Lee bowing

[dom]

Yes, of course. But generally speaking lee bowing will have little noticeable effect on apparent wind unless the speed of wind and current are fairly close (or current > wind of course). I probably could have put that better!

The best way to think of the true wind is that experienced by stopped vessel floating freely in the current. It follows that lee-bowing will have a zero influence on the difference between true and apparent wind, for everything takes place on that floating carpet.

The moored buoy on the other hand experiences the ground wind and we must consider its frame of reference to successfully round it. In practice, tidal flows bend, shift, and eddy, which can in turn influence the ground wind, adding an extra complication.

As for tides having a negligible effect on true wind vectors; believe it or not they can exert a truly significant influence and a mistake here can see a boat swiftly buried even if his boat-speed is top notch.

Edit. Example:imagine a ground wind dead ahead of 10kts and a tidal flow of 3kts running perpendicular to it. Nothing special there. This will shift the true wind by over 16 degrees!

 

[ghostlymoron]

Yes! Quite right, it really is as simple as that.

I don't know why some people make such a fuss about it.

Quite. My question was answered ages ago.

 

[lw395]

Quite. My question was answered ages ago.

I find it very interesting, the various ways people try to get their understanding of this kind of thing across.
It's not always about people being right or wrong, but sometimes a different thought process or way of looking at things. I'm a do-er not a teacher at the best of times and sometimes struggle to explain this kind of thing to people who've perhaps not used vectors in their day job.

 

[lw395]

....
As for tides having a negligible effect on true wind vectors; believe it or not they can exert a truly significant influence and a mistake here can see a boat swiftly buried even if his boat-speed is top notch.

Edit. Example:imagine a ground wind dead ahead of 10kts and a tidal flow of 3kts running perpendicular to it. Nothing special there. This will shift the true wind by over 16 degrees!

This is true, but we are often oblivious to the ground wind, the true wind is what we can feel and measure relative to the water.
When we're two miles offshore, I think we tend to use the water as our frame of reference, when we get close to the mark, we become aware of the tide.
Racing on the river, the land is close and there are lots of moored boats, so the land is the frame of reference?

 

[dom]

This is true, but we are often oblivious to the ground wind, the true wind is what we can feel and measure relative to the water.
When we're two miles offshore, I think we tend to use the water as our frame of reference, when we get close to the mark, we become aware of the tide.
Racing on the river, the land is close and there are lots of moored boats, so the land is the frame of reference?

On rivers I just follow the pipe-smoking old goat with new carbon sails and dyneema lines!

Seriously, fully agree that ground references are too abstract to imagine much above rivers. For example, a ground reference a mile off Lymington with a 3kt+ tide running seems obvious to a spectator on the pier, but one still sees boats making disastrous tactical decisions apparently oblivious to what is going on. I guess on a bigger boat, the tactician occupies himself with the ground reference and the crew just sail; and woe betide tacticians who say make a mistake in a flood tide off Cowes/Gurnard, where getting it right can increase one's true wind in addition to providing a useful COG component.

Dinghies are different in this respect, hence why the crew(s) are are either heavily briefed, or do a lot of homework before the race. And why big races are often held a little way offshore to somewhat reduce local complications.

You know, I'm beginning to think this whole lee-bowing concept causes more trouble than it solves

 

[grumpy_o_g]

Pinching is sailing slightly closer to the wind than your best close hauled course. Generally you will see a rather sharp drop in speed, but it may be tactically useful in a race situation.

Yep or, to put it another pointing higher into the wind than is the angle for the VMG (Velocity Made Good) towards you next destination. You will be sailing more directly towards it but your boat will have slowed down so much it will take longer to get there. It's a bit like your car's sat-nav having a quickest and a shortest route. Fastest route takes you a greater distance but at a higher speed.

The nice thing about pinching is that it can mean making a mark or avoiding an obstruction so that you don't have to put in another tack. When sailing between the mooring in Burnham it was common practice to luff up completely in to wind if it meant we could get past a moored boat without tacking - you just had to have enough inertia in the boat to keep it moving so you could bear away afterwards.

 

[johnalison]

Yep or, to put it another pointing higher into the wind than is the angle for the VMG (Velocity Made Good) towards you next destination. You will be sailing more directly towards it but your boat will have slowed down so much it will take longer to get there. It's a bit like your car's sat-nav having a quickest and a shortest route. Fastest route takes you a greater distance but at a higher speed.
.

It may have something to do with the hour I spent in the SC this morning but I don't understand that. In my book, VMG is a velocity, and towards the wind, or occasionally destination as in your case. In either case, this direction will be well to windward of where you can sail, and thus well to windward of where you might be tempted to pinch. In my simple world, pinching is just sailing above one's proper course when sailing to windward.

 

[lw395]

.... In my simple world, pinching is just sailing above one's proper course when sailing to windward.

'Proper course' has a special meaning in the racing rules, and does not exclude pinching.

VMG is a funny old thing, people use the term is various subtly or grossly different ways.
On a beat, it's generally more useful to define VMG as 'the windward component of your ground track'.
But is that 'windward' defined by the average wind, the instantaneous wind, or the wind the navigator was planning for?
On a river, you might usefully consider VMG to be the 'upstream' component of your velocity, at least for the 3/4 of the race you spend going uphill.
On a long passage, you might consider VMG to be the component towards you destination, as you'd expect the wind and current not to be constant for the duration.

I'm not sure VMG is always a useful concept racing in current, sometimes on our river, you have to accept the fastest way to the upstream mark involves losing ground on starboard tack and making ground on port.

 

[johnalison]

'Proper course' has a special meaning in the racing rules, and does not exclude pinching.

VMG is a funny old thing, people use the term is various subtly or grossly different ways.
On a beat, it's generally more useful to define VMG as 'the windward component of your ground track'.
But is that 'windward' defined by the average wind, the instantaneous wind, or the wind the navigator was planning for?
On a river, you might usefully consider VMG to be the 'upstream' component of your velocity, at least for the 3/4 of the race you spend going uphill.
On a long passage, you might consider VMG to be the component towards you destination, as you'd expect the wind and current not to be constant for the duration.

I'm not sure VMG is always a useful concept racing in current, sometimes on our river, you have to accept the fastest way to the upstream mark involves losing ground on starboard tack and making ground on port.

I thought as I typed 'proper' that I was using the wrong word; perhaps 'ideal' would have been better.

For me VMG means velocity in relation to the true wind at any instant. This wind will of course vary, which is part of the reason why a boat's track will have to vary. It is also what my boat's VMG meter tells me (roughly, but not including some of the functions on my Graphic Repeater which give VMG to destination without notice). When I mean VMG to destination, I will state this.

 

[TLouth7]

Yep or, to put it another pointing higher into the wind than is the angle for the best VMG (Velocity Made Good) towards you next destination.

Perhaps grumpy_o_g's post would align with other people's understanding of VMG with the addition of the word best (added in bold).

 

[Kukri]

This thread went above my pay grade several pages back.

I shall just continue to think, to paraphrase Nelson, that, “No helmsman can do very much wrong if he places the tidal stream on the lee bow!”

 

[grumpy_o_g]

Perhaps grumpy_o_g's post would align with other people's understanding of VMG with the addition of the word best (added in bold).

Agreed and that was a typo on my part.

Per the esteemed johnalison's post, I'm still stuck in the good old days of course, track and heading and had never considered velocity to be relative to anything other than a fixed point on the Earth's surface. We live and learn...

 

[anoccasionalyachtsman]

I think that there's a bit of an insoluble problem with definitions here. What I think some people are describing is 'shooting' in my book, that is a luff from full speed that will 'just' get you round a mark in adverse tide. Successfully done it's immensely satisfying, but it's such a seat of the pants thing and almost impossible to be certain that it'll work. Despite people's best efforts here I still can't see any justification for what I'd call pinching (sailing at less than optimum vmg) for more than a boatlength or so (see' shooting' above!). But by all means carry on, especially if you're racing anywhere that I am.

 

[flaming]

I think that there's a bit of an insoluble problem with definitions here. What I think some people are describing is 'shooting' in my book, that is a luff from full speed that will 'just' get you round a mark in adverse tide. Successfully done it's immensely satisfying, but it's such a seat of the pants thing and almost impossible to be certain that it'll work. Despite people's best efforts here I still can't see any justification for what I'd call pinching (sailing at less than optimum vmg) for more than a boatlength or so (see' shooting' above!). But by all means carry on, especially if you're racing anywhere that I am.

If the tide is expected to be even across the course, then there is never any justification in sailing anything other than best VMG except for "shooting" as you describe.

Where, tactically, it can get a bit more interesting is if by pinching slightly you can reduce the number of tacks required or stop yourself from going out into bad tide. A classic example might be tacking up the green at Cowes against the tide in a SW. So the Port tack is the long tack but it is standing out into the tide. If by pinching just a bit you can actually get parallel to the shore (and tide) then this might work well as you can see that the loss of VMG you are seeing by sailing at (say) 6 knots pinched a bit, Vs 7 knots on your best angles is more than compensated by not sailing into the extra knot or more of foul tide further out and then also having to do more tacks.
What some people seem to think however, is that it is the act of getting the tide on the lee bow here that is important, and does something magical. It isn't, it's a tactical consideration to trade VMG now for positioning on the race track.

Try the same trick, i.e pinching so that you get parallel with the tide in open water and even tide and the boat that sails it's best VMG is very likely to cross in front of you after they tack.

 

[lw395]

If the tide is expected to be even across the course, then there is never any justification in sailing anything other than best VMG except for "shooting" as you describe......

That is a very bold statement that some would take issue with.

 

[flaming]

That is a very bold statement that some would take issue with.

So what justification would there be for pinching somewhere with even tide?

 

[dom]

So what justification would there be for pinching somewhere with even tide?

I can think of lots of cases where a gaggle of boats are in close proximity to a turning mark!

 

[flaming]

I can think of lots of cases where a gaggle of boats are in close proximity to a turning mark!

That's tactical considerations and "shooting". I'm talking about getting upwind as fast as possible in clear air and even tide. Angle the tide any way you like in relation to the boat, and you will always be fastest doing the best VMG for your boat, not pinching.
Tactically in close proximity to other boats you frequently do things other than sail your boat as efficiently as possible, but I'm talking about where you're just trying to get to the mark as fast as possible,

 

[johnalison]

What some people seem to think however, is that it is the act of getting the tide on the lee bow here that is important, and does something magical. It isn't, it's a tactical consideration to trade VMG now for positioning on the race track.
.

I am not going to attribute anything mystical to lee-bowing, but the effect can indeed appear magical. I might, for instance, be close-hauled on my boat's normal best approach with the tide just on my weather bow and failing to clear a mark or bend in the river. If I then make a pact with the devil and pinch up a fraction, the apparent wind moves aft and I find that I am mysteriously able to round the mark or bend with ease. It's all about vectors of course, but part of me is happy to attribute it to magic.

 

[flaming]

I am not going to attribute anything mystical to lee-bowing, but the effect can indeed appear magical. I might, for instance, be close-hauled on my boat's normal best approach with the tide just on my weather bow and failing to clear a mark or bend in the river. If I then make a pact with the devil and pinch up a fraction, the apparent wind moves aft and I find that I am mysteriously able to round the mark or bend with ease. It's all about vectors of course, but part of me is happy to attribute it to magic.

But there's the difference... When you do that pinching you are concentrating so much harder. You've just improved the performance of your boat, not done anything special with the tide etc.