Genuine Lee-Bow Question for GRF (not a p*ss-take)
Printed From: Yachts and Yachting Online
Category: Dinghy classes
Forum Name: Dinghy development
Forum Discription: The latest moves in the dinghy market
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=11449
Printed Date: 16 Jul 25 at 7:31pm
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Topic: Genuine Lee-Bow Question for GRF (not a p*ss-take)
Posted By: GarethT
Subject: Genuine Lee-Bow Question for GRF (not a p*ss-take)
Date Posted: 30 Apr 14 at 10:23am
|
A quick question on behalf of a young windsurfer: Assuming ‘your’ lee-bow effect is the same as mine (tide
pushes you towards the wind thus increasing the apparent wind and moving it round
giving you a ‘lift’), does it have the same impact when you’re planing upwind
on the fin as it does in more of a ‘displacement’ mode, or is it reduced as
there is much less of the board in contact with the water? Thanks |
Replies:
Posted By: L123456
Date Posted: 30 Apr 14 at 11:34am
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Before you start off the exponent of perpetual motion you'd do well to start of by defining your terms. What are you describing when you talk about the lee bow effect ... remember you are not anchored to the sea bed but moving on the water as that moves over the seabed if there is current ...
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Posted By: GarethT
Date Posted: 30 Apr 14 at 11:38am
| I thought I did define what I was talking about. |
Posted By: iGRF
Date Posted: 30 Apr 14 at 11:46am
In answer to your question yes. There are often times here at Hythe when the wind is a light sea breeze from the East, if the tide turns it becomes possible to plane on a shortboard because of the additional input of a couple of knots on not just the fin, but everything which enables you to get enough momentum to get on the plane generate more created wind the combination of which gives you full planing apparent wind. Here in Dinghy world there have been a couple of would be big boat book sellers saying there's no such thing as lee bow effect, which is total bollox. The key particularly for us windsurfers is the added element that the tide brings to the true wind enabling us to albeit often dynamically, but just the same get ourselves up and on the plane. Up wind off the Fin? yes it still works but at our venue not quite as well because often the angle is too shallow, but I can assure you, you'll go faster, cover more ground on the tack with the tide on your lee bow than you will on the other downside tack, particularly if the planing threshold is part of the equation. Now finally, where it doesn't make any difference and the big boat boys have their point, offshore, open water, it does make no odds, given what you gain on one tack you lose on the other, however the point I used to make on tactical lectures was always go faster earlier, why? The same reason you don't screw up the start. At the start of a race with sixty odd boats make a couple of seconds mistake at the start you lose sixty places, make the same couple of seconds error at the top mark you might only lose one or two places if that, so following that logic, better to go faster earlier.. The thing about foil size is just relevant to the speed, if you're just using the fin then chances are you're planing or trying to, and centreboards are only efficient in sub planing mode anyway, so it's horses for courses and more energy is more energy wherever it comes form, the more you have the faster you go.. So Tide either powers you up or depowers you, it's that simple. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Rupert
Date Posted: 30 Apr 14 at 11:47am
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Tide moves boat, causes apparent wind. Works for me. Either you benefit or you have things worse. Even the RYA learning to sail books have it in.
So the basic question is, does the tide move an item with a small surface area more slowly than one with a large surface area? I want to say no, they move at the same speed, but I'm a pondie, who what do I know?! ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: iGRF
Date Posted: 30 Apr 14 at 11:57am
Tide moves everything in it, which is often enough to sail from even if there is absolutely no wind. We did a race on the Thames once, it was dead still, yet we raced on both tacks all the way from Putney Bridge to Barnes or wherever 120+ boards all purely using just the river flow. Lee bow both tacks, lovely jubbly and loads of pumping protests.. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: L123456
Date Posted: 30 Apr 14 at 12:00pm
I fear what you describe is a misunderstanding of physics ... I start with a simple question ... Imagine you are out at sea beyond the site of land ... You are sailing in 5 knots of breeze ... How do you know if that is 5 knots of gradient wind or 0 knots of gradient wind and 5 knots of current?
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Posted By: NeilP
Date Posted: 30 Apr 14 at 12:00pm
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Doesn't necessarily move it more slowly, certainly exerts less force, which is what we're concerned with... ------------- No FD? No Comment! |
Posted By: GarethT
Date Posted: 30 Apr 14 at 12:04pm
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That's the bit I'm struggling with. School-boy physics was a long time ago....... Assuming that motion is the result of forces acting on the craft, the mass would stay the same but as you get planing and much less surface is in contact with the tide the force pushing you upwind would reduce proportionally (or perhaps proportional to the square?), whilst the force pushing forward would stay the same. If this assumption is correct then I'm supposing that the impact on the apparent wind of the lee-bow tide will reduce once the board is up and flying (but as Graeme says, the affect will help you get up and flying).
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Posted By: GarethT
Date Posted: 30 Apr 14 at 12:09pm
Maybe one might do one's homework and know what the tide is doing. Then one can choose in certain conditions whether to sail with the tide on your lee-bow or your transom where the tide is strongest (e.g. crossing a channel), thus choosing whether to be lifted or headed where the effect is at its biggest.
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Posted By: L123456
Date Posted: 30 Apr 14 at 12:11pm
Best do some revision; nothing special is happening when you plane ... Current creates apparent wind that is added to the gradient wind which results in the actual sailing wind we experience. If the gradient wind is constant and the current changes direction then we will experience a change in the wind we are experiencing when sailing ... nothing more mystical is happening than that. There are those who think the current flows over their foils in strange ways creating mystical benefits but they are deluded ... your foils are passing through the water ... what is happening to them is no different if that body of water is stationary relative to the land or moving (i.e. there is current) ...
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Posted By: GarethT
Date Posted: 30 Apr 14 at 12:14pm
My question is about simple forces, not about strange flows over foils. Motion is the result of multiple forces. I'm questionning if less of the craft is contacting the water, will the water apply less force to the craft. If all other forces remain the same, the resultant direction will be different. No?
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Posted By: L123456
Date Posted: 30 Apr 14 at 12:14pm
You are not addressing the simple question ... you are out at see miles from anywhere ... the wind/current are constant ... you have no GPS, charts or internet ... you just have 5 knots of sailing wind ... how can you tell if it is current or gradient or a mix of both? ... Here is a clue ... you cant ...
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Posted By: L123456
Date Posted: 30 Apr 14 at 12:17pm
Well if your craft is anchored to the sea bed then there may be a discussion to be had as the current is creating flow over the hull & foils but as I assume you are not anchored nothing changes.
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Posted By: GarethT
Date Posted: 30 Apr 14 at 12:47pm
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Have younot read any of my questions? The tide has an impact on apparent wind, yes? The force applied by the tide on the boat is proportional to the amount of boat/board in contact with the water (or perhaps the square of the amount as it's area), yes? That's all I want to know. Windsurfers tend not to race miles out at sea where no-one knows what the tide is doing, so I don't know how my questions lead you there.
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Posted By: L123456
Date Posted: 30 Apr 14 at 1:03pm
yes - current as a component of apparent wind to the gradient wind creating the sailing wind you experience ...
Tide does not apply any force to the boat ... I think this is where you are getting confused. Unless of course your boat is anchored; if it is anchored the current will flow over the hull and foils creating forces ... If you boat if free floating the boat will move with the current which is why you experience the apparent wind you talk about above ... |
Posted By: GarethT
Date Posted: 30 Apr 14 at 1:05pm
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So the boat will move without a force being applied to it? Wow. Someone should tell Newton. I'm just going to have to let you be wrong on this. Thanks Graeme for answering the question.
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Posted By: L123456
Date Posted: 30 Apr 14 at 1:17pm
The boat moves (relative to the land) in tide because the whole body of water is moving not because there are forces being applied to the hull and foils by current ... You are not the only one who struggles with this ... I suspect it is because most people can't detach their brain from referencing everything to the land ... you need to think about these issues relative to the water ... which may well be moving over land. This whole conceptual mind bender becomes even more confusing, for some, as we race round marks that are fixed to the land and as such our whole playing surface is moving relative to the land and the turning points that form the course. Because you can't get your head around this issue don't assume I am wrong; go and do some reading and educate yourself... |
Posted By: GarethT
Date Posted: 30 Apr 14 at 1:19pm
| Read Newton |
Posted By: L123456
Date Posted: 30 Apr 14 at 1:22pm
Yes ... you'd do well to start there ...
I assume your "education" was more biased towards the arts & humanities ... Anyway ... I have tried to help you; I can do no more. I have every confidence in my own education and understanding on this matter ... |
Posted By: JimC
Date Posted: 30 Apr 14 at 1:23pm
No. The energy to propel the boat comes from the relative motion of the air and the water. Which one is moving how much in relation to the sea bed or stars above makes no difference to how the boat sails relative to the wind and the water - hence grfs current example. What really confuses this debate online is that what, for example, grf calls a lee bow effext is quite a different thing from what some books in the 50s gave the same name... |
Posted By: GarethT
Date Posted: 30 Apr 14 at 1:24pm
| Wrong again. Physics, maths, and a chartered engineer, but crack on. |
Posted By: GarethT
Date Posted: 30 Apr 14 at 1:27pm
| Sorry Jim if I wasn't clear. In my head I'm isolating individual forces, to understand if they vary in the different states, then putting them back together for a resultant force. |
Posted By: L123456
Date Posted: 30 Apr 14 at 1:31pm
Exactly ... hence my earlier 5 knot example ...
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Posted By: GarethT
Date Posted: 30 Apr 14 at 1:35pm
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Again, I'm not talking about propelling the boat. I'm talking about the sideways component of the force on the boat, in the absence of all other forces.
Of course, you perpetual motion machine has something moving in a 3 dimensional space without a force being attached. A question. How does the boat not sink. What applies a force equal to the force due to gravity? |
Posted By: iGRF
Date Posted: 30 Apr 14 at 1:38pm
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They get so confused, it's because they're sitting on their brains..
As to what's happening, you have to ask yourself what happens when you spin out.. Is the spin out any better or worse depending on the size of the fin? No it isn't. Both foils, the sail and the fin act in concert to generate lift, all the action of the water does is either benefit or take away from the power being generated in the sail, if you've windsurfed as you probably have it becomes second nature because you feel it so much more readily than sat in a boat. We have tidal lifts and headers to deal with as well as wind lifts and headers, where we sail there's a tidal bend and it works just like a wind bend, you have to get the middle right or pay a terrible price. OK that's a bit off the subject, which was wether the fin size makes a difference to the pressure the tide is applying and tbh I don't have tank test statistics to back up what I'm writing, but the logic is you should match the fin to the sail anyway to provide what you need, in which case no it doesn't given you're sizing for optimum performance anyway. As to the term lee bow effect, there are two common things, one is the effect we're talking about here with tide on the lee bow and the old chestnut used to be wether pinching to get your nose above it works or not which I would say probably not in boats, but with a board and pumping it certainly feels that it does in sub planing conditions but I'm not going to go out on any limbs arguing the point. The other Lee Bow effect is that prevalent on the start line if you let the boat underneath you get it's nose ahead and the wind bends between you and the boat on your lee bow which heads you making you fall back even further which then causes you to be buried by the boat above. Hence the one in three division rule just after the gun which is important that you become one of, then again a few minutes later as the boats/boards settle in their tracks. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: GarethT
Date Posted: 30 Apr 14 at 1:42pm
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Anyway, I'm done. Don't need to convince anyone else.
Have a jolly afternoon. |
Posted By: iGRF
Date Posted: 30 Apr 14 at 2:35pm
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I just had a thought, the answer to the original question is that the effect is reduced. Not due to any physical differences, it's time. Because you'll spend less time in the tide planing off the fin than you would displacement sailing with a plate, the effect tide plays as part of your windward effort is reduced. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Rupert
Date Posted: 30 Apr 14 at 2:45pm
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I love these arguements... everyone is actually saying the same thing, but in different ways.
Stand up in a convertable when driving along the road. You are the boat, the car is the tide, the thing blowing in your face is apparent wind. You are still going the same speed as the car whether you are hiding on the floor (large amount in the water) or standing on the seat (small amount in the water). ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: iGRF
Date Posted: 30 Apr 14 at 2:58pm
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It's still a valid question though, and as it turns out the opposite to what I'd originally thought.
Which would be the same answer to foiling moths for instance. Tidal lee bow would play less of an overall effect than if they were lowriding, not because necessarily the physical size of the plate or area beneath the boat, but just because the time they'd spend in the tide would be less if they were up on the foils. Then again if that tide helped them to get on the foils in the first place and I bet there are instances where that can happen, I.E. they could foil on one tack but not on the other because of the tide... Then which tack would you take off the start line, the answer to which completely throws all that counter lee bow revisionism written by those idiots, right out of the window... ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: L123456
Date Posted: 30 Apr 14 at 3:05pm
I'd be happier if I actually thought that to be the case ... I fear some people struggle to understand the interaction of current and how that impacts apparent wind experienced on boats that are not tethered to the earth when racing around bouys that are ... It is simple vector arithmetic ... |
Posted By: GarethT
Date Posted: 30 Apr 14 at 3:20pm
| So by that are you saying that you agree that with the tide on your lee-bow ".....tide pushes you towards the wind thus increasing the apparent wind and moving it round giving you a ‘lift’......" or not? |
Posted By: L123456
Date Posted: 30 Apr 14 at 3:30pm
I think the way you are expressing the above indicates confusion. If the current is running perpendicular to the gradient wind the sailing wind would be backed or veered depending on the direction of the current. My course over the ground with the current on my lee bow would be higher than if there was no current.
|
Posted By: GarethT
Date Posted: 30 Apr 14 at 3:32pm
| So you mean yes? |
Posted By: GarethT
Date Posted: 30 Apr 14 at 3:40pm
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And for the balancing forces bit, the best analagy I can come up with is imagine 2 balloons, one filled 3 quarters with water, and one filled with air, with just enough water to stop it blowing away. If drop them in a stream, I would expect the one with 75% water to be taken predominantly by the current, whilst the one that's mostly air would be taken predominatly by the wind. This is due to a different balance of forces acting on them. My question re a planing board is how different the balance of forces are and whether the significance of the tidal force is reduced.
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Posted By: L123456
Date Posted: 30 Apr 14 at 3:43pm
Well probably no they way you have expressed it ... but I suspect you mean something similar. When we talk about lifts and headers we are talking about variances of the wind around a mean that we can exploit for tactical advantage. I would not describe this effect as a lift. The current, assuming it is constant for the period of time under discussion, would not be a lift but rather a permanent change in sailing wind direction that would be unchanged until there was a change in current or gradient wind. |
Posted By: GarethT
Date Posted: 30 Apr 14 at 3:46pm
Whatever. Everyone else knew what I meant. |
Posted By: JimC
Date Posted: 30 Apr 14 at 4:03pm
I fear that many on line arguments I've witnessed and participated in have demonsrrated that there is nothing simple about vector arithmetic involving multiple frames of reference. Next DDWFTTTW... |
Posted By: L123456
Date Posted: 30 Apr 14 at 4:08pm
Indeed; but the impact of current on sailing wind is pretty simple ...
|
Posted By: GarethT
Date Posted: 30 Apr 14 at 4:20pm
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Back to the balloons. They're in the same wind and tide, yet due to their different physical characteristics they experience different forces and different things happen to them.
Back to the board. In displacement mode (mast track forward, dagger board down, 2.9m in contact with water) the physical characteristics are very different to in planing mode (mast track back, daggerboard up, 1m in contact with the water) hence questioning if the impact of wind and current will be different, as with the balloons. |
Posted By: Bootscooter
Date Posted: 30 Apr 14 at 6:26pm
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I totally understand your question Gareth, but sadly am unqualified to answer.
Perhaps a windsurfing forum would be more productive... ------------- |
Posted By: GarethT
Date Posted: 30 Apr 14 at 6:49pm
| Well, that was why I addressed the original post as I did, not realising I'd engaged the pompous troll magnet. |
Posted By: Rupert
Date Posted: 30 Apr 14 at 7:26pm
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You'd think the sail/wind would become the more important factor, just through logic, and I like the balloon example, but the difference is that the boat is using the wind as a driving force, whereas the balloon is simply blowing down wind with the tide altering direction/rate slightly. Whether this difference makes any difference, I don't know.------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: iGRF
Date Posted: 30 Apr 14 at 7:57pm
ha, unlikely, chances are you'd get the same answer from the same old t**ser.. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Presuming Ed
Date Posted: 30 Apr 14 at 9:47pm
You've done it now... |
Posted By: Kev M
Date Posted: 30 Apr 14 at 10:58pm
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Does a boat/board in tide with no wind move at the same speed as the tide relative to the land? Rupert's analogy of the car is fine except the co-efficient of friction between the car and the person is massive which makes the person travel at the same speed as the car. Water is slippery, so does the object move at the same speed as the water or does the water move past the object faster with sufficient friction to take the object with it but with not enough friction to take it at the same speed? ------------- Successfully confusing ambition with ability since 1980. |
Posted By: GarethT
Date Posted: 30 Apr 14 at 11:14pm
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I think that in the absence of other forces the tide would eventually accelerate the boat to be travelling at tide speed and direction, but In the real world there would be forces due to windage/leeway acting in the opposite direction preventing this.
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Posted By: Rupert
Date Posted: 30 Apr 14 at 11:15pm
I hope so - the alternative is painful... As to whether it happens on water, there must be some loss - is it more or less for a large object compared to small, or does it make no difference? ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: L123456
Date Posted: 01 May 14 at 9:42am
Yes ... or as close to as is possible to measure. Water is not as slippery as you think which is why dinghy sailing is so pedestrian compared to ice sailing. Even a foiling moth which has a performance jump over conventional dinghies due to considerably less wetted area would be considered an utter dog compared to an ice yacht. I suspect this in part is the crux of the OPs question; when a craft moves from displacement to planing they are still moving over the land on the "magic carpet" created by the tide. |
Posted By: GarethT
Date Posted: 01 May 14 at 10:07am
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I’ll have one last go….. I’m supposing that the ‘simple vector arithmetic’ approach
assumes a steady state condition, with the vessel up to maximum speed (over the
ground) induced by the tide. In real life, the tide is not a conveyor belt that
instantaneously accelerates the vessel to that speed. The acceleration to the
steady state will depend on the forces acting on the vessel. Whilst racing round a course, ‘steady state’ does not exist
for very long as it will always be impacted other factors (waves, course changes,
etc) so I am interested in the moments before steady state is achieved, e.g.
the time it takes to get back to a steady state. I am thinking on the basis of the force applied by the tide
on the vessel is pressure x area, and force also equals mass x acceleration.
Thus, acceleration = (pressure x area)/mass. As the steady state is approached
the pressure tends to zero, so this is looking just at how quickly we
accelerate to the steady state. Now, for my example (board in 2 different configurations)
the mass will remain the same, as will the pressure, so I think I’m concluding
that the acceleration is proportional to the area. In conclusion, once the tide has had it’s full effect on
both configurations the apparent wind change would be the same for both, but
with the daggerboard down and the mast track forward you would reach the point
of maximum tidal assistance sooner but the maximum would be the same. Clearly this is still a very big simplification. Still not sure if I can answer the question I was originally
asked though, which was if the effect of tide on the lee bow should be
considered when choosing when to switch from one configuration to the other? |
Posted By: L123456
Date Posted: 01 May 14 at 10:26am
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I think if you make your datum the water rather than the land you will find your own answer ... unless of course you are anchored. |
Posted By: GarethT
Date Posted: 01 May 14 at 10:31am
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Thanks Sheldon.
Does anyone else have a constructive comment on my conclusion? |
Posted By: L123456
Date Posted: 01 May 14 at 10:35am
That was constructive; I think you are struggling with the concepts because you continue to use the land as your datum ... the current does not act upon a vessel floating upon it, once a steady state has been reached, as the whole mass and anything floating in it all moves as one at a constant speed over the land ... constant speed means no change in velocity i.e. no acceleration which means no forces actioning upon the vessel.
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Posted By: GarethT
Date Posted: 01 May 14 at 10:37am
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Once a steady state has been reached?
Wasn't that the whole point of what I wrote? |
Posted By: Rupert
Date Posted: 01 May 14 at 11:59am
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I can't believe there is a real world noticable difference (one that would decide strategy) between the time it takes for a planing board and a displacement board to reach the point of steady state, compared to the decision that will need to be made over where the tide or wind is strongest or most favorable in direction. I'm glad you did that last explanation - I hadn't figured out that it was the transition time you were interested in - how long does it take a piece of wood (say) thrown into a current to accelerate up to max speed? Much more than the blink of an eye? An easy experiment if you live near a river! ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: GarethT
Date Posted: 01 May 14 at 12:05pm
| I think the more significant factor will be that you point lower when on the fin, so it might be that one configuration gets the tide on the lee bow while the other doesn't. |
Posted By: iGRF
Date Posted: 01 May 14 at 1:00pm
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"Still not sure if I can answer the question I was originally asked though, which was if the effect of tide on the lee bow should be considered when choosing when to switch from one configuration to the other?"
If that's the question you need to answer then it's simple, if the tide is sufficient to ensure you can plane off the fin upwind then you should switch. This happens quite a lot in the RSX class where the centreboard is so pathetically small and the board is so short, it's not that efficient anyway, so every opportunity to sail off the fin is favoured. The answer therefore (If it is RSX or Techno)is most definitely yes, switch and get up on the fin, unless of course by doing so you slip from lee to weather bow with the tide, then you're screwed. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: GarethT
Date Posted: 01 May 14 at 1:03pm
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Cheers Graeme. |
Posted By: L123456
Date Posted: 01 May 14 at 4:45pm
I fear you are slipping back into the mythical lee bow myth that something magical happens if you can pinch up and get the current on your lee bow rather than the weather bow ... sadly it doesn't. All current does is add an apparent component to the gradient wind to create the sailing wind ... |
Posted By: iGRF
Date Posted: 01 May 14 at 4:49pm
I fear you're sadly slipping into the mythical delusion that sailing a laser qualifies your opinion to be regarded as anything much more than a retarded childs.... sadly it doesn't, so nobody cares what you think. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: GarethT
Date Posted: 01 May 14 at 4:56pm
*sigh* |
Posted By: L123456
Date Posted: 01 May 14 at 4:57pm
iGRF you have already proven you have no idea with your laughable attempts at boat design and explanations of perpetual motion ... anyway ... I'm clearly wasting my time here so I shall leave you to further dispense your infinite wisdom ... no doubt you will want the last word on this topic so off you go fill your boots ....
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Posted By: laser193713
Date Posted: 01 May 14 at 4:58pm
Seeing as all the marks on the course are anchored to the land I would say it would be pretty good to use it as the datum, wouldn't you?
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Posted By: Do Different
Date Posted: 01 May 14 at 5:09pm
Anchored marks  Well I've been reading this go around and around and thought the same. |
Posted By: L123456
Date Posted: 01 May 14 at 5:11pm
If course it is relevant when thinking about racing strategy over the course but not that helpful when trying to discuss the "lee-bow effect" if indeed such a phenomena exists ... Clearly an internet forum isn't a suitable place for explaining such things ... a pen, paper and a pint would achieve a result far quicker ... anyway I shall leave you in the genius hands of tactical guru iGRF ... the man who whipped a load of dingos at his first attempt the RS100 nationals ... |
Posted By: scotsfinn
Date Posted: 01 May 14 at 5:14pm
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Depends on the quality of the mark laying team - been to regattas where the marks aren't anchored to the ground a few times (not a constructive comment I know .... but true all the same) - let's not get too serious Where are the gems from iGrf - thought we'd get more GRFSCIENCE than we've had so far. Is he unwell .... or is he getting shy in his old age? ------------- Largs Sailing Club. D-Zero GBR 57, B14 744 www.blueseaconsultingllp.com |
Posted By: iGRF
Date Posted: 01 May 14 at 7:44pm
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It's a windsurfing question I've answered it, confirmed what Gareth thought anyway, we're both in agreement and we know the answer is FACT, not opinion, conjecture, weird Laser science and provided by a Racing windsurfer of Olympic standard who once coached the current RYA coach who now coaches our sailor and who's nephew is the No 2 Olympic contender.
Nothing to do with Lasers really, we only tried to help as one would a 'special' person who can't quite understand things... ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: GarethT
Date Posted: 01 May 14 at 7:56pm
| Interestingly, the same theory was also taught to my laser sailing son by the RYA head coach whilst away at an international event. |
Posted By: iGRF
Date Posted: 01 May 14 at 8:27pm
|
Well ironically the same theory also works for me in my Laser as well, so maybe Eric (Twiname) who taught it to me all those years ago wasn't wrong after all.. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Rupert
Date Posted: 01 May 14 at 10:29pm
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The theory isn't wrong, just the name.
------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: Chris 249
Date Posted: 02 May 14 at 3:15am
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I may have missed something but hasn't Rupert's nailed it? It seems that some people are slinging off at each other because of a naming issue that has them talking at cross purposes. Some old-worlde big boat navigators (among others) used to talk of a "mythical lee bow myth that something magical happens if you can pinch up and get the current on your lee bow rather than the weather bow", as 192444 says. The mythical lee bow effect is a claim that merely changing the angle of the boat in the tide, irrespective of apparent wind effects, can push a boat to windward. It's a claim demolished by modern navigation programmes, articles (like http://www.j105.org/docs/noleebow.pdf for a Dave Perry piece, or http://www.ockam.com/2013/05/18/lee-bow-effect/ for something by Ockam Instruments) and even the simple experiment of sitting in a river or playing with sticks in a gutter. When "would be big boat book sellers" say to Grumpf that it does not exist they are perfectly correct. (EDIT - Actually it seems from looking further into the thread that people do believe the "olde lee bow myth" exploded by the articles referred to above). However that lee bow myth referred to above is different from the fact that a weather-going tide can affect the apparent wind. The latter effect is different because it doesn't pretend that there is something miraculous about the precise heading of the craft in relationship to the direction of the tide. as the old "lee bow effect" myth claims. |
Posted By: L123456
Date Posted: 02 May 14 at 8:34am
I have been explaining this but sadly some seem to want to hang onto the myth ...
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Posted By: johnreekie1980
Date Posted: 02 May 14 at 8:54am
| Class. 8 pages on. No sketch or actual math but everyone claiming they are right by the laws of physics. I am glad engineering discussions at my work don't follow this format. We could never convey any actual information concisely. |
Posted By: GarethT
Date Posted: 02 May 14 at 9:10am
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Posted By: iGRF
Date Posted: 02 May 14 at 9:48am
That is neither what the 'lee bow effect' claims, nor what is in discussion here, and the 'would be book sellers' have debunked something that was never claimed in the first place and in doing so thrown the whole tactical understanding of sailing in tides into question, so as a result our imbeciles no longer coach it's use to kids'. This discussion wasn't talking about changing angles or pinching, which if by so doing you get a tidal flow which is exactly on the nose, onto the lee bow as we do every other tuesday night and your Antipodean Chum Aaron Mackintosh failed to spot one time when five of us nailed him to the first mark, works just fine. Big Boats on Open water with large navigational distances? The tide may as well just be a conveyor belt and you can ignore it for the purposes of inter boat tactics I agree, unless of course there are variations in its flow rate over the bottom. However Assuming full tide on the lee side on a sailboard the question was does it have more effect on a centreboard in displacement mode and less effect sailing off the fin because of the lack of area in the water of the fin, the answer to which has been adequately explained to those who wanted to know the rest is just morons larking about who have probably never sailed and won a race in tide in their lives never mind taking a 12 minute lead from the entire British Olympic Team in one beat, when their coach practised what I can only presume he read in one of those fools books. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: Chris 249
Date Posted: 02 May 14 at 11:39am
Yes it is what the mythical lee bow effect claims, and yes it is claimed in the first place. You may be shattered to find this out, but you don't know the way every term is used in every sector of the sailing world. In many places (especially among older offshore racers in my experience) it IS used as I said. For proof, take this description, from Buddy Melges' book on racing technique; "This brings up the famous lee-bow effect. If the current is coming at you at an angle that is very close to the course you are sailing and if, by pinching just a little bit, you can get your lee bow into the flow of the current, the movement of the water is going to push against the hull, the keel, and the rudder, and it is goign to drive you up to windward even though you are going slower over the bottom. If you are on the other tack the current is going to be hitting you broadside and pushing you down." The above is proof that you are wrong - the claim IS made as I noted earlier. And with respect to Buddy, as Olympian Andrew Campbell says, this is incorrect; see http://campbellsailing.com/?m=200806 Your continual stream of abuse towards others, whether they are coaches, windsurfers or dinghy sailors, is getting very tiresome, especially when your dinghy results show no sign of this tactical genius you keep boasting about. There are lots of very good people out there in the sailing world, and many of them sail very well. Have you ever considered respecting people like Aaron (a world Olympic class champ) or in fact any other dinghy sailors and windsurfers apart from your own beloved self? |
Posted By: iGRF
Date Posted: 02 May 14 at 12:49pm
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It's what 'some latter day idiots' are claiming the lee bow effect is, that was never claimed in my day,
Pinching to go slower in order to get the tide the right side won't have any effect. Unless the sails derive more power from the tidal flow benefit in making the boat/board travel faster in which case it'll go further and sail higher. I've never read those sailing books, and to my knowledge other than anecdotal knowledge transfer by word of mouth, in the windsurf world not much has been writ other than in the odd article, but at no time do I believe has anyone advocated stuffing higher in order for the current to drive you upwind, but in any event this is not what we're talking about on this thread. I pre date Aaron Mackintosh, have known him personally so no, I don't need to respect him or any Antipodean who choses to litter up the same space I'm currently occupying and in a thread where my considerable experience has been called upon. Now my latter day dinghy experience may be nothing more than a half reasonable club sailor, but I can assure you that my sailing of boards in major events in tide has been on the whole more successful than most and over a longer period than anyone else still active, so do yourself a favour, ignore any thread I'm on if you don't want a counter argument to what you believe to be facts. You and they are wrong more often than you're right, Aaron however does have a reasonable grasp of what's what, but in tide? He hasn't proved himself to me I'm afraid and until he does I'll go on assuming he believes the same nonsense you do. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: L123456
Date Posted: 02 May 14 at 2:19pm
Indeed; and if iGRF and took the time to read my previous posts and Dave Perry's excellent summary you will see he made many of the references I have mentioned on these pages ... Here is a the link again that Chris249 has posted . http://www.j105.org/docs/noleebow.pdf" rel="nofollow - http://www.j105.org/docs/noleebow.pdf Chris249 also posted this which also provides diagrams and makes excellent reading: http://campbellsailing.com/?m=200806" rel="nofollow - http://campbellsailing.com/?m=200806 I recommend GarethT & iGRF read and digest both of these excellent texts and thanks Chris249 for posting these links ... "At the risk of being flicked into oblivion as I tug on Superman’s cape, the lee-bow effect does not exist when racing against other boats." the final paragraph is also a great summary ... Monday Morning Tactician Says: The best way to look at current while racing is as if the water your sailing on is a conveyor belt moving across the racecourse. The marks are moving relative your normal sailing tracks. It is important to realize, if the current is different on one part of the racecourse than on another, then the strategy becomes significantly more complex, and may be worth discussion in future MMT columns. However, if the current is moving across the racecourse in a uniform fashion, then it is better to not even worry about the current EXCEPT for dealing with 1. Laylines, 2. Mark Roundings, 3. Starting strategy. |
Posted By: kneewrecker
Date Posted: 02 May 14 at 2:24pm
yes but what about in handicap racing? Take for example average laps.... could you factor in the current into a new formula? It seems really mean for a boat completing extra laps if a previously-fair current has gone slack?
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Posted By: L123456
Date Posted: 02 May 14 at 2:32pm
Please don't complicate things ... we are still trying to generate understanding of the basics here ... But yes with PY racing tidal changes mid-race and completely skew the results.
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Posted By: GarethT
Date Posted: 02 May 14 at 2:34pm
| Not for an average lap time race, surely? |
Posted By: Bootscooter
Date Posted: 02 May 14 at 2:36pm
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*sniggers* ------------- |
Posted By: kneewrecker
Date Posted: 02 May 14 at 2:37pm
of course they do.... sailing upwind with the tide, hit the windward mark as the tide changes, and ride it back down again- kite up, full chat.... Poor old matey in his Oppy is then slogging away into the foul tide to make the weather mark, with only the promise of lee bowing it to cling to. (And some of you would deny him that little comfort with your vector maths and sensible discussion? You callous b**tards...) (assumes average laps of a very big course and a total disregard for the Rule of Twelfths)
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Posted By: L123456
Date Posted: 02 May 14 at 2:37pm
That is one for a new topic if you want help with that ... try and focus on the lee bow effect for now ...
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Posted By: GarethT
Date Posted: 02 May 14 at 2:42pm
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Posted By: iGRF
Date Posted: 02 May 14 at 2:52pm
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The most absurd quotes in the history of sailing part 1...
"At the risk of being flicked into oblivion as I tug on Superman’s cape, the lee-bow effect does not exist when racing against other boats." the final paragraph is also a great summary ... (Which is fine and was exactly what I'd said if you bother to read it, but and here's the but, the last 3 items, Laylines, Mark Rounding and Starting Strategy, if there's no such thing as lee bow effect then why even consider it at these points?) Monday Morning Tactician Says: The best way to look at current while racing is as if the water your sailing on is a conveyor belt moving across the racecourse. The marks are moving relative your normal sailing tracks. It is important to realize, if the current is different on one part of the racecourse than on another, then the strategy becomes significantly more complex, and may be worth discussion in future MMT columns. However, if the current is moving across the racecourse in a uniform fashion, then it is better to not even worry about the current EXCEPT for dealing with 1. Laylines, 2. Mark Roundings, 3. Starting strategy. Tell me chum how often do you race in tide? And where? This is becoming so ridiculous, quoting authors from Offshore Saiing where the rules are very different to inshore courses. Inshore courses have a big variety of tidal effects, although fundamentally any tactician worth is salt would tell you to race to find the shortest route around the course rather than race against other boats, but know this, all those boats that pay heed to the tide will have a better chance of victory than boats that follow that advice. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: L123456
Date Posted: 02 May 14 at 3:06pm
read again ... it is not saying consider the lee bow effect at these points ... because it does not exist. ... it is saying ... "... if the current is moving across the racecourse in a uniform fashion, then it is better to not even worry about the current EXCEPT for dealing with 1. Laylines, 2. Mark Roundings, 3. Starting strategy." This must be how special needs teachers feel  |
Posted By: iGRF
Date Posted: 02 May 14 at 3:10pm
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Dude you are so wrong, and here's the irony if I'd just won half a dozen dinghy events in tide you wouldn't even be arguing, you'd be queuing up at the book signing..
So, Pop Quiz, starting strategy lets say hmm Stokes Bay tide right to left 3kts wind South, speed say 5-8 knots forecast to drop, 1st leg length say 1000 yds. Start line set dead square say 200 yds long Starboard biased committee boat end. Which end are you going to start and why? And what would your 1st beat strategy be and why? ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: kneewrecker
Date Posted: 02 May 14 at 3:12pm
but there's the nub.... racing inshore, especially on estuaries or bendy rivers in slow displacement dinghies, the tide has a major habit of being different strengths in different parts of the course. It's quite easy to feel that you are being 'sucked to windward' on one specific tack, especially if you've got your foils engaged nicely, the boat flat and your sitting in a different tidal stream from your competitors on another tack. Experience can perpetuate a myth. ------------- |
Posted By: L123456
Date Posted: 02 May 14 at 3:19pm
Well at this point there is nothing more I can add except say get yourself in print as clearly the existing authors have no idea ...
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Posted By: JimC
Date Posted: 02 May 14 at 3:19pm
The original lee bow theory that Chris quotes had already been exploded by your day, and so board sailors never came across it. Unfortunately the term seems to have been recycled for different usage, leaving us with the comical situation where we have two sets of folks arguing viciously, one set saying there's no such thing - and are correct, and the other set saying there is a lee bow effect - and they are correct too!! |
Posted By: Rupert
Date Posted: 02 May 14 at 3:19pm
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I'd have said you need to consider the tide in your approach to the marks long before you have hit the layline. Its a bugger if you overstand and have to fight back up tide simply to round the mark. Even making the assumption of even tide over the course, the decisions made on the approach to the mark are going to be affected by tide. But this is just basic tactics - nothing to do with where the lee bow is. But then, what the hell, I'm one of the people who can't possibly know anything because I wasn't once in a race against Olympic windsurfing wannabees. ------------- Firefly 2324, Puffin 229, Minisail 3446 Mirror 70686 |
Posted By: iGRF
Date Posted: 02 May 14 at 3:21pm
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Next Question same course Tide Opposite, only this time it's a gate start.
Are you going early or late? And Why? ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: L123456
Date Posted: 02 May 14 at 3:22pm
You are quite correct; experience is perpetuating the myth because in those circumstances the situation gets complex but it does not change the physics of what is going on; there is no lee bow effect; it is put forward by people (such as our friend iGRF) who observe what is happening but mis understand the fundamentals.
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Posted By: iGRF
Date Posted: 02 May 14 at 3:26pm
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'My Day" was 1979 Jim and I can ashore you tidal lee bow was just as relevant then as it is today, we just didn't think about 'pinching' in order to make it function, that is self defeating. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: iGRF
Date Posted: 02 May 14 at 3:30pm
Well my deluded pseudo scientific friend if there is no such thing then explain to me why my board often gets on the plane sailing in one direction which just happens to co incide with the tidal current being on my lee bow, yet when I sail the other way the board will not plane. Give me another name and I'll use that instead. Or does it not happen and I've made it up? And I'm still waiting for your tidal starting strategy... Or hasn't the calculator delivered it yet? ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: GarethT
Date Posted: 02 May 14 at 3:32pm
| Graeme - are you left or right handed? Maybe it's that. |
Posted By: iGRF
Date Posted: 02 May 14 at 3:37pm
ftfy (see if you can spot your deliberate mistake) ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: iGRF
Date Posted: 02 May 14 at 3:39pm
Could be, all these years sailing with the strongest tide from the right. ------------- https://www.corekite.co.uk/snow-accessories-11-c.asp" rel="nofollow - Snow Equipment Deals https://www.corekite.co.uk" rel="nofollow - New Core Kite website |
Posted By: JimC
Date Posted: 02 May 14 at 3:58pm
Like I said, before your day... |