Wednesday, April 1, 2015

Persistent Shift Q&A

Here are some questions and answers about the first two blogs.  Please feel free to contact me with more questions and I will see if I can find time to make the answers into more posts. 

1  What is the definition of a persistent shift?  Is it a shift that persists going in one directional (with some pauses perhaps) throughout one upwind leg of a course, (and can include some minor oscillations during the leg?)

Yes I would say that hits the nail on the head for a definition.  The wind could be moving gradually, in bits and pieces, even oscillating, but as it oscillates it generally trends more to one side.  I would even include big one time shifts that don’t come back as persistent shifts because the strategies are similar.   

A difference with the one time event is that if you miss it, it is harder to come back, whereas often in gradual persistent or oscillating-persistent shifts, you can make a small mistake at the beginning of the leg treating it as purely oscillating, but then realize your mistake and pick your time to dig in fairly hard to the side that the shift is coming from.  This way you may be able to recover your losses by getting to that side before the worst of the shift comes through.   

The key thing for a persistent shift is that if the wind goes one way, it does not come back in the time before you round the next mark or sail back to the middle of the fleet (consolidate you losses or gains).  So it is obviously a persistent shift if the wind was never going to come back like with the transition from a gradient driven wind to a thermal driven wind, but if the wind is oscillating on a long time scale and there is potential for it to come back then it matters how far away the next mark it.  If it doesn’t come back before the next mark then over the course of the leg, the long time scale oscillating shift was effectively a persistent shift, or another way to say it would be to say that the oscillating shift was so slow that persistent shift strategy works  By persistent shift strategy I mean: getting to the side towards which the wind is going to shift before that shift happens (for a one time shift), or getting to the side towards which the wind will continue to shift (for a gradual shift).  I will get to oscillating-persistent shifts in upcoming blogs.

2  In your basic advice about oscillating shifts in Part 1 of the Persistent Shift Blogs, what is the difference between the basic advice "tack on knocks" and "tack on knocks past the median"?

The second strategy is just a more sophisticated version of the first strategy.  Often in oscillating breeze, there are just two directions that the wind oscillates between, so if you tack every time you get knocked (which is the result of the first and second strategy) you will do fine.  If on the other hand there are multiple wind directions, then when the wind is in the extreme right you need to be on starboard and if the wind is in the extreme left you have to be on port, but if the wind is in the middle it is more of a judgement call and you can play out your boat-on-boat tactics or if tacking on an extreme shift takes you away from your plan, you can use the next shift to a middle wind direction to get back to executing your overall strategy.

Here are some ideas for what to do with a middle phase, that is, if the wind shifts to the middle of the course (blowing down the rhumb line).  If you are closer to the top of the course you probably want to sail towards the rhumb line to avoid risking overshooting the layline.  If the wind shifts to the middle direction at the beginning of the leg you can do whatever you like: if the course is skewed, I would recommend spending your time during the median phase sailing the longer leg or sailing into the current if there is cross-course current, since you will have to spend more time sailing on that tack over the course of the leg anyway.  To convince yourself of that, think of the consequence of doing the opposite.  If you sailed the shorter tack on the middle phase (especially at the beginning of a beat), you might use up that tack (be very close to the layline) and not be able later in the beat to tack on an extreme shift that puts you on the short tack without sailing over the layline while your competition could make big gains on the extreme shift if they are well clear of the layline.

Other decisions for what to do with your middle phase at the beginning of the leg would be sailing towards the side that you think is favored: tide or current, wind speed, any other factors.   

If you have already made some gains from a good start or some good shifts etc.  You can spend your median phase tacking back across to windward of your competition.  This reduces the leverage between you and your competition so that it is not easy for your competition to find a way to take your gains back from you.  Two terms to describe that decision are: ‘cashing in’, or ‘consolidating’.

If the wind is smoothly pivoting right and left to varying degrees it is more difficult to decide what the middle wind direction is.  This is where you have to make a judgement call on what is the median.  One strategy is to take the mathematical median from your compass bearings and call the middle of the two most extreme right and left wind shifts the median.  If you do this, how far do you think back before forgetting your old extreme shifts?  Another strategy is to just make a judgement call on which general wind direction tends to reoccur most, call that the median and then tack whenever the wind heads you past that heading.  At any rate, somehow use observations and judgment to you chose your median wind direction.  If you have a compass, and depending on which model of compass you have, you will need a number for the heading you should have when sailing the median on Starboard and a number for your heading when sailing the median on port.  These numbers should subtract to make up a credible tacking angle.  Many people, though, are doing this by intuition:
“Hmm yes, this feels like the normal wind direction"
"Okay I am headed, but not as far as before, I'll say it feels like the middle wind direction" 
"My bow looks like it is pointing on a line that is roughly 45 degrees to the rhumb line, so I figure I am close to the median."

If you get lifted from whatever you are calling your median heading then you just continue to sail.  If you get headed back down to that same heading you just continue to sail, don’t tack unless you have some other reason to tack (as mentioned in the ideas for what to do in a middle phase).  This is what separates the first simple strategy from the second, because the first strategy of tacking on the knocks suggests that you should tack when the wind heads you down to to the median which is not necessarily your best move.  However if you get knocked below that median heading, only then do you tack.  You have to be pretty confident in that median to make the call of not tacking when you get headed down to it.  I will post an online sailing game in an upcoming post that is great for trying to pick a better median than the computer algorithm picks.   

To bring this back on topic:  in a persistent shift you have to realize that there is no median, that is, there is no direction that the wind will eventually come back to or shift back and forth about fairly reliably, at least not on this leg.  Once you realize that, you throw out your median and just try to get inside the shift (persistent shift tactics).

3  From the previous blogs, your advice about oscillating shifts was clear, simple, and easy to remember.  Your advice on persistent shifts is a bit buried, but I think it is:

get to the side that is going to be (more) upwind before the worst of the shift happens

If you start a leg believing it to be a persistent shift I guess the advice is go to the side that is more upwind?  Is there a snappier kind of advice that might be easily remembered?

Your rephrasing of the advice to "go to the side that is more upwind" is close, but actually that makes it incorrect in many cases.  It is important that the advice be: get to the side that is GOING to be (more) upwind.  The key with a persistent shift is that you are acting on what is GOING to happen in the future.  That is why I emphasize that you should really only act on persistent shift strategies if you are very confident about what is going to happen.  If you are unsure, stick to the fleet, stay safe (less leverage) and try to collect more information.  I throw in the (more) because the wind does not always go back, it is also possible that the wind starts slightly to one side and then it goes more to that side, the (more) is in brackets because that is not always the case as in the scenario below.

Here is a scenario where the "side that is more upwind" is actually the side you want to sail away from:

If you have a long phase oscillating shift and you are rounding the leeward mark in the farthest right of a right phase or you round just as the wind shows the first hints of coming back left, then even though the right is currently noticeably upwind, the left will soon become upwind.  So in here you want to get to the left side now while it is easy to get to because the left side is GOING to be upwind as the wind shifts that way.  If you make it to the left of the fleet then as the left becomes upwind you make it upwind of your competition.

In this scenario someone using the oscillating wind strategy of tacking when the wind first knocks you would start going left on the lifted tack, but then would tack as soon as they realize that they are being knocked.  

In the same scenario someone using the more refined strategy of eating the knock until the wind direction crosses the median might wait until the wind direction has shifted left past the rhumb line (if that is a credible median direction) and then they would tack.

However the sailor in this scenario who realizes that the wind will not have time to oscillate back to the right on this leg because of the long phase of the oscillation will keep on sailing left on the knock until they think that by tacking now, they will get lifted up to the layline.  A safer approach would be to give that layline a bit of safety and just tack once you have a lot of leverage on the fleet – play the fleet not the course- to be safe.

How is this for snappy advice: 

If you REALLY think it is persistent, get inside the shift.

Unfortunately that involves understanding the jargon 'get inside the shift,' but it is just another way of saying the long-winded “get to the side that is going to be (more) upwind before the worst of the shift happens and put some leverage on the fleet.”
Notice that for brevity we have forgotten to add that you should do this without overshooting the mark.

4  Could you define "lifted tack" for the glossary?

Lifted Tack:    The tack that takes you closer to the median, or when there is no discernible median, it is the tack that brings you closer to the mark.

It is tempting to say that the lifted tack is the tack whose angle is closer to being lined up with the rhumb line, but since windward legs are often skewed, especially if you are dealing with persistent shifts which are hard to set courses for, the lifted tack (the tack that takes you closer to the median wind direction) could end up being the tack that takes you away from the mark and in that case it would actually be closer to being perpendicular to the rhumb line.  If you find yourself in the skewed course situation where the lifted tack takes you away from the mark, you have to decide when is your best time to sail the tack that takes you closer to the mark.  Your options are to spend some time sailing on the headed tack (opposite of the lifted tack), or to wait for another favourable oscillation to take you towards the mark but to risk sailing to the layline in the meantime.  If a median phase came along, this would be a good time to use it to go to the mark since sailing the header back to the mark could be costly.

5  Assume the wind has shifted a couple of times — oscillating — on an upwind leg and I am in the last third of the leg — should I treat that last third as a persistent shift if I do not think the wind will shift back again before I get to the windward mark?

Two answers depending on the prediction for what will happen next.  Firstly if you think the wind will continue shifting more to the left for now, but will go right after you have rounded.  In this case get left for the last part of the leg: get inside the shift.  This is if we are speaking only of strategy and it is safe to ignore boat-on-boat tactics.

On the other hand it is a different answer if the wind has already shifted left and you are confident that the wind will stay that way for the rest of the leg.  In this case there is no upcoming shift for you to get inside for the persistent shift strategy.  In this case you are expecting no more changes on the leg, so it is as if we are considering the rest of the leg as a small, skewed leg in stable breeze.  There would be no more advantages to be gained by wind shift strategy so putting yourself in a position to win the tactical battles becomes the only factor.

As I say above, this talk of strategy of the last third of the leg is all based on the usually invalid assumption that there are no boat-on-boat tactics.  In the last third of the beat tactics usually overrule everything else especially in larger and larger fleets.  I was going to say that tactics might not come into play if you were alone out in front, but even then you should usually tack to windward of your competition to deny them leverage.  Maybe I can think up a scenario where there would be negligible tactics on the last bit of the beat, though:

If you were in second place, well ahead of third in the last day of the regatta and nobody can catch you on the scoreboard, but points-wise you can catch first place if you beat them, then first place will just be tacking on you and staying between you and the mark, so it is your job as the second place boat to call the strategy.  However if it is the first place boat that can’t be caught in the standings, the second place boat might just be covering the fleet (reducing leverage) and more or less ignoring strategy.

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