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Tides, Currents & UnderCurrents
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rgomez



Joined: 13 Dec 2012
Posts: 54

PostPosted: Sun Jun 30, 2013 11:10 pm    Post subject: Tides, Currents & UnderCurrents Reply with quote

So I finally got the balls to venture out in the sea during the Indian monsoons and had a blast with 20-30knot gusts.

However, I keep getting warned by family and friends about strong undercurrents and tides...This may seem like a stupid question but do currents, undercurrents and tides really affect a windsurfer?

Thanks.
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slinky



Joined: 24 Aug 2007
Posts: 396
Location: Old Saybrook Ct.

PostPosted: Mon Jul 01, 2013 4:46 am    Post subject: Reply with quote

I got caught in a rip current once about 50 yards from shore. The wind had died. Had to ditch my rig, luckilly I got it back.

Currents here can be very strong at times. Depending on where you are tides may vary little or greatly, as much as 40 feet!
I always make it a point to check the tide. There is something called the ordinal rule of 12. Most places have 2 tide cycles per 24 hour period, two high tides and 2 low tides. There is roughly 6 hrs. between a high tide and a low tide. If total tidal variation is 12 feet:

In the first hour 1/12th of the tide occurs = 1ft.
second hour 2/12ths =2 ft.
third hour 3/12ths = 3 ft.
fourth hour 3/12th= 3ft.
fifth hour 2/12th= 2ft.
sixth hour 1/12=1 ft.

Watch out durring the 3rd, and 4th hours as half of the tidal change occurs during these 2 hours! This means STRONG currents.

Always know what the tides are doing before venturing out! Your life may depend on it!
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whitevan01



Joined: 29 Jun 2007
Posts: 423

PostPosted: Mon Jul 01, 2013 6:18 am    Post subject: Reply with quote

Even in more benign tidal conditions, they can and do affect windsurfers. For instance, if you are going in a direction that has a component WITH the tide, the wind you sail "sees" will be less than the actual wind. If you are going in a direction that has a component AGAINST the tide, the wind your sail "sees" will be more than the actual wind. If you ever have those days where it's a bit harder to get going on one tack than the other, this is probably the explanation.

Fully agree with slinky's post, tides are extremely important and one should always know what they are doing.
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rgomez



Joined: 13 Dec 2012
Posts: 54

PostPosted: Mon Jul 01, 2013 6:37 am    Post subject: Reply with quote

Ok..so the more variation in tides the stronger will be the currents...and these currents can pull me with them if the wind dies on me.

This is helpfull cause even though the place I sail at is a bay and hardly has a few feet of variation....I have seen a few beaches where the low tide was a couple of kms out and the water pulled back really fast.

Also another point i should mention is the monsoon wind provides a permanent side onshore wind...is there anything I should be worried about?

@Dennis....Im not sure if what you mean....shouldnt you go faster with the tide and slower against it instead of the other way around.
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whitevan01



Joined: 29 Jun 2007
Posts: 423

PostPosted: Mon Jul 01, 2013 7:10 am    Post subject: Reply with quote

Here is what I mean (wish I could draw a picture on here):

It is all about vector addition.

Suppose the tide and wind are both towards the South. If the wind is blowing 10 mph (relative to someone standing still), but the tide is 3 mph (relative to someone standing still), the apparent wind that your sail sees will be 7 mph. That's because the tide is taking you away from the wind at 3 mph.

The opposite is true if tide and wind are in opposite directions. The tide will be taking you into the wind, so your sail would see 13 mph in the above example.

Maybe think about it like this, if there was no wind, and you were just floating along on the tide, you would measure an apparent wind of 3 mph. this would add to the true wind speed if you were going into the wind and subtract from the true wind speed if you were going away from the wind.

Of course, the effect is diminished when you start moving across the wind (like when reaching) but can still be noticeable.
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rgomez



Joined: 13 Dec 2012
Posts: 54

PostPosted: Mon Jul 01, 2013 7:48 am    Post subject: Reply with quote

Aah..I get it..your referring to the apparant wind.

So if i have an onshore wind with high tide...I should be able to be able to move faster out to sea than back to shore with the same amount of wind.

Thats interesting, I never really considered that.
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slinky



Joined: 24 Aug 2007
Posts: 396
Location: Old Saybrook Ct.

PostPosted: Mon Jul 01, 2013 10:03 am    Post subject: Reply with quote

At high tide there is no current! Same at low tide, no current.

It's what the tide is doing that matters. Is it coming in or going out?
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cgoudie1



Joined: 10 Apr 2006
Posts: 1127
Location: Killer Sturgeon Cove

PostPosted: Mon Jul 01, 2013 12:08 pm    Post subject: Reply with quote

High and low tide should have very little current, it's the time in between
that develops current. Going faster isn't exactly the way I would look at it
either. In the direction where you sail with the wind against the current,
you'll plane up earlier and have more available power when planed. In the
direction where you sail the wind with the current, you'll plane up slower
(or maybe not at all), and you'll have less available power when planed.

-Craig

rgomez wrote:
Aah..I get it..your referring to the apparant wind.

So if i have an onshore wind with high tide...I should be able to be able to move faster out to sea than back to shore with the same amount of wind.

Thats interesting, I never really considered that.
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zirtaeb



Joined: 03 Jul 2009
Posts: 2147

PostPosted: Mon Jul 01, 2013 12:46 pm    Post subject: Reply with quote

Currents and rips have more to do with topography and waves than tide movement.
Peaks and valleys of tides can have extreme rips and currents, if water is flowing into an acclerated area from a wider, slower area.
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swchandler



Joined: 08 Nov 1993
Posts: 5476

PostPosted: Mon Jul 01, 2013 2:03 pm    Post subject: Reply with quote

The thing to remember about tides is that they can vary greatly depending on your sailing location. For example, the tides in Southern California will vary hugely in comparison with the tides in Alaska. With the latter location, you really need to aware of tidal activity to be safe. Also, like LeeD (zirtaeb) says, at some places like in the San Francisco Bay and Delta areas, tidal action can really affect things. You can really tell the differences between wide and narrow areas in the Delta like The Access and Powerlines. Although they're only a few miles apart, the action on the water is noticeably different because the width of the river.

Lastly, riptides and currents can be dramatically affected by ground swell. I can remember windless days surfing where you had to constantly keep paddling just to stay in the line-up. Also, paddling out through the surf the ground swell generated current would rip you down the beach at an incredible rate. However, a few days later after the ground swell passed, the current at the same spot would be negligible. So, weather events often originating far far away can have a dramatic effect on conditions.
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