Cruisers Forum
 


Reply
 
Thread Tools Search this Thread Rate Thread Display Modes
Old 17-07-2021, 11:45   #16
Registered User

Join Date: Apr 2007
Location: New England/FL
Boat: lagoon 380 s2
Posts: 872
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by waterman46 View Post
The limit on downwind speed has zero to do with force vs. drag. It has everything to do with apparent wind. No, a wind powered boat, car or whatever cannot go faster than true wind when facing dead downwind, even if drag is completely eliminated. Think how ridiculous that would be. The apparent wind would then be coming from the bow or front of the vehicle, thereby slowing it down again to exactly the speed of the wind. Apparent wind is why a balloon, which has zero drag, only travels exactly the speed and direction of the wind, but no faster or slower. Zero apparent wind means no force on the wind turbine, thus no thrust.

If you ever sailed a fast boat with a spinnaker you'd understand it without explanation.

The video about a bet concerning downwind speed shows several examples of real life situations, some showing upwind motion but none to prove moving downwind faster than the true wind, other than temporarily when the true windspeed drops. Several tricky devices are used. The little wheels under the beam are moving because of external force applied from motion of the beam over the floor. The little devices on the treadmill are actually taking power from the motion of the wheels on the treadmill then transferring it to the air propeller, which is operating in still air as a thrust device, just the opposite of a power generating device.

The graph shows a car where they do 27mph in a true 10mph "tailwind". If this was true windspeed, it is clearly impossible, for the car would be experiencing a 15mph headwind, which would force the propeller the wrong way, slowing the car back to true windspeed (zero apparent wind). Why was there no apparent wind direction and speed device installed on the car itself?

The final statement that tells you that all this is pure BS is "with sufficiently low energy loss, any speed is possible". Really? Then why don't airplanes use this method for power - no engines would be needed! Simply put props fore and aft on the plane connected by a straight shaft.



As for all the complicated math, it is full of bad assumptions (like the one that when the propeller is "driving the vehicle forward" at greater than true windspeed, a negative force on the propeller is the same direction as positive force).


I'd guess the whole thing about the bet was just a joke on the unthinking.
Tell me you have a PhD in Physics, specifically in aero or hydro dynamics and I will believe what you say.

This isn't about a sail. I think everyone agrees that Aw = Tw + Bs (vectors). If your boat is going 5mph directly into a 5mph wind, there is 10mph of apparent wind. If you are doing the same DDW, you have 0 mph of apparent wind. For a sailboat, this last scenario doesn't work with sails.

However, this experiment uses a propeller. So if I could mount a 500' propeller (wind turbine) on my car, and in 5mph of breeze it can generate 500hp, are you saying I can only go 5mph?
jbinbi is offline   Reply With Quote
Old 17-07-2021, 12:02   #17
Moderator

Join Date: Jun 2015
Posts: 4,515
Re: Novel Propeller propulsion, going faster downwind than the wind

Don't know what anyone else is saying, but I'm saying that when the apparent wind velocity is zero, then your 500 foot prop - or even a 5,000 foot prop - can only extract zero power from the wind.

Talk to Vestas or any of the other wind turbine manufacturers. They will tell you that when there is NO WIND, i.e. the apparent wind velocity is zero, their turbines generate squat. For a wind turbine the apparent wind is ALWAYS the true wind.

All things purveyed by YouTube should be dismissed as untrustworthy UNLESS independent, disinterested corroboration is to hand.

TP
TrentePieds is offline   Reply With Quote
Old 17-07-2021, 16:25   #18
Registered User

Join Date: Feb 2010
Location: Australia
Posts: 995
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by jbinbi View Post
Yes. This. I am not talking about a sailboat. I am talking about a boat, that has a propulsion system like this, a mast with a propeller (wind turbine), and say water wheels, or something to propel the boat thru the water.



As mentioned above, if your true boat speed is equal to the wind speed from DDW, on a sailboat that is zero apparent wind, so that can't ever work.


Well, the Professor is real as is the panel of independent observers and the original video with the inventors certainly answers most of the questions raised. That rig has a lot going on with the pitch control and the gearing.
If this was a deepfake, a lot of respectable people and institutions have risked losing their credibility forever.
Pete.
skipperpete is online now   Reply With Quote
Old 17-07-2021, 17:41   #19
Registered User
 
Kelkara's Avatar

Join Date: Oct 2016
Location: Vancouver Island
Boat: Hullmaster 27
Posts: 760
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by TrentePieds View Post
Don't know what anyone else is saying, but I'm saying that when the apparent wind velocity is zero, then your 500 foot prop - or even a 5,000 foot prop - can only extract zero power from the wind.
As I understand the physics, you are looking at it backwards ... you are assuming that the big prop in the air is a turbine extracting energy from the speed of the wind rushing past the boat, to be used to drive an underwater propulsion propellor.

In fact the big prop in the air is the propellor driving the boat forwards just like an aeroplane propellor. But what is driving this propellor? It is driven by the underwater prop acting as a water-turbine to extract energy from the speed of the water rushing past the hull (or in the case of the landyacht, it is the turning of the wheels running across the road that is used to drive the big prop).

So although there is zero AWS while the boat is travelling downwind at TWS, the big prop hasn't stopped turning since it is coupled to the underwater prop which is still turning (just as it does on all our boats unless we lock the transmission). And since the big prop is turning, it is generating thrust, which will accelerate the boat still faster ... until the friction and drag forces catch up with this thrust.

Whether it is possible to engineer a boat such that the friction and drag is minimised enough to exceed TWS downwind I don't know, but clearly for the landyacht it was possible.
Kelkara is offline   Reply With Quote
Old 17-07-2021, 18:52   #20
Registered User
 
Mr B's Avatar

Join Date: Aug 2011
Location: Melbourne Australia
Boat: Paper Tiger 14 foot, Gemini 105MC 34 foot Catamaran Hull no 825
Posts: 2,874
Re: Novel Propeller propulsion, going faster downwind than the wind

Plenty of 3 legged sail boats on ice skates in Canada doing incredibley high speeds on the ice,
Mr B is offline   Reply With Quote
Old 17-07-2021, 22:38   #21
Registered User

Join Date: Feb 2015
Location: Somewhere warm
Boat: Morgan 462
Posts: 1,759
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by jbinbi View Post
Tell me you have a PhD in Physics, specifically in aero or hydro dynamics and I will believe what you say.

This isn't about a sail. I think everyone agrees that Aw = Tw + Bs (vectors). If your boat is going 5mph directly into a 5mph wind, there is 10mph of apparent wind. If you are doing the same DDW, you have 0 mph of apparent wind. For a sailboat, this last scenario doesn't work with sails.

However, this experiment uses a propeller. So if I could mount a 500' propeller (wind turbine) on my car, and in 5mph of breeze it can generate 500hp, are you saying I can only go 5mph?
Yes, and really not quite 5mph. You will certainly start up from a standstill very fast with 500hp. But that available power will decrease and go to zero just before you reach 5mph.

If you could actually go 5mph DDW in a 5mph true wind there is zero wind force acting on your huge propeller. Apparent wind = zero. Nada. Zilch. You said the same thing. Oh, the wind turbine blades will still be turning since it is coupled to the wheels. But if you analyze what's happening to the air around the blades, if you do make it up to 5 mph then all the blades will be stalled since there is no air flow in the axis of the propeller. No lift (the rotational force in a prop) can be generated if all blades are in full stall.

Notice I said, IF you could actually go 5mph. You can never quite get there because no matter how good is the blade design, and even if you vary the pitch, they will still stall as you approach zero apparent wind, as they are still rotating at the speed determined by the gearing from the wheels.

None of the videos answered the question of how they can get power from zero apparent wind.
__________________
No shirt, no shoes, no problem!
waterman46 is offline   Reply With Quote
Old 17-07-2021, 22:46   #22
Registered User

Join Date: Feb 2015
Location: Somewhere warm
Boat: Morgan 462
Posts: 1,759
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by Mr B View Post
Plenty of 3 legged sail boats on ice skates in Canada doing incredibley high speeds on the ice,

This is absolutely true as they go on a reach they can double the true wind speed but they can't go faster than the wind if they are heading DDW.
__________________
No shirt, no shoes, no problem!
waterman46 is offline   Reply With Quote
Old 17-07-2021, 23:02   #23
Registered User

Join Date: Feb 2015
Location: Somewhere warm
Boat: Morgan 462
Posts: 1,759
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by Kelkara View Post
As I understand the physics, you are looking at it backwards ... you are assuming that the big prop in the air is a turbine extracting energy from the speed of the wind rushing past the boat, to be used to drive an underwater propulsion propellor.

In fact the big prop in the air is the propellor driving the boat forwards just like an aeroplane propellor. But what is driving this propellor? It is driven by the underwater prop acting as a water-turbine to extract energy from the speed of the water rushing past the hull (or in the case of the landyacht, it is the turning of the wheels running across the road that is used to drive the big prop).

So although there is zero AWS while the boat is travelling downwind at TWS, the big prop hasn't stopped turning since it is coupled to the underwater prop which is still turning (just as it does on all our boats unless we lock the transmission). And since the big prop is turning, it is generating thrust, which will accelerate the boat still faster ... until the friction and drag forces catch up with this thrust.

Whether it is possible to engineer a boat such that the friction and drag is minimised enough to exceed TWS downwind I don't know, but clearly for the landyacht it was possible.

Chicken and egg. In your scenario you will need outside power from somewhere to push the vehicle to start the wheels turning to provide power for prop rotating in a direction that can pull the vehicle forward. As it moves forward it gains speed, moving the propellor faster and then it can move faster and faster and faster until . . .


Think of it another way. Given a constant direction of rotation, the pitch of the prop required to extract power from the wind is opposite from the pitch required to pull the vehicle forward. So as you approach zero apparent wind, the prop just stalls and if you try to go faster with the same pitch prop, the prop will be pushing you backwards, slowing you down.
__________________
No shirt, no shoes, no problem!
waterman46 is offline   Reply With Quote
Old 17-07-2021, 23:31   #24
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 5,034
Images: 7
Re: Novel Propeller propulsion, going faster downwind than the wind

Perpetual motion at last.
__________________
Satiriker ist verboten, la conformité est obligatoire
RaymondR is offline   Reply With Quote
Old 18-07-2021, 00:04   #25
Registered User
 
Dave_S's Avatar

Join Date: Jun 2016
Location: Brisbane Australia
Boat: Schionning Waterline 1480
Posts: 1,684
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by waterman46 View Post
The limit on downwind speed has zero to do with force vs. drag. It has everything to do with apparent wind. No, a wind powered boat, car or whatever cannot go faster than true wind when facing dead downwind, even if drag is completely eliminated. Think how ridiculous that would be. The apparent wind would then be coming from the bow or front of the vehicle, thereby slowing it down again to exactly the speed of the wind. Apparent wind is why a balloon, which has zero drag, only travels exactly the speed and direction of the wind, but no faster or slower. Zero apparent wind means no force on the wind turbine, thus no thrust.

If you ever sailed a fast boat with a spinnaker you'd understand it without explanation.

The video about a bet concerning downwind speed shows several examples of real life situations, some showing upwind motion but none to prove moving downwind faster than the true wind, other than temporarily when the true windspeed drops. Several tricky devices are used. The little wheels under the beam are moving because of external force applied from motion of the beam over the floor. The little devices on the treadmill are actually taking power from the motion of the wheels on the treadmill then transferring it to the air propeller, which is operating in still air as a thrust device, just the opposite of a power generating device.

The graph shows a car where they do 27mph in a true 10mph "tailwind". If this was true windspeed, it is clearly impossible, for the car would be experiencing a 15mph headwind, which would force the propeller the wrong way, slowing the car back to true windspeed (zero apparent wind). Why was there no apparent wind direction and speed device installed on the car itself?

The final statement that tells you that all this is pure BS is "with sufficiently low energy loss, any speed is possible". Really? Then why don't airplanes use this method for power - no engines would be needed! Simply put props fore and aft on the plane connected by a straight shaft.



As for all the complicated math, it is full of bad assumptions (like the one that when the propeller is "driving the vehicle forward" at greater than true windspeed, a negative force on the propeller is the same direction as positive force).


I'd guess the whole thing about the bet was just a joke on the unthinking.
You must have two elements at different speeds to leverage the differential between them. You can do this in an aeroplane if you you can get between the levels in wind shear, they do it in RC gliders and achieve and sustain 800kph+ in 110kph wind speed.

Wind speed is only a barrier if you are using a parachute type mechanism to drive DDW.

In the land vehicles that travel DDW or DUW they leverage the speed differential between the land and the true ground speed of the breeze. If there is no TWS it won't work. DDW the wheels drive the propeller and DUW the propeller drives the wheels. Even when AWS = 0 DDW you have apparent air flow over the propeller because it's rotating at 90° to the TWD and has flow over the blades. Because they are a foil moving through a fluid (air) they create lift, providing that lift is greater than drag the vehicle will continue to accelerate.
__________________
Regards
Dave
Dave_S is offline   Reply With Quote
Old 18-07-2021, 00:09   #26
Registered User
 
Dave_S's Avatar

Join Date: Jun 2016
Location: Brisbane Australia
Boat: Schionning Waterline 1480
Posts: 1,684
Re: Novel Propeller propulsion, going faster downwind than the wind

P.S. In some videos the vehicle does have a telltale on the front which shows the 180° change in apparent wind.
__________________
Regards
Dave
Dave_S is offline   Reply With Quote
Old 18-07-2021, 07:01   #27
Registered User
 
Kelkara's Avatar

Join Date: Oct 2016
Location: Vancouver Island
Boat: Hullmaster 27
Posts: 760
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by waterman46 View Post
Chicken and egg. In your scenario you will need outside power from somewhere to push the vehicle [The Wind - nobody yet on this thread has suggested that the wind won't push it to almost TWS ... the wheels will be turning] to start the wheels turning to provide power for prop rotating in a direction that can pull the vehicle forward. As it moves forward it gains speed, moving the propellor faster and then it can move faster and faster and faster until [until drag from the air resistance of the now apparent headwind matches the thrust produced from the prop - at zero AWS there will be zero air resistance, this will the increase fairly quickly to a terminal velocity ]. . .

There is no perpetual motion ... stop the wind and the vehicle stops, blow harder and it goes faster.

Think of it another way. Given a constant direction of rotation, the pitch of the prop required to extract power from the wind is opposite from the pitch required to pull the vehicle forward [variable pitch props have already been invented]. So as you approach zero apparent wind, the prop just stalls and if you try to go faster with the same pitch prop, the prop will be pushing you backwards, slowing you down.
Since there is zero drag from air resistance at zero AWS, the only force slowing the vehicle down will be friction in the wheels, bearings and propshaft ... with no additional thrust except the wind, this friction is what will prevent it from ever actually reaching TWS, the question is can you design a prop which generates more thrust than the friction in its bearings ... if so then you can nudge the vehicle past TWS until air resistance takes over as the dominant form of drag.

It seems to me as if the design of the prop and the design of the bearings are two independent problems ... for a boat it seems unlikely that a slippery enough hull will ever be invented, but well oiled wheels on the right track can have astonishingly low resistance.
Kelkara is offline   Reply With Quote
Old 18-07-2021, 07:50   #28
Registered User
 
Dave_S's Avatar

Join Date: Jun 2016
Location: Brisbane Australia
Boat: Schionning Waterline 1480
Posts: 1,684
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by waterman46 View Post
Yes, and really not quite 5mph. You will certainly start up from a standstill very fast with 500hp. But that available power will decrease and go to zero just before you reach 5mph.

If you could actually go 5mph DDW in a 5mph true wind there is zero wind force acting on your huge propeller. Apparent wind = zero. Nada. Zilch. You said the same thing. Oh, the wind turbine blades will still be turning since it is coupled to the wheels. But if you analyze what's happening to the air around the blades, if you do make it up to 5 mph then all the blades will be stalled since there is no air flow in the axis of the propeller. No lift (the rotational force in a prop) can be generated if all blades are in full stall.

Notice I said, IF you could actually go 5mph. You can never quite get there because no matter how good is the blade design, and even if you vary the pitch, they will still stall as you approach zero apparent wind, as they are still rotating at the speed determined by the gearing from the wheels.

None of the videos answered the question of how they can get power from zero apparent wind.
Only the vehicle will move through a point of 0 AW Never the propeller, the propeller never sees zero apparent wind and always maintains an angle of attack to the airflow.
__________________
Regards
Dave
Dave_S is offline   Reply With Quote
Old 18-07-2021, 12:15   #29
Registered User

Join Date: Apr 2007
Location: Australia
Boat: Island Packet 40
Posts: 5,034
Images: 7
Re: Novel Propeller propulsion, going faster downwind than the wind

Dunno mate, it appears that interruption to a mass of air is somehow concurrently providing enough energy to somehow displace a sufficient mass of air in the opposite direction so as to provide the interrupter with a forward motion in excess of the velocity of the forward thrusting air mass without any external energy inputs. Sounds like some sort of perpetual motion scheme to me.
__________________
Satiriker ist verboten, la conformité est obligatoire
RaymondR is offline   Reply With Quote
Old 18-07-2021, 18:28   #30
Registered User

Join Date: Feb 2015
Location: Somewhere warm
Boat: Morgan 462
Posts: 1,759
Re: Novel Propeller propulsion, going faster downwind than the wind

Quote:
Originally Posted by Dave_S View Post
You must have two elements at different speeds to leverage the differential between them. You can do this in an aeroplane if you you can get between the levels in wind shear, they do it in RC gliders and achieve and sustain 800kph+ in 110kph wind speed.

Wind speed is only a barrier if you are using a parachute type mechanism to drive DDW.

In the land vehicles that travel DDW or DUW they leverage the speed differential between the land and the true ground speed of the breeze. If there is no TWS it won't work. DDW the wheels drive the propeller and DUW the propeller drives the wheels. Even when AWS = 0 DDW you have apparent air flow over the propeller because it's rotating at 90° to the TWD and has flow over the blades. Because they are a foil moving through a fluid (air) they create lift, providing that lift is greater than drag the vehicle will continue to accelerate.

I'm sure it is tempting to think that once the vehicle reaches a speed equal to true wind DDW, and apparent wind is then zero, that the wheels, being in contact with the ground, can somehow extract power from that motion that can spin the propeller and draw the vehicle forward. As I understand it, this is your argument and there seem to be many who tend to agree with this.


However it is not possible. To generate forward thrust, the prop would need to extract power from the wheels. When you extract power from a moving object, that object has to slow down. This is extremely basic physics and I am ashamed to think that some Professor of Physics graduated from a UC engineering school who doesn't know this fact.

Besides, when switching from speed less than true wind to an imaginary speed greater than true wind, will require a reversal of pitch of the propeller. Did any of the video's mention a reversible pitch prop?
__________________
No shirt, no shoes, no problem!
waterman46 is offline   Reply With Quote
Reply

Tags
propeller, propulsion, rope, wind

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Faster winds and faster currents disputin Weather | Gear, Reports and Resources 16 16-03-2020 17:46
Vestas Sailrocket 2 - Faster and Faster We Go SV Bacchus General Sailing Forum 2 13-09-2018 13:25
New tech shows its possible to go faster than the wind, dead downwind foolishsailor Deck hardware: Rigging, Sails & Hoisting 3 28-09-2012 17:04
Faster than Wind Agility Multihull Sailboats 0 08-05-2009 06:41

Advertise Here


All times are GMT -7. The time now is 03:22.


Google+
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Social Knowledge Networks
Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2021, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.