Boat Design Forums  |  Boat Design Directory  |  Boat Design Gallery  |  Boat Design Book Store  |  Thanks to Our Site Sponsors

Go Back   Boat Design Forums > Design > Boat Design

Reply
 
Thread Tools Search this Thread Display Modes
  #46  
Old 08-30-2010, 11:34 PM
rwatson's Avatar
rwatson rwatson is offline
Senior Member
 
Join Date: Aug 2007
Rep: 1753 Posts: 4,913
Location: Tasmania,Australia
Dinghy comments

Quote:
Originally Posted by dskira View Post
Something is wrong in this demonstration.
No end plate, the rotor can't propels, since the difference of pressure is sliding away on the top.
The rotor is conical, can't have any propulsive effect. Doesn't make sense.
I don't think it is what he want us to see.
A rotor will not make the boat heel. Perhaps the windage on a very high wind can have a heeling effect, that I don't know.

But I can be wrong.
Daniel
Good observations there.

I understand that any rotating cylinder, even with conical shaping will certainly provide lift, but as you very correctly pointed out, without "gates" at bottom and top, and even one near the centre, the efficiency will be greatly reduced. This is similar to a plane wings with "tips" or "winglets" and the "flow directors" on the top of the lifting surface on jets. The "gates" do not provide forward lift, but merely control the surface boundary layer on the rotor that does provide the lift.

The heeling effect is a secondary result, which is greatly reduced by the propensity of a rotor to "claw' its way back to windward.

I would say that without "gates", this model is suffering from much increased resistance to the wind without the corresponding "lift" of an efficient rotor design.
Reply With Quote
  #47  
Old 08-31-2010, 12:29 AM
DennisRB's Avatar
DennisRB DennisRB is online now
Senior Member
 
Join Date: Sep 2004
Rep: 228 Posts: 1,224
Location: Brisbane
Quote:
So, in some sense, as a sailboat is like a glider, a rotor ship is like a powered airplane.
A powered airplane creates its own wind to produce lift and will work the same on a day with no wind (after takeoff). A rotor ship still needs apparent wind from an angle to work. So I'm not sure if you can compare it to a powered plane as the rotor ship is converting energy from the wind into power.

I was going to mention the wingtiplets on air craft wings as a likeness to the gate at the end of the rotor to reduce spanwise flow. The fact is they are proven to work on planes but looking at a large cross section of aircraft in use to day most don't use them so its not like it makes or breaks the design of a wing. Wingsail yachts don't seem to have them usually. Also different shaped wings needed them more than others. Just like different shaped rotors would.
Reply With Quote
  #48  
Old 08-31-2010, 01:19 AM
rwatson's Avatar
rwatson rwatson is offline
Senior Member
 
Join Date: Aug 2007
Rep: 1753 Posts: 4,913
Location: Tasmania,Australia
Quote:
Originally Posted by DennisRB View Post
A powered airplane creates its own wind to produce lift and will work the same on a day with no wind (after takeoff). A rotor ship still needs apparent wind from an angle to work. So I'm not sure if you can compare it to a powered plane as the rotor ship is converting energy from the wind into power.

I was going to mention the wingtiplets on air craft wings as a likeness to the gate at the end of the rotor to reduce spanwise flow. The fact is they are proven to work on planes but looking at a large cross section of aircraft in use to day most don't use them so its not like it makes or breaks the design of a wing. Wingsail yachts don't seem to have them usually. Also different shaped wings needed them more than others. Just like different shaped rotors would.
Well, I did say "in some sense", in an effort to stress that engines to force wind (artificial or natural) across solid surfaces are by no means counter intuitive or abnormal. I note that jet passenger planes take a lot of trouble to plot courses that encounter beneficial air flow (natural wind) to make huge savings in fuel - so they are not totally divorced from natural phenomena as they can seem.

Re the wing tips and gates - there are pros and cons for plane wings. Typical boundary layer velocities, drag implications, manufacturing and design expense etc. are all part of a complex equation.

Flettner himself started with plain spinning tubes, but expert aerodynamicist that he was, he proved that the rotor environment was pecularly suited to "gating" on early models, (see attached experimental vessel - leaning to windward, I note) and the gates produced very real performance benefits.

Basically, the suitability and benefit of the "gates" for a rotor ship is not an artifical construct or style decision, but based on extensive research.
Attached Thumbnails
Everything Old is new again - Flettner Rotor Ship is launched-testship.jpg  
Reply With Quote
  #49  
Old 08-31-2010, 01:25 AM
DennisRB's Avatar
DennisRB DennisRB is online now
Senior Member
 
Join Date: Sep 2004
Rep: 228 Posts: 1,224
Location: Brisbane
My comments were mainly aimed at Daniel who appeared to think they were required for it to work, therefore dismissing the boat I posted as a Flettner rotor. Did Flettner ever try a tapered rotor?
Reply With Quote
  #50  
Old 08-31-2010, 01:36 AM
rwatson's Avatar
rwatson rwatson is offline
Senior Member
 
Join Date: Aug 2007
Rep: 1753 Posts: 4,913
Location: Tasmania,Australia
Quote:
Originally Posted by DennisRB View Post
My comments were mainly aimed at Daniel who appeared to think they were required for it to work, therefore dismissing the boat I posted as a Flettner rotor. Did Flettner ever try a tapered rotor?
Fair enough - I hope my comments re-inforced the principle too.

I have never seen a tapered rotor anywhere but in that particular website - and for yachts seeking improved righting moments , it may have real benefits.

Lots of fun research to do on the whole concept still, I would imagine.
Reply With Quote
  #51  
Old 08-31-2010, 01:55 AM
DennisRB's Avatar
DennisRB DennisRB is online now
Senior Member
 
Join Date: Sep 2004
Rep: 228 Posts: 1,224
Location: Brisbane
Makes me want to buy a cheap RC keel boat from ebay and set a rotor up on it...

I think the taper would also help take care of the probs associated higher wind speed further from the ocean surface? It would appear to be much more difficult and expensive to build with a taper.
Reply With Quote
  #52  
Old 08-31-2010, 03:02 AM
rwatson's Avatar
rwatson rwatson is offline
Senior Member
 
Join Date: Aug 2007
Rep: 1753 Posts: 4,913
Location: Tasmania,Australia
"thom gates" on Flettner Rotors

I came across this article from rotor enthusiast and naval architect Joseph Norwood.

He calculates the co-efficient of drag and lift based on zero to multiple "gates" or "Thom fences " for Flettner Rotors in a discussion on rotor catamaran design.

I am keen on the idea of trying out rotors on "harry proas", or should I say Joseph Norwood Proas, as he was proposing the large windward hull concept very early on.
Attached Files
File Type: doc Flettner cat.doc (1.59 MB, 511 views)

Last edited by rwatson : 08-31-2010 at 03:04 AM. Reason: extra info
Reply With Quote
  #53  
Old 08-31-2010, 06:21 AM
rwatson's Avatar
rwatson rwatson is offline
Senior Member
 
Join Date: Aug 2007
Rep: 1753 Posts: 4,913
Location: Tasmania,Australia
An actual rotor vessel, with multiple "Thom Fences"

http://rsta.royalsocietypublishing.o...1882/3989.full
Attached Thumbnails
Everything Old is new again - Flettner Rotor Ship is launched-cloudia.gif  
Reply With Quote
  #54  
Old 08-31-2010, 06:36 AM
dskira dskira is offline
Previous Member
 
Quote:
Originally Posted by DennisRB View Post
My comments were mainly aimed at Daniel who appeared to think they were required for it to work, therefore dismissing the boat I posted as a Flettner rotor. Did Flettner ever try a tapered rotor?
Don't take it personally, it is not your boat.
I made a technical observation no less no more, you can call that dismiss.
Show more proof than a search on Google, and I will gladly change my mind.


Daniel
Reply With Quote
  #55  
Old 08-31-2010, 06:52 AM
rwatson's Avatar
rwatson rwatson is offline
Senior Member
 
Join Date: Aug 2007
Rep: 1753 Posts: 4,913
Location: Tasmania,Australia
Quote:
Originally Posted by dskira View Post
Don't take it personally, it is not your boat.
I made a technical observation no less no more, you can call that dismiss.
Show more more proof than a search on Google, and I will gladly change my mind.


Daniel
I think the documentation by Joseph Norwood, at post 52 will provide some usefull info on the effect that the "gates" or "fences" have on the rotors.
Reply With Quote
  #56  
Old 08-31-2010, 07:12 AM
dskira dskira is offline
Previous Member
 
Quote:
Originally Posted by rwatson View Post
I think the documentation by Joseph Norwood, at post 52 will provide some usefull info on the effect that the "gates" or "fences" have on the rotors.
Interresting, I agree.
I was talking about this version, which I find difficult to beleive.
I will need some more proof than a video.
But as I said I can be wrong

Daniel

Reply With Quote
  #57  
Old 08-31-2010, 07:20 AM
apex1
Guest
 
Posts: n/a
Quote:
Originally Posted by rwatson View Post
It does indeed have a rotor on this artists impression, but I am positive that the boat that Coustea ( not Calypsos successive owners) visited the USA in had the large chord wing masts, as I vividly remember a documentary on it.
As I said, all I remember was that he planned a Flettner Rotor on Calypso. The picture is not a artists impression, but was the NA´s proposal.
Have never been a great fan of Cousteau, so I did not follow the process further.

Thanks for the deeper insight you provided on the topic in general!

Although I personally don´t think it can outperform the Skysail system (which definetively does NOT have the disadvantages you describe), it is at least a valid solution and may be the better way of alternative propulsion on really large vessels like Ore carriers or Tankers.

Regards
Richard
Reply With Quote
  #58  
Old 08-31-2010, 12:41 PM
Clarkey Clarkey is offline
Junior Member
 
Join Date: Aug 2010
Rep: 10 Posts: 63
Location: UK
Interesting paper here on the Flettner Rotor ship:
http://naca.central.cranfield.ac.uk/...aca-tn-228.pdf

The endplates certainly improved efficiency in these early experiments but are by no means necessary for the rotor to work. Like winglets on 'planes it is probably more efficient to just add span (height) to the rotor if it is not limited by other factors.

I think that the rotor on www.rotorboat.com is an elegant solution - the tapered form should help reduce the loading at the top of the rotor and mitigate to some extent spanwise flow. It works for wings and since a rotor is very much like them the idea probably has merit. The boat performed at Weymouth speed week and was timed over the 500m course. I forget the exact speed but at least it has been verified in a credible setting.

The problem I see with small rotors is that in high winds they must rotate very fast to maintain the necessary ratio between circumferential velocity of the rotor and the speed of the wind. As this ratio dips below about 1.7, the l/d becomes marginal for upwind sailing. mind you, this also happens with conventional rigs as you reef them.
Reply With Quote
  #59  
Old 08-31-2010, 01:21 PM
DougCim DougCim is offline
Junior Member
 
Join Date: Jul 2010
Rep: 42 Posts: 40
Location: IL,USA
Quote:
Originally Posted by rwatson View Post
An actual rotor vessel, with multiple "Thom Fences"

http://rsta.royalsocietypublishing.o...1882/3989.full
I'm not sure what would be the reason for using multiple disks like that, since as others noted, the loss of pressure differential can only occur off the ends of the tube. Perhaps there was a structural reason?

Two other questions about that boat spring to mind:
....the text notes that "with only 600 watts, it could sail faster than the wind"... but they don't say how fast the wind was. Will that boat go 30+ knots in a 30-knot wind? I'd bet not. (especially on a cloudy day)
....I also immediately wonder how fast an identical boat would go in the same conditions that still had the regular sail rigging on it... -or even had a rigid wing sail of comparable area instead.

The problem with all the info I've seen so far is that none of it is a real-world comparison. For that you'd need one boat hull (or multiple otherwise-identical boats) and the ability to switch between using the three different types of "sails"--fabric sails, a rigid wing sail and Flettner rotor. Has this ever been done?

-------

I still maintain that the Flettner rotor is a motor drive, not a sail.
The rotor is entirely dependent upon rotating to function, that much is agreed on--but since nobody seems to be able to figure out how to rotate the rotor using wind power, that leads me to believe that the motor is putting more power into rotating the tube than the tube is producing in lift. It's highly unlikely the rotor is functioning at 100% efficient energy conversion, and even more unlikely it's working at over 100%.
~
Reply With Quote


  #60  
Old 08-31-2010, 01:51 PM
Clarkey Clarkey is offline
Junior Member
 
Join Date: Aug 2010
Rep: 10 Posts: 63
Location: UK
I need to find the source but I remember reading that this yacht:


Raced around a triangular course with a conventionally rigged yacht of the same type. Apparently the conventional rig just won but it was a close competition.

I think most of the available data shows that a rotor is able to extract considerably more power from the wind than is required to turn it. I am not sure that I would characterise this as 'greater than 100% efficiency' because the energy driving the boat comes from the wind, not from the motor. By the same measure a conventional sail would be infinitely efficient - and that is a good thing!

My interest in rotors is due to their ease of handling and maneuverability, not performance (although this seems to be reasonably good). Of course I also like them because they are different but I would not pretend that they are the best thing since sliced bread for every application.
Reply With Quote
Reply



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Spirit Of Balto Launched alaskatrawler Metal Boat Building 9 10-15-2010
02:33 AM 
Ship with 2 screw mkovac67 Boat Design 0 04-06-2007
08:09 AM 
Free ship alpamis34 Boat Design 3 02-02-2007
08:48 AM 
Armand Rousso launched X3D Technologies Corporation. eager Education 1 04-03-2005
07:11 AM 
Better Freedom Ship Dook Boat Design 5 03-13-2005
06:00 PM 

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.

All times are GMT -5. The time now is 10:20 PM.


Powered by: vBulletin Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Web Site Design and Content Copyright ©1999 - 2017 Boat Design Net