Here is a discussion that is going on on another forum: When sailing if you lock your transmission in reverse or set the shaft-lock, do you have more drag or less? Meaning, if you let your shaft 'freewheel' do you have less drag of more? Some trans can do it without damage, like an A4, but is there more drag?
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I'm no physics expert, but...
It seems to me that there will be more pressure on a locked shaft, thereby displacing more water. I spinning shaft "gives" to the water displacement somewhat so I'd think that there would be less drag freewheeling. Again, please read disclaimer in title. Trevor
It seems to me that there will be more pressure on a locked shaft, thereby displacing more water. I spinning shaft "gives" to the water displacement somewhat so I'd think that there would be less drag freewheeling. Again, please read disclaimer in title. Trevor
Fantastic View!
Hey swabs, check out this site of a "waterbridge' in Europe, a waterway for ferrys over an existing river. Great photograph!
Hey swabs, check out this site of a "waterbridge' in Europe, a waterway for ferrys over an existing river. Great photograph!
Channel Bridge over the River Elbe
Trevor, I have no idea other than always locking to protect the transmission. This is a 'professional' debate going on, I'll let you know the outcome, there are some really smart folks here, thought i'd see what they say...;-) I could not just click the link, but think the address is right for this engineering marval: Six years, 500 million Euros, 918 meters long. This is the Channel Bridge over the River Elbe and joins the former East and West Germany, as part of the unification project. It is located in the city of Magdeburg, near Berlin. Photo taken the day of inaguration. Awsome picture...Engineering...Wow.
Trevor, I have no idea other than always locking to protect the transmission. This is a 'professional' debate going on, I'll let you know the outcome, there are some really smart folks here, thought i'd see what they say...;-) I could not just click the link, but think the address is right for this engineering marval: Six years, 500 million Euros, 918 meters long. This is the Channel Bridge over the River Elbe and joins the former East and West Germany, as part of the unification project. It is located in the city of Magdeburg, near Berlin. Photo taken the day of inaguration. Awsome picture...Engineering...Wow.
Spinning Prop
I believe the spinning prop leaves more turbulence, hence more drag. Think about this: a fixed prop of 15" diameter with a maximum blade width of 4" would have a frontal area of say 45-50 square inches; however, the area of a 15" circle representing the spinning prop is pi r2 or 3.14 x (7.5"x7.5")= 176.8 square inches. The turbulence in front of your rudder also causes you to use a little more helm, hence a little more drag from the rudder as well.
I believe the spinning prop leaves more turbulence, hence more drag. Think about this: a fixed prop of 15" diameter with a maximum blade width of 4" would have a frontal area of say 45-50 square inches; however, the area of a 15" circle representing the spinning prop is pi r2 or 3.14 x (7.5"x7.5")= 176.8 square inches. The turbulence in front of your rudder also causes you to use a little more helm, hence a little more drag from the rudder as well.
There is another way to look at this
helicopters can auto rotate to a soft crash landing in the event of an engine failure. You will reduce drag if you lock the prop, by how much you reduce the drag you can determine by sailing in steady winds and checking your speed locked and not locked.
helicopters can auto rotate to a soft crash landing in the event of an engine failure. You will reduce drag if you lock the prop, by how much you reduce the drag you can determine by sailing in steady winds and checking your speed locked and not locked.
Ask Any Pilot and Especially A Helicopter Pilot
A spinning prop creates way more drag. Waaayyy more. I have autorotated to landings soft as any normal landing if that rotor ever stopped spinning there would be very little drag and a not so soft landing. As small as the props are on sail boats it is probably not as huge a deal why not try it. Set the auto pilot or tie down the wheel and shift the thing back and forth for about five minutes each over an hour and watch the speed on the GPS.
A spinning prop creates way more drag. Waaayyy more. I have autorotated to landings soft as any normal landing if that rotor ever stopped spinning there would be very little drag and a not so soft landing. As small as the props are on sail boats it is probably not as huge a deal why not try it. Set the auto pilot or tie down the wheel and shift the thing back and forth for about five minutes each over an hour and watch the speed on the GPS.
Freewheel = more drag
Any time now someone will chime in and say that their boat is faster with the prop spinning.
There is a possibility of a freewheeling prop having lower drag ... if: The speed through the water and the prop pitch are such that the drag from friction turning the shaft is lower than the drag from turbulence around the fixed prop. The speed/drag graph is not linear for a freewheeling prop. At low speeds the prop will turn and the flow over the blades is attached and the prop will spin. As the speed is increased the drag will go up until you get the high drag condition of a helicopter rotor acting like a parachute. In most all cases the locked prop has less drag.
Any time now someone will chime in and say that their boat is faster with the prop spinning.
There is a possibility of a freewheeling prop having lower drag ... if: The speed through the water and the prop pitch are such that the drag from friction turning the shaft is lower than the drag from turbulence around the fixed prop. The speed/drag graph is not linear for a freewheeling prop. At low speeds the prop will turn and the flow over the blades is attached and the prop will spin. As the speed is increased the drag will go up until you get the high drag condition of a helicopter rotor acting like a parachute. In most all cases the locked prop has less drag.This issue comes up...
..every couple of months, but this is the first time I've seen any new ideas. I like Rick's helicopter thinking, as well as Sauer's math. I might just actually test this myself this weekend. I will add that my owner's manual says leave it in neutral, as this "is just good sailing practice", whatever that means.
..every couple of months, but this is the first time I've seen any new ideas. I like Rick's helicopter thinking, as well as Sauer's math. I might just actually test this myself this weekend. I will add that my owner's manual says leave it in neutral, as this "is just good sailing practice", whatever that means.
The Falkirk Wheel
Any of you mates seen this? A friend just sent a slide show, an attachment, but here is an address of this Falkirk Wheel. I thought I'd seen it all with that bridge channel at Magdebung, but this is like a science fiction piece...;-)
Any of you mates seen this? A friend just sent a slide show, an attachment, but here is an address of this Falkirk Wheel. I thought I'd seen it all with that bridge channel at Magdebung, but this is like a science fiction piece...;-)
Mates, when you lock your shaft in reverse
don't forget to slow the boat down before trying to shift back to neutral. It just reduces undue stress in the transmission's shifting mechanism. Down to 1.5 knots or less is good. The helicopter observation makes sense about increased drag in a freewheeling prop. This could be interesting for those racers out there.
don't forget to slow the boat down before trying to shift back to neutral. It just reduces undue stress in the transmission's shifting mechanism. Down to 1.5 knots or less is good. The helicopter observation makes sense about increased drag in a freewheeling prop. This could be interesting for those racers out there.
Hydrodynamic Lift??
That is supposed to be the advantage of a screw as compared to a paddle. A paddlewheel just drag through the water to pull a boat forward. But a screw typed propeller creates lift by the water on the front creating a vaccum that is muchmore efficent. when the propis staionary it is just dragging through the water like a paddle. When it is freewheeling it is generating hydrodynamic lift which produces more drag.
That is supposed to be the advantage of a screw as compared to a paddle. A paddlewheel just drag through the water to pull a boat forward. But a screw typed propeller creates lift by the water on the front creating a vaccum that is muchmore efficent. when the propis staionary it is just dragging through the water like a paddle. When it is freewheeling it is generating hydrodynamic lift which produces more drag.
Less drag when freewheeling
From a study at MIT by Lurie and Taylor and published in Marine Technology (July 1995) entitled "Comparison of Ten Sailboat Propellers": "The conclusion...is that a substantial reduction in drag, and thus in boatspeed, can be realized when a fixed pitch propeller is allowed to freewheel". (They estimate a 3-blade prop will have twice the drag when fixed then when freewheeling).
From a study at MIT by Lurie and Taylor and published in Marine Technology (July 1995) entitled "Comparison of Ten Sailboat Propellers": "The conclusion...is that a substantial reduction in drag, and thus in boatspeed, can be realized when a fixed pitch propeller is allowed to freewheel". (They estimate a 3-blade prop will have twice the drag when fixed then when freewheeling).
With Ron
I am going to have to gree with Ron on this one. Especially the waayy more part. Lift creates drag.
I am going to have to gree with Ron on this one. Especially the waayy more part. Lift creates drag.
Guys from MIT are right (duh)...
With only the freewheeling prop considered, freewheeling has less drag. But let me employ additional considerations: Many boats have transmissions that do not take kindly to freewheeling, so folks lock the prop to save the tranny from undue wear. Also, many boats have the prop a very short distance behind the keel, and a two blade prop oriented vertically behind the keel can essentially "draft" behind it like the bicyclists in the tour de france, creating less drag than freewheeling. Happy (& speedy) sailing!
With only the freewheeling prop considered, freewheeling has less drag. But let me employ additional considerations: Many boats have transmissions that do not take kindly to freewheeling, so folks lock the prop to save the tranny from undue wear. Also, many boats have the prop a very short distance behind the keel, and a two blade prop oriented vertically behind the keel can essentially "draft" behind it like the bicyclists in the tour de france, creating less drag than freewheeling. Happy (& speedy) sailing!
Hurth gear box - reverse only
I recently asked this question about the Hurth transmission on my Perkins. Their tech people instructed me to leave it in reverse or damage can occur to the unit. I don't see why leavin g it in neutral would hurt, but I'm not the guy the designed it.
I recently asked this question about the Hurth transmission on my Perkins. Their tech people instructed me to leave it in reverse or damage can occur to the unit. I don't see why leavin g it in neutral would hurt, but I'm not the guy the designed it.
I guess we guys still refuse to read the
written directions *yks For HURTH transmisions, try this from the C34 website http://www.c34.org/faq-pages/faq-transmission-position-sailing.html Find out what your transmission is. It is NOT your boat or your engine, it is a sepaarte piece bolted onto the back of your engine, not all the same on all boats or engines.
written directions *yks For HURTH transmisions, try this from the C34 website http://www.c34.org/faq-pages/faq-transmission-position-sailing.html Find out what your transmission is. It is NOT your boat or your engine, it is a sepaarte piece bolted onto the back of your engine, not all the same on all boats or engines.
Stu
I am aware of the manual, I had it in hand while I was asking their tech a related question. On behalf of a friend with a 310, what would cause a "siren" type sound from the transmission/shaft area while under sail with the transmision in neutral ? He said the drip rate was good. First I've heard of that.
I am aware of the manual, I had it in hand while I was asking their tech a related question. On behalf of a friend with a 310, what would cause a "siren" type sound from the transmission/shaft area while under sail with the transmision in neutral ? He said the drip rate was good. First I've heard of that.
What Gear
The boat speed attained in Fwd, Neut or Rev is really irrelevant...if you care about the equipment in your boat. Sailing should be with the trans in the gear specified by the manufacturer. I have a Kanzaki mated to a Yanmar 3GM30F. From the manual: Best: Rev Okay: Neut Never: Fwd
The boat speed attained in Fwd, Neut or Rev is really irrelevant...if you care about the equipment in your boat. Sailing should be with the trans in the gear specified by the manufacturer. I have a Kanzaki mated to a Yanmar 3GM30F. From the manual: Best: Rev Okay: Neut Never: Fwd
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