Re: Evinrude e-tec or Yamaha 4 Stroke
Lets see..... understand that two motors given the same PROPSHAFT HP have the same potential. OK? One turns a little faster, the other a little slower...same hp, OK
Come on. We could get the same propshaft HP through any combination of gear reduction and RPM.
<br /><br />50 HP could equal 100 RPM at 2626 ftlbs Torque. Or 50 HP could equal 1,000 RPM at 262 ftlbs Torque. Or 10,000 RPM at 26 ftlbs. With me?<br /><br />The object is to match up gearing the best for what the
engine can handle for its use. And that is the issue here. Why must the E-Tech engine multiply torque through gearing and drop prop RPM to achieve the same HP? <br /><br />Gear reduction is a torque multiplier and a RPM reducer. And HP is a function of Torque and RPM. HP = Torque X RPM/5252.<br /><br />Besides, you're only looking at max HP at WOT. The high 2.67 gear ratio effects the
entire RPM range.<br /><br />Backfire, ask yourself why outboards don't just run a 1:1 raito? Could it be that the engine can't drive the prop and maintain RPM? Why must the E-Tech engine turn almost one additional revolution for each prop rotation, than comparable hp outboards? <br /><br />
Now we need a transmison, in boat lingo-we call it a prop, capable of absorbing, say 50 hp.
Huh?
<br /><br />All the propping in the world won't change the fact tat the engine turns 2.67 times for each revolution of the prop. See, the
real transmission in an outboard is its lower unit gear reduction. Propping merely fine tunes the transmission for various applications in order to get the
engine to perform within its operating range. <br /><br />Regardless, all transmissions are designed around the
engine's torque and rpm capabilities. You can't just put a 25 pitch prop on a 40 hp with a 1:1 ratio. It won't maintain RPM.<br /><br />
After 100 years of about every conceivable contraption and design, it<br />is generally accepted that a larger,slower turning prop, as in diameter and blade area, propels through the water more effeciently than a<br />smaller diameter-less blade area prop.
I don't think so. These are't submarines and tankers. They're outboards running at 5000-6000 RPM. <br /><br />Plus, you're forgetting pitch. The whole point was that the E-Tech, with it's higher gear ratio, must run a higher
pitch prop. Otherwise it can't make up for the speed it loses in the RPM drop. <br /><br />BTW, higher pitch props generally have more slip, which relates to less efficiency. And more blade area and bigger diameter props will always have more drag. More drag also relates to less efficiency. Ever see a race prop? 2 blades and very small. <br /><br />
Now if every manufacturer optimized every motor hp for a given application, each would probably have a different gear ratio/lower unit and extensive selection of propellers for that unit only. Manufacturing expenses, warehouse space-mfgr.and dealer, none of the mechanics or owners would have any hair left,so it resolves to a compromise.
What's your point? All manufacturers "compromise" their model lines for general applications and the average consumer. My point is why the highly uncommon gear ratio of 2.67 to do it? It's hardly a compromise. Couldn't they do the same with a 2.0 or 1.85 ratio? After all, the engine's operating range is a common 5-6K RPM like everyone else's.<br /> <br />
So when you say this ratio "makes no sense", perhaps you can now say that it makes the MOST sense.
Uhh...I don't think so. No other manufacture runs these high ratios. And they've been making outboards a lot longer than Bombardier. <br /><br />
Also there is no need for a "high thrust" option engine to get reasonable performance on heavy boats,or any reverse thrust power.
I have to agree with that! Even most specialized "High Thrust" models don't run ratios this high! The high gear ratio does make for lots of torque...but at a loss of speed.<br /><br />High thrust applications are specialized. And I have no problem recognizing that this ratio would fit that application. However, I do have a problem with it
also fitting more common (faster) applications by
propping alone. <br /><br />Yamaha uses the same engine between their "High Thrust" models and their standard models, but they use completely different gear cases, gear ratios, and props to do it. Look at the F50 vs. their High Thrust 50. Both operate at 5000-6000 rpm, but Yamaha gave the High Thrust model a higher gear ratio and a different prop. Two different applications...two different ratios.<br /><br />It appears to me that the high gear ratio of the E-Tech is at the far end of the scale, rather than a compromise for general applications. This leaves propping to fill the rest of the scale. And IMO, trying to get the engine to perform best through propping will always be less efficient than getting it to perform best through gearing. Again, propping should be for fine tuning.
