Multihulls and 70' waves

[ImaginaryNumber]

A few days ago a monohull was hit by a large wave off of Sydney, Australia, dismasted, ran out of fuel, set off his EPIRB, and was rescued. In the news report by Today News it was stated that it was hit by a 70' wave.

My first question is what happens to a 'typical' cruising catamaran or trimaran when they are hit by a 70-foot (breaking?) wave? I assume they will flip over. Will they break apart, or not?

And second, how common are 70-foot waves off eastern Australia? Is this a bad time of year to be sailing in the Tasman Sea?

 

[masalai]

Begs the question - - - Why go out to see when the weather is appalling... Why marry a partner known for violent and aggressive mood swings... Why try to cross a road where there is a lot of hoons racing their cars in a demolition derby, all with murder on their minds...

Methinks there may be more to that tale that has not been told... Forecasts here may have been advisable before departure... http://www.bom.gov.au/australia/charts/viewer/index.shtml?type=sigWaveHgt&tz=AEST&area=Au&model=WG for sea and swell direction & height, http://www.bom.gov.au/australia/cha...pe=windbarb&level=10m&tz=AEST&area=Au&model=G for wind speed and direction, and http://www.bom.gov.au/australia/charts/synoptic_col.shtml for synoptic charts

Note the wave height in the first image, 10 to 15 metres PLUS

Why not check the weather forecast REGULARLY, carry back-up systems (I have 3 gps devices on my boat)... Mark my position regularly on paper charts and record in the ships log (written in pencil - so it won't smudge of 'run')... Know my boat is predictable in seas up to 5 metres... Am comfortable in my capacity to navigate without GPS,.. Have several planned 'safe havens" located and always within comfortable reach and to which I can head should some 'disaster' strike... If caught out I can quickly and easily set up to be 'hove-to' and when conditions ease, rig some form of jury rig to get under way again...

I travelled solo from Brisbane to Cairns, in my boat CNO, sheltering when appropriate, resting at night safe at anchor for the prevailing weather and forecast up to 4 days forward... Common sense seems to be a personal attribute lacking in so many...

The Tasman sea is renown for rapid mood swings, both in Bass Strait and to the south of Tasmania... Not my preferred cruising region by a long shot... A place where insanity and foolhardiness are likely to prevail... If you have a death wish traverse the globe in the southern latitudes often referred to as the "Roaring 40's" because it is more southerly that 40 degrees and the second image shows 48 to 64 knots in one front passing eastwards...

 

[Corley]

Jerry Heutink survived a massive rogue wave on his cruising trimaran. I cant really say anything more about it as I haven't read the book. But apparently he managed to surf the wave on his boat. Wave heights are always a bone of contention I'd like to know the actual height of the wave in question. We know rogue waves exist and occur more in wind against current areas such as in the Agulhas current in reality they are a statistically predictable event but they often appear and vanish in a small timeframe and most sailors will luckily never see or experience a true rogue wave.

The outcome of an encounter on a small boat of any type with a rogue wave is unpredictable sometimes they survive sometimes they dont. For example the yacht Winston Churchill sank after an encounter with a large breaking wave and the trimaran gulf streamer was capsized by a large breaking rogue wave in the Gulf Stream. Wave heights have been recorded in excess of 100ft by oil rigs in storms in the North Sea.

 

[cavalier mk2]

I read the book Corley. He was in the Bermuda Triangle and had the help of "divine" guidance....for some that would have summoned pink flamingos but he was told to steer straight (always helpful).....The wave was steep enough to bury the boat in green water, the peak passing someway up the mast but the Cross 46 tracked straight and emerged out the back of the wave as it passed though water was shipped through open hatches. They were told such waves were not unusual for the area....

 

[cavalier mk2]

I just looked at the book again, Jerry felt a reassuring presence and a voice told him to look behind him where he saw "the mammoth killer wave". While contemplating the end he had more help. "It was not I who held the wheel , but someone grasped the spokes and held us on a unerring course.' Shades of Slocum....he doesn't estimate the height of the wave but while steering from the pilot house tells of the light going dark as the boat was buried in water, unable to rise to the steep, fast moving slope. It took hours for the electric bilge pumps to clear the water that came in the open hatches. Later in the chapter he speculates about the "white seas" seen by Columbus and others since that time as possibly being large methane bubbles rising to the surface, something to think about while crossing the increasingly active volcanic areas because as Jerry points out, ships can't float on a bubble...which makes the waves look a bit better.

 

[auscat]

Rathma.Google the story.Amazing what a multihull can survive without crew.

 

[Frosty]

Waves are like fish , they tend to be exaggerated.

As far as I remember to measure a wave it is not from the trough to the crest, it is half of that.

A 70 foot wave would mean that if you were in a dinghy in the trough the crest would be 140 feet above you.

I think that is bigger than any other wave in the world isnt it?

 

[ImaginaryNumber]

Wikipedia: Wave height

In fluid dynamics, the wave height of a surface wave is the difference between the elevations of a crest and a neighbouring trough.

For a sine wave, the wave height H is twice the amplitude:

For a periodic wave it is simply the difference between the maximum and minimum of the surface elevation z = η(x – cp t):

In random waves at sea, when the surface elevations are measured with a wave buoy, the individual wave height Hm of each individual wave—with an integer label m, running from 1 to N, to denote its position in a sequence of N waves—is the difference in elevation between a wave crest and trough in that wave. For this to be possible, it is necessary to first split the measured time series of the surface elevation into individual waves. Commonly, an individual wave is denoted as the time interval between two successive downward-crossings through the average surface elevation (upward crossings might also be used). Then the individual wave height of each wave is again the difference between maximum and minimum elevation in the time interval of the wave under consideration.

 

[ImaginaryNumber]

Begs the question - - - Why go out to see when the weather is appalling...

The Tasman sea is renown for rapid mood swings, both in Bass Strait and to the south of Tasmania... Not my preferred cruising region by a long shot... A place where insanity and foolhardiness are likely to prevail... If you have a death wish traverse the globe in the southern latitudes often referred to as the "Roaring 40's" because it is more southerly that 40 degrees and the second image shows 48 to 64 knots in one front passing eastwards...

As I understand it the yacht was dismasted east of Sydney, not in the Bass Strait or south of Tasmania.

The two charts you posted don't show appalling weather in the area a few hundred miles east of Sydney -- at least not on the day you collected the charts. Some pretty nasty weather in the Indian Ocean, SW of Australia.

 

[ImaginaryNumber]

...We know rogue waves exist and occur more in wind against current areas such as in the Agulhas current in reality they are a statistically predictable event but they often appear and vanish in a small timeframe and most sailors will luckily never see or experience a true rogue wave...

Are the areas off eastern Australia known for strong currents and adverse winds, creating large waves?

 

[Corley]

There is a current that runs down the Australian coastline and when combined with a storm can create violent seas as witnessed in the 1998 Sydney to Hobart race. Seven boats were abandoned at sea and five sank. Fifty-seven sailors were rescued from the decks of damaged boats or from the sea itself, six sailors died.

There was a wave height study that was done by the Bureau of meteorology you might be interested in reading it.

http://www.cawcr.gov.au/bmrc/ocean/staff/dag/Sydhob/sld001.htm

 

[brian eiland]

Note: reference source, Lock Crowther Designs

"This work (tank testing at Southampton Univ) has indicated that the well designed catamaran is remarkably safe in breaking waves up to considerable height, even when beam on, we were unable to capsize a power catamaran yacht in the largest wave which could be generated. This corresponded to a 52' wave for a catamaran of 40' beam. Scaling this down to a typical 24' beam cruising cat means she should be O.K. in a 31' breaking beam sea. An equivalent size mono-hull power boat was easily capsized by a 25' breaking sea, and in tests with conventional yachts after the Fastnet disaster, it was found that a 40' mono-hull yacht could capsized in a 12' breaking sea"

 

[MikeJohns]

A power cat wave tank RAO doesn't extrapolate to a sailing multihull, they are quite different vessels.

There is a thread http://www.boatdesign.net/forums/multihulls/multihull-capsize-prevention-split-43251.html

That is worth reading in it's entirety

 

[ImaginaryNumber]

There is a current that runs down the Australian coastline and when combined with a storm can create violent seas as witnessed in the 1998 Sydney to Hobart race. Seven boats were abandoned at sea and five sank. Fifty-seven sailors were rescued from the decks of damaged boats or from the sea itself, six sailors died.

There was a wave height study that was done by the Bureau of meteorology you might be interested in reading it.

http://www.cawcr.gov.au/bmrc/ocean/staff/dag/Sydhob/sld001.htm

Thanks for the link. I enjoyed reading it. The Sydney-Hobart race took place in the latter part of December, which according to Adlard Coles' 'Heavy Weather Sailing' is the 'main season' for cyclones in that area. According to the link average wave heights during the height of the storm were ~10m/33', with max heights of ~15m/50'

But this incident took place in October, which appears to be outside of even the early-late time frame for cyclones. So I presume an 18m/70' wave would be very unusual.

 

[Frosty]

Arm chair sailing is always fun is'nt it.