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didlydon View Drop Down
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    Posted: 11 Oct 11 at 1:58pm
It's probably been discussed here before, but someone in my club mentioned the Lee Bow Effect after racing on a light breeze day when the tide was running strongly...... I just nodded & thought I understood, but to be honest didn't really.... So can anyone explain it to me please? Thanx. Geek
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My understanding is that when beating against the tide, if the tide is coming at your bow from the lee side then it is effectively pushing you into the wind. This is good because firstly it counteracts leeway and secondly gives you stronger apparent wind as you get pushed into the wind. Sometimes the difference between stuffing and footing is the lee bow effect, which therefore makes it pay to stuff.

Obviously if tide is on the windward side upwind then you are fighting both wind and tide, so can sail anyway near as high or fast.
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Posts: 280 		Post Options Post Options   Quote didlydon Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 2:13pm
Stuffing & footing Pinch............ Please explain as well.......
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Posts: 2965 		Post Options Post Options   Quote Jack Sparrow Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 2:22pm
Stuffing (pinching) into wind for height. Footing... Easing off the wind for speed.
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didlydon View Drop Down
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Posts: 280 		Post Options Post Options   Quote didlydon Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 2:33pm
Ahhhhh..... Thanx! I do know how to sail - honest - just not familiar with the (Slang?) terminology.
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Posts: 6661 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 2:44pm
The lee bow thing is largely a myth...

The theory goes that if you point up so that the tide is one degree on the lee bow instead of 1 degree on the windward bow then you'll magically go much better. Of course if you sail your [expurgated] off so that you point two degrees higher *without slowing down* then you don't need any complicated theories about tide to explain why you're suddenly going better up the beat...

Yes, the tide pushes you across the track, but the apparent wind clocks back the other way as a result. Nothing special happens when the tide goes from 0.1 degrees one side to 0.1 degrees the other. It takes ages and a lot of drawing of force triangles to explain why, but that's what happens.

Remember all that counts is what the wind is doing relative to the sails and the water is doing relative to the foils. The boat hasn't got a clue what the sand on the bottom of the river is doing... In tide the effective wind direction and speed is not what you get in a moored boat, but what you get in a boat drifting in the current.

Of course if the tide is not constant in speed and direction across the race track there are enormous gains to be made by exploiting the differences, but that's something else again: not what was traditionally called the lee bow effect.


Edited by JimC - 11 Oct 11 at 2:48pm
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Posts: 1020 		Post Options Post Options   Quote Oli Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 3:19pm
jim my understanding of it is that i dont point higher with a tidal lee bow but for the same tacking angle i can effectively sail a shorter distance to the mark as the tide is pushing me into the "as the crow flys" line (crabbing).  a velocity diagram may show you as sailing slower but at a better angle, its all down to vmg to the mark as to whether its beneficial.
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Posts: 8956 		Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 4:17pm
The lee bow effect is one of those things like asymmetric spinnakers lifting the bow - easy to disprove with science, but less easy to explain why it still appears to work in real life!
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Posts: 4028 		Post Options Post Options   Quote G.R.F. Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 4:27pm
Lee Bow is my particular expertise, have had arguments with Olympics coaches then demonstrated my point by taking ten minutes, yes ten minutes out of the entire Olympic Squad in one instance by it's correct application as against the advice the coaches gave to the squad, a delicious moment.

Anyone who doubts it's effect hasn't had thirty years of tidal racing and sailing, including that muppet that tried to write a lame book debunking it.

On a sailboard you actually get to 'feel' the effect it has on the driving forward force of the board, it is very much less in a dinghy.

The other Lee Bow effect is that force prevalent at the start of the race when all the boats (boards) are lined up, the sail on boat to your lee bow, if allowed to creep ahead, diverts the wind between both boats and effectively heads the windward boat. So you fight to get your nose ahead, to stuff the guy upwind of you with lee bow, whilst covering the boat to leeward, it's how the fleet divides by approx 1/3rd within minutes of the gun firing.

Back to the tide, leaving the line, imperative to take the tide on the lee bow initially to help speed if at all possible, even though the water you're on should be thought of as a conveyor belt, the boats speed over it is not the same. (assuming in this instance a left to right tide within which tidal lee bow would play a part.

Kind of difficult doing this in words, sailing in tide is an entire lecture in it's own right and events get won and lost by the correct application and timing of when to 'go for' tide on the lee. Tide on the lee bow can be like a lift whereas tide on the weather bow is almost certainly heading. Just as with wind shifts there are times to play either or, depending on your position in the fleet at any given moment.


Edited by G.R.F. - 11 Oct 11 at 4:28pm
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Posts: 641 		Post Options Post Options   Quote Presuming Ed Quote  Post ReplyReply Direct Link To This Post Posted: 11 Oct 11 at 4:38pm
THERE IS NO LEE-BOW EFFECT - Dave Perry
One of the most fascinating and timeless controversies in our sport is over what effect current has on how we sail and race our boats. Beginning in early 1979, Peter Isler and I filled hours of time debating the effects of current, and it wasn't until mid-1980 that he finally parted my clouds and shook me loose from years of misconceptions and incorrect assumptions. Here then is my understanding of the effects of current, substantiated by several of my more mathematically-clever friends.

Assuming that we're sailing in constant current direction and strength, No! As we've determined, the direction and strength of the current created wind is the same no matter at what angle the boat is aiming or at what speed it is moving. The presumption of the lee-bow effect is that if you are sailing directly into the current you can pinch slightly, putting the current on your leeward bow, and the current will push you up to weather. This is obviously false because the only direction the current can move you is in the direction it is going (the stick on the river).

The presumption of those who believe that in current a boat will have a different apparent wind direction and strength on opposite tacks, is that on one tack the boat will be slowed more by the current than on the other. The extreme example is when port tack takes you right into the current, and starboard tack takes you across it. The illusion is that on port tack it would seem that the boat is still going forward toward the wind, but that on starboard the boat is being swept away from the wind by the current. Therefore, the apparent winds must be different on the two tacks.

The fallacy here, though, is that the judgment of going toward the wind and being swept away are made in reference to fixed objects such as the mark, an anchored boat, or land. In reality, both boats are being affected equally by the current and the wind "sees" both boats in the same way. In other words, if you were following the race in a motorboat and were in the ocean where you couldn't see any land for reference, the boats would look identical on either tack, and in fact you would have no clue that there even was current unless you knew from charts or perhaps from the surface condition of the water. Put another way, if you're sailing on a boat with wind strength and direction instruments, they'll read the same on both tacks because the boat is affected in the same way by the current on either tacks (the stick in the river again).
-- Excerpt from Winning in One-Designs by Dave Perry,
http://www.ussailing.org/member/library/wiodcurrent.htm

Of course, there is an argument that if your opposition _do_ believe in the "lee bow effect", then the last thing you actually want to do is disabuse them of their belief. If they believe that stuffing the bow up and sailing slowly is the best way to win a race, then who are we to try and dissuade them....
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