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Sailing in tide..quiz. |
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
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Topic: Sailing in tide..quiz. Posted: 02 Oct 17 at 9:28pm |
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So this is actually what happened. Blue arrives at island before red tacks to cross channel. Edited by iGRF - 02 Oct 17 at 9:31pm |
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Post Options Quote Reply Posted: 02 Oct 17 at 9:37pm | |||
So do I get any brownie points for getting it right?
You'd also imagine the boats coming out of the headland on port would get a tidal lift, of course as they went further right they'd know they'd have to come back in the corresponding header (I just think he tacking angle out of the headland on port would be better). But the above scenario is just the tide changing the apparent wind. I want you to explain how changing mode in tide can lead to a better VMG.
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KazRob
Far too distracted from work Joined: 22 Oct 16 Location: Scotland Online Status: Offline Posts: 245 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:43pm | |||
Are you sure you didn't just get lucky taking a flier?
Still don't understand your tide assisted speed or your lee bow stuff. When you head back out from the shore the tide is heading NE-ish so you should get pushed that way and in a reduced wind strength. I can see if you made it to where the tide runs west you will get more breeze but your still being pushed away from where you want to go. |
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sargesail
Really should get out more Joined: 14 Jan 06 Location: United Kingdom Online Status: Offline Posts: 1459 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:51pm | |||
Exactly - so I'm not worried about the header!
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sargesail
Really should get out more Joined: 14 Jan 06 Location: United Kingdom Online Status: Offline Posts: 1459 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:54pm | |||
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?
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Post Options Quote Reply Posted: 02 Oct 17 at 9:54pm | |||
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.
Edited by mozzy - 02 Oct 17 at 9:57pm |
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iGRF
Really should get out more Joined: 07 Mar 11 Location: Hythe Online Status: Offline Posts: 6496 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:57pm | |||
No it wasn't a flier, it gets back to my explanation on the Gate start thread, we are using the energy from three sources instead of two.
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. That's it really. By harnessing an extra 4 knots on the centreboard, it combines with the 8 knots in the sail to drive the craft faster, the fact the water is also moving like a conveyor belt is irrelevant, what is important is the board/boat speed over the ground and relative to everyone else. Edited by iGRF - 02 Oct 17 at 10:00pm |
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sargesail
Really should get out more Joined: 14 Jan 06 Location: United Kingdom Online Status: Offline Posts: 1459 |
Post Options Quote Reply Posted: 02 Oct 17 at 9:58pm | |||
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?
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Post Options Quote Reply Posted: 02 Oct 17 at 10:00pm | |||
Getting pushing north east is pushing you in to and accross the wind. You will feel an apparent increase in wind and apparent backing (lift on port).
Do you mean heading west running tide. The only place the tide is running west is at the start?
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sargesail
Really should get out more Joined: 14 Jan 06 Location: United Kingdom Online Status: Offline Posts: 1459 |
Post Options Quote Reply Posted: 02 Oct 17 at 10:04pm | |||
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!).
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