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Old 13-11-2013, 03:44   #196
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Originally Posted by IdoraKeeper View Post
In theory I can see how choosing the correct CTS can average out the advantage/disadvantage between tacks with respect to the current. ( Assuming constant wind speed/direction as a sum of all the relevant vectors.)
What would be useful (to me at least) would be an understanding of how to best compute when/at what location to tack to take best advantage of proper CTS. When any of the variables changes the spot to tack moves. Sometimes I can sense it. More often I see the other guy get closer to correct.
Yes, big issue, one that I have had at the back of my mind to deal with. I will next try and come to grips with this. After having time on my hands all summer, this would have to be time I am flat out with other things on board and shore. Frustrating for me LOL, as I would love to just sit undistracted and have a look at all this.

If the current alters in direction and cancels out for the journey (which it probably very roughly does for something like the Channel crossing given the length of the journey - Dockhead may want to comment if this is the case), and the ground speed is roughly constant, then it is dead easy, just travel close hauled on one tack (heading will vary as the current flow is changing in amount) the entire time the current is flowing in one direction (obviously choose the tack that has a heading closest to the CTS, ie the favourable tack), then tack the instant the current reverses.

When the current is unsymmetrical or purely flowing in one direction the whole time, but varying in amount, when to tack is not is simply obvious. This will have a reasonably easy solution I think (or at least a rough way getting it nearly right).

None of what I have been doing is rocket science. Nor has it required any complicated maths (no differential equations etc). I am just playing with vectors in a fresh way or at least I should say with fresh eyes.

So stay tuned .

PS I would welcome any thoughts from anyone, even incorrect ones. Sometimes all it needs is for a small comment to spark something.
Don't be afraid of making mistakes (you can see from this thread I am not, I have said lots of stupid things LOL). If you are not making mistakes, you are not stretching yourself. It was really comments from members that resulted in the new method of determining CTS that I came up with earlier in the year.
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Old 13-11-2013, 04:39   #197
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Seaworthy:
Your offer of you pulling the findings of the CTS thread would be a great help, it would save the mistakes taking me off in the wrong direction !!
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Old 13-11-2013, 04:46   #198
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Seaworthy:
Your offer of you pulling the findings of the CTS thread would be a great help, it would save the mistakes taking me off in the wrong direction !!
LOL, just head for where the beer is .

I will do this then at some stage. It is something that can be done relaxing with a glass of wine, so I will maybe do this over the next few days, while the lee bow thread is running and some people are interested in the issues). Understanding CTS (and having some idea how to calculate it) is critical in this discussion. There were hundreds of posts in two threads to wade through and the vital bits evolved, so just reading a bit of the threads does not help. It shouldn't take long for me to do this.
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Old 13-11-2013, 05:13   #199
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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LOL, just head for where the beer is .

I will do this then at some stage. It is something that can be done relaxing with a glass of wine, so I will maybe do this over the next few days, while the lee bow thread is running and some people are interested in the issues). Understanding CTS (and having some idea how to calculate it) is critical in this discussion. There were hundreds of posts in two threads to wade through and the vital bits evolved, so just reading a bit of the threads does not help. It shouldn't take long for me to do this.
thankyou
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Old 13-11-2013, 05:44   #200
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

ok ... I know I said I would leave you more knowledgeables to it .... but

so .... lee bowing does not just involve tidal stream (current) wind and its affect on the boats passage to a windward mark?
so... are we back to other influences on the boats ability to go to a windward destination ?

there is no doubt the term is used and in my dinghy racing ( mainly done in a handicapped fleet in a strong tidal harbour ) experience, is an advantage in low wind conditions . its won races

Dare I say ...... we cannot just do away with the term... because we don't know why it works!
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Old 13-11-2013, 06:16   #201
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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NOT THE LEE BOW EFFECT AT ALL:

No one at all has comment on my discovery LOL. I woke up keen to see responses from who had been awake while I slept and there was nothing. You lot are a tough crowd .

OK, this is it with technicolor drawings if that helps. It is so beautifully elegant and simple. The change in true wind direction has nothing to do with whether or not the current is on your lee bow.

It is purely which side of the ground wind the wind induced by current falls (this may be the lee bow, but it may also be the windward bow, it depends where your heading fits in this picture - am I about to be burned at the stake for blasphemy again LOL?).

I have drawn a simple diagram with just 8 points around the compass (any more lines and it becomes cluttered.
Lee Bowing the tide

lee ..... the side away from the wind
Bow .... the pointy end until it comes to the beam
Tide..... ok, it means the tidal current/ stream, its direction and rate

sorry...... but its not a cts thread
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Old 13-11-2013, 06:17   #202
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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ok ... I know I said I would leave you more knowledgeables to it .... but

so .... lee bowing does not just involve tidal stream (current) wind and its affect on the boats passage to a windward mark?
so... are we back to other influences on the boats ability to go to a windward destination ?

Not that I am aware of. We are just discussing current and if there is an advantage keeping current on the lee side of your boat.

there is no doubt the term is used and in my dinghy racing ( mainly done in a handicapped fleet in a strong tidal harbour ) experience, is an advantage in low wind conditions . its won races

Dare I say ...... we cannot just do away with the term... because we don't know why it works!
Using the term will not win any races, applying the term will LOL.

So how was it applied when you dinghy raced? Maybe those racing can chime in and contribute. Although I have frequently sailed, I have not raced in tidal waters so never thought much about this (easy when just cruising, you just pick your prime times for going anywhere ).

What I am keen to know from you and other members who have used this technique:
- Do you think it is advantageous to keep the current just on your lee bow or on the whole lee side of your boat?
- When do you use it? I presume only to windward LOL, otherwise you would follow your CTS. Someone suggested they use it in other circumstances.
- What do you do if you only have the choice of putting the current on your windward side on BOTH tacks?
- Whatever you do, is it particularly useful in strong or light air relative to the current strength?
- Do you use the technique without any consideration for what the tide is doing for the rest of the leg?

Lots of other questions bubbling on how this technique is used in practice. Don't worry about giving answers that prove to be the wrong thing to do. It will only help your performance in future races .

Are there any tacticians reading this or racers who are aware why certain tacks have been chosen in a race? Can anyone help by responding? Some feedback about what is done in practice would be really helpful
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Old 13-11-2013, 06:31   #203
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All



I think i have posted re: foils (keel and rudder for the cruisers) and there angle to the current and the wind against tide waves on the bow... it is logical ! but i will probs get shouted at
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Old 13-11-2013, 07:41   #204
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Huh? You are being lee bowed when the current is on your lee bow when you are close hauled. Unless the current is more than 90 degrees off your bow (ie not off your bow any longer) it will be pushing you away from the mark. Not towards it.

My interpretation is that the current is forward of amidships on the downwind side of the bow while trying to make way into the wind. Is this NOT what you mean by lee bowed to the current? If so then nothing I said makes sense, and I have no idea what you are discussing. And my comments should be ignored.


Huh? How can the current on your lee bow sweep you to the mark if is is on your bow. Have you managed to somehow overshoot the mark?
In this example lets say you round the leeward mark and are headed due north towards the windward mark. The current OS strong and out of the west so after rounding the leeward mark you set off on starboard tack. Along the way, the wind is dying/the current building, so it appears you could quite possibly fetch without tacking. As you near the mark it becomes apparent that you will likely leave the mark to starboard. The SI requires port roundings, so you are barely not fetching. The current is strong the winds are light, by pinching you reduce forward motion to slow the boat enough to allow the currie to sweep you past the mark so that it can be rounded to port. This is used where the time and distance lost by tacking twice would be greater than that lost by pinching.

From reading your arguments (both of you) I'm beginning to think that you are not arguing whether the current on the lee bow brings better wind, rather than improved VMG. In that case the answer is theoretically yes but in practice not enough to matter, except in extreme cases, like when there is no wind at all.
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Old 13-11-2013, 08:49   #205
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

this brings us right back to post *4 bt Dockhead who posted a link to this

Lee-Bow Effect: This brings up the famous lee-bow effect. If the current is coming at you at an angle that is very close to the course you are sailing and if, by pinching just a little bit, you can get your lee bow into the flow of the current, the movement of the water is going to push against the hull, the keel, and the rudder, and it is goign to drive you up to windward even though you are going slower over the bottom. If you are on the other tack the current is going to be hitting you broadside and pushing you down. If you can get the lee-bow effect to push you to windward, I feel you also increase the wind pressure on the sails. If I am on the tack that goes across the current I feel I am losing speed and distance to the mark. That is why, unless there is an obvious way to get out of the current entirely, or at least to a slower flow, I think you should always make your longest tack to the next mark sailing in the lee-bow position. And I would do this even if it meant pinching a bit to do so.

the guy who tries to debunk it is showing the tide on the beam..... it really does come down to using the technique in the few right conditions

the other use of the term is when you are heading on an favoured tack ( what you consider to be the gaining tack after a cts) edgeing your bets on a decrease or change of direction to the true (ground ) wind where by using the tide ( current) allows you to use the current on your bow to pinch and make the mark

when i was dinghy raceing , in very light winds the crew and helm would end up in a bunched position hugging the leeward shroud, this would lift the drag of the stern and rudder and bring the point of rotation forward thus allowing the bow to be pushed by a lee bow current into the wind to make a windward mark ..... i await the throng of abuse
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Old 13-11-2013, 08:53   #206
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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In this example lets say you round the leeward mark and are headed due north towards the windward mark. The current OS strong and out of the west so after rounding the leeward mark you set off on starboard tack. Along the way, the wind is dying/the current building, so it appears you could quite possibly fetch without tacking. As you near the mark it becomes apparent that you will likely leave the mark to starboard. The SI requires port roundings, so you are barely not fetching. The current is strong the winds are light, by pinching you reduce forward motion to slow the boat enough to allow the currie to sweep you past the mark so that it can be rounded to port. This is used where the time and distance lost by tacking twice would be greater than that lost by pinching.
Hi Grind
What you are describing has absolutely nothing to do with the 'Lee Bow effect' is is just managing current.

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From reading your arguments (both of you) I'm beginning to think that you are not arguing whether the current on the lee bow brings better wind, rather than improved VMG.
What we are discussing is what governs which of the two tacking options is best. If you look at my diagram of changes in true wind with current, then you can see it actually has nothing to do with the lee bow, despite this being called the 'lee bow effect'. I haven't quite got my head around it, but the tack which is lifted more by current than the other is the one where the current is closer to being directly on the bow, either bow (or something like that, that is not quite right, I am still thinking on this between chores ).

I am beginning to wonder though why this effect is relevant at all. Your instruments gather info about true wind. If the current is steady you just sail the true wind to the destination. Why worry at all which side of the boat the current is on? Why come up with the term 'Lee Bow' effect at all? First it is current on either bow that will give you a better angle, second the lift tack is still not necessarily the favoured one, it depends where the mark is. What on earth is so special about it? With constant current you just look at the true wind before the start and you sail to that.

Changing current is a whole different kettle of fish, but that has nothing to do with lee bow either.

I must say I am really puzzled how people in practice use this effect of current altering true wind (whatever you care to call it) .
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Old 13-11-2013, 09:19   #207
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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I am beginning to wonder though why this effect is relevant at all. Your instruments gather info about true wind. If the current is steady you just sail the true wind to the destination. Why worry at all which side of the boat the current is on? Why come up with the term 'Lee Bow' effect at all? First it is current on either bow that will give you a better angle, second the lift tack is still not necessarily the favoured one, it depends where the mark is. What on earth is so special about it? With constant current you just look at the true wind before the start and you sail to that.
Yes!!!

Can someone who is defending the lee-bow effect please explain this? A diagram would be great, but numbers would be OK too.
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Old 13-11-2013, 09:40   #208
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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Yes!!!

Can someone who is defending the lee-bow effect please explain this? A diagram would be great, but numbers would be OK too.
It is a raceing tactic commonly used to edge your bets on a wind veer !
it was never ment to be some awesome calculation worked into a cts.

the above post sums it up to me .... the current needs to be near your pointing angle with the current i would say between 0 to 45 degrees off your bow i am sure the affect of the current angle to the keel and rudder have a influence why it works, but i will leave that to someone who knows more about hull and foil design than me
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Old 13-11-2013, 09:55   #209
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

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It is a raceing tactic commonly used to edge your bets on a wind veer !
What IS the tactic LOL?

No one has actually said what the tactic is or when it is used.

One tactic when beating is to be on the favourable tack. This is not necessarily the tack with current on the lee bow, it may be current on the windward bow. Or it may actually be the opposite tack that is favourable if the mark is not directly into wind.

So how are people using this effect that I think is entirely mythical?
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Old 13-11-2013, 10:09   #210
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Re: Let's Get to the Bottom of the Lee-Bow Effect Once and For All

English version

True
/tru/ Show Spelled [troo] Show IPA adjective, tru∑er, tru∑est, noun, adverb, verb, trued, tru∑ing or true∑ing.
adjective 1. being in accordance with the actual state or conditions; conforming to reality or fact; not false: a true story.


true wind = un affected by any other factors

Apparent applies to that which can readily be seen or perceived:

Apparent wind = what is perceived to be the wind direction at the helm position

angle and velocity influenced by induced heading wind , leeway, current/ tidal stream and any thing else that affects what you feel .... including bean induced
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