With your back to the wind, there will be more wind on the shoreline to your right since the wind backs over the land in relation to the wind over the water and hence converges with it.
On the shoreline to your left, the backing of the wind over the land causes it to diverge from that over the water, giving you less.
The difference can be a few knots, up to about 25% difference in wind speed. The effect extends as much as 3 miles offshore. Getting out of a convergence zone can be well worthwhile if beating into a strong blow. Getting into one can provide relief from slatting and banging sails when running in barely enough breeze. Past Tarifa you'll be doing one or the other most days of the year. The wind there knows little of north or south.
Results 11 to 17 of 17
14-04-12, 00:38 #11
Last edited by Simondjuk; 14-04-12 at 00:41.
14-04-12, 10:19 #12
Hmm, I suspect that any convergence effect is lost in the 'venturi' effect of the strait. Whichever way the wind blows, E or W, it increases in the direction of flow through the strait.
We came in from the W with a forecast W F4/5, saw just over 20kts at Tarifa and somewhere in the mid 40s rounding Punta Carnera. Since we stayed close to the N shore, you might have expected the wind to diverge and decrease - didnt happen!
Last edited by RobbieW; 14-04-12 at 10:22.If you're not confused, you're probably misinformed
14-04-12, 11:47 #13
Totally agree, Robbie. You would have to be a very astute observer to pull out any coastal friction from all the other stuff going on.
The tides, current, drift current, venturi, headland windshifts, downdrafts from hills etc give you enough to think about!
Stiil, off up to Seville at end of month so if I notice anything different from the last 80 odd transits, I will of course report in. Over a glass of tinto??
14-04-12, 13:00 #14
Last year I went in and out between Gibraltar/Ceuta/Smir and what was then my home port of Barbate, 15-20 times.
At first I tried hard working the tidal atlas, but found it so inaccurate and variable I gave up and just made sure the wind was from astern - or very light and motored.
Because of the time it takes to get through, you are almost inevitably going to get some fair and some foul tide. On one occasion, Tarifa was interesting with gusts to 60k and its wonderful how fast a boat will go downwind with just a few inches of head-sail out!
It really is the wind strength and direction that's important and don't be fooled by what it's like in Marina Bay or Queensway Quay... Worth listening to the Tarifa or Tangier radio, hourly broadcasts of actual and forecast conditions - they call on 16 then change to a working channel.
14-04-12, 13:09 #15
I agree that the effects I mention will often be masked by more pronounced effects caused by the geography of the area. I intended to mention it but ran out of enthusiasm for typing on a phone keyboard.
On occasion I've definitely picked up more wind in light westerley conditions by closing the southern shore. I guess I'm either very astute, or the wind has just happened to have been on the up anyway. If it wasn't astuteness, which is quite possible , I'll console myself that the notion of gaining a freeing effect was beneficial too, tides and currents permitting of course.
14-04-12, 14:39 #16
Sometimes, to be honest, I just go! Did that 2 weeks ago on a trip to Cadiz, entered Straits at Carnero, lunchtime, tied up in Barbatte 2300ish!
Re VHF, forecasts alternate as you mention but every 2 hours. Starting1215 UTC at Tarifa 0n ch10, then 2 hours later 1415 UTC ch69 Tanger. Obviously 2 hour time difference now. Often late though, must have wasted years of my life waiting for forecast!
And always, downwind end will be windier. A east 3 off Europa will be 5 or 6 at Tarifa and beyond, W4 at Tarifa will be old boots between Gib and Ceuta. Honking today!
14-04-12, 14:43 #17