LEE BOW EFFECT

   But doesn't the RO notice the tidal current, and offset the windward mark?

It can be good to 'lee-bow ' the tide, but only because the tide is always variable across the course.

If you can stay close to the shore in weaker current by pinching a bit, it does gain a lot over those who foot off into stronger adverse current, - reducing the apparent wind, so they sag off even more - and they also have to do extra tacks.

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I luv Wight Send Private Message Find Member's Posts Visit Member's Homepage Really should get out more Joined: 28 Jan 05 Location: United Kingdom Online Status: Offline Posts: 628	Post Options Post Reply Quote I luv Wight Report Post Quote Reply Topic: LEE BOW EFFECT Posted: 12 Oct 11 at 6:11pm
	But doesn't the RO notice the tidal current, and offset the windward mark? It can be good to 'lee-bow ' the tide, but only because the tide is always variable across the course. If you can stay close to the shore in weaker current by pinching a bit, it does gain a lot over those who foot off into stronger adverse current, - reducing the apparent wind, so they sag off even more - and they also have to do extra tacks.
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2547 Send Private Message Find Member's Posts Really should get out more Joined: 11 Aug 11 Online Status: Offline Posts: 1151	Post Options Post Reply Quote 2547 Report Post Quote Reply Posted: 12 Oct 11 at 5:42pm
	Poor old GRP gibbon ... he's having a bit of trouble with his maths ... If you have a true wind of 5 knots (i.e. the wind over the ground) and a 5 knot cross tide (i.e. 90 degrees to the true wind running left to right) you have a apparent wind of 7.07 knots which is 45 degress different to the true wind ... in the gibbons example you sail straight to the windward mark on starboard ... if it's laid square to the line by a race officer who has laid a windward leg to the true wind as he is anchored to the land and isn't experienceing the apparent wind which all sail boats do ... This example is nothing to do with the lee bow effect .... which as JimC says is a fallacy ... Edited by seamonkey - 12 Oct 11 at 5:43pm

JimC Send Private Message Find Member's Posts Visit Member's Homepage Really should get out more Joined: 17 May 04 Location: United Kingdom Online Status: Offline Posts: 6662	Post Options Post Reply Quote JimC Report Post Quote Reply Posted: 12 Oct 11 at 4:36pm
	OK, GRF I think I see what you are talking about... To my mind that's an entirely different thing to the classic "lee bow/tide" fallacy. Am I right in thinking you're saying there's (often?) a tactical advantage to taking the tack that gets you nearest to the mark most quickly... Edited by JimC - 12 Oct 11 at 4:36pm

G.R.F. Send Private Message Find Member's Posts Visit Member's Homepage Really should get out more Joined: 10 Aug 08 Location: United Kingdom Online Status: Offline Posts: 4028	Post Options Post Reply Quote G.R.F. Report Post Quote Reply Posted: 12 Oct 11 at 4:15pm
	OK just for the slow (and probably ever so slightly retarded) I will explain why, even in a constant tide, it is better to take the lee bow first, if it is on offer. Read any tactical book, they'll all explain about getting away in clean air at the start, and as I used to say during those heady days when people would queue for hours just to hear me speak on the subject, in a 60 strong start line, make any kind of mistake at the gun and potentially you can lose 59 places in one seconds hesitation, make that same mistake at the weather mark and you might not even lose one place. So at the start there are two tacks you can take (assuming you can get out the back door of the pin end) there is say a 5 knot cross tide (And ignoring any time/tidal calculation you might have made re time of the beat and virtual position of the weather mark in relation to the end of the line you start at.) there is only 5knots true wind, so on the one tack lets say starboard with the tide going right to left across the course, with the water heading your way you'll be going down tide at five knots and <insert appropriate tide v wind calculation to establish boat speed over the water> say six knots over the water, whereas on the other tack you'll be maintaining station over the bottom but making windward ground at <insert calculation of combined forces of five knots tide and five knots wind, say nine knots, so those elements of the fleet that have taken the down tide tack first will be travelling faster over the bottom sideways, but slower through the water toward the weather mark than the boats that take the uptide tack initially, they move slower sideways over the bottom but make ground to weather and over the water faster, so at the half way mark are closer to their final destination. OK, logic says yeah but.. the reverse will be true in the second leg, but hey you're a tactical racer, where would you rather be at the half way mark? And how many races have you ever experienced where conditions remain exactly constant throughout an entire beat, never mind the whole race. Sure in deep water Ocean racing with miles of mind numbing boredom going on, it may make no odds, but this is about the cut and thrust of small boat tactical division by error and he who makes least wins.. I know what I'd do. Edited by G.R.F. - 12 Oct 11 at 7:42pm
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2547 Send Private Message Find Member's Posts Really should get out more Joined: 11 Aug 11 Online Status: Offline Posts: 1151	Post Options Post Reply Quote 2547 Report Post Quote Reply Posted: 12 Oct 11 at 9:49am
	Definition: "The lee-bow effect" is a term used to describe what may or may not happen when sailing directly into tide upwind and what may or may not happen if you pinch up to put the tide on your lee bow ... assume linear tidal flow over the area. Some silly gibbons think something magical happens if you pinch up and have the tide on the lee bow as to opposed to footing off and having it on the weather bow. These are the same people who are deluded enough to try and invent perpetual motion machines Clever monkeys like JimC and Mr. Perry know how to add vectors and know it does not exist. Now of course it is a jungle out there and clever monkeys know that the tide is often stronger or weaker in different places and taking advantage of this can make huge differences but this is not some juju magic of the mythical leebow effect ... I think Perry's mid ocean example should be able to be understood be even the most feeble minded gibbons.

didlydon Send Private Message Find Member's Posts Far too distracted from work Joined: 15 Oct 08 Location: Margate England Online Status: Offline Posts: 280	Post Options Post Reply Quote didlydon Report Post Quote Reply Posted: 12 Oct 11 at 9:13am
	Would I be right in saying that you'd get extra "lift" on one tack with the action of the additional tide flow over the foils pulling them to windward? Whereas, on the other tack, you wouldn't cos the tide will be pushing you away? We need some sort of animation / pictures to show this.... anybody?
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osproject Send Private Message Find Member's Posts Visit Member's Homepage Newbie Joined: 06 Oct 11 Online Status: Offline Posts: 1	Post Options Post Reply Quote osproject Report Post Quote Reply Posted: 12 Oct 11 at 8:58am
	You wont physically point higher. You can only sail as high as your sails will let you. But your COG will be higher. Try sailing in 7knots of tide and see what happens on opposite tacks. :-)

Pierre Send Private Message Find Member's Posts Visit Member's Homepage Really should get out more Joined: 15 Mar 04 Location: United Kingdom Online Status: Offline Posts: 1532	Post Options Post Reply Quote Pierre Report Post Quote Reply Posted: 12 Oct 11 at 8:15am
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Rockhopper Send Private Message Find Member's Posts Really should get out more Joined: 16 Nov 07 Location: Eastry Online Status: Offline Posts: 642	Post Options Post Reply Quote Rockhopper Report Post Quote Reply Posted: 12 Oct 11 at 8:14am
	The tide at our place is never the same strengh over the course we have rips when the ground is say five six feet shallow than other areas creating more tide closer to the shore you get less tide and to top it all off on the back of the pier the tide goes the opposite way It does take a while to learn the tides and how and when to use the lew bow effect but ti does work wonders in three knots of tide
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sargesail Send Private Message Find Member's Posts Really should get out more Joined: 14 Jan 06 Location: United Kingdom Online Status: Offline Posts: 1459	Post Options Post Reply Quote sargesail Report Post Quote Reply Posted: 12 Oct 11 at 8:03am
	Maniac, Except that when you try and prove that it doesn't work. And again I agree with your last point - but that doesn't explain why in those circumstances one "feels" the lee bow effect.