Rogue Waves

[fisherman]

One of the best breaks in Cornwall is reckoned to be Porthleven.
I can assure you the swell gets to the Lizard, it is due E from the Wolf Rock, then comes round the corner. The depth comes from 47 fm to 25fm along a line W from the point, roughly, then up to 10fm on top of the Bows, WNW of the point. Seen it break there.

 

[Seajet]

Is that a ' break ' as in holiday or surf ?! :ambivalence:

 

[rotrax]

47' sounds a bit much, but I've been out in 10'+ swells in the western Channel and it was as smooth as you like. It was a bit like a road I drove down once, dead straight, up a hill, over the top, down the other side and up the next one. Repeat for several miles. A world of difference from a 10' chop in the Solent - that's one big chunk of no thanks.

What makes the difference is the Solent chop, even when it's only a few feet, has a wavelength of maybe 3 times the height, the swells had a wavelength of 100 yards or more

I went on a sport fishing charter out of San Francisco in september 1982. The boat was an almost new 45 foot aluminium twin engined vessel specificaly designed for the job of trolling anchovies on a long leader for Pacific Salmon before they migrated up the rivers.

The swells were long, high and slow. The Skipper estimated them at close to 40 feet. When in a trough, all you would see was the tops of the swells, when on the peak the Golden Gate Bridge could be seen at distance, along with the mountain tops.

When playing a Salmon - they went to 30 LBS - the rod was constantly being adjusted as one minute it was below you in a trough, the next above you in a peak! The hooked fish could clearly be seen fighting in the peak of the swell thirty odd feet above your head!

Never experienced anything like it since.

 

[jimi]

I’ve surfed porthleven, it’s a reef break and gets very interesting ?at low tide

 

[Stemar]

That's the thing, big swells in deep water are harmless as long the weather system that produced them is at a safe distance. It's when the water shallows and the swells start to drag their feet on the bottom that things liven up a bit. Biscay's a typical example, it's reputation isn't only built on square riggers getting embayed, but on the sea that builds up out of a benign Atlantic swell as the water shallows

 

[geem]

That's the thing, big swells in deep water are harmless as long the weather system that produced them is at a safe distance. It's when the water shallows and the swells start to drag their feet on the bottom that things liven up a bit. Biscay's a typical example, it's reputation isn't only built on square riggers getting embayed, but on the sea that builds up out of a benign Atlantic swell as the water shallows

We got hit by a rogue wave on route from Portugal to Madeira in 2004. We had N wind and swell of 5m in a F7 wind on the beam. We were in a Prout Snowgoose37. Seas were nasty and breaking on their tops and slamming the side of the hull. Not life threatening conditions until an incredibly fast wave twice the size of the others came through. We were taken sideways by the wave some distance before the cat broke over the back of the wave in a very violent manner. We were lucky not to be inverted. I think the shallow keels allowed us to slip sideways. If we had had daggerboards with more grip I suspect we would have flipped. The inside of the boat afterwards looked like we had been ransacked. Everything was tipped out and and spread across the boat. It was probably our worse moment in a lifetime of sailing. It partly influenced my decision to have a monohull next time around. After the event we realised that we had sail over a seamount. The depth shallowed to only 50metres. We have since sailed around every seamount in bumpy weather

 

[Ohlin Karcher]

We got hit by a rogue wave on route from Portugal to Madeira in 2004. We had N wind and swell of 5m in a F7 wind on the beam. We were in a Prout Snowgoose37. Seas were nasty and breaking on their tops and slamming the side of the hull. Not life threatening conditions until an incredibly fast wave twice the size of the others came through. We were taken sideways by the wave some distance before the cat broke over the back of the wave in a very violent manner. We were lucky not to be inverted. I think the shallow keels allowed us to slip sideways. If we had had daggerboards with more grip I suspect we would have flipped. The inside of the boat afterwards looked like we had been ransacked. Everything was tipped out and and spread across the boat. It was probably our worse moment in a lifetime of sailing. It partly influenced my decision to have a monohull next time around. After the event we realised that we had sail over a seamount. The depth shallowed to only 50metres. We have since sailed around every seamount in bumpy weather

Good story, it echos a couple of things I learned..we delivered a big cat (Outremer 55 ) out of Vilamouro and I was strictly warned not to go over the sea mounts to the NW, as the swell was building, and the skip (Brendan C ex of this parish, lovely chap) pointed out that ocean swells can reduce a 10 m sounding on the chart, to a drying height, quite easily..
also in (for me at least) worryingly huge swells, we also had to raise the daggers, to let her slip sideways down the faces of waves, that worked very well.
I avoided going over the tops of the seamounts..by going between them that was foolhardy, but we we were hard on the wind and they were on track..

 

[stephen_h]

We passed the same seamounts from Madeira to Portugal in very rough weather on a Wharram.
We were about 5 miles leeward of them and the waves were very large. In fact they smashed the front cross
beam to pieces and later the mizzen mast fell over!
Next time in any weather I will give them 50 miles clearance

After passing the mounts it calmed a bit but I saw a much larger wave break in front of us. It just kept rolling along leaving a very long white track of foam. Glad we missed that one.

Still sail catamarans but without dagger boards because they do slide sidways when hit.

 

[Ohlin Karcher]

We passed the same seamounts from Madeira to Portugal in very rough weather on a Wharram.
We were about 5 miles leeward of them and the waves were very large. In fact they smashed the front cross
beam to pieces and later the mizzen mast fell over!
Next time in any weather I will give them 50 miles clearance

After passing the mounts it calmed a bit but I saw a much larger wave break in front of us. It just kept rolling along leaving a very long white track of foam. Glad we missed that one.

Still sail catamarans but without dagger boards because they do slide sidways when hit.

That's a very good heads up, that seamounts can set up waves which carry miles downwind. Sounds like quite a trip!!