Mercury classic 200hp carbed is not much less efficient than a 200hp Optimax or 4 stroke? Or are you saying that you are confused why a 2004 Carbed 200hp is not more efficient than your 1984 carbed 200hp? If the latter, reason being a carb is a carb and a 2 stroke is a 2 stroke. The efficiency for carbed technology is old and CAN"T be upgraded, even a 200EFI 2 stroke is about the same in GPH as carbed. The ONLY things efficient are DFI and 4 strokes. The block of a DFI engine is similar to a carbed, it is all in the computer and injection system(for the most part). The 4 strokes are a whole different breed that you either desire or don't. i know of nobody who hates their 4 stroke over their previous engine. I know of many who hate their DFI engines but that is not the case since about 2002 or so. Everybody loves their conventional carb engines but hate to stop at the gas station.....myself included.
rehenderson posted 02-04-2004 03:50 PM ET (US)     Profile for rehenderson  Send Email to rehenderson     
Sorry to have confused you, Bigshot. My observation is that, with respect to cruising mileage in boats somewhat comparable to the 22' Revenge and powered by 200-235 hp engines, "all the modern motors seem to yield about the same 3.25 or so mpg maximum efficiency, irrespective of technology". Best I can tell that's substantially the case, but I'd love to be set straight if the facts are otherwise.
Sal DiMercurio posted 02-04-2004 05:05 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
You can't compare an engine thats on a deep V hull with the same engine on a flatter bottom boat, because the deep V hull with the same engine will use much more fuel then the same engine on the flatter bottom hull.
Theres no way you can compare a carbed 235 hp engine to a DFI 225 hp injected engine.
It seems like the older 235 hp carbed engines [ Johnson ] uses "at least" twice the fuel.
Hell, Nick has one on his boat & i'm pretty sure he never got over 2 mpg even while on the trailer behind the truck while not even running,.....they aren't shy about fuel stops.
Where on the other hand if he were running a 225 hp DFI Evinrude, he would be getting 4 mpg unless it were run at 5,000 rpms or above then they all need fire hoses for fuel lines even the 4 strokes.
The DFI engines are far better on fuel then any of the carbed same hp .
By the way Nick, hows the rebuild coming?

Bigshot posted 02-05-2004 12:19 PM ET (US)     Profile for Bigshot  Send Email to Bigshot     
Rebuild is done with about 5 hours runtime so far. Painted the block teal to match the decals....looks trick.

Actually Sal with my 225(Looper) and the boat weighing 2200lbs I get over 2.5mpg at cruise(31mph @ 12+/-gph), not too bad for a carbed engine. I would get close to 4 with a DFI or 4 stroke though.

rehenderson posted 02-05-2004 01:30 PM ET (US)     Profile for rehenderson  Send Email to rehenderson     
How do you guys rate the 200 hp Yamaha OX66? I gather this is a "throttle body" injection system, which wouldn't be the newest technology, but everyone seems to describe as "an awesome motor". Opinions for my 22'?
jimh posted 02-05-2004 09:02 PM ET (US)     Profile for jimh  Send Email to jimh     
The OX-66 series of Yamaha engines are just conventional 2-stroke engines with fuel injection albeit with some improved electronics and sensors. I do not believe their fuel economy is anything special and is probably on par with other 2-stroke EFI engines like the Mercury 200 EFI.

With 200-HP on a 22-foot Whaler you will be using quite a bit of throttle and I would not expect the fuel economy to be particularly impressive. I am sure that on the Yamaha website you can find performance bulletins for this engine on a boat that is similar in weight and size to yours. That data should give you some hard numbers to consider.

My guess would be at minimum plane you will be using about 120-HP. That will burn roughly 60-lbs of fuel an hour, or 9 gallons. Your speed would probably be in the 22-25 MPH range, which would translate into fuel economy of about 2.4 to 2.7 MPG.

Again, see the Yamaha website--which usually has excellent performance reports with fuel consumption data--for more accurate real-world information about the fuel economy for that engine.

lhg posted 02-05-2004 09:14 PM ET (US)     Profile for lhg    
My experience is that an EFI 2-stroke gets about 10-15% better overall fuel economy than the same carbureted engine.
They also put out a little more top end speed and quicker acceleration. And are much quieter running.
Peter posted 02-05-2004 09:50 PM ET (US)     Profile for Peter  Send Email to Peter     
Had a 22 Revenge with Yamaha 225 Ox66 EFI equipped with Yamaha Saltwater Series 15 x 17 propeller. At 38 to 3900 RPM it would cruise at 30 MPH. Consumption at that engine speed was about 10 to 10.5 GPH so mileage was about 2.9 to 3.0 MPG. Sweet spot for cruising was between 3500 and 4000 RPM (26 to 32 MPH).

The OX66 is a proven design. Weakest link on the entire motor is the O2 sensor which can get dirty. If the O2 sensor gets dirty, eventually the plugs will foul. The trick to keeping it clean is to use the Yamaha fuel additive called RingFree. It is much simpler than a direct fuel injection motor such as an Optimax, HPDI or FICHT. I had mine for nearly four seasons without any incidents and I always used Yamalube oil and the RingFree additive.

The 200 uses a 2.6 liter block rather than the 3.1 liter block of the 225 and runs through a 1.86:1 gearcase rather than a 1.81:1. Thus the 200 will probably be running a little faster at 30 MPH, so fuel economy might be the same or even a little lower. If a new 200 Ox66 is a repower candidate for you, I would act sooner rather than later. I wouldn't be surprised if this is the last year for the 200 as it got virtually no space in the Yamaha catalog.

Assuming a price difference of $2,000 between the 200 Ox66 and the HPDI, it will take numerous 50 hour seasons of cruising at 30 MPH to recover, by way of fuel savings, the premium spent on the higher tech engine. If you don't care whether the engine smokes or not, then the only advantage I see in the 4 stroke or the DI 2 stroke is it could extend your crusing range by 15 to 20 percent.

My outlook is that in a southern climate where the boating season is long, the 2-stroke DIs or 4-strokes make more sense, economically, but in northern climates where the boating season is short, they don't.

jimh posted 02-05-2004 11:58 PM ET (US)     Profile for jimh  Send Email to jimh     
Peter--I had not thought of the latitude factor in the re-powering financial analysis, but it certainly is appropriate. As an example, in 2003 my "northern" boat was only in the water for about 16 days total, and that is a rather short season.
lhg posted 02-06-2004 12:24 AM ET (US)     Profile for lhg    
Jim - I think you need to do more boating and less website management! My whaler has more than 16 days on it since Thanksgiving.
rehenderson posted 02-06-2004 11:40 AM ET (US)     Profile for rehenderson  Send Email to rehenderson     
Thanks for some very informative responses guys.....sounds like the 225 might be a smarter choice.
lhg posted 02-06-2004 02:33 PM ET (US)     Profile for lhg    
I think for single engine power on a 22 Outrage/Revenge, the 225HP size is the optimal way to go. Choose brand and technology of your choice.
But, if you can afford to wait a little, you could add the ultra new 225 HP version of the Project X Merc 4-stroke to your list of options. I would not buy any new 225/250 engine without at least considering this new machine.
John from Madison CT posted 02-06-2004 02:43 PM ET (US)     Profile for John from Madison CT  Send Email to John from Madison CT     
Boat: 22' Outrage with Whaler Drive and Tee Top. Front Curtains on Tee Top.

Engine: Yamaha 250hp '98 Ox66 EFI. Extremely reliable engine.

At cruise I get a solid 3mpg running ~ 30mph.

Hope this helps.


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