4.5m waves at Gascogne Buoy
- Thread starter compie1
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ValleyForge
Well-Known Member
Edge of Biscay, Spring Equinox, you mean too calm ?
Plomong
Well-Known Member
5 m swells along the North Spanish coast (I'm in Bilbao) and the West coast of France are not at all uncommon -- quite the opposite. A depression anywhere NW, W or SW of Ireland creates significant swell down here. Great for the surfers!!!
If on top of that there is a 50 knot wind from the NW, all the way down from Greenland, we get a very interesting sea state!!!
The Bay of Biscay (Bizkaia here in Basque Land) was notorious in the days of sailing ships precisely because wind and sea state could force a SW-bound vessel coming out of the English Channel (Western Approaches) down into the bay, and become embayed there. Likewise a NE-bound vessel returning from parts West or from Africa, rounding the north-west part of Spain could be blown down on that coast (called costa da morte, the coast of death, in Galicia), or in like manner embayed, not being able to enter the Western Approaches.
In those days neither Bilbao nor Gijon were suitable harbours of refuge, the former because it was a funnel-shaped bay open directly to the north west with a narrow (150 m wide) entrance at the apex of the funnel into the river across a dangerous bar. The bar was permanently removed at the beginning of the 20-th century by eliminating the meanders in the river and constructing a training wall at the northern side of the river mouth.
Gijon at that time had no useful port for large vessels.
The Garonne entrance also was not an option -- Banc de la Mauvaise and Banc du Matelier made entry impossible except in relatively calm conditions. Today, the entrance channel must be continually dredged to maintain 13 m. Leave it alone for two storms and the channel would just disappear !!! Leaving just a few meters of water over a large area.
As for large waves, and wild conditions, if any of you know the Bilbao harbour entrance you will have seen the massive Punto Lucero breakwater, some 25 m high above high water level. Wave height here in stormy weather can exceed 13 m (40 ft) at the breakwater.
What never ceases to amaze me is how the installers of these ODAS buoys manage to anchor those things in the open ocean, and often in very deep water, at that.
If on top of that there is a 50 knot wind from the NW, all the way down from Greenland, we get a very interesting sea state!!!
The Bay of Biscay (Bizkaia here in Basque Land) was notorious in the days of sailing ships precisely because wind and sea state could force a SW-bound vessel coming out of the English Channel (Western Approaches) down into the bay, and become embayed there. Likewise a NE-bound vessel returning from parts West or from Africa, rounding the north-west part of Spain could be blown down on that coast (called costa da morte, the coast of death, in Galicia), or in like manner embayed, not being able to enter the Western Approaches.
In those days neither Bilbao nor Gijon were suitable harbours of refuge, the former because it was a funnel-shaped bay open directly to the north west with a narrow (150 m wide) entrance at the apex of the funnel into the river across a dangerous bar. The bar was permanently removed at the beginning of the 20-th century by eliminating the meanders in the river and constructing a training wall at the northern side of the river mouth.
Gijon at that time had no useful port for large vessels.
The Garonne entrance also was not an option -- Banc de la Mauvaise and Banc du Matelier made entry impossible except in relatively calm conditions. Today, the entrance channel must be continually dredged to maintain 13 m. Leave it alone for two storms and the channel would just disappear !!! Leaving just a few meters of water over a large area.
As for large waves, and wild conditions, if any of you know the Bilbao harbour entrance you will have seen the massive Punto Lucero breakwater, some 25 m high above high water level. Wave height here in stormy weather can exceed 13 m (40 ft) at the breakwater.
What never ceases to amaze me is how the installers of these ODAS buoys manage to anchor those things in the open ocean, and often in very deep water, at that.
compie1
Well-Known Member
Thanks for the info, we plan to do La Rochelle to Ostend this summer...
guernseyman
Well-Known Member
On a fine summer's day we once encountered 40 ft swell waves off Morlaix (that's from an estimate that they were 3 metres over the top of our mainmast). My first instinct was to turn and run, but I could see they were travelling faster than we could. As the first one, lower than the rest, got closer it turned out to be not as steep as it had looked, and we sailed up and over it. The next one was the full height and, still terrified, we found it was no problem. We continued more happily and without incident until we were far enough into the Bay of Lannion to escape them.
We've never seem anything like that again, but it is just as well to know that stuff like that happens.
We've never seem anything like that again, but it is just as well to know that stuff like that happens.
Robin
Well-Known Member
French Met forecasts in Brittany/Biscay areas always forecast the swell height and direction as well, 'La Houle' and 5m swells are not unusual if there has been a period of bad weather out in the Atlantic. But remember this is 'swell' not wave height, swell is easily ridden but you can be going along happily alongside another yacht yet occasionally only see the top 3ft of his mast, makes for good photos though. Places especially prone to big swells (usually from the west) are the NW corner by L'Aberwrac'h/Chenal Du Four/Ushant, the Raz De Sein - Penmarc'h and from L'Aberwrac'h east along the N Brittany coast to the Channel Islands, Trebeurden in the Baie de Morlaix has it sometimes. On the English side of the Channel, such swells usually diminish significantly when east of Start Point but in central Channel will still be seen.
Plomong
Well-Known Member
I seem to remember that a swell wave of length X meters begins to "feel the bottom" when the water depth shallows to 3/4 X, or 75 m for a 100 m length wave. In my opinion, the effects are not noticeable to a yacht until X/2 meters depth is reached.
Down the west coast of France, the 50 meter contour is quite some way out to sea, and depth shallows gradually, both optimum conditions for incoming swell waves to behave in almost perfect agreement with theory.
By the time depth has reached 20 m the deep ocean swell waves of maybe 3 m, but with wave length maybe 300 m, can have grown to 10m height and have length reduced to 90 m or so. Makes for interesting sailing, as someone has pointed out --- You may only see the mast top of another yacht when both are in a trough!!! But sailing in those conditions is in no way dangerous, just visually surprising!!!
Down the west coast of France, the 50 meter contour is quite some way out to sea, and depth shallows gradually, both optimum conditions for incoming swell waves to behave in almost perfect agreement with theory.
By the time depth has reached 20 m the deep ocean swell waves of maybe 3 m, but with wave length maybe 300 m, can have grown to 10m height and have length reduced to 90 m or so. Makes for interesting sailing, as someone has pointed out --- You may only see the mast top of another yacht when both are in a trough!!! But sailing in those conditions is in no way dangerous, just visually surprising!!!