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Sailing in tide..quiz.

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Post Options Post Options   Quote mozzy Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:05pm
Originally posted by iGRF


1) Energy from the true wind drives the boat/board, this generates, then combines with
2)The created wind of the board boat moving OVER THE GROUND
3)The third force is the water which as a fluid also moving over the ground, like the wind can either combine with the wind to act in concert (the force is greater, the more angled the lower foil is (think sheeting it in)) or it can act against and reduce the energy from the true wind.

In the scenario you describe, I think you made the right choice. But those three point above make no sense. 

You sail on the difference between air and water. Two things. Over the ground is only relevant in that as the tide is moving it makes the apparent wind different on water compared to land. Its not a separate for to true wind. 

Your third point is crap. Leeway over foils is about 3-4 degrees. This doesn't change if you are in tide or not. 


Edited by mozzy - 02 Oct 17 at 10:05pm
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Post Options Post Options   Quote KazRob Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:08pm
Oops - got my tide directions mixed up. For NE read NW and for West read East. That's basically why I'm cr*p in tides I guess
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:10pm
Originally posted by sargesail


Originally posted by iGRF



So this is actually what happened.

Blue arrives at island before red tacks to cross channel.

So tell me why it wouldn't have been faster for blue to do a hybrid of the two: short tack like red and then do a starboard leg from the end of the headland until meeting the port layline drawn?


Pretty much what we'd been doing earlier in the week when the windward mark was sited just at the tip of that left arrow. The main reason to go left (as also pointed out by Mozzie, credit where it's due) was the likelihood there would be a better lift off the opposite cliffs, which would get the nose into the tide earlier than rounding the headland where the lift off the land petered out, quite why they didn't harden up to head out to sea I'll never know, they were not stupid, some were Hayling sailors so not tidal neophytes, but then again who knows what squads have to do when their coach is dictating the route.

I didn't win the race, I spent too long berating the coaching team who were moored at the island, about listening to lectures on tide and not arguing the point when I bother to drive down to weymouth at my own expense to try and help them, but then it's not in a paid professional coach's interest to have anyone around with superior tactical advice is it? Then I always was naive..

Edited by iGRF - 02 Oct 17 at 10:11pm
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Post Options Post Options   Quote mozzy Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:15pm
Originally posted by sargesail

Originally posted by mozzy

When he tacks out from the left shore the tide is first mostly on the head, but becomes increasing cross and even slightly against the wind. In teh boat it would feel like the breeze was increasing and lifting as you come back in on port. 

Looking at the vectors (3.5 knot tide, 9 knot true wind) this would feel like a 10-20 degree lift (assuming tide was slack or against on the north shore (far left of the beat). 

The component of the tide which is running in to the wind obviously increases the apparent wind strength for both port and starboard boats; however, the cross tide component would lift the port boats (and head equally the starboard). 

Basically, as the boats on the right come out from the head land, back toward the middle, they would feel the breeze increase as the tide gets on their stern, but also get a header. 

Yes - I know that.  But what I'm getting at is that blue still has to make to the south into a north or north-west going tide.  Even if the diagram is not as drawn and the east going flood starts further west (unlikely) then it still starts as a north-easterly flow and turns east as you get east.  So going south before you are in north going flow is always a gain (other things being equal - which they're not!).

I think iGRF has drawn the lines a bit wrong. The way he's shown it both tacks are lifted in to the windward mark, which is impossible. 

As I said in another post  the right would look okay, until they came out from the shore. They would get a lift on port from the incoming tide, but when you're the furthest boat right on the course, the last thing you want is a lift on port! They, would have to get out of that right hand side at the top of the beat by sailing on starboard. Starboard tack will be feel an apparent header. 

Also, I wouldn't see going right as that much of a gain at the start either (unless there is a big back eddy which isn't shown). The tidal stream will be diverging in the middle as it splits (divergent) to two channels so the north bank probably won't see strong adverse tide, especially mid way up the beat. 

Then on top of that, iGRF does say the wind was in the right phase at the start, so you'd have to sail a ten degree header to get to that right shore. 


Edited by mozzy - 02 Oct 17 at 10:25pm
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:21pm
Originally posted by mozzy


]You sail on the difference between air and water. Two things. Over the ground is only relevant in that as the tide is moving it makes the apparent wind different on water compared to land. Its not a separate for to true wind. 
Your third point is crap. Leeway over foils is about 3-4 degrees. This doesn't change if you are in tide or not. 



You only move because the water provides resistance to the wind.

That then enables created wind which also combines against the static resistance of the water to enable forward motion.

If the water moves away from the wind at the same pace, no forward movement of the boat will take place.

If the water were moving toward the wind at the same speed then the boat will move forward as if the wind speed were double.

I'm sorry but whoever told you all that doesn't entirely understand what is going on, where the Energy is coming from.

Three elements, not two.

Edited by iGRF - 02 Oct 17 at 10:24pm
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Post Options Post Options   Quote mozzy Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:29pm
Okay, I get what you're saying. But I don't think you're phrasing it very well. The true wind over ground, plus the tidal vector = the wind you feel if you were floating stationary. Depending on direction the tide will shift, add to, or decrease the true wind (from what is experienced on land (or moored up). 

But, in the boat, you can't feel that. the boat can't 'feel' that. All the energy comes from the sheer between air and water. Those two things, nothing else. Whether it's just the air that's moving (lake) or air and water (sea) it is still just the sheer between the two.  

Also, you'd still not explained the 3rd point of tide hitting the foils etc etc. 
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Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:30pm
Originally posted by iGRF

Originally posted by sargesail


Originally posted by iGRF



So this is actually what happened.

Blue arrives at island before red tacks to cross channel.

So tell me why it wouldn't have been faster for blue to do a hybrid of the two: short tack like red and then do a starboard leg from the end of the headland until meeting the port layline drawn?


Pretty much what we'd been doing earlier in the week when the windward mark was sited just at the tip of that left arrow. The main reason to go left (as also pointed out by Mozzie, credit where it's due) was the likelihood there would be a better lift off the opposite cliffs, which would get the nose into the tide earlier than rounding the headland where the lift off the land petered out, quite why they didn't harden up to head out to sea I'll never know, they were not stupid, some were Hayling sailors so not tidal neophytes, but then again who knows what squads have to do when their coach is dictating the route.

I didn't win the race, I spent too long berating the coaching team who were moored at the island, about listening to lectures on tide and not arguing the point when I bother to drive down to weymouth at my own expense to try and help them, but then it's not in a paid professional coach's interest to have anyone around with superior tactical advice is it? Then I always was naive..

I feel your pain in terms of the interaction with the coaches.....

But I also put it to you that the lead you established that day was due to the lift off the northern cliffs, and not some inexplicable tidal magic?
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:35pm
Originally posted by sargesail


Originally posted by iGRF



So this is actually what happened.

Blue arrives at island before red tacks to cross channel.

OK - so talk me through the curved laylines.  Why does blue gradually get lifted on port?
Why does red gradually get headed?
And where can I get one of these windsurfers which point so high that the tacking angle looks like 40 degrees?


The curve indicates the strength of the tide 'lifting' the board higher, tidal lee bow, as classic as that, is twofold, not only does the board physically go faster thanks to the energy provided by the tidal flow, but the direction in which the tide is headed lifts the craft upwind.

The reds stayed out of the tide.

You can buy race boards for next to nothing on eBay and I'd strongly recommend any sailor trying one out if for no other reason, than to actually feel all that knowledge you obviously have, in the palms of your hands, you'd find it exhilarating.

Edited by iGRF - 02 Oct 17 at 10:36pm
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Post Options Post Options   Quote sargesail Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:39pm
Originally posted by mozzy

Okay, I get what you're saying. But I don't think you're phrasing it very well. The true wind over ground, plus the tidal vector = the wind you feel if you were floating stationary. Depending on direction the tide will shift, add to, or decrease the true wind (from what is experienced on land (or moored up). 

But, in the boat, you can't feel that. the boat can't 'feel' that. All the energy comes from the sheer between air and water. Those two things, nothing else. Whether it's just the air that's moving (lake) or air and water (sea) it is still just the sheer between the two.  

Also, you'd still not explained the 3rd point of tide hitting the foils etc etc. 

Ahhh Mozzy - I've been here with GRF before.  I can't wait to see what he comes up with this time.  I've been waiting to hear about the wonder race that would prove his theory for years.  And there it was.....and I see nothing in it that remotely proves his theory.  In fact the decisive factor appears to have had nothing to do with the tide at all....

So either I'm still as dumb as I used to be for letting him troll me again....or I'm not the dumb one....
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Post Options Post Options   Quote KazRob Quote  Post ReplyReply Direct Link To This Post Posted: 02 Oct 17 at 10:44pm
All that talk about energies makes me think that he'll be invoking crystals and vibrations on a higher plane next!
But seriously as Mozzy points out, the board/boat doesn'tt know about the ground (unless it's anchored) in the same way it doesn't know it's spinning through space at thousands of miles an hour. If your anchored you'll get 'lift' off the tidal stream but floating free your foils are moving with and relative to the water. Transpose the scenario si there's no no land present and see if it still makes sense
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