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Old 19-10-2020, 14:06   #1
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Wind Against Current

Ever since I started sailing about a decade ago, I have read admonitions of all kinds about never ever getting into a situation where the wind direction is opposite the current direction. Apparently this situation causes massive waves, sea monsters, boat-eating whirlpools and a variety of other "avoid at all cost" conditions. I have tried, without much success, to make sense of this. Here's why: Current is a term that describes the relative motion between the water part of the planet and the dirt part. If you are sailing along in between the water part and the air part, the only effect that current, per se, has on you is that it affects when you are going to get where you are going and what direction you have to point to get there. Its effect on the interface between the water part and the air part is that the current vector gets subtracted from true wind if the directions are the same and added to true wind if the directions are opposed. If the directions are anything else, the result is in between and you need to figure out the appropriate crab angle if you plan on going anywhere specific relative to the dirt part. So, assuming I am not missing something, the relative motion between the air part and the water part are the same for a true wind of fifteen knots and no current, a true wind of thirteen knots and an opposed two knot current and a true wind of seventeen knots and a following two knot current. The local effect of wind and current on sea conditions should be the same for all of these conditions. I know from personal experience that transitioning between bodies of water going in different directions at different speeds can be exhilarating. I also understand that there are isolated places where the current can be in the teens and that in very shallow areas, there may be special effects but in open seas, currents are generally between 0 and 4 knots, that or some lesser amount being the amount to be added to or subtracted from true wind to figure out what effect the combined conditions might have on sea state. If I am traveling happily northbound along the Florida coast in a 15 knot north wind and run into the Gulf Stream, my speed over the ground and the apparent wind will increase by 4 knots. If I am sailing, I need to make some trim changes just as I would if the wind speed increased by 4 knots but where did the sea monsters come from?

I was a pilot long before I became a sailor but we only had to deal with one kind of fluid (if our name wasn't Sullenberger) so the question didn't come up. We did have to deal with mountain waves though.
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Old 19-10-2020, 14:56   #2
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Re: Wind Against Current

Try this

https://rmets.onlinelibrary.wiley.co...0.1002/wea.606
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Old 19-10-2020, 15:02   #3
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Re: Wind Against Current

Jackdale beat me to it

The key takeaway:

Quote:
...As an example, if a wave of wavelength 15m and speed 5m/s (10kn) enters an opposing stream of strength 1m/s (2kn), its wavelength will be reduced by 50% while its height is increased by 75%, giving a dramatic increase in steepness. It can be shown that if the opposing current is great enough so that the current speed is no greater than Co/4 (i.e. 1.25m/s in this case), then the wave becomes infinitely steep and will break. In fact opposing currents of only a few knots will cause most waves encountered to exceed the steepness limit and partially break...
The waves get steeper and shorter period, both of which make them less comfortable than their counterparts in wind with current or no current situations. How much less comfortable (or safe) depends on the size of the waves, the strength of the wind, and the speed of the current. It can be anything from a minor annoyance to somewhat dangerous.
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Old 19-10-2020, 15:54   #4
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Re: Wind Against Current

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Originally Posted by Dsanduril View Post
Jackdale beat me to it

The key takeaway:



The waves get steeper and shorter period, both of which make them less comfortable than their counterparts in wind with current or no current situations. How much less comfortable (or safe) depends on the size of the waves, the strength of the wind, and the speed of the current. It can be anything from a minor annoyance to somewhat dangerous.

And the size of a vessel. What is somewhat dangerous on a smaller vessel can be literally a ripple for a larger vessel. So, it depends.

Charts generally have “standing waves” in print and icons at locations where these are common at certain states of tide and/or current. Wind against current are more dependent on weather conditions rather than tide, so usually aren’t marked on charts. Keep track of current directions and pay attention to wind direction.
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Old 19-10-2020, 16:43   #5
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Re: Wind Against Current

A bit of semantics, but oceans have currents. The Gulf Stream is like a river within the ocean. And finally, there are a tidal streams which produce wind-over-tide conditions.

They are very different - so wind-over-current is essentially a mischaracterization.

It is wind-over-tide (wind blowing in the opposite direction of the tidal stream - which is either rising/coming in, or falling/going out) which produces local alarming seas.

Then you have something like wind against the Gulf Stream - which, again, is a magnitude greater than a local wind-over-tide, and unique to the Atlantic Ocean.

I guess you'll just have to experience it for yourself sometime to see why it's so dire. We almost sunk our boat once going across Poole Bay in wind-over-tide. It was the beginning of an ocean race and the boat was bashed about so badly the deck/hull seam began to open up....

We retired to Weymouth and thanked our lucky stars!

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Old 19-10-2020, 17:16   #6
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Re: Wind Against Current

Streams vs. currents depends on your side of the pond

https://www.naturalnavigator.com/the...idal-currents/
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Old 19-10-2020, 17:34   #7
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Re: Wind Against Current

Quote:
Originally Posted by hallejj View Post
...If I am traveling happily northbound along the Florida coast in a 15 knot north wind and run into the Gulf Stream, my speed over the ground and the apparent wind will increase by 4 knots. If I am sailing, I need to make some trim changes just as I would if the wind speed increased by 4 knots but where did the sea monsters come from?..
As Dsanduril quoted (and jackdale, who did not say a thing, just sent us off like good schoolchildren to read what he reads, linked) there are mathematics involved when water moves the opposite direction as the wind.

The monsters come up when wind builds waves and the water, flowing against the wind, compresses them together.

Trust me, it can get nasty.
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Old 19-10-2020, 17:37   #8
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Re: Wind Against Current

Try going NW up Johnstone Strait with the ebb when the NW winds are blowing. Not fun.
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Old 19-10-2020, 17:44   #9
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Re: Wind Against Current

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Try going NW up Johnstone Strait with the ebb when the NW winds are blowing. Not fun.
Been there, done that. In the right boat it can be quite fun, the waves are not as big as some places, just short and steep. You need to be close winded (short tacks) and with fine bow sections. Sheet in tight, put on a foulie jacket, and go!

The scenery is beautiful.
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Old 19-10-2020, 18:08   #10
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Re: Wind Against Current

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Originally Posted by sv_pelagia View Post
Try going NW up Johnstone Strait with the ebb when the NW winds are blowing. Not fun.
Or ride an ebb tide out the Big Bra d’Or with a good NE wind. Thought I Would through the mast out.

Ugly!!!
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Old 19-10-2020, 18:34   #11
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Re: Wind Against Current

Or the cape cod canal headed south west on a summer afternoon with a full tide against the fully developed and funneled down sea breeze.
4-5 knots current against 15-20 knots breeze. And narrow like Big Bras D’Or.
Steep and sloppy.
Just a summer afternoon. Yuk.
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Old 19-10-2020, 19:09   #12
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Re: Wind Against Current

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Originally Posted by sv_pelagia View Post
Try going NW up Johnstone Strait with the ebb when the NW winds are blowing. Not fun.
Been there, done. I have been around Vancouver Island a dozen time and done about 6 trips up to Hardy and back. I spend as time as possible in Johnstone Straits. I head for the Broughtons ASAP.
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Old 20-10-2020, 07:29   #13
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Re: Wind Against Current

"If I am traveling happily northbound along the Florida coast in a 15 knot north wind and run into the Gulf Stream, my speed over the ground and the apparent wind will increase by 4 knots. If I am sailing, I need to make some trim changes just as I would if the wind speed increased by 4 knots but where did the sea monsters come from?" Hallejj

Hi, H,
Being a man of Science, why not see for yourself. Take your boat in the 4 knot section of the Gulf Stream with a 20 knot North wind opposed to it. This is the best empirical evidence you can have. Good luck and safe sailing . . . Rognvald
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Old 20-10-2020, 08:03   #14
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Re: Wind Against Current

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Originally Posted by jackdale View Post
Been there, done. I have been around Vancouver Island a dozen time and done about 6 trips up to Hardy and back. I spend as time as possible in Johnstone Straits. I head for the Broughtons ASAP.
I spend as (a) little (b) much (c)?? time as possible in Johnstone...

My choice would be (a)
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Old 20-10-2020, 08:09   #15
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Re: Wind Against Current

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Originally Posted by sv_pelagia View Post
I spend as (a) little (b) much (c)?? time as possible in Johnstone...

My choice would be (a)
Duh.

That would be my choice as well.
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