Bay of Biscay Crossing

[Akestor]

Hi.. i recently crossed the bay of Biscay from France going southwest. The winds were coming from the land , NE about 20 knts to 28 (true wind) rarely for few seconds. The waves were big but nothing too much. Wondering what the waves would be with the same wind speed but from NW direction were the sea would build up in the ocean. Having in mind that for the first 50 miles from the land the Bay has less than 100 meters depth that would exagerate the waves more. Any comments from real experiences are welcome!

 

[Roberto]

The usual graphs say a 25kt winds with a 10M fetch yield a 1.4m significant wave height (minimum wind duration 2 hours), Swh then increases linearly with fetch before topping, at 100M fetch it is 3m (min wind duration 12 hours).
A 25kt wind with unlimited fetch and minimum 48h duration gives a fully developed sea state with Swh slightly less than 4m.
That's of course only wind waves, then there is swell.

Oh, depth
The fully developed sea wave period is about 7s, waves would be "deep water waves" with depths above 35-40m.

 

[25931]

I´ve crossed numerous times, summer and winter with conditions varying from flat calm to a winter snowstorm but never experienced enormous waves but I´ve usually been on the outside route to or from England.

 

[Akestor]

The usual graphs say a 25kt winds with a 10M fetch yield a 1.4m significant wave height (minimum wind duration 2 hours), Swh then increases linearly with fetch before topping, at 100M fetch it is 3m (min wind duration 12 hours).
A 25kt wind with unlimited fetch and minimum 48h duration gives a fully developed sea state with Swh slightly less than 4m.
That's of course only wind waves, then there is swell.

Oh, depth
The fully developed sea wave period is about 7s, waves would be "deep water waves" with depths above 35-40m.

Thanks very informative!

 

[Akestor]

I´ve crossed numerous times, summer and winter with conditions varying from flat calm to a winter snowstorm but never experienced enormous waves but I´ve usually been on the outside route to or from England.

Do you have Centaur ? I got Longbow but crossed with a 41 Catamaran.

 

[25931]

Do you have Centaur ? I got Longbow but crossed with a 41 Catamaran.

No, La Roca is a Seamaster Sailer but I haven't crossed Biscay in her.

 

[Akestor]

No, La Roca is a Seamaster Sailer but I haven't crossed Biscay in her.

As i see also by Laurent Giles. His designs can be recognised even looking a thumbnail!

 

[25931]

As i see also by Laurent Giles. His designs can be recognised even looking a thumbnail!

Indeed,great little boats and perfectly capable of crossing Biscay.

 

[sailaboutvic]

It's not boats that have problem crossing the bay

 

[25931]

It's not boats that have problem crossing the bay

Too true.

 

[AndrewB]

While I agree that Biscay's reputation has tended to be exaggerated, it is by no means innocuous.

Firstly, in a west or south-west gale there is a danger of being embayed towards the dangerous Plateau de Rochbonne. So it means active sailing in those conditions, not just heaving-to and allowing the yacht to look after itself.

Secondly, though I've never heard it mentioned elsewhere, on several crossings I've made there has been a significant line of rough water, perhaps half a mile wide, just where the Continental Shelf rises. (For example, crossing from southern Brittany to Gijon, at something like 46°15'N, 4°15'W). This was particularly severe one time when I crossed it in a westerly gale.

Both of these are a good argument for keeping well out to the west when crossing with an iffy forecast.

 

[scotty123]

While I agree that Biscay's reputation has tended to be exaggerated, it is by no means innocuous.

Firstly, in a west or south-west gale there is a danger of being embayed towards the dangerous Plateau de Rochbonne. So it means active sailing in those conditions, not just heaving-to and allowing the yacht to look after itself.

Secondly, though I've never heard it mentioned elsewhere, on several crossings I've made there has been a significant line of rough water, perhaps half a mile wide, just where the Continental Shelf rises. (For example, crossing from southern Brittany to Gijon, at something like 46°15'N, 4°15'W). This was particularly severe one time when I crossed it in a westerly gale.

Both of these are a good argument for keeping well out to the west when crossing with an iffy forecast.

Finisterre is the danger area for yots.

 

[franksingleton]

Much of Biscay’s reputation dates from square rigger days when ships could not beat to wind very well. With forecasting these days, there should be little problem in waiting for a 5 or 6 day window. As someone noted, the danger area can be near Cabo Finisterre. Winds there might not be predicted well a few days in advance.worst may well be in a NEly.

 

[AndrewB]

As someone noted, the danger area can be near Cabo Finisterre. ...

I am bit surprised by this opinion. Most Biscay crossings aim for Gijon, Corunna or Camarinas: Finisterre is the next leg.

Maybe its just luck, but the worst problem I've had with Cabo Finisterre is fog. It's a walk in the park relative to the passage around the corner of NW France, by Ushant and the Pt du Raz. That features not only fog but heavy shipping, fearsome tides and extensive reefs.

 

[sailaboutvic]

I am bit surprised by this opinion. Most Biscay crossings aim for Gijon, Corunna or Camarinas: Finisterre is the next leg.

Maybe its just luck, but the worst problem I've had with Cabo Finisterre is fog. It's a walk in the park relative to the passage around the corner of NW France, by Ushant and the Pt du Raz. That features not only fog but heavy shipping, fearsome tides and extensive reefs.

I second that with three crossing under my belt , fog and the bloody fishing buoys right along that coast

 

[franksingleton]

I was not saying that it would necessarily take 5 or 6 days to cross Biscay. I was really trying to say thst forecasts are good enough these days to be fairly sure of not being caught out. Many years ago, we had to divert to Audierne when a favourable forecast went wrong. But, I hear of many that go direct from the U.K. at least to A Coruña. Dartmouth, my home port to A Coruna in our boat is about 5 days. Finisterre is notorious for its erect in the wind but, do also is Cabo Ortegal. Approaching on one occasion with AEMet saying F4-5, we gout up to 7-8. It is not a headland to be taken lightly,
Fog is a hazard in that area due to the cold water. But, in some 8 riundingd, fog Was never a problem although we did experience fog in the Rias. Maybe, we were lucky. Of course, if there is fog when making landfall is a problem you can stand off and go further or approach using your radar.

 

[scotty123]

I was not saying that it would necessarily take 5 or 6 days to cross Biscay. I was really trying to say thst forecasts are good enough these days to be fairly sure of not being caught out. Many years ago, we had to divert to Audierne when a favourable forecast went wrong. But, I hear of many that go direct from the U.K. at least to A Coruña. Dartmouth, my home port to A Coruna in our boat is about 5 days. Finisterre is notorious for its erect in the wind but, do also is Cabo Ortegal. Approaching on one occasion with AEMet saying F4-5, we gout up to 7-8. It is not a headland to be taken lightly,
Fog is a hazard in that area due to the cold water. But, in some 8 riundingd, fog Was never a problem although we did experience fog in the Rias. Maybe, we were lucky. Of course, if there is fog when making landfall is a problem you can stand off and go further or approach using your radar.

The sea bottom there also a major contributor to large seas, which can hazard most yachts.

 

[franksingleton]

Posted in error

 

[25931]

I was not saying that it would necessarily take 5 or 6 days to cross Biscay. I was really trying to say thst forecasts are good enough these days to be fairly sure of not being caught out. Many years ago, we had to divert to Audierne when a favourable forecast went wrong. But, I hear of many that go direct from the U.K. at least to A Coruña. Dartmouth, my home port to A Coruna in our boat is about 5 days. Finisterre is notorious for its erect in the wind but, do also is Cabo Ortegal. Approaching on one occasion with AEMet saying F4-5, we gout up to 7-8. It is not a headland to be taken lightly,
Fog is a hazard in that area due to the cold water. But, in some 8 riundingd, fog Was never a problem although we did experience fog in the Rias. Maybe, we were lucky. Of course, if there is fog when making landfall is a problem you can stand off and go further or approach using your radar.

 

[25931]

On the one occasion that I met fog I had to stand off and carry on - I've never had radar on either my own or delivery boats.