New Posts New Posts RSS Feed: Lee-Bow..... Windsurfers...etc (Dons tin hat)
  FAQ FAQ  Forum Search   Register Register  Login Login

Lee-Bow..... Windsurfers...etc (Dons tin hat)
 Post Reply Post Reply Page  <1 2930313233 36>
Author
  Share Topic Share Topic  Topic Search Topic Search  Topic Options Topic Options
rich96 View Drop Down
Really should get out more
Really should get out more


Joined: 20 Jan 05
Online Status: Offline
Posts: 596 		Post Options Post Options   Quote rich96 Quote  Post ReplyReply Direct Link To This Post Topic: Lee-Bow..... Windsurfers...etc (Dons tin hat)
    Posted: 18 Sep 19 at 3:43pm
Can the RYA please tell everyone who wants to sail that firstly - the lee bow effect DOES NOT EXIST ?

You can only then get an RYA Level 1 if you accept this

We would not have to read this mythical nonsense again and again

Why can people not understand very simple physics ?

If it existed it would be coached, talked about by high level sailors, be included in racing books etc etc - its not for a reason

This thread (again)is another fantastic way for the better sailors to leave this forum in droves

STOP!

Back to Top
Guests View Drop Down
Guest Group
Guest Group
Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 2:38pm
Originally posted by H2

Mozzy - either the ferry boat effect is real or it is not. If its real then you get that pressure relative to a foil can produce lift. A foil that is so lifted will benefit a boat that enjoys both the wind shift and the tide lift more than one that received only the wind shift.
 

A ferry glide isn't an 'effect'. It's a technique. 

The ferry glide is a real technique, that's for sure. 

The ferry glide is approaching land from down current and using the throttle to match your speed so you're stationary or at least moving very slowly relative to the pontoon / dock. However, because you're still moving through the water you retain good steerage and thus control. You then use steering to slowly traverse in to the dock.

Its the same reason airplanes take off and land in to the head wind. It allows them to take off and land a slower ground speed for the required airspeed. As a result runways can be shorter and landing smoother.  

Originally posted by H2

I think we might be saying the same thing.
I can't see any consensus yet. 
Back to Top
Oatsandbeans View Drop Down
Far too distracted from work
Far too distracted from work


Joined: 19 Sep 05
Location: United Kingdom
Online Status: Offline
Posts: 382 		Post Options Post Options   Quote Oatsandbeans Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 2:37pm
Taking Mozzy’s analogy to the next stage drop the anchor off your raft and watch the effects of angling the dagger board on what the raft does!!
If only we raced in a tidal stream with the anchor down we would see a lot more of the lee bow effect 😸
Back to Top
H2 View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 26 Jul 17
Online Status: Offline
Posts: 750 		Post Options Post Options   Quote H2 Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 2:14pm
Mozzy - either the ferry boat effect is real or it is not. If its real then you get that pressure relative to a foil can produce lift. A foil that is so lifted will benefit a boat that enjoys both the wind shift and the tide lift more than one that received only the wind shift. I think we might be saying the same thing.
H2 #115 (sold)
H2 145
OK 2082
Back to Top
Guests View Drop Down
Guest Group
Guest Group
Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 2:05pm
Originally posted by H2

Sit on a pontoon with your dagger board between your legs and alter the angle of the foil relative to the water moving and I am pretty sure you will agree that a foil can generate lift that is affected in part by the direction of the water moving over it.

A small shift that allows some boats to put the force of the tide on the leeward side of the board when others have the same tide pushing on the windward side of the board will amplify the benefit of the shift for those that get it.

Sit on a raft with your dagger board between your legs and alter the angle of the foil relative to the water in which you are stationary and I am pretty sure you will agree that it is isn't affected by the direction of the water moving relative to land.

A small shift that allows some boats to sail higher will benefit those that get it.
 




Edited by mozzy - 18 Sep 19 at 2:07pm
Back to Top
Guests View Drop Down
Guest Group
Guest Group
Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 1:55pm
Originally posted by sargesail

I wonder if the roots of the myth, as set out in the seminal early works of dinghy tactics, can be found in tidal shifts in the apparent wind.
...
 I can thus see how sailors might perceive empirical evidence for the Lee bow myth. 
Yes, possibly, but the shifts would just feel like regular shifts. 

... but this does let me tell an anecdote from the 800 nationals. On the last day the wind was generally dropping from just under 10 knots to just under 5. The committee boat set what they thought was true line, but with 2 knots of cross current from left to right, it actually felt quite committee boat biased. Adding to that everyone was getting swept to the committee boat end and we struggled to get the starts off. 

As any good race officer would the pin end was moved up, but as the breeze dropped, the tidal apparent became a larger component of our combined wind. Holding a string on the committee boat the line would have appeared almost uncross-able on starboard. 

But what was really interesting was we ended up with a finely set line, where as the final increases and drops in pressure came through they shifted the apparent so much that different ends of the line were favoured. Every-time the wind increased, it favoured the pin, and every time it dropped the committee boat was the place to be. 

Of course, gusts lift on port generally, so maybe that contributed. But it's a nice story. 
 
Back to Top
H2 View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 26 Jul 17
Online Status: Offline
Posts: 750 		Post Options Post Options   Quote H2 Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 1:54pm
Sit on a pontoon with your dagger board between your legs and alter the angle of the foil relative to the water moving and I am pretty sure you will agree that a foil can generate lift that is affected in part by the direction of the water moving over it.

A small shift that allows some boats to put the force of the tide on the leeward side of the board when others have the same tide pushing on the windward side of the board will amplify the benefit of the shift for those that get it.
H2 #115 (sold)
H2 145
OK 2082
Back to Top
Guests View Drop Down
Guest Group
Guest Group
Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 1:28pm
Originally posted by H2

to me it is just really obvious that boats sailing to windward with the same wind strength so they are moving through the water at the same speed all other things being equal then those that get a "ferry glide" lift off their foils will get pushed to windward and that this will result in a better VMG to the windward mark.
But, there is no lift on the foils. The boats just sailed a wind shift. Of course if you sail a 5 degree lift your VMG will be better. It's nothing to do with tide. 

If there is 1 boat lengths per second (blps) of tide against them and their boat speed is 2 blps then if some boats get a 5 degree lift, it will take them 10 boat lengths of sailing (through the water) over 5 seconds to see an almost 1 boat length gain. 

From the shore, referenced to our terra firma frame it will appear that the 1 boat length gain was made not over 10 boat lengths of sailing, but a mere 5, because the boats will have been moving back in the flow at 1 blps over 5 seconds. And it will look all weird because even though they only changed their heading by 5 degrees, the gain they made over those 5 (land based) boat lengths was more like a 10 degree shift! 

But, the reality remains, the boats are racing through the water and over time. The gain made is 1 boat length in 5 seconds. The gain made is almost 1 boat length for 10 boats lengths sailed through the water. There is no additional VMG advantage that you would not get with an identical shift on a pond. 

The shifts appear exaggerated because to the fooled observer the boats appear to be travelling slower (over land) than they actually are (through the water)! 

We're just so rooted in our land based reference frame. Maybe the fish perceive the seas as stationary whilst the earth giggles about beneath in rhythm with waxing and waning of the moon?  

Originally posted by H2

That is my experience and I have seen it happen and everyone in the fleet knew it had happened as we all talked about it for weeks afterwards!
Same thing happened to me and an even larger group of people after watching a Dynamo gig. 


Edited by mozzy - 18 Sep 19 at 1:31pm
Back to Top
JimC View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 17 May 04
Location: United Kingdom
Online Status: Offline
Posts: 6662 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 1:04pm
If you believe the lee bow myth you probably concentrate like crazy and sail your a*** off to get those few degrees higher without losing speed. And sailing your a*** off and getting a few degrees higher will always see you gaining against people who aren't...
Back to Top
sargesail View Drop Down
Really should get out more
Really should get out more
Avatar

Joined: 14 Jan 06
Location: United Kingdom
Online Status: Offline
Posts: 1459 		Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 18 Sep 19 at 12:56pm
And then there’s GRF’s trolling!
Back to Top
 Post Reply Post Reply Page  <1 2930313233 36>

Forum Jump Forum Permissions View Drop Down

Bulletin Board Software by Web Wiz Forums® version 9.665y
Copyright ©2001-2010 Web Wiz
Change your personal settings, or read our privacy policy