posted 12-29-2007 09:44 AM ET (US)        

90-HP Motor Comparison
http://continuouswave.com/whaler/reference/compare90.html

which appears in the REFERENCE section of the website.

posted 12-29-2007 11:56 AM ET (US)            

So far, the results are in agreement with another general principle: a boat's speed is proportional to its engine's horsepower. If we obtained a result which was inconsistent with this general principle, it would raise a question about the method.

Keep the relationship between torque, rotational speed, and horsepower in mind when engine speed increases. Torque tends to decrease at extreme engine speeds. If it did not, horsepower would simply increase with engine speed. While horsepower does generally increase with engine speed, at the upper range of speed the torque output tends to fall. This makes the horsepower tend to not continue to increase with engine speed. So even though a particular engine might be able to run at a higher rotational speed than has been used in making these comparisons, a higher speed in itself does not make the engine produce more horsepower.

In actual boat performance, I have observed that often the very last few hundred RPM of engine speed create the most improvement in boat speed in terms of RPM for MPH. This result is generally explained by other phenomenon. Influences such as a change in hull factor or a reduction in drag from the gear case often contribute to those effects. That is to say, a sudden and otherwise secret boost in engine horsepower should not be inferred.

posted 12-29-2007 05:38 PM ET (US)         

Is there no difference in torque between a 2-stroke and 4-stroke engine running at the same RPM, across the RPM band?

"Le Petit E-tec 90". Has a nice French Canadian ring to it.

It would also be nice to see this comparison with a classic 2-stroke Merc 90, 5000-5500 RPM band. Several people here, including Erik who has run both, tells us the Merc has a lot more power. Erik has also told us the Merc 90 EFI is sold in Europe on the Montauk 170 as a 100, and furnished us a photo of one. What's up with that?

posted 12-29-2007 07:43 PM ET (US)            

"...the engines DO NOT put the same HP into the water.."

I disagree. And here is why:

The assumption that the engines DO have the same power output is the first assumption made in my analysis. I make this assumption because the manufacturers state that both engines make 90-HP. The fundamental difference is the rotational speed at which the two engines reach that power output. But they both make 90-HP.

A set of gears cannot tell what engine is turning them. As far as the gears are concerned there is a 90-HP engine on one side and a propeller on the other side. If there is any difference in the power transmission through a gear case, the trend is probably to have more power loss as the gear ratio increases. If anything, this would tend to reduce the "HP into the water" for the engine with a higher gear ratio.

A propeller cannot tell what engine is turning it, or if the torque comes from the engine or from the multiplier effect of the gear case. A propeller will work as well for one engine as for another, as long as it is turned at the same speed.

I cannot find any mechanism in the system which provides for the engines to put different amounts of "HP into the water" unless you assume that they have different amount of power output at their crankshaft.

posted 12-29-2007 11:00 PM ET (US)            

JimH has done a fine job of presenting his performance comparison between two fine outboard motors and their respective stats as claimed by the makers of these motors.

I have tested classic and post classic 17' hulls with 90e-tec's, 90 Yamaha's (two and four stroke), 90 Mercs (two and four stroke), 90 Evenrude FICHT and 90 Honda's (carbed and VTEC).

Every combination of motor mounting height and prop pitch for each motor was also investigated (with the great help of this forum and its members).

I agree that a database of 90hp motors on Classic Whalers/Post Classic Whalers should be included on this great site. My only reservation is that some information presented is not "real world" data and may lead some into false assumptions about a specific boat/motor combination.
(Feel free to call me on my BS, I just spent $12K to repower my Classic Montauk)

As I stated earlier, prop selection, mounting heigh, primary function of the boat/motor will all play a part in the "real world" data of the true performance of any of these motors.

Again, JimH has provided us with a great forum to discuss all of our CW related issues and I hope this only adds to the the high quality content of this forum.

Just my .02

posted 12-30-2007 01:07 AM ET (US)            

http://whaler.com/rec/pdfs/performance/6.pdf

which show that with a 20-inch pitch propeller and the 90-HP FOURSTROKE engine turning at 5,500-RPM a boat speed of 41.5-MPH is obtained. This is in excellent agreement with the predicted speed, which according to the method used in the analysis should have been 40.23. The difference is 1.2-MPH, or a variation of about three percent. This is really only a case of the real propeller SLIP being different than the assumed propeller's slip. The analysis assumed about ten percent slip, but the real world test produced just seven percent slip. In terms of propeller performance, that is a terrific figure for a single engine outboard boat, and it probably is indicative of the actual pitch of the propeller being a bit higher than the rated pitch. In my own experience, that behavior is often seen in Mercury-brand propellers.

The argument raised that if the E-TEC were tested on this same boat it could not reach the same speeds as predicted by the method is based on assumptions of "of basic engine power, the 10% rule and prop efficiencies." I will be glad to explore these.

"Basic engine power" is apparently a belief that the E-TEC engine must not be as powerful as the FOURSTROKE, even though they are rated at the same power level. Again, this is speculative. To assume that one is more powerful than its rated power and one is less powerful is really not a useful way to explore the question of how the gear ratio affects the outcome. We already know that if we assume one engine is more powerful than another it will produce faster boat speed. A proposal is often made that certain brands of engines are inherently more powerful than other brands. This analysis does not provide for any special interpretation of horsepower on the basis of brand of motor.

"The 10% rule" is a reference to the allowance of a ten percent variation for production engines to vary from their rated power. There is nothing in the ten percent rule which indicates that it only applies one way or to only one brand of motors. If one wishes to arbitrarily increase or decrease the horsepower of a motor by ten percent from its rating before making a comparison, we already know the outcome. If you input less horsepower into the analysis the result will be less boat speed. "The 10% rule" is really just another way to speculate about variation in horsepower by brand.

"Prop efficiencies" is a reference to a notion that certain pitch/diameter ratios of propellers can be more efficient than others. In the method used in this analysis the propellers vary only by one inch in pitch. This is not a great variation and it is unlikely that one could assume a large amount of difference in the efficiency of the propeller based on the small difference in pitch which is assumed.

In the end, any speculation that actual testing of a 90-HP FOURSTROKE has produced results which the 90-HP E-TEC cannot match tend to resolve to a single underlying assumption: the 90-HP FOURSTROKE is assumed to produce more power.

It is impossible to raise an argument against a proposal that a boat with a more powerful engine will go faster than one with a less powerful engine.

posted 12-30-2007 04:40 AM ET (US)            

Larry, I would also like to mention that not only does Mercury sell their 90-HP FourStroke as a 100-HP FourStroke engine here in Europe. Yamaha does this as well:

http://www.yamaha-motor.co.uk/products/marine/outboards/four_stroke/ f100_f80.jsp?view=techinfo

http://www.yamaha-motor.com/outboard/products/subcatspecs/2/specs.aspx

At the moment I am running a 90-hp, ELPTO Mercury on my 170 Montauk and my buddy Eddy is running a 90-ETEC on his classic 17-ft Montauk. Both boats are fairly equal in holeshot. My 170 Montauk is a tad faster at WOT. Now if I were to exchange my 90-HP, ELPTO Merc with my buddy's 90-E-TEC on my much heavier 170 Montauk compared to his classic 17-ft Montauk, I doubt if I could ever keep up with him. The E-TEC is running a 15P prop and I have a 21P. I think I would need some serious prop advice to get anywhere near the top speed that my 90-hp Mercury 2-stroke could achieve on that classic. My point is that the weight of the boat is important to take into account when choosing the right engine. I can't see the 90-ETEC with the small gearbox ratio running a 21P prop. My personal opinion is that anyone who would put this 90-ETEC on his 170 Montauk would be disappointed in it's performance. From what I have felt during tests with the latest version of the 170 Montauk carrying the new 100-hp (Euro) Mercury FourStroke is that this combination is awesome. The engine is a beast, really. Once you get used to the physical size of the engine you can start to appreciate the power, silence and efficiency of the engine. No comparison to the previous carbureted,4-stroke.

On the other hand: All I can say is that the 90-ETEC has it's advantages as well. In all honesty it is a fine engine for the classic 17-ft Whaler hulls. Weight vs power is ideal for these hulls. It's small size fits the classic lines beautifully. It is relatively quiet and super fuel efficient.

I am also curious the the new 90-hp Honda engines as I think these would also hold great potential for re-powering classic 17-ft Whalers.

I have also re-powered a 17-ft Guardian with a 70-hp Suzuki. Great engine, reliable, silent, sips fuel, but.....they are not part of this discussion and I don't want to get into a clinch with Nick...he has a Belgian browning you see :-).

posted 12-30-2007 10:25 AM ET (US)            

As for speculation that the 90-HP FOURSTROKE is more powerful, I find that there is a good basis for that. It very well may be that when you bolt on a 90-HP FOURSTROKE (and here I mean the Mercury 90 FOURSTROKE, not just any generic four-stroke engine) you may be getting more horsepower than you do from a 90-HP E-TEC. Now I hope none of my readers are saying, "Gosh, did he just say that?" Yes, I did just say that. It is not particularly revolutionary. Let's compare the engines.

While both are rated at 90-HP, they are quite different engines. One is a three-cylinder, the other is four. One has 1.295-liter displacement, the other has 1.732-liter. One weighs 320-lbs, the other weighs 399-lbs.

If we look at other models which share the same dimension, we find that Mercury uses this same basic block to produce up to 115-HP, and when supercharged up to 200-HP, while Evinrude only makes a 75-HP variant with these dimension. In one engine family we are at the top of the ratings, in the other family we are at the bottom of the ratings. (Well, I guess Mercury makes a 75-HP version of this engine, but that is really an under-rated engine if there ever was one.)

When you add up all these factors, it is not much of a leap to conclude there is room for extra horsepower in the Mercury motor, while the Evinrude is at the top of its rating.

If you want to compare Mercury and Evinrude on the basis of the physical dimension, there really is a very good match for the 90-HP FOURSTROKE in the Evinrude line-up: it's the 115-HP E-TEC. It matches up very well, physically. Let's see:

E-TEC v FOURSTROKE
Displacement = 1.726 versus 1.732 liters
Cylinders = 4 versus 4
Weight = 369 versus 399-lbs

posted 12-31-2007 12:56 AM ET (US)            

If Greg Lemond and I were racing 20 speed bicycles and Greg could only use 1st gear and I could use the 20th gear, the fat out of shape guy (me) would have a higher top speed. And I bet I produce a lot less horse power.

posted 12-31-2007 04:17 AM ET (US)            

quote:

---

If a 90-HP rated FOURSTROKE pushes a 170 MONTAUK faster than a 90-HP rated E-TEC, it is because it has more horsepower than the other, and not because it has the right gear ratio.

---

This could be true Jim but in order to get the 90-hp you have to be able to get the RPM's specified for the 90-hp. I was comparing the heavier 170 Montauk to the classic Montauk and as I said, I would need some serious prop advise for the 90-ETEC to get those rev's efficiently up to spec values on the 170 Montauk. In this case gear ratio could make a difference? No?
IMO if you are comparing these engines to each other you also have to somehow look at the application as well. Meaning type of boat, weight expected speed and so on. But again it's just my opinion.

Erik

posted 12-31-2007 09:56 AM ET (US)            

However, as Rob points out, to make the analogy really appropriate you have to be peddling uphill, and perhaps even uphill in mud.

Erik--I also agree with your point. In selecting a gear ratio for each outboard motor, the manufacturer is fitting the power of the motor to a particular range of loads expected. You can see this quite clearly in the Mercury BIGFOOT series available in some of their motors, like their 60-HP for example. If you are going to put the 60-HP on a pontoon boat they recommend a gear case with a larger gear reduction, but it you put it on a small skiff, you use a gear case with less gear reduction.

Of course, no sooner have I written that than I think of the Boston Whaler 150 SPORT. Some might call it a small skiff and there the designers have chosen the BIGFOOT option for the engine. I think that some proponents would like to make the inference that the choice of the BIGFOOT motor was made to improve performance compared to the same motor without the big gear case. This is a reasonable explanation, however, we don't have any performance data for the other option, so it only speculation.

http://whaler.com/rec/pdfs/performance/4.pdf

Trucks are another application in which multiple gear ratio options are sometimes available. My own truck, for example, can be configured with a rear axle ratios of 3.53, 3.73, or 4.11 to one. The greater the gear reduction, the higher towing capacity for the truck.

To get back to our famous comparison of the Mercury 90-HP FOURSTROKE with the Evinrude 90-HP E-TEC, I have to point out something very interesting in the ratings for the Mercury motor. The RPM range for the 90 is specified as 5,000 to 6,000-RPM. The RPM range for the 115 model is specified at 5,800 to 6,400-RPM. Let us investigate that for a moment using the relationship between horsepower, torque, and rotational speed.

From the 90-HP specifications we deduced the torque to be 86-FT-LBS. If we maintain that same torque but increase the rotational speed to 6,100-RPM (the mid-point of the higher range), we would have a more powerful engine:

HP = (FT-LBS * RPM) / 5252
HP = (86 * 6100) /5252
HP = 100

To get to the 115-HP rating we will need some extra torque; we can't just ramp up the rotational speed to reach that horsepower level. However, it looks like there might be some room in the 90-HP engine for a bit of bonus horsepower, if it can maintain its torque and spin up to these higher speeds.

The topic of power band has also been introduced in the discussion. In general one can say that an engine which can produce torque over a wide range of engine speeds is preferable to an engine which produces its torque in a narrow band. This is especially true in an outboard motor where there is no transmission to provide a succession of different gear ratios to fit the engine's power to the load. I don't make any claim to understand this, but it is my experience that one way to produce torque over a wide range of engine speed is to have a lot of displacement.

posted 12-31-2007 11:41 AM ET (US)            

A 300hp 454CID Chevy will smoke a 300hp 350CID small block. The more CID, the more torque and torque is what an engine will do, HP is how fast it will do it. Put a 400hp 4cyl twin turbo charged Honda race engine in a Ford Dually F350 and a 200hp Diesel would be faster. As you also mentioned outboards are getting higher redlines. People have a "thing" about 4000rpm being the cruise or max cruise for an outboard. That was fine when engines redlined at 5000-5500 but now that we are seeing 6500rpm, should'nt maybe 5000 be a good cruise? I notice that Boating magazine usually gives cruise quotes at 4500rpm now.

I think my 70 Suzuki performed so well due to it's 4cyl and 1.3L engine along with a pretty aggressive gear ratio allowng it to spin a larger 13x18" prop.

posted 12-31-2007 01:03 PM ET (US)            

Theoretically, because of the “twice the number of power strokes” difference, a 2 stroke could produce the same amount of power with half the displacement. The reality is that this is not the case due to the inherent inefficiencies in the 2 stroke design.

Looking at the displacement differences between the E-Tec and the Mercury one can clearly see the E-Tec has 75% of the displacement the Mercury has. While some of this is to make up for the inefficiency of the 2 stroke design, part of this difference explains the higher torque on the E-Tec.

The design as well as the mechanical and electronic controls (the brain) of any given motor will affect the torque curves. As a general rule of thumb, 2 strokes have a broader flatter curve then 4 strokes, with 4 strokes typically having higher torques at higher rpms. This doesn’t mean that the E-Tec simply makes more power then the Mercury (or any other 4 stroke), it is a general statement about one of the typical differences between the engine designs.

While it sounds as though I am swayed towards 2 strokes, they do have their disadvantages. These include lower efficiencies (poorer mileage), faster wear, more noise and more environmental impact. While the modern 2 strokes have improved with technology, these disadvantages are still seen in today’s motors.

This is the type of topic that seems to create so much controversy; I think the important thing to consider is that there are good choices for motors out there with advantages and disadvantages to each. You need to do your homework and pick the motor that is right for you. The reality is that the availability of good service is probably the most important aspect of the decision on which is best for you and that is completely independent of the number of strokes.

posted 12-31-2007 01:38 PM ET (US)            

quote:

---

I don't make any claim to understand this, but it is my experience that one way to produce torque over a wide range of engine speed is to have a lot of displacement.

---

posted 12-31-2007 02:51 PM ET (US)            

examples of 2 stroke vrs 4 stroke power bands are forthcoming. No time today.

posted 12-31-2007 04:48 PM ET (US)            

I also understand the OEM engine has a certain amount of tolorance within suggested operating range to add or subtract dia/pitch depending on needs...after the fact.
This means you have bought your boat and engine as package, took it out, found out the prop is inefficent and start experimenting with raising, lowering, tilt, moving weight around and...experimenting with different props.

In my case, I am repowering a 18, seeking POWER over SPEED. I want to get from point A to point B (on plane) faster. I want to carry more weight than average, tow longer & harder. I hope more backing power of a pitched wheel will result in better maneauvering in tight spots at slower speeds. More bight should reduce cavitation...all without exceeding OEM tolorances. I expect up to a 15% reduction in top & speed/gal per mile in return for a 15% increase in power.

I have a elementary understanding of the 2 stroke vrs 4 stroke operation. I was thinking 4 strokes per revolution would be MORE powerful than 2. Please help me out here. I am hung up on many years of running 2 and 4 stroke sand quads and one thing I do know, all 2 stroke quads I have riden or been around have a high rpm power bands.

There is a place on the SW Oregon Coast called BANSHEE HILL. In spots, you can stand upright on the hill and reach out 90 degrees and almost touch the incline for 500 ft. There is a little room to run down a side hill to gather some momentum (gears and RPM) before you start up...just like a Semi may try to gain speed prior to going up a steep hill. Almost ALL 2 strokes take a run at this hill.

5 years ago, maybe longer...along comes lightweight 4 stroke performance quads. To make a long story short, the 4 strokes dont need to take a run at the hill to make it up. My kid can actually come down, stop before the bottom, turn around and go back up. Eyes roll. 450 Honda TRX 4 stroke.
My point is, the 4 strokes have proven to me that they have more power at lower RPMs than the 2 strokes.
But, once you get into the higher RPMs, the 2 strokes run just as fast or faster. Ford vrs Chev.

The reason the 2 strokes cant "hole shot" at the bottom of a hill, they drop RPMs going from 1st to 2nd or 2nd to 3rd, the shift down takes them out of the narrow power band when they need it most. The modified Banshees and best riders can usually handle it but 90% of average riders just dig in and when they hit 2nd, the engine lugs and they burn up the clutch. This is not relative to cu in or HP or even gear ratio's. All Im sayin, each quad has similar weight and tire setups.

I dont have any problem with the peak HP (wot) SOG numbers.
What I want to know, which engine/gear ratio is better suited to handle a POWER prop. I have run Tugboats that make 12-14 mph running light, 10 mph pushing 8k tons net spread out in 3 barges. Higher gears on the same wheels would make the Tug run faster running lite but tow slower and possibly ruin the engine or reduction gear under a load.

I understand and agree a similar HP engine would have very little effect on the average recreational boater since his primary concern may be cruising speed or Gal per mile. But, if a boater has a specific reason or purpose to go faster or needs more power on the same hull/HP rating, I cant imagine how power band & gear ratio's would not be important factors to consider.

mk

posted 12-31-2007 05:12 PM ET (US)            

I don't discredit the effort, but in the end it is circular. Nothing is proven except the assumptions.

A greater reduction gear with a little more pitch gives equal performance assuming the same slip percentage. Not surprising.

The issue regarding the prop efficiency, which is about the only point to the reduction gear debate, is not considered. Consequently, you got what you assumed: equal performance from equal power.

One paragraph in your comments needs to be examined:

"In actual boat performance, I have observed that often the very last few hundred RPM of engine speed create the most improvement in boat speed in terms of RPM for MPH. This result is generally explained by other phenomenon. Influences such as a change in hull factor or a reduction in drag from the gear case often contribute to those effects. That is to say, a sudden and otherwise secret boost in engine horsepower should not be inferred."

Well, this is not quite correct in tone, although I generally agree with the conclusion. There is additional horsepower at the top of the RPM band, but it does not magically move the boat. The only thing the boat knows is prop RPM. It takes a certain amount of power to turn the prop in a certain setting. At a certain RPM it takes a certain amount of torque. If you have more torque, you get to increase RPM. If the power band of the engine permits it, and the rev limiter or the srength of materials permits it, you increase RPM. The engine and prop know nothing more, so indeed, there is no point in considering a "secret boost" in hp. If it existed it would be felt through increased RPM, or not at all.

If that makes sense I will go on.

posted 12-31-2007 05:22 PM ET (US)            

You cannot get more power than is there. What you mean is you want better low speed thrust. This can be achieved by reduction gearing (higher numerical) and/or propeller pitch (less) or if possible propeller diameter (more).

Since power is speed times thrust, you can't get more thrust at higher speed at the same power. One horsepower is 550 ft-lbs/sec, which can be 550 lbs delivered at 1 ft/sec, or 1 lb delivered at 550 ft/sec, or anthing in between.

If you need 1000 lbs of thrust, and you have 100 hp delivered into the water, you can deliver it at 55 ft/sec (or less). If you gear the engine or prop for a maximum power output at 55 ft/sec, it will (without a multi gear transmission) run way out of its RPM possibility at, say, 75 ft/sec. If you want 75 ft/sec to be possible (albeit at less thrust), then you have to gear accordingly. At 55 ft/sec, the 75 ft/sec rig will not produce its rated horsepower, nor 1000 lbs of thrust. How much less depends on the torque curve of the engine.

posted 12-31-2007 05:45 PM ET (US)            

This reference or observation is contrary to conventional tested wisdom. Before one can concretely conclude that the 4-stroke has more power at lower RPM, you need to know what the displacement of the 4-stroke is and also any gear reduction that takes place between the powerhead and the final driven element, i.e., propeller or wheels.

The only time 4-strokes have equal or more power at lower RPMs than a 2-stroke is when they have much more displacement or they are using forced induction or have a severe gear reduction (which will cause a loss of performance at the high end). Again, I will refer the group to Paul Dawson's excellent comparative article which in fact compares a 90 HP 2-stroke with a 90 HP 4-stroke, each having the same amount of displacement. See members.iinet.net.au/~pauldawson/gen/Iame24-4strokes.pdf .

As I had stated in another thread about 10 months ago with respect to Dawson's article:

quote:

---

See the power curve graph designated as Figure 1 of Dawson's article and take note that the two-stroke power curve is above the four-stroke curve at all points on the graph. Draw a line up from the 3000 RPM point on the X-axis. Note that the four-stroke produces a maximum of 50 HP at 3000 RPM and the two-stroke produces a maximum of 75 HP. Now draw a line across at the 60 HP level and note that the two-stroke can produce that HP at 2500 RPM and the four-stroke requires about 3600 RPM to get the same output.

What does all this mean in practical terms? A couple of things which I think Mr. Dawson does an excellent job. First, his power curve charts illustrate the point that "horses are not always horses" when it comes to comparing different types of engines. To that point, he explains that "the maximum power ratings shown on the motor covers are definitely not the full story when it comes to boat engines as these charts show. On a similar hull the two 90 HP motors would have close top speeds, but the acceleration and [more importantly] the load carrying capacity would vary markedly." In other words, the 90 four-stroke in this example would be much more sensitive to weight loading on the boat.

He goes onto further point out that "the two 70 HP motors, however, would be very close in both top speed and
acceleration". This is because the 70 HP four-stroke in the example has something close to 25 percent more displacement than the 70 HP two-stroke in contrast to the 90 HP examples where the displacement was nearly the same. Of course, the greater displacement to get a traditional 70 HP two-stroke power curve also means increased weight on the transom.

---

"What I want to know, which engine/gear ratio is better suited to handle a POWER prop."

posted 01-01-2008 03:46 AM ET (US)            

Im sure glad its 2008, I never did like going into a straight line after so many O's...now its just a continuous O stroke

happy new yerz.

posted 01-01-2008 11:36 AM ET (US)            

In the analysis the values used for horsepower and rotational speed are the values the manufacturer provides as the rated power. If you start with the premise that the engines are equal in power, you see that they can both move the boat at the same speeds, even if they have different gear ratios.

The analysis does not try to deal with or refute the notion that certain propellers with certain PITCH/DIAMETER ratios may produce slightly more efficient conversion of the power applied to them into thrust which moves the boat. Analysis of propeller performance is far beyond my scope of knowledge. For that I rely on the published works of naval architects, and previously I cited the work of Gerr, who has published his opinion on this topic. Gerr says that propeller efficiency does vary somewhat with PITCH/DIAMETER ratio, and that a ratio of around 1.4 is generally the best.

posted 01-01-2008 11:54 AM ET (US)            

We have a few members in the Michigan area who have repowered a classic 17' Montauk with 90 HP E-TEC motors.

Let's set a date in July and have others, who have repowered their Montauk's with Yamaha, Mercury, Honda and Suzuki motors to come on over to Lake St. Clair for an early morning test run. JimH will be the tester, and we can take an "offering" to get some test propellers.

We can make it a picnic day - perhaps a nice rendezvous. I'll cook on the barbecue, and we can all hang out at one of Detroit's great Metroparks to observe the testing.

We'll get a big whiteboard and record results throughout the day.

At the end of the day, we'll have some more beer, burgers, and perhaps, fresh caught fish from other "rendezvousers" and put this dog to rest in good spirits and good company.

What say ye?

Wait a minute....has anyone repowered a classic Montauk with the 399 lb Mercury FOURSTROKE?

posted 01-02-2008 08:27 AM ET (US)            

I have to disagree that the predicted boat speeds should be identical. They should not. In the analysis the choice of propeller pitch was made in one-inch increments. A one-inch change in propeller pitch is about the smallest difference in pitch which you can anticipate finding among available propellers. The differences in propeller shaft speed were not completely proportional to the differences in propeller pitch. Because of that, the predicted speeds are slightly different for each case.

The pitch selection was based on some real-world data. The FOURSTROKE has been tested with a 20-inch pitch propeller. So I just used that as the baseline. If another engine has more torque, I figure it can turn a higher pitch, and, accordingly, if another engine has less torque I figure it cannot turn as much pitch and use a lower figure.

As for having too much precision in the calculations, you can apply the rounding to the final result. If you apply the rounding to each calculation along the way, the rounding errors might tend to accumulate in one direction and affect the results.

Speaking of rounding errors, this is the basis of explanation for speculations that these motors, while all rated as 90-HP motors, might have real differences in their power output. The horsepower rating system does allow for some variation between a motor's actual power output and its rated power. This is explained in another reference article I wrote. See

posted 01-03-2008 04:27 PM ET (US)            

While I really appreciate the opportunity to learn every technical aspect of gear ratio's offered by Members, really, I just want to confirm whether or not low gear ratio engines would be better than a high ratio engine with similar HP for pulling purposes ie, water skiing, towing. Bubba (yep, thats his name) confirms that low gears are better suited for this purpose.

And wouldnt you know it, he tossed two more engines* into the fire.

1. Twin Yam carbed 70 2 strokes w/2.33 gears lead the pack, but, will be thirsty compared to:
2. Twin Big Foot 4 stroke 60s w/2.33 gears.
*3. Etec Commercial 65s with 2.67 gears. This engine is set up with tiller and rope start. Does not have power tilt, will need kits. sigh.
*4. Etec Commercial 60s with 2.67 gears, no kits needed, incl power tilt. 1 yr warrantees on Commercial Etecs.

SO, the question is figuring out the difference in performance between the Yamaha 70s extra 20 hp using substantially more fuel compared to the Etec 60s .33 lower gears (torque) and better mileage/emissions/resale factors?

AND...Bubba ballpark quotes a non commercial 150 Etec with a Tihatsu bare bones kicker is $300 less than Etec 60s twin package. Both setups run in $15k range.
You are not going to get me to badmouth a single setup on a sport boat, I just prefer twins over two different engines. Both have advantages.

Portland Boat show kicks off Today.

mk

posted 01-03-2008 05:21 PM ET (US)            

one boat, 2 sets of oars with different lengths, same sized blades; I understand dia vrs pitch but I am still not clear on how the HP and gear ratios relate when one has a definite target...otherwise, "it depends" works.

If I wanted to go faster in water with very little resistance, I would use the long handle oars (increase prop dia?).
If I wanted to stem the current or pull something, I would use the shorter handled oars (same blade) to move the oars in/out of the water faster with the same effort (increase pitch?).

But, pulling uses the same effort (HP), my body is making more movement (RPMs) to accomplish this. Can I conclude this movement is far more efficient (easier on my body) than trying to accomplish the same thing using the long oars?

run outa time.

posted 01-06-2008 12:37 AM ET (US)            

Strictly speaking, gearing does not affect "efficiency." However, the human body is very complex and efficiency of muscle movement depends a great deal on the relationship between force and speed. Bicycle racers are very dependent on gearing to keep their legs moving at just the right speed.

Gearing affects efficiency in outboards by allowing propellers of different size, some of which are more efficient than others.

The issue of propeller diameter is slightly different. Large diameter props accelerate a larger amount of water sternward at a lower change in speed. This is more efficient than a smaller water column accelerated to a higher speed. However, diameter is limited by gearcase size, and large diameter blades have more parasitic drag. Very large diameter props are used in towboats and heavy ships.

posted 01-06-2008 01:43 PM ET (US)            

"Can I conclude this (short oar) movement is far more efficient (easier on my body) than trying to accomplish the same thing using the long oars?"

Just want to make sure we are talking apples about "efficiency".

Im really not too concerned about prop efficiency or power at the prop. The topic is the effect of gear ratio's on outboard engines...not on effect of props tho it seems senseless not to consider that. Im not debating you. Im learning and trying to draw a conclusion based on the info here and my own experiances with engines/gears.

Lets examine (review) effects of gear ratio's PRIOR to adapting a prop to the 90 hp examples;
Both have same HP and OEM safe operating RPMs within around 15% of the total range of RPMs.
And lets conclude that the 2 stroke will have a tiny bit more torque than the 4 but the 4 will use substantially less fuel...thus the only major difference at this point is the gear ratio's.
Prior to adapting a prop, we can also put specific numbers on hull weight, hull efficiency and PURPOSE. Tom mentions long ago..."it depends". I didnt understand why. Thanks to you guys, I am close to drawing a conclusion.

In general, a boat will have 3 purposes.
1. Achieving top speed within OEM transom/engine specs.
2. General boating. (Baseline for OEM outboard props)
3. Achieving most pulling power within OEM specs.

Whether bicycle, oar length, quads, truck towing, in every example, the lower gear ratios are more "efficient" to keep the engine within safe operating RPMs under a exceptional load (purpose) than the taller gears.

18 ft Outrage Guardian repower with twins?
Yamaha carbed 70's w/2.33 vrs Etec 60's w/2.67?
Ok, I will post it as a topic. thanks all.

posted 01-06-2008 03:06 PM ET (US)         

http://www.mercurymarine.com/look_deeper/head_to_head.php?ID=52& Filter=11 .

As mentioned elsewhere currently, fuel economy is relatively dismal. Since Mercury avoids acceleration data, it would appear the Evinrude might be faster, but not good for top end and mileage.