Lee Bow Effect.

[Mark-1]

Lee bowing is a definite certainty, I have used it in racing on an incoming tide, in the river to almost ferry glide over the river to the next mark.

That's what I understood the Lee Bow Effect to mean, and is consitent with the effect described in the links I posted.

Can dt4134's second definition be right?

I think not. I can't find it anywhere except PBO. The Lee Bow Effect is discussed endlessly amongst Dinghy sailors, how many of them sail across two tides in one race; I sailed inland on a River for my formative years - the stream only went in one direction - and the Lee Bow Effect was a hot topic for us.

 

[monkfish24]

I've just been reading a blog from a non-tidal sailor who disputes the lee bow effect. Interesting as I have never heard anything but "Lee bowing works".

I've been racing for 12 years now and 10 of those was spent on the Tamar. You'd be outcast for saying lee bowing is ballox when it quite obviously works in a situation where you have sometimes 2-3 kts of tide running. It becomes very apparent that it works then.

 

[bedouin]

That's what I understood the Lee Bow Effect to mean, and is consitent with the effect described in the links I posted.

Can dt4134's second definition be right?

I think not. I can't find it anywhere except PBO. The Lee Bow Effect is discussed endlessly amongst Dinghy sailors, how many of them sail across two tides in one race; I sailed inland on a River for my formative years - the stream only went in one direction - and the Lee Bow Effect was a hot topic for us.

(2) is the way I use the term "Lee Bowing" - it applies when tacking across a stretch of water where the tide will change. If you check the figures it is pretty easy to see that you will make the crossing fastest by keeping the tide on the lee bow as the tide gives you a lift.

 

[Keen_Ed]

"The lee-bow effect is an illusion, and does not exist."

Three types of wind: ground wind (as felt on an anchored boat, or on land), true wind - ground wind as altered by the tide/current (as felt by boat moving with the tide) and apparent wind (wind as felt on a boat sailing).

The tide alters the true wind relative to the ground wind. So you get a tide shift - if it's tide across wind, the true wind will be shifted relative to ground wind. The tack where the tide is on the lee bow will be lifted (comped to ground wind), but the other tack will be headed (caeteris paribus). So it all evens out.

If the tide is even across the course - or the leg of your passage - then there is no gain on the lee bow tack.

If the tide isn't even across the course/leg or will be changing while you're sailing, then the degree of tidal shift will change, which can be planned for and acted on.

There are those who believe that if the tide is aligned with one tack, then by sailing high and "taking the tide on the lee bow", you somehow get "pushed upwind". To make this work, you need to be able to sail higher at the same speed. Oddly enough, sailing higher at the same speed works pretty well when sailing in water without current.

http://www.j105.org/docs/noleebow.pdf

 

[Mark-1]

(2) is the way I use the term "Lee Bowing" - it applies when tacking across a stretch of water where the tide will change.

Thanks, but that can't be the "Lee Bow Effect" I have in mind.

I am certain the Lee Bow Effect I'm talking about is the one in my links, the one monkfish24's mentions & the one mentioned at the end of Keen_Ed's post.

Unfortunate, that the term has been used to describe so many different things.

 

[monkfish24]

I think that is what is confusing the whole idea. So many different meanings for one word.

I can understand the dispute over you're just travelling the same distances etc and apparent winds. But the most important factor for lee bowing is VMG towards the mark/waypoint where you otherwise would have to beat towards it.

 

[PeterR]

Lee bowing as an action one takes in respect to another yacht is a racing tactic whereby when sailing to windward you place your boat slightly to leeward and slightly ahead of the other boat. The resultant effect on the apparent wind flow experienced by the windward boat means she cannot sail as high as the boat in front and will gradually sag down to leeward unless she tacks off. Tide has no relevance to this definition of lee bowing.

The lee bowing to which I believe the OP is referring to is the ability of the tide to lift a boat to windward when beating with the tide under the lee bow as opposed to the rather depressing opposite effect when tide on the windward bow pushes you away from your course. These effects certainly exist but some go further to imply that when the tide is almost dead ahead you can gain the magical effects of lee bowing by pointing slightly higher allowing the tide to push you up to windward. In this instance you have not changed the tidal vector you experience by one iota. Your boat speed will fall as will your VMG. You will indeed appear to be lifting to windward but this is merely due to the fact you are pointing higher whilst travelling more slowly. Occasionally this effect can be of use, for instance when trying to squeeze up to a mark, but in general you are best to sail at your optimum wind angle for boat speed and if the tide happens to be under your lee bow so much the better.

 

[Salty John]

The RYA manual on navigation refers to a lee-bow tide giving an advantage on a long cross-tide leg. It suggests you tack to keep the stream on the lee-bow and provides this illustration:

 

[Racecruiser]

Lee bowing as an action one takes in respect to another yacht is a racing tactic whereby when sailing to windward you place your boat slightly to leeward and slightly ahead of the other boat. The resultant effect on the apparent wind flow experienced by the windward boat means she cannot sail as high as the boat in front and will gradually sag down to leeward unless she tacks off. Tide has no relevance to this definition of lee bowing.

The lee bowing to which I believe the OP is referring to is the ability of the tide to lift a boat to windward when beating with the tide under the lee bow as opposed to the rather depressing opposite effect when tide on the windward bow pushes you away from your course. These effects certainly exist but some go further to imply that when the tide is almost dead ahead you can gain the magical effects of lee bowing by pointing slightly higher allowing the tide to push you up to windward. In this instance you have not changed the tidal vector you experience by one iota. Your boat speed will fall as will your VMG. You will indeed appear to be lifting to windward but this is merely due to the fact you are pointing higher whilst travelling more slowly. Occasionally this effect can be of use, for instance when trying to squeeze up to a mark, but in general you are best to sail at your optimum wind angle for boat speed and if the tide happens to be under your lee bow so much the better.

Nicely summed up I think. I'm sure you will know this, others may not; refering to your first para (racing tactics) if you get a lee bow tack right, the boat you do it too has to tack away or they will slip behind quickly usually into your wake - very satisfactory! Only recommended on the race course as could be a little edgy when cruising ....

 

[Mark-1]

The RYA manual on navigation refers to a lee-bow tide giving an advantage on a long cross-tide leg. It suggests you tack to keep the stream on the lee-bow and provides this illustration:

Thankyou. Looks like the Lee Bow Effect I'm familiar with is just a misunderstanding of that diagram, which clears up the mystery for me.

In reality nobody's getting any mystical advantage. Relative to the wind as they experience it, boat a and boat b are moving equal distance and speed to windward. One tack is obviously favourable with regard to the destination, and that would be apparent to both boats even if they had no idea what tide and true wind were doing. (If I were to erase true wind and tide from that diagram someone could still say which was the best tack relative to the destination.)

Thankyou Salty John, It's easy to see how someone could look at that diagram without thinking about it and come away with the impression that the boat with the flow on the lee is always faster and-or higher. I bet that's what's been happening all these years.

 

[Keen_Ed]

The RYA manual on navigation refers to a lee-bow tide giving an advantage on a long cross-tide leg. It suggests you tack to keep the stream on the lee-bow and provides this illustration:

Yes, but that's a situation where the tide is changing during the duration of your passage. By taking the tide on the lee bow on both tacks, you're simply making best use of the tidal wind shift, and sailing on the lifted tack.

 

[wklein]

The RYA manual on navigation refers to a lee-bow tide giving an advantage on a long cross-tide leg. It suggests you tack to keep the stream on the lee-bow and provides this illustration:

This is what i understood as lee bowing. However when beating you need to spend time on both tacks. One will help, the other will hinder. I don't see how any advantage could be achieved unless the tide changed as you tacked. I have heard it used for cross channel beats when the tide will change half way. How you could use it in a short tacking situation is a mystery.

 

[Mark-1]

This is what i understood as lee bowing. However when beating you need to spend time on both tacks. One will help, the other will hinder. I don't see how any advantage could be achieved unless the tide changed as you tacked.

To get a benefit you'd need to have a whole day with no headers or lifts and there would need to be no other bias of any kind. Hasn't happened to me yet.

I don't have a huge amount of offshore racing experience (two years as a student) but in that time nobody ever mentioned lee bow effect in that context. I hadn't heard of it 'till yesterday. Has their been a RORC race in the last 10 years with a leg with opposing periods of tide directly into the true wind with no bias at all, which is what you'd need for the bias created by a couple of knots of wind to be significant enough to think about.

 

[lw395]

It means different things to different people.
In my mind the biggest thing is when the tide is basically against you, it makes a disproportionate difference whether the tide is 10 degrees on your lee bow or 10 degrees on your weather bow.
Particularly in a situation where you have options to tack out of the worst of the tide, or cross a channel sooner or later. Being in the right place with respect to the windshifts can make a huge difference.
Even in a 1 hour dinghy race, the tide is not usually constant across the course or with time, neither is the wind.

 

[dt4134]

In the end it is just an extra bit of information you can use. There might come a time during a race when it allows you to tack earlier and still lay the mark whereas boats that ignore it will overstand. Or in cruising, just gets you home half an hour earlier on a cold wet night.

 

[Mark-1]

In the end it is just an extra bit of information you can use. There might come a time during a race when it allows you to tack earlier and still lay the mark whereas boats that ignore it will overstand.

I can't see how that could ever happen in this case because the fact that one tack is better than the other will be perfectly apparent from the wind you experience on the boat. The burgee on the boat has already taken the Lee Bow Effect into account. You don't care what factors created the wind you're feeling on the water.

(This is the RYA's version from the diagram, not the Lee Bow Effect in my links and in my memory, which appears to me to be a misunderstood version of that diagram.)


EDIT 22 Nov 2017:

Unfortunate, that the term has been used to describe so many different things.

He misses out one of ours!

http://www.sailingtoday.co.uk/practical/lee-bowing/