Re: [Cal_Boats] Re: Gear level when sailing?

I got caught up in the helicopter comparison and re-used it before really thinking it through......... It is true that it was not the same thing as letting the prop on a sailboat free-wheel while not under power. the Helicopter, after experiencing an engine failure becomes a "gyro-Glider" to somewhat safely land, that is just as you say... the free-wheeling rotors become a spinning wing allowing it to "glide" to the ground to make more of a landing than a crash. Thus, it becomes more like a gyro-copter (not the most efficient one, but still.... like a gyro copter the rotor would be a rotating wing, providing lift.) without forward power.... but as long as the rotor spins, it is providing some lift as a wing, not as a propeller. I stand corrected on that. I still stand by the tire comparison though, as what I was referring to is that the tires will still rotate in the same direction while coasting as they would while powering the car. it would be impossible for them to rotate backwards as the car rolls forward, just as it would not be possible for the sailboat propeller to rotate backwards as the boat moves forward under sail. A free-wheeling prop rotating backwards under sail would be like expecting a screw to twist (screw) itself into a board while you exert a straight, pulling force away from the board. Rod Johnson, "SUNBIRD" 1979 O'DAY DS II was: co-owner of "NODROG" 1970 CAL 21 On 18 Apr 2015 19:00:24 -0700 "mo… [at] aol.com [Cal_Boats]" <Ca… [at] yahoogroups.com> writes: ---In Ca… [at] yahoogroups.com, <oshnek@...> wrote : Pretty much everything in this post is mistaken. I'm pretty sure that a free wheeling prop will always rotate in the opposite direction as a powered prop. The analogy of the car tires doesn't apply because tires are not working as a screw; the prop is. And a helicopter in free fall would be slowed even more if the rotor was turning faster--not less. also: when a helicopter is in auto-gyro the rotors (it's not a propeller but a rotating wing) are pitched in such a way that the air moving past the rotors, as the chopper falls, causes the rotor to turn as it normally would. this happens even though the air is moving backwards from the direction it normally flows over the blades. why? well, rotors are angled so that the air pushes against the trailing lower edge of the rotor. in this way, it is acting the same as a propeller; screwing through the air. since the wind flying by the rotors has the turning as they normally would, the leading upper edge of the rotors creates lift, as it normally would. this lift is what slows the chopper as it falls. so, of course it would be slowed more if the rotors were spining faster. in fact, spin them fast enough and it would still be flying. but, really , the helicopter is not a good analogy. a helicopter is a rotory winged aircraft. it is not an aircraft with a big propeller on top of it. a propeller is an air (or water) screw. the rotor of a helicopter is really spinning wings; the spinning is what forces air over the foil to create lift just as a jet or propellerd plane forces air over the foils of the wings by pushing the plane through the air. 4 Fish to Never Eat Click to Learn 4 Fish to NEVER Eat &#40;avoid these like the plague!&#41; http://thirdpartyoffers.juno.com/TGL3141/55333246536132456a67st03duc

With regards to which produces more drag, a spinning or a fixed prop, I say, the best idea would be to simply try it either way, and check the instantaneous speed change with reference to a knotmeter, or at least, a late model GPS set up for it's most sensitive reading. I can see the argument going either way, and I'm not convinced a prop and a helicopter rotor are all that different. After all, a hydrofoil will make a light weight boat fly out of the water with a tiny surface and a slow speed with respect to an much bigger, much faster moving airplane wing. Also, a sail with air moving across it's surface will develop twice the power as a sail working in simple drag going dead down wind, which is the reason high performance boats jibe at alternate angles when going down wind.In the video, I'm not sure how or what they are testing to reach their conclusions. No amount of armchair theorizing can trump empirical testing. After all everyone believed Aristotle's hypothesis that a large rock falls faster than a smaller rock, until Gallileo tried it and proved it wasn't so, and got thrown in jail for being a 'smart ass'. Gerald Sobel-Cal 24 Shpritz. On Saturday, April 18, 2015 9:41 PM, "rj… [at] juno.com [Cal_Boats]" <Ca… [at] yahoogroups.com> wrote: I got caught up in the helicopter comparison and re-used it before really thinking it through......... It is true that it was not the same thing as letting the prop on a sailboat free-wheel while not under power. the Helicopter, after experiencing an engine failure becomes a "gyro-Glider" to somewhat safely land, that is just as you say... the free-wheeling rotors become a spinning wing allowing it to "glide" to the ground to make more of a landing than a crash. Thus, it becomes more like a gyro-copter (not the most efficient one, but still.... like a gyro copter the rotor would be a rotating wing, providing lift.) without forward power.... but as long as the rotor spins, it is providing some lift as a wing, not as a propeller. I stand corrected on that.I still stand by the tire comparison though, as what I was referring to is that the tires will still rotate in the same direction while coasting as they would while powering the car. it would be impossible for them to rotate backwards as the car rolls forward, just as it would not be possible for the sailboat propeller to rotate backwards as the boat moves forward under sail.A free-wheeling prop rotating backwards under sail would be like expecting a screw to twist (screw) itself into a board while you exert a straight, pulling force away from the board. Rod Johnson, "SUNBIRD"1979 O'DAY DS IIwas: co-owner of "NODROG"1970 CAL 21 On 18 Apr 2015 19:00:24 -0700 "mo… [at] aol.com [Cal_Boats]" <Ca… [at] yahoogroups.com> writes: ---In Ca… [at] yahoogroups.com, <oshnek@...> wrote : Pretty much everything in this post is mistaken. I'm pretty sure that a free wheeling prop will always rotate in the opposite direction as a powered prop. The analogy of the car tires doesn't apply because tires are not working as a screw; the prop is. And a helicopter in free fall would be slowed even more if the rotor was turning faster--not less. also: when a helicopter is in auto-gyro the rotors (it's not a propeller but a rotating wing) are pitched in such a way that the air moving past the rotors, as the chopper falls, causes the rotor to turn as it normally would. this happens even though the air is moving backwards from the direction it normally flows over the blades. why? well, rotors are angled so that the air pushes against the trailing lower edge of the rotor. in this way, it is acting the same as a propeller; screwing through the air. since the wind flying by the rotors has the turning as they normally would, the leading upper edge of the rotors creates lift, as it normally would. this lift is what slows the chopper as it falls. so, of course it would be slowed more if the rotors were spining faster. in fact, spin them fast enough and it would still be flying. but, really , the helicopter is not a good analogy. a helicopter is a rotory winged aircraft. it is not an aircraft with a big propeller on top of it. a propeller is an air (or water) screw. the rotor of a helicopter is really spinning wings; the spinning is what forces air over the foil to create lift just as a jet or propellerd plane forces air over the foils of the wings by pushing the plane through the air. 4 Fish to Never Eat Click to Learn 4 Fish to NEVER Eat (avoid these like the plague!) 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Except that when the prop is rotating due to being "dragged" through the water while sailing it is rotating slower than it would if it were propelling the boat under power. The drag is caused by the inefficiency of the prop's rotation, the prop is rotating slower due to friction between the shaft and the cutlass bearing, friction in the transmission, and the slip of the prop (a propeller is not really a totally effective "screw", ie: a prop with a 12" pitch does not actually move 12" per revolution due to this slip). Even under power, a prop is not 100% efficient, due to frictional losses. If a prop were 100% efficient, my old 8' pram pushed by a 2hp outboard would have had a top speed of 9.1 mph (4" pitch, engine rotated at 5000rpm through a 0.48 reduction ratio, equals 9.1 mph), but due to various inefficiencies and drag, top speed was more like 4.5 mph. In order to add thrust, a propeller needs to rotate fast enough to create a low-pressure area ahead of the prop and a high-pressure area astern of the prop. Essentially, a prop rotating due to being dragged through the water (as a boat sails with engine off) created a high-pressure area ahead of the prop that acts against the pitch of the blades to rotate the prop and then will have a slight low-pressure area aft of the prop that results in turbulence. The best way to demonstrate the action of a prop rotating as the boat sails along would be to film a pinwheel being turned by the wind with some kind of "smoke" in the air stream to make the turbulence visible, I'm not sure how to easily show the speed difference between the wind and the rotation of the pinwheel.... and to really understand it we would need to know the pitch of the pinwheel's "blades". Rod Johnson, "SUNBIRD" 1979 O'DAY DS II was: "NODROG" 1970 CAL 21 On Mon, 20 Apr 2015 22:22:21 -0400 "John b je… [at] gmail.com [Cal_Boats]" <Ca… [at] yahoogroups.com> writes: If the prop is rotating in a forward direction when the transmission is left in neutral wouldn't this rotation be adding thrust? Since many laws of physics say that the prop is adding drag wouldn't the only way you would get drag would be by rotating backwards? On Apr 20, 2015 7:56 PM, "David Field fi… [at] yahoo.com [Cal_Boats]" <Ca… [at] yahoogroups.com> wrote: Does anyone know if a Cal 27 Mark III with a 1Yanmar engine would generally have a Hurth transmission? I'm not at the boat... is the name usually printed on the transmission? David On Saturday, April 18, 2015 12:14 PM, "th… [at] hotmail.com [Cal_Boats]" <Ca… [at] yahoogroups.com> wrote: If you have a Hurth brand gearbox (many of the original Cal's did) then you must leave it in reverse per the gearbox manual instructions. My Cal 31 sloop with a Hurth gearbox even has a Hurth printed tag attached to the gearbox with the warning on it. The rear bearing of the gearbox is not lubricated unless the input shaft is spinning-- you'l run the output bearing dry if you spin only the output shaft. About the shaft drag-- the free spinning does seem to be significantly lower drag per this one test: https://www.youtube.com/watch?v=jI-UG9RSlJo Prop Drag Test Movie Prop Drag Test Movie This feature is not available right now. Please try again later. View on www.youtube.com Preview by Yahoo Old School Yearbook Pics View Class Yearbooks Online Free. Search by School & Year. Look Now! http://thirdpartyoffers.juno.com/TGL3141/5536b7eaeaaa137ea60e8st01duc