Strategy in tide??
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Category: Dinghy classes
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URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=4696
Printed Date: 24 Nov 25 at 10:00am
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Topic: Strategy in tide??
Posted By: Oatsandbeans
Subject: Strategy in tide??
Date Posted: 29 Sep 08 at 1:23pm
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I am a bit confused over when starting with a tide running parallel to the
line should you start at the uptide end (all other things being equal) or does it make no difference as. Most books plump for this (uptide end), but I suspect that it doesn't make any difference. Any thoughts?? |
Replies:
Posted By: G.R.F.
Date Posted: 29 Sep 08 at 2:56pm
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Starting in any amount of tide offers the astute tactical tidal sailor
options.. These options rely obviously also on the wind. There is a school of thought that sailing in tide is like riding an elevator it's the same for everyone, but in lots of cases it aint. The lighter the wind, the more the tide has an effect, only yesterday I watched our commodore go from 1st to last in one tack off the line when he strayed into a tidal back eddy, and the funny thing, we're a tidal club, but no-one had even noticed it, yet there it was plain as day described in darker coloured ripples for all but the partially sited to view. Again, in danger of turning a post on a thread into a chapter of a tactical sailing book, as a rough rule of thumb if you can start with the tide pushing against your lee bow, you will move faster off the line than all the boats with the tide on their weather bow. Being on Port or Starboard is obviously the overiding factor, or if you could get a port flyer and have the tide on your lee bow whilst the fleet head off on starboard with a tidal weather bow, you would have to do something dramatically wrong not to beat them to the first mark. There is also another fundamental point to back this, in the seconds after the gun, particularly in a big fleet, you can lose tens of places per second, make an error at the top of the triangle and you maybe lose one or two places, so another reason to grab any tidal gains early on. I'll not stray into course bias, but I would be concerned not to over cook a favorable tide then end up over shooting the buoy allowing boats previously under you to overtake by pointing high whilst you're having to free off. This sort of discussion needs illustrations or a chalk board - I'm available for lectures 
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Posted By: Guest
Date Posted: 29 Sep 08 at 3:03pm
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Makes no difference so other factors dominate. That is assuming the line is square to the apparent wind not the actual wind as measured on the mored committee boat. ------------- |
Posted By: radixon
Date Posted: 29 Sep 08 at 3:34pm
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Surely you would start up tide, so when sailing the beat, you will end up drifting slightly with the tide and not have to correct yourself. Got bored trying to draw a diagram, if you start at the down tide end, you will constantly be batteling tide so may end up drifting further away from the windward mark. At least starting upwid, you can tack and sail with the tide assisting you if needed.
(sorry probably waffling rubbish!) ------------- |
Posted By: Guest
Date Posted: 29 Sep 08 at 3:34pm
This is and idealised situation; if the tide is perfectly parallel to a line that is perfectly square to the apparent wind (not actual wind) then it makes no difference. I refer you to mark Rushall's excellent book Tactics. What I am calling apparent wind he calls sailing wind and it's the resultant experienced wind which is made up of the actual wind over the land as experienced on the commitee boat and the tide. If the line is layed square to what the race officer experiences as wind on the committee boat start at the down tide end. A good race offcier would know this and drop the pin back to compensate for this. Fig 6.5 on page 72 illustrates this ... ------------- |
Posted By: G.R.F.
Date Posted: 29 Sep 08 at 3:46pm
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Deletes lengthy post.
Is it worth arguing the point? I suppose it's why there can only ever be one winner.. 
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Posted By: FireballNeil
Date Posted: 29 Sep 08 at 3:53pm
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On the topic of tides, can someone tell me the basics of Hayling tide? Ive not been before, I have hardly sailed in tide and Im going this weekend! ------------- Neil 
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Posted By: Phil eltringham
Date Posted: 29 Sep 08 at 3:54pm
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This assumes all other things are equal!: If the tide is at 90 degrees to the wind i'd say start at the right hand end of the line every time. If its going right to left, starting at the right hand end means you can tack off earlier and get the lee bow up the first half of the beat and hopefully cross the fleet later on. If its going left to right, need to be carful you don't get pushed onto the committee boat, but you'll start with lee bow on startboard (along with everyone else), but at right hand end, have a better chance of clear air. I'm probably wrong about this so comments please... ------------- FLAT IS FAST! Shifts Happen |
Posted By: Guest
Date Posted: 29 Sep 08 at 4:09pm
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At Draycote I am sure that is always the case I think many people don't understand the difference between the sailing wind the competitors experience and the true wind the race officer experiences. Without understanding this I think people will never be able to win at a tidal venue. ------------- |
Posted By: Guest
Date Posted: 29 Sep 08 at 4:58pm
All covered in Mark's Book. http://www.rushall.net/Shop.htm - http://www.rushall.net/Shop.htm ------------- |
Posted By: G.R.F.
Date Posted: 29 Sep 08 at 5:12pm
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That's a contradiction in terms RYA & Tactics
Well it is in our world (windsurfing) as tactically clueless a bunch as ever failed to spot a wind bending into a tidal lee bow as ever sailed..
I must give it a read, if only for a chortle, you never know, it always pays to take the time, just in case someone brings something new to the table. |
Posted By: mike ellis
Date Posted: 29 Sep 08 at 6:05pm
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tidal lee bow? i assume this isn't the same as having the tide on your lee bow (i understand that). Is a tidal lee bow something to do with the tide giving you a header or something? And how does the tide bend the wind??????? I'm happy to admit i'm totally clueless as to any of what GRF is saying. I think i understand Rushall's book though. And i've been sailing in tides for years. ------------- 600 732, will call it Sticks and Stones when i get round to it. Also International 14, 1318 |
Posted By: Roy Race
Date Posted: 29 Sep 08 at 6:11pm
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Not wrong at all. Nice to see someone who doesn't immediately snort coffee all over their keyboards at the mention of the words "lee" and "bow"! I guess your description depends on how many other boats are racing and therefore how hard it would be to tack off. It's probably easier to reduce this to a scenario where you're the only boat and can tack at will, just for the sake of simplifying things. So if the scenario is: no other boats, line dead square to true wind, windward mark plumb straight towards true wind, tide right to left and constant up the course, then in most wind strengths I'd start on port at the down-tide (left) end of the line. This way, I'd get to do the biggest amount of the lee-bow tack possible, which is always, always, always the golden rule when sailing in tide. If the tidal strength isn't constant up the course, say it's stronger nearer the w/ward mark, then the thing to do would be to go middle-left and set up so you approach the mark on starboard, doing your lee-bow tack in the strongest tide. |
Posted By: Guest
Date Posted: 29 Sep 08 at 6:13pm
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Join the club ... ------------- |
Posted By: Roy Race
Date Posted: 29 Sep 08 at 6:14pm
| Also, in the above scenario with constant tide, it's important to remember that port will be the longer tack, so you'd better have a damn good reason not to do it first. |
Posted By: Roy Race
Date Posted: 29 Sep 08 at 6:35pm
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As you can see, by starting downtide, boat A sails less distance to the top mark than boat B, who starts uptide. The differences in course are marked in blue. This would apply in most wind strengths. In very light air however, I'd start at the uptide end, so if it turns into a crapshoot, there's something in the bank. |
Posted By: Guest
Date Posted: 29 Sep 08 at 6:45pm
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Where is the wind on your diagram? and I mean the true wind not the sailing wind. ------------- |
Posted By: mike ellis
Date Posted: 29 Sep 08 at 6:49pm
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it looks like it's straight down the page to me. ------------- 600 732, will call it Sticks and Stones when i get round to it. Also International 14, 1318 |
Posted By: Roy Race
Date Posted: 29 Sep 08 at 6:57pm
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Oops! True wind straight down the screen, due north if you like. "Sailing" or "Tidal" wind gets knocked left by the tide, hence the lift on port. I agree that a top-rate race officer would compensate by dropping the pin-end to leeward and moving the w/ward mark to the left. If that was the case, then the blue lines would be back to equal length, as they would be if there was no tide. |
Posted By: Oatsandbeans
Date Posted: 29 Sep 08 at 7:08pm
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I think that I am in agreement with Rich Perkins, and am complete
dissagreement with the "lee bow effect" man - but I will have to remind myself about this next time and not start at the uptide end of the line. PS and if you want my views on what is written in books - well how many books go on about the "leebow effect" and starting uptide, well they are probably not worth the paper they are printed on!! |
Posted By: Guest
Date Posted: 29 Sep 08 at 7:15pm
If the true wind is straight down the page all you have shown in your diagram is that if you started at the biased end of the line then you sail less distance to the mark ... the bias in you diagram is created of course by the tide. I guess the OP's question was perhaps not specific enough for some ... He said that the tide as running along the line and all other things were equal. From that I would assume the line had no bias to the sailing wind. Your diagram shows a biased line to port which does not fit with the OP's scenario. The bias of course is created in your diagram by the tide as you say.
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Posted By: Roy Race
Date Posted: 29 Sep 08 at 7:30pm
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Yep.
Ok, if the line has no bias to the sailing wind, then it doesn't matter which end you start at. However, I've seen courses like this hundreds of times, because if you show me one race officer who takes tide into account when standing on his anchored commitee boat, I'll show you ten who don't. Of course, then the down-tide end will biased to the sailing wind like you say, but even so I've still seen plenty of people ignore that and go and purposely start at the other end just because it's uptide. |
Posted By: Guest
Date Posted: 29 Sep 08 at 7:48pm
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We are in complete agreement then; the challenege for the race officer is that if they correct the beat for the tide then the run is not square ... Tough job to do well but all the best race officers would allow for the tide when setting their lines. ------------- |
Posted By: G.R.F.
Date Posted: 29 Sep 08 at 9:20pm
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Guys this is too simplistic a view.
For a start that diagram is meaningless without distances, speed of the tide and speed of the wind. I could paint 2 scenarios one in which Boat A gets it and the other that Boat B . Not that both boats would ever get off the line on Port. If ever you get faced with this scenario, you time the flow down the line, roughly calculate it against the time for the first beat. That will give you a rough idea how far down tide you should start, without running the risk of over standing for example. The diagram makes no allowance for the curved course the boats would actually sail. It is correct in it's approach to that particular beat. The longest tack should be made with tide on the lee bow and in reality, all things being equal faced with that line and no obvious wind bias the safest bet out of that line wold be on starboard at the pin end with the back door open to bang over onto Port at the first possible opportunity. |
Posted By: JimC
Date Posted: 29 Sep 08 at 10:33pm
They would? In the extraordinarily unlikely case of the tide being exactly the same for every part of the entire race course then surely they'd still be sailing straight lines... its just the true wind as experienced by a boat drifting with the tide is at a different angle to that experienced by an anchored boat. As soon as there's any variation in the tide, as there always is, its quite another story. |
Posted By: Guest
Date Posted: 29 Sep 08 at 10:48pm
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The OP made no comment on other features that could impact the outcome of the race. Ours is a complex sport and the answer to his question is that it makes no difference if the line is square to the sailing wind and you assume the beat is of a resonable length relative to the line which is usually the case. There are many issues that could give the line bias even if it's square to the sailing wind such as beat length & bias, land features, tidal changes etc etc but the questions was posed on the basis of all other things being equal. If you can understand the question the answer is simple; if you want to introduce other conditions then it gets more complex. ------------- |
Posted By: G.R.F.
Date Posted: 29 Sep 08 at 11:19pm
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Think of it as a graph.
Plot the speed over the water in the given direction Plot the speed of the actual water The time taken to make the windward distance would make the course sailed over the bottom "curve" initially below, then finally above the actual sailing angle possible in the given wind over the given water if it were static. Again depending on the relative speed of the tide over the wind. And depending on the wind staying totally constant. Given one would also sail fast and free initially then tightening higher as one closes on the mark. And in a lot of cases the 'lee bow' effect tightens your angle on the wind especially if there is a 'curve' in the coast for example and for example you started in shallower water than the water at the mark, so many variables as i said it's a bit simplistic. I'm also beginning to wonder if we notice this stuff more on boards than you guys do in your boats, but it really is important to us, races get won and lost by getting it right or wrong and you'll have to trust me when I tell you over the years i haven't had a bad average. You'll have to excuse me for appearing patronising, I know how it can wind y'all up, but tide and light winds are/were my speciality as were racing tactics. If the event were a championship, I'm sure i wouldn't have been the only guy who'd checked the local charts for water depth, scoped the course at low water for channels. PS as a rider to Jim C and the anchored boat v drifting boat comment they would both experience the same 'true' wind strength, but the created wind of the drifting boat would obviously vary the apparent wind on the tack in the direction the boat is drifting, but the effect it has is, depending on the tide speed, to be further forward and therefore not permit the boat to sail as high. However, the boat using it's true wind in opposition to the tide has the 'true' wind strengthened it then in turn creates a stonger created wind over the water flow, but and here's the difference, the tide moves that element of the 'apparent' wind further back permitting the boat to be sailed higher. Again this is only relevant at sub planing speed and when the tide has a larger speed in ratio to the wind speed. There, clear as mud isn't it? |
Posted By: Laser 173312
Date Posted: 30 Sep 08 at 9:03am
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I would of thought a boat would be effected more due to the greater displacement, but as you say there are so many variables it is often a case of learning each venue. I'd always want to start uptide on the lee bow if possible, but then you need to balance this against changes in depth and tide speed, where the wind is on the course, and if the tide is going to turn. Having said that if your uptide and the wind drops you can often still make the mark, if your down tide your stuffed.
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Posted By: Guest
Date Posted: 30 Sep 08 at 9:18am
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Grumpf, I have no idea when I read your posts if you get this or not as you never seem to answer the origional posters question. If ALL other factors are equal and the line is square to the sailing wind and the tide running along the line do you start: a) Uptide ------------- |
Posted By: G.R.F.
Date Posted: 30 Sep 08 at 10:44am
That would depend on the speed of the tide along the line, if it was fast (the tide) in relation to the wind I'd start up tide. (Why? because I wouldn't want to risk over standing) If it was slow but still significant I'd start down tide, but in both cases with it on my lee bow for the longest tack. (Why because I wouldn't want to exclude other tactical options like significant shifts) What is fast or slow? I couldn't quantify in words nor work out in percentages, it's just a feeling I guess your experience gives you (and if you've done that particular venue before) Edit you know re-reading this it could be construed as exactly the opposite of what I mean so I've edited the up/down tide bit. Go back to the sketch if the tide were significant and fast I'd be Boat B, if it were slow I'd go with Boat A for the reasons given (and other probable scenarios) |
Posted By: Guest
Date Posted: 30 Sep 08 at 11:13am
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I think you get this stuff Grumpf but you do a good job of giving the impression that you havn't got a clue ... ------------- |
Posted By: G.R.F.
Date Posted: 30 Sep 08 at 11:20am
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Race me sometime..
I'll show you
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Posted By: Guest
Date Posted: 30 Sep 08 at 11:43am
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Well some of your club mates come over to Westbere in the winter for Laser racing; good close tactical racing with a fair sized fleet. Come along and show us how it's done; no tide of course but very shifty. ------------- |
Posted By: G.R.F.
Date Posted: 30 Sep 08 at 11:58am
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I'm trying to book a last minute dot com half term special with Minorca.
Sort this MPS thing out once and for all. Then I might wander over to Whitstable and remind young Reynolds Perkins et al what happens when you screw with a jedi master of light wind & tide... There's a lovely back eddy over there at certain states of the tide and I remember exactly where it is . That's the thing with us old folk, ask me
what I did yesterday I couldn't tell you, ask me what happened up the final beat in the third race in the Hayling Nationals in '79..... Who goes over to Westbere from our club? Reaches for the black ball.. |
Posted By: 29er310
Date Posted: 30 Sep 08 at 12:00pm
I can vouch for that, absolute tactical nightmare that place, I will be there this afternoon. ------------- ---------------------- International 14 GBR1485 29er 310 for sale Laser 138462 for sale Optimist 4626 For sale |
Posted By: Guest
Date Posted: 30 Sep 08 at 12:02pm
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Let us know when you're ready ...
Dodsey turned up last year ... I don't know if any of these other names are from the dark side http://www.wfsa.info/page001.html - http://www.wfsa.info/page001.html ------------- |