The Rogue wave and the sailor

[Qayaq]

On passage from BVI to Bocas Panama, about half way, nasty night, quite blowy. Got the mast just in the water in a 40ft Amel. Figure rogue wave mixed up with a sea mount, been passage planning to avoid sea mounts ever since. When you start looking for them you find that there are a lot more sea mounts than you first thought..

[mabowers]

Thread drift but I made ETC on her in '90.

A buddy who was an OS on the bridge when that wave hit said it covered the flight deck back to the "Belknap pole" before breaking. I was in my rack, felt the bow climbing, climbing, climbing, then a sphincter tightening freefall that felt like a minute but was actually 4 or 5 seconds, then "WHAAAANG", followed by GQ alarm. Like newhaul said, between 2 storms and we were also I believe where 2 major currents met, weird waves can/do happen.

Originally Posted by newhaul

on the chuck wagon
the waterline was mid deck 4 so approx 60 ft from flight deck to the lwl at full combat load .
And the rogue that swept the deck was at a minimum of 75' .

When was your cousin on that prison .

( ht3 to HTC '86-'92 on her)

[sheldon957]

Just an add on to Dan Mosby's little tirade on the conversions:

In 1983 a Boeing 767 Passenger Jet became a glider after a conversion mixup of fuel. FYI. Their glide ratio sucks.

This flight is infamously known as the Gimli Glider. (for you Three Amigo's fans, Infamous means more than famous )

https://www.nytimes.com/1983/07/30/u...on-errors.html

[a64pilot]

The NY Times article is full of errors and omissions.
This is a better account of what actually happened and how
https://en.m.wikipedia.org/wiki/Gimli_Glider

Almost always, always an accident is a chain of events, and every single link of the chain has to fail one after another, or there is no accident. Once you understand how the Gimili incident happened, you should be surprised a large Commercial aircraft is allowed to fly with its fuel gauges inoperative, but they let it go in a revenue flight.

The glide ratio of a 767 is about 11 to 1, which ain’t bad at all actually, average little Cessna is only about 9 to 1, so a 767 will glide further, but have a higher approach speed of course.

This one is really impressive to me, super bad wx etc and the Pic has the sense to start the APU to power the aircraft.
https://en.m.wikipedia.org/wiki/TACA_Flight_110

Seemingly the one thing that is almost always present in successful Commercial aircraft emergencies is the PIC nearly always has significant Military experience.

[Dan Mosby]

Originally Posted by Qayaq

... been passage planning to avoid sea mounts ever since.

Undersea geography is something I didn't take into consideration much during route planning. After looking into these damn waves, it has made me realize that small dips, depressions and valleys on the ocean floor can have a far larger impact on the surface than I would have expected.

[Don C L]

Originally Posted by wingssail

On the east coast of Africa, where Agulhas Current meets southerly storms, many ships have been lost due to huge waves. (This caused a lot of anxiety on the Wings crew as we anticipated an approach to Africa.)

However, there is pretty good weather forecasting now and it is possible to avoid travelling on that coast if the conditions are going to get bad. However, when the weather radio broadcasts a warning about "abnormal waves", you need to get to shallow water asap (inside 100mt depth there is much less current and the waves don't get so big).

In this photo we just got "that" warning, and we're running for it. Never saw a big wave though, lucky us.

Interesting, I would have thought that the deeper water would be the safer. Don't the waves travel into the shallower water with greater likelihood of breaking?

edit:
Ah I see, they are localized features resulting from the speed of the current and opposing wind? As the current slows the waves subside?

[wingssail]

Originally Posted by Don C L

Interesting, I would have thought that the deeper water would be the safer. Don't the waves travel into the shallower water with greater likelihood of breaking?

edit:
Ah I see, they are localized features resulting from the speed of the current and opposing wind? As the current slows the waves subside?

Yes, the Agulhas current is a river, like the Gulf Stream. It runs basically off shore of the 100mt line. The big waves are wind against current. No current, no waves.

[Seighlor]

Originally Posted by wingssail

Yes, the Agulhas current is a river, like the Gulf Stream. It runs basically off shore of the 100mt line. The big waves are wind against current. No current, no waves.

Or put another way, no wind, no waves. I'm certain the current is a constant; the wind is variable, both in terms of velocity and direction. The roughest seas are created when the wind and current flow in opposition to each other.

[Dan Mosby]

Originally Posted by Seighlor

The roughest seas are created when the wind and current flow in opposition to each other....

....over restrictive or undulating terrain beneath the sea that's responsible for forcing below surface water to increase velocity and or abruptly change direction in a manner that has a detrimental impact to surface vessels.

I think the underwater geography is something most of us completely overlook.

[barnakiel]

Originally Posted by Seighlor

Or put another way, no wind, no waves. I'm certain the current is a constant; the wind is variable, both in terms of velocity and direction. The roughest seas are created when the wind and current flow in opposition to each other.

Good guess, but actually on the edges there will be swirls (miles across) and inshore there will be a back current, which makes the whole wave situation one level more complex!


In RSA boats run for inshore, into the counter-current, when the blow arrives.


And yet, neither the Stream nor Agulhas are the ultimate booby traps. In the waters between Tonga and NZ ocean currents do this:


http://calib.org/marine/currents/NZcirc.jpg


I can tell you one thing: we were slowly sailing upwind in a typical bad frontal weather when our boat got lifted, tossed and placed upside down in the soup! When she re-righted I went on deck to judge the damage only to see a Teahupoo sized roller not too far from our boat. I was actually shocked into thinking we went over some shallows that I did not notice when planning.


No such thing. One hour later the sea was back to regular 6 meter pattern and only that broken spreader, our cuts and bruises and a gran bordello below confirmed we did get hit. Ah, yes, the dodger was gone too ;-)


My naive and silly faith in seaworthiness of small boats has been replaced with UTTER RESPECT FOR THE UNLIMITED POWER OF THE OCEAN.



Big waves, once met, completely change your vision of small craft safety. They also change ones opinion on what makes a small boat.


Cheers,
b.

[Dan Mosby]

Originally Posted by barnakiel

And yet, neither the Stream nor Agulhas are the ultimate booby traps. In the waters between Tonga and NZ ocean currents do this:


http://calib.org/marine/currents/NZcirc.jpg

That's an excellent image to convey the impact undersea geography has on surface currents and such.

[barnakiel]

Well. Yes and no.


Remember water below the currents (the big ocean ones) may or will flow in the opposite direction!


Or it may 'stand still'.


Doh.


When a sea mountain comes close to the surface, no doubt we should give the place a wide berth.


When the features are deep below, well, at times yes at times no and most of the time we do not know - oceans are way less understood than the land.


b.

[CassidyNZ]

Originally Posted by barnakiel

Good guess, but actually on the edges there will be swirls (miles across) and inshore there will be a back current, which makes the whole wave situation one level more complex!

The counter current is not always evident but the Stream is not as noticeable inshore. That said, there are places where the Stream comes literally within half a mile from the shore and this changes from season to season.

We sailed up the coast from Durban to Nose Bay (Madagascar) in early 2004 and successfully used the counter currents to get us above Beira and then we were confronted with Gafilo! That had us run for cover, we holed up in Isle da Mocambique for four days to let the weather settle.

Image below of Gafilo, the coast on left is east coast of Madagascar. The cyclone went over the island into the channel until the eye was just 150nm from our hideaway (red dot in second image).

[barnakiel]

Disturbing to think of how much suffering this one brought to Madagascar people!


b.

[CassidyNZ]

Originally Posted by barnakiel

Disturbing to think of how much suffering this one brought to Madagascar people!

Yes, it fairly wrecked the already fragile infrastructure but it never dampened the spirit of the people. We made an involuntary contribution to their economic well-being - we left without our dingy or outboard motor

One interesting thing about that region (to bring us back on topic) is that the south equatorial current flows directly over the top end of Madagascar (and contributes to the Agulhas Stream) and it hits undersea mounts south of the Farquhar Island chain causing up-wellings that create a very disturbed sea surface even in calm weather.

It’s very disconcerting to suddenly sail into very actively rippling water where the boat appears to go where it wishes, slewing from side to side with seemingly no control on the helm and maintaining boatspeed becomes a full-on challenge. These up-wellings can stretch on for several miles of madly rippling and audibly noisy water. I reckon in heavy weather rogue waves probably happen there quite frequently, thankfully we went through the area with 15kn of beam weather. Still, on one day we logged just 73nm where we would normally do 135nm in a day’s work.