Waves steeper in the Med, because water denser..

[JumbleDuck]

There are different Plimsoll lines for different conditons/seasons....

I know, but none of these are explicitly for the Med or the Baltic, or indeed for higher densities at all.

 

[OceanSprint]

Shines a new light on 'hiding under a layer' as submariners do!

Please don't think that density varaiation in the sea is irrelevant. It is, when you consider the density difference between water and air, at the surface where wind waves are created.

But within the sea even tiny density differences, can have major effects, creating vertical layering, vertical movement of water and horizontal currents. The "global conveyor belt" is driven by density differences in the ocean

 

[capnsensible]

Please don't think that density varaiation in the sea is irrelevant. It is, when you consider the density difference between water and air, at the surface where wind waves are created.

But within the sea even tiny density differences, can have major effects, creating vertical layering, vertical movement of water and horizontal currents. The "global conveyor belt" is driven by density differences in the ocean

Indeed. Many years sat in the control rooms of dived submarines taught me that with particular regard to sound travel.

My reference to beer was, however, a joke. But I do also have lots of experience of drinking it......... :encouragement:

 

[Hydrozoan]

...But within the sea even tiny density differences, can have major effects, creating vertical layering, vertical movement of water and horizontal currents. The "global conveyor belt" is driven by density differences in the ocean

Indeed, and the need for accurate measurements of small differences in seawater density drove the development of accurate measurements of salinity.

Please don't think that density varaiation in the sea is irrelevant. It is, when you consider the density difference between water and air, at the surface where wind waves are created.

Internal waves can also be generated at the boundary between waters of different densities - e.g melt water lying above saltier, more dense seawater. This gives rise to the phenomenon called "dead water" (first described by Nansen on the Fram) in which the propellor, lying at the interface, dissipates its energy in creating such waves rather than propelling the vessel.

 

[Sans Bateau]

A short chop can soon become a horrendous surge with a strong wind behind it in the Med. The photo below is of a winter storm with a fierce Easterly at Port de Borme in the South of France

When we were there in Sept we had 34knts of wind from the same direction with only a little spray coming over the sea wall, not enough to move our cars. So you can imaging the wind speed whipping this one up.

 

[jimbaerselman]

There are 5 principal factors in wave formation

Wind speed
Water depth
Fetch
Width of fetch
Duration of wind

The small variation in water density caused by salinity changes has negligible effect on wave properties.

The difference between waves in different regions, including lakes, is due to differences in the five factors above, and how they vary with time and with location in any one area.

Complete sense at last!

I have just read in an on-line cruising guide to the Med, ' newcomers soon learn that a headwind of 15 knots or so kicks up a particularly nasty short chop, due to the denser water of the Mediterranean'.
True it's a (little) bit denser, but the nasty short chop was the writer trying to launch an urban myth..wasn't it?
The source was an association, for cruising yachtsmen.

Urban myth.

If you're referring to The Cruising Association as the source, please let me know where to find these quotes, since I can't find them. I will then arrange for them to be corrected.

If it's another source, please let me know.

 

[jerrytug]

Complete sense at last!



Urban myth.

If you're referring to The Cruising Association as the source, please let me know where to find these quotes, since I can't find them. I will then arrange for them to be corrected.

If it's another source, please let me know.

PM coming..

 

[jimbaerselman]

Ooops! Found and corrected with jerrytug's help. Many thanks. Indeed, a lesson in how urban myths arise - by accident!

 

[KellysEye]

>Because in many places its from 1000 or 2000 meters

The average depth of the Mediterranean Sea is 1,500 metres. On passage over Biscay in strong winds the pilot book says stay outside the 1,000 fathom line, 1,828 metres, the reason is beyond that line the waves/swell are shorter and higher, exactly the same conditions as the Med in strong winds.

 

[mjcoon]

>Because in many places its from 1000 or 2000 meters

The average depth of the Mediterranean Sea is 1,500 metres. On passage over Biscay in strong winds the pilot book says stay outside the 1,000 fathom line, 1,828 metres, the reason is beyond that line the waves/swell are shorter and higher, exactly the same conditions as the Med in strong winds.

Where "beyond" means "inside", the opposite of "outside"?

Mike.

 

[Roberto]

It's 100 fathoms, not 1000

100 fathoms roughly equals 200m; wave theory states a wave begins to be modified by depth when depth becomes less than one half of wavelength, in the North Atlantic ocean maximum wave periods are what, 16-17 seconds ? That means wavelengths in the order of 350-400m, which is consistent with the 100 fathoms advice.
Wave periods (hence lengths) in the Med are considerably lower, so depths that cause wave transition are relatively shallower than those affecting ocean wave.

Also, 100 fathoms also often corresponds to the area of continental shelf, where all sorts of other phenomena may be felt on a boat, for example stronger current, overfalls, etc