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#41
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On Mon, 30 Aug 2004 22:48:22 GMT, Brian Whatcott
wrote: On Mon, 30 Aug 2004 18:00:32 -0400, Rodney Myrvaagnes wrote: On Mon, 30 Aug 2004 07:33:32 -0400, DSK wrote: More power = more speed. This has an asymptotical limit, though. // I am puzzled. What quantity approaches an asymptote and against what independent variable? Rodney Myrvaagnes NYC Comments from the lunatic fringe aside: if one plots power versus water speed for any water borne hull there is an upper limit to speed no matter HOW much power is applied to the hull. (motive power is ultimately limited by flotation. Speed is ultimately limited by propeller immersion or hull stability) Count me as lunatic fringe. I see planing boats every day. What you describe is not an asymptotic relation. Rodney Myrvaagnes J36 Gjo/a Let us restore integrity and honor to the White House |
#42
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Rodney Myrvaagnes wrote:
Count me as lunatic fringe. I see planing boats every day. Planing boats have the same limit, in other words as they go faster, each incremental increase in speed takes an increasing increment in power. Eventually the power/speed curve gets just as steep as displacement hulls... What you describe is not an asymptotic relation. ? Looks like it to me. It's just much farther to the right on the graph Fresh Breezes- Doug King |
#43
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On Tue, 31 Aug 2004 12:42:04 -0400, DSK wrote:
Rodney Myrvaagnes wrote: Count me as lunatic fringe. I see planing boats every day. Planing boats have the same limit, in other words as they go faster, each incremental increase in speed takes an increasing increment in power. Eventually the power/speed curve gets just as steep as displacement hulls... What you describe is not an asymptotic relation. ? Looks like it to me. It's just much farther to the right on the graph In neither case does it get vertical, as an asymptote would. In the case of planing boats, the slope of the curve doesn't even increase everywhere, buty goes over a hump at the onset of planing. But ordinary medium-to-light-displacement sailboats zip right past hull speed when the wind rises. Rodney Myrvaagnes J36 Gjo/a Let us restore integrity and honor to the White House |
#44
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Looks like it to me. It's just much farther to the right on the graph
Rodney Myrvaagnes wrote: In neither case does it get vertical, as an asymptote would. 1- an asymptote doesn't have to be vertical (or horizontal) on the graph 2- if the power/speed curve does not go vertical (or approach it very very very closely) then you're saying that the boat can reach infinite speed. This is impossible, nyet? In the case of planing boats, the slope of the curve doesn't even increase everywhere, buty goes over a hump at the onset of planing. Depends on the boat. Some don't have much of a hump at all. "Hump" is kind of a misnomer IMHO... what happens is that the boat's power/speed curve trends increasingly upward as marginal power increases faster than speed, then flattens out again as it starts planing. It's not a hump, more of a plateau or shelf. But ordinary medium-to-light-displacement sailboats zip right past hull speed when the wind rises. Do they reach infinite speed? You're right about fast boats zipping right past hull speed like it's not there... that's why I always say that "hull speed" is not a hard limit... also you have to consider the speed-length ratio (or Froude number if you prefer) is not the same for all boats. Two different boats (say, a J-35 and an Island Packet 35) should not really have the same "hull speed" even if their LWL is exactly the same. The power/speed curve of all boats... power, sail, diplacement, planing, mulithull, whatever... trends toward vertical as the speed increases. For some boats it's way to the right, at impressively high speeds. But it's there! Fresh Breezes- Doug King |
#45
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You are using "asymptote" in a metaphoric, rather than mathematical
sense. On Tue, 31 Aug 2004 13:31:46 -0400, DSK wrote: Looks like it to me. It's just much farther to the right on the graph Rodney Myrvaagnes wrote: In neither case does it get vertical, as an asymptote would. 1- an asymptote doesn't have to be vertical (or horizontal) on the graph 2- if the power/speed curve does not go vertical (or approach it very very very closely) then you're saying that the boat can reach infinite speed. This is impossible, nyet? In the case of planing boats, the slope of the curve doesn't even increase everywhere, buty goes over a hump at the onset of planing. Depends on the boat. Some don't have much of a hump at all. "Hump" is kind of a misnomer IMHO... what happens is that the boat's power/speed curve trends increasingly upward as marginal power increases faster than speed, then flattens out again as it starts planing. It's not a hump, more of a plateau or shelf. But ordinary medium-to-light-displacement sailboats zip right past hull speed when the wind rises. Do they reach infinite speed? You're right about fast boats zipping right past hull speed like it's not there... that's why I always say that "hull speed" is not a hard limit... also you have to consider the speed-length ratio (or Froude number if you prefer) is not the same for all boats. Two different boats (say, a J-35 and an Island Packet 35) should not really have the same "hull speed" even if their LWL is exactly the same. The power/speed curve of all boats... power, sail, diplacement, planing, mulithull, whatever... trends toward vertical as the speed increases. For some boats it's way to the right, at impressively high speeds. But it's there! Fresh Breezes- Doug King Rodney Myrvaagnes NYC J36 Gjo/a "Religious wisdom is to wisdom as military music is to music." |
#46
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I've really resisted jumping into this one, but....
I guess that if you consider VERY high speeds (approaching the speed of light), it does go asymptotic. However, at anything significantly below that, to suggest that there is some "brick wall" velocity that cannot be surpassed no matter how much thrust is applied is just plain incorrect. Now, the thrust required may not be achievable by any normal engineering and forces on the hull may cause any it to disintegrate if built out of any of the standard materials and methods. And even if you could build it strong enough, stability and control problems will rear their ugly heads when you start going fast enough. Afterall, if you could keep it from pitch poling first, and pushed my Tayana fast enough, you'd get seperation occuring with the water flow where my hull starts curving back to the stern. Once the rudder is high and dry in this seperation area, it'd be a might difficult to control. So in the real world, I guess that there is a limit to how fast my Tayana can go no matter how many JATO units you strap onto it. But it is a pratical matter, not some theoretical "hull speed" value beyond which the resistance somehow becomes infinite. A quick thought experiment to show the point: Picture yourself speeding along on glassy smooth water in a speed boat. You have a small model of a displacement hull sailboat in your hand (only a few inches long). Now, since the hull speed of this model is only a fraction of a knot, if there were a hard and fast limit beyound which it is impossible to go, then you could not reach over the side and drag this toy through the water. It would wrench your arm off. If you had it somehow affixed to the boat, it would stop the speed boat cold. Can we find something else to agrue about now? Rodney Myrvaagnes wrote: You are using "asymptote" in a metaphoric, rather than mathematical sense. On Tue, 31 Aug 2004 13:31:46 -0400, DSK wrote: Looks like it to me. It's just much farther to the right on the graph Rodney Myrvaagnes wrote: In neither case does it get vertical, as an asymptote would. 1- an asymptote doesn't have to be vertical (or horizontal) on the graph 2- if the power/speed curve does not go vertical (or approach it very very very closely) then you're saying that the boat can reach infinite speed. This is impossible, nyet? In the case of planing boats, the slope of the curve doesn't even increase everywhere, buty goes over a hump at the onset of planing. Depends on the boat. Some don't have much of a hump at all. "Hump" is kind of a misnomer IMHO... what happens is that the boat's power/speed curve trends increasingly upward as marginal power increases faster than speed, then flattens out again as it starts planing. It's not a hump, more of a plateau or shelf. But ordinary medium-to-light-displacement sailboats zip right past hull speed when the wind rises. Do they reach infinite speed? You're right about fast boats zipping right past hull speed like it's not there... that's why I always say that "hull speed" is not a hard limit... also you have to consider the speed-length ratio (or Froude number if you prefer) is not the same for all boats. Two different boats (say, a J-35 and an Island Packet 35) should not really have the same "hull speed" even if their LWL is exactly the same. The power/speed curve of all boats... power, sail, diplacement, planing, mulithull, whatever... trends toward vertical as the speed increases. For some boats it's way to the right, at impressively high speeds. But it's there! Fresh Breezes- Doug King Rodney Myrvaagnes NYC J36 Gjo/a "Religious wisdom is to wisdom as military music is to music." -- Dan Best - (707) 431-1662, Healdsburg, CA 95448 B-2/75 1977-1979 Tayana 37 #192, "Tricia Jean" http://rangerbest.home.comcast.net/TriciaJean.JPG |
#47
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On Tue, 31 Aug 2004 00:22:00 -0400, Rodney Myrvaagnes
wrote: I am puzzled. What quantity approaches an asymptote and against what independent variable? Rodney Myrvaagnes NYC Comments from the lunatic fringe aside: if one plots power versus water speed for any water borne hull there is an upper limit to speed no matter HOW much power is applied to the hull. (motive power is ultimately limited by flotation. Speed is ultimately limited by propeller immersion or hull stability) Count me as lunatic fringe. I see planing boats every day. What you describe is not an asymptotic relation. Rodney Myrvaagnes J36 Gjo/a Hmmm...you feel that if a boat planes, then it has no upper speed limit? 100 mph? 500 mph? 1000 mph? And if you wish a planing hull to go faster, you merely fit a more powerful engine: 100 HP? 1000 HP?? 10,000 HP??? 100,000 HP???? If on further consideration, you might allow that there is SOME upper power and speed for a given hull, then perhaps you might even describe the relation as asymptotic? I hold that the situation I describe, though fanciful, is aptly called asymptotic. Telling me that my description is not asymptotic as I describe it, is called an assertion "Ex Cathedra". How are your ecclesiastical affiliations? :-) Brian Whatcott Altus OK |
#48
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On Tue, 31 Aug 2004 17:01:57 -0400, Rodney Myrvaagnes
wrote: You are using "asymptote" in a metaphoric, rather than mathematical sense. Hah, another bald statement of what's right and what's wrong: let's go for some clarifications: [lifted from a math site] Definition of a horizontal asymptote: The line y = y0 is a "horizontal asymptote" of f(x) if and only if f(x) approaches y0 as x approaches + or - inf Definition of a vertical asymptote: The line x = x0 is a "vertical asymptote" of f(x) if and only if f(x) approaches + or - inf as x approaches x0 from the left or from the right. Definition of a slant asymptote: the line y = ax + b is a "slant asymptote" of f(x) if and only if lim (x--+/-) f(x) = ax + b. ************************************************** ******************* Does this clarify your thoughts on what is and is not asymptotic? :-) Brian W |
#49
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Rodney Myrvaagnes wrote:
You are using "asymptote" in a metaphoric, rather than mathematical sense. Not at all. Some realistic numbers, for example: Let's say 1 horsepower (applied) will drive a given boat 4 knots. 2 horsepower will drive it 5.5 knots 3 horsepower will drive it 6.7 4 horsepower will drive it 7.5 6 horsepower will drive it 8.1 8 horsepower will drive it 8.5 12 horsepower will drive it 8.7 20 horsepower will drive it 8.8 50 horsepower will drive it 8.85 Now, is this a boat capable of planing? If yes, then we'll see an increase in the amount increased speed for the next increase in horsepower... then the trend will reappear. Next thing you know, each increased bit of speed, down to hundredths of knot increments, require many hundreds of horsepower to attain. Is this asymptotic enough for you? No? Okay, let's keep going... we have hypothetically infinite horsepower If we were adding millions of horsepower for each hundredth of a knot increase in speed, is *that* asymptotic enough for you? No? How far do we continue this trend? We're inventing new universes to contain the number of added horsepower for each increased femto-knot. For the last umptysquintillion trillion horsepower we've added, we have not seen a 1/8 knot increase.... Let me guess, you don't consider that asymptotic? I would, and so would most mathematicians & most yacht designers. YMMV Fresh Breezes- Doug King |
#50
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dougies, knock it off. you are not even attempting to fool newbees any more.
too much alcohol or age or DGAF. From: DSK Date: 8/31/2004 12:42 PM Eastern Daylight Time Message-id: Rodney Myrvaagnes wrote: Count me as lunatic fringe. I see planing boats every day. Planing boats have the same limit, in other words as they go faster, each incremental increase in speed takes an increasing increment in power. Eventually the power/speed curve gets just as steep as displacement hulls... What you describe is not an asymptotic relation. ? Looks like it to me. It's just much farther to the right on the graph Fresh Breezes- Doug King |
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