Lee bowing

[dom]

Imagine a zero ground wind as one departs UK coast; destination to the SW. Tide is 6kts flowing due west.

The boat experiences a TWS of 6kts from the west, allowing it to sail at 6tks on a S heading.
AWS: SW 8.5kts, AWA 45 deg, COG SW 8.5kts. Magic!

Edit: Now tack
Or try bearing off

 

[lw395]

You are really not getting this are you - the full effects of lee bowing are when ....

I completely get what you are saying, but it is a mere subset of what other people ramble on about under the heading of 'lee bowing'.

 

[ghostlymoron]

Thanks everyone, it's now perfectly clear. ?

 

[[3889]]

Sail slowly into a current? good way to minimise VMG!

I think I'll join Minn banging my head against a wall.

Try this:
https://www.bbc.com/bitesize/guides/zgcrjty/revision/1

Lee bowing is lee bowing. Some people refer to gybing as tacking but it doesn't make gybing tacking. It makes those people incorrect.

 

[lw395]

I think I'll join Minn banging my head against a wall.

.....

Good idea!

 

[TLouth7]

Lee bowing is lee bowing. Some people refer to gybing as tacking but it doesn't make gybing tacking. It makes those people incorrect.

And pinching to gain some magical lee bow benefit is definitely incorrect.

 

[Kukri]

And pinching to gain some magical lee bow benefit is definitely incorrect.

Not in the situation that was described by Jonalison - racing in an estuary. In that situation, it can and does make perfect sense to pinch if - if - that means you can lee bow the tide and thus get a lift past a headland that you would otherwise have to tack for.

 

[Kurrawong_Kid]

And pinching to gain some magical lee bow benefit is definitely incorrect.

in theory yes, in practice no! Many racing Dinghy helmspersons have experienced the thrill of going well to windward with the tide under the bow with gentle pinching and the despair when you cannot “get in the groove” and fail to point as well as others on the same tack despite normally being able to sail as well to windward! There are so many factors involved in making a sailing craft go to windward at peak efficiency that effective “lee bowing” the tide is probably an illusion but it makes a great excuse for poor performance when you can’t do it!

 

[lw395]

Not in the situation that was described by Jonalison - racing in an estuary. In that situation, it can and does make perfect sense to pinch if - if - that means you can lee bow the tide and thus get a lift past a headland that you would otherwise have to tack for.

Racing on rivers, which I've done a lot of, it often pays to pinch like crazy at the edges where the current is less, or there's even a back-eddy. If the wind is at an angle to the current, then pinching may allow you to get into less current. On a small river, luffing higher than you can pinch can take you into better current sometimes. That kind of thing is Lee Bowing of a sort, but other people mean different things by it, sometimes!

 

[lpdsn]

I will try again:

If a boat is close hauled, she will make leeway. Put her on the tack on which the tidal stream or the current is on the lee bow and the tide will reduce the leeway that she makes.

Sorry, four words of two syllables, there.

I find it easier to think of it in terms of the wind, although the effect is the same. Movement of the boat through the air by the tide gives you a component of the wind you experience on the boat. By lee bowing you're effectively being lifted on that tack. Until the tide changes then you tack and get lifted on the other tack.

It can easily be drawn out with vectors.

Of course in racing circles lee-bowing means something completely different. It means completing a tack so that you're on the lee bow of a competitor about half a boat length to leeward. The airflow over the mainsail is such that this seriously disadvantages the competitor so that you can then pull ahead.

In offshore racing both meanings apply.

 

[RupertW]

I completely get what you are saying, but it is a mere subset of what other people ramble on about under the heading of 'lee bowing'.

Agreed. Talk of pinching, leeway and calculating a fixed heading to cross a varying tidal stream are all good things to work on but none of them are anything to do with lee bowing.

 

[lw395]

One other description of 'the lee bow effect'
Imagine you are sailing fairly close hauled, headed directly upstream, headed for the windward mark.
If you pinch up, you slow down, but easily leave the mark to leeward. Putting the current on your lee bow 'lifts you to windward'
If your boat could tack without losing speed, it would be quicker to sail at best VMG, even if you had to put two tacks in.
In that fairly common scenario, the difference between having the tide on your lee bow or weather bow is disproportionate, and lee bowing with right of way can often beat better VMG and being the 'keep clear' boat. And of course, less tacks will usually pay unless you are edgily good at roll tacking.

A lot of river sailors can out-pinch a Dobermann, then don't understand why it doesn't pay on a big lake.

 

[[3889]]

And pinching to gain some magical lee bow benefit is definitely incorrect.

OK. I'll go and ponder whether to accept your verdict or that of a double world champion (Darts and Cadets) and national Olympic coach, plus my own rationale. I don't think it will take long.

 

[lw395]

Agreed. Talk of pinching, leeway and calculating a fixed heading to cross a varying tidal stream are all good things to work on but none of them are anything to do with lee bowing.

I just take the view that when somebody says 'lee bowing' etc., they might mean several different things or a mix of all of them.

 

[grumpy_o_g]

I never knew it was all so complicated I just think of it as "let the current push me towards where I want to go instead of away from it".

 

[TLouth7]

One other description of 'the lee bow effect'
Imagine you are sailing fairly close hauled, headed directly upstream, headed for the windward mark.
If you pinch up, you slow down, but easily leave the mark to leeward. Putting the current on your lee bow 'lifts you to windward'
If your boat could tack without losing speed, it would be quicker to sail at best VMG, even if you had to put two tacks in.
In that fairly common scenario, the difference between having the tide on your lee bow or weather bow is disproportionate, and lee bowing with right of way can often beat better VMG and being the 'keep clear' boat.

Unfortunately the tide does not "lift you to windward" in this scenario. The reason that you can leave the mark to leeward is that you have sailed a higher course by pinching. The presence of tide makes the beat longer in this case (think of the mark being towed uptide in still water), but it cannot magically create some sideways force on the boat.

 

[dom]

So we have a thread here interspersed with one, possibly more regional/national silverware holders arguing over ‘lee bowing’, while all meaning the same thing! For those who deploy wind/tide/boat-polar vectors are bound to arrive at the correct answer.

It's the old problem: us humans like to think we carefully work things out, but that's too computationally heavy. So, we rely on a system of learnt beliefs to simply the world and it is surprisingly difficult to unlearn incorrect notions. 'Lee bowing' is a good example, helpful if correctly applied, but so vague it is bound to cause problems.

At the heart is the difference between ground wind and true wind and many threads bear witness to misunderstandings here. A boat floating in a steady tidal steam experiences its true wind as it sits static in the water. A turning mark is anchored, which simply means one must travel as fast as one can to a point dislocated from the mark. Ignore the tide, just get there quickly. And the true wind the mark experiences is different to the boat's.

Now add tidal bends, shallow water, back-eddies, river bank effects, etc. to a faulty GWS, GWA, TWS and TWA equation, and one has no chance of correctly combining this with wind bends, shift patterns, etc. There are so many parameters here, everyone can prove whatever they want! Imagine a 10m wide stream flowing at 15kts as it meanders around the course: just sail into it, drop the sails, relax and soak up the rays and win the race by a country mile. Unless someone figured it might be best to raise their sails part of the time

And we see this all the time; the lead boat, while a tad quicker off the line, can seem an astonishing distance ahead after the first beat. If it's a dinghy the sailor(s) won't even have a computer. Back to learnt beliefs, a personal set of mnemonics really, and mnemonics don't have to be logical.

 

[NormanS]

One other description of 'the lee bow effect'
Imagine you are sailing fairly close hauled, headed directly upstream, headed for the windward mark.
If you pinch up, you slow down, but easily leave the mark to leeward. Putting the current on your lee bow 'lifts you to windward'
If your boat could tack without losing speed, it would be quicker to sail at best VMG, even if you had to put two tacks in.
In that fairly common scenario, the difference between having the tide on your lee bow or weather bow is disproportionate, and lee bowing with right of way can often beat better VMG and being the 'keep clear' boat. And of course, less tacks will usually pay unless you are edgily good at roll tacking.

A lot of river sailors can out-pinch a Dobermann, then don't understand why it doesn't pay on a big lake.

If you are heading "directly upstream" you don't have tide under your lee bow.

 

[awol]

And I thought lee bowing was getting your boat in front of and slightly to leeward of another boat on a beat so that they suffered from disturbed wind.

 

[ghostlymoron]

Surely that tactic won't work for long as the other boat will fall back and be in clean wind again.
By the way, now I understand lee bowing, what is pinching. (In one sentence).

And I thought lee bowing was getting your boat in front of and slightly to leeward of another boat on a beat so that they suffered from disturbed wind.