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Text of the page (random words):
ort is the lifted tack in the time that a has been paying attention she does not encounter the red or maroon wind directions n aturally a starts on the lifted tack and every time a gets knocked she tacks fair enough b looked at the windward mark and realized that in the orange phase she was pointing closer to the windward mark on port so maybe b started on port or maybe she started at the barge on starboard and then immediately after the start she tacked onto port b would have been happy after the first shift when she was lifted onto the yellow course even closer to the mark but then when she was knocked back onto the orange course b tacked to stay in phase with the shifts so b continues tacking on the shifts which usually works back home on small courses on say chestermere lake or cadboro bay maybe c had been out on the course checking the wind for 45 minutes before the start which let her notice that although there are bunch of 6 degree oscillations that come and go there are bigger 14 degree oscillations that come and go more rarely c didn t need to know those exact numbers just the feeling of bigger and smaller shifts and a sense of where they come from so c builds a strategy that she should only play the big oscillations and forget about the little ones stay in phase with only the big shifts maybe c didn t even do 45 minutes of research with a compass maybe c just eavesdropped on the race committee channel that was playing at high volume from the pin boat or a coach boat and c overheard the following conversation markset are you happy with the position of mark 1 you look a little right to me affirmative we have been doing a wind trace and as well as some small shifts there are 14 degree oscillations perfectly about our rhumb line at this bearing good work markset then we will leave mark 1 there so c thought perfect oscillations about the rhumb line eh in that case i ll just try to stay on whichever tack takes me closer to the windward mark when i showed this diagram to my partner maura who is a strong radial sailor she was uncomfortable because she thought that i was in danger of encouraging people to bang corners for this reason i have not drawn in the windward mark with some imagination we could put this diagram and scenario in different contexts firstly we could have the windward mark just at the top of thr diagram with c on or just below the layline getting ready to round secondly we could say that the diagram only shows the first third of the beat and c continues on to cross a and b for another four minor oscillations before she tacks again on the next major oscillation in this case c would continue to make similar gains as the big phases roll through alternately if we put the windward mark half way up the diagram for a short course a and b would win because c would have to tack back onto the layline before making it to the big right shift that she had been calling for and without the benefit of having tacked on the small shifts segue about sailing in the middle of the course there are many primarily tactical reasons not to sail in the middle of a big fleet as a and b would have done with this strategy some of the reasons are that the combined effect of dirty air from many boats makes it generally slower if you are not well out in front puffs and shifts often come in from a side and dissipate and can t be used by the time they make it to the middle in the middle with boats to both sides of you no matter which way the wind goes lose to someone in the case of the above diagram especially the boats in the middle have tacked a lot in the diagram i have made tacks cost nothing but a and b have done 7 or 8 more tacks than c so in reality they should be even further behind in almost all boats in almost all conditions tacks are significantly slower than sailing straight unless the tactical gain from playing the shift pays for the cost of slowing down through the tack however in the above diagram you see that a and b s strategy actually hurt them even before taking into account the cost of the tacks to continue on with that train of thought for a bit a tack often has a double cost if you had been purposefully executing a strategy for example you had been sailing out towards pressure or out of some adverse current but then you tack on a nice shift after tacking on that shift you have to throw in another tack to get back to heading out towards the puff or current relief the cost of tacking can be even bigger if you bring in the tactical consideration that while you throw in this hitch tacking and tacking back the rest of the boats around you that didn t tack will be continuing out towards the favoured side this lateral separation on the race course becomes leverage against you if you are sailing towards a shift if you were sailing to a puff throwing in the hitch means you spend less time out in the stronger wind of the puff at the edge of the course if you were sailing out of adverse current the hitch keeps you in that current for longer so if you throw in the hitch it had better gain you a bunch of ground to pay for all those disadvantages the payoff to emphasize the slight difference in course position resulting from the different strategies in the above diagram at the top of the diagram i have drawn thin black ladder rungs i drew these ladder rungs perpendicular to the rhumb line because according to the race committee the course is perfectly square but there are other ways of thinking about the relative position of the three boats if we don t take the rhumb line into account and stay in the present we have the red ladder rung red for the red wind phase corresponding to the instantaneous wind direction which shows that c is even further ahead of any boats to the left of her i have also drawn in a brown ladder rung corresponding to the average of the red and maroon wind directions because c is not differentiating between these smaller wind fluctuations and is calling them one phase according to this brown ladder rung corresponding to the major right phase a is even further ahead of the boats to her left it is worth noting that because c is directly upwind of b she has no leverage on b so the different angles of the ladder rungs have essentially no effect a last scenario in a fourth and final scenario for the diagram we can imagine that there is no major phase that is there is no back and forth to the larger oscillations instead the 14 degree right shift was a one time event for example c saw a wind line on the right that a and b overlooked and so c ignored the oscillations put all her eggs in one basket and pinned it out right the wind line magically came in at the right time and c just beat a and b to the mark in this scenario where the 14 degree wind shift was a one time event this is effectively a persistent shift and this scenario would make c is a corner banger one of the big things that i am trying to illustrate is that by comparing the fourth scenario with the first you can see that that the winning strategy for a persistent shift is the same as for a long phase oscillating pattern that takes longer to oscillate through its major phase than the length of one beat here we come back to the importance of time scale often in a very slow oscillating shift the legs of the race must be raced like persistent shifts this one of my justifications for talking so much about oscillating strategy in a series supposedly about persistent shifts for your homework today try playing this game http www sailracer net windgame when i was searching around for online software or games that could help me illustrate these racing scenarios i came across this interesting site it claims to use a real weather station as the input for the game s wind wind oscillation is real from ultra sonic weather station at nannycay marina bvi so no wind no game the point of the game is to try to beat sail racer s strategy algorithm there is no dirty air no racing rules of sailing or collisions the boats are always sailing close hauled at the same speed except for out of a tack but tacks are very inexpensive a mere 10 of boat speed for one second so it is almost completely a strategy game though you do have the computer s boat to check in with and copy if you are a defensive minded tactician enjoy the next blog will use an example from this game posted by ian e at 5 08 pm no comments email this blogthis share to x share to facebook share to pinterest 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 i f the wind shifts to the middle direction at the beginning of the leg you can do whatever you like i f 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 t wo 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 fir...
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