Steepness of Mediterranean seas: causes?

[alahol2]

Very many moons ago I remember hitch hiking along the Jugoslavian coast road toward Greece. One evening we climbed down a small cliff to spend the night on a flat rock a couple of metres above sea level. The sea was glassy calm. After dark there was a terrific thunderstorm that lasted maybe 15 minutes. Once the storm had passed we settled down again for the night, sea still flat. 15 minutes later very violent waves started to crash over our rock, we managed to scale the cliff out of there in a panic. The event lingers in my memory as one of those that could have been the end of me.

 

[LittleSister]

I wonder if all that sun, not to mention the diet of olives and retsina, affects one's perception of how steep the sea is.

 

[CAPTAIN FANTASTIC]

I wonder if all that sun, not to mention the diet of olives and retsina, affects one's perception of how steep the sea is.

The retsina is definitely a contributing factor for seeing things double

 

[BrianH]

In 1982, Des Sleightholme, then editor of Yachting Monthly, was loaned a Gib Sea 31 charter boat and had a week in the northern Adriatic when he experienced a sudden gale-force sirocco, which he summarised in YM. In it, he describes the waves it generated and may be relevant to this thread.

The wind was light to moderate south to south-westerly, the barometer. was high and showing little sign of movement and it was mid-morning. We saw another yacht rounding up and stowing all sail in something of a hurry. Instinctively I glanced astern. There appeared to be a bank of mist at sea level.

The white squall came down with shocking speed. there was a rising roar, the boat staggered as the wind and rain hit us then we were off. The whole sea became a flying mass of rain and spray that cut the visibility to a bare length ahead. The boat rose on a plane with her bow wave curling aft into her wake with the roar of water adding to the din of wind and rigging.

We both expected the squall to pass as quickly as it had arrived. That it reached storm Force 10 I do not doubt but I hung on and let her go waiting for the lull when I could do something about our grossly over-canvassed state. The lull never came. These were the facts.
1. I dare not hand over the helm in order to get the sails down and I was not going to send my wife forward. I doubted that the sails could be hauled down anyway. I couldn't navigate.
2. An attempt to round up threw the boat on her beam ends with her lee guardrail under and in that short time a wickedly steep sea created a motion that made it barely possible to hang on let alone work. Lying there she refused her helm until I managed to reach the ignition key and start the engine. Although the propeller was half out of the water, after some minutes she came off on the run again.

We tore on downwind before a rising sea. The halyards were led aft to the cockpit and Joyce let them both go at the run but the sails came only half-way down and of course flogged continually so that I was worried about losing them. Our speed though did drop a little, to 8-9 knots on the clock. We had, by then, been running for an hour or more parallel to the Adriatic coast on our starboard side and distant some couple of miles but visible only as an occasional dark blur.

The sea was rapidly building up into hollow, steep waves of perhaps 6-9ft in height which, coupled with the fact at our speed, suggested that it was high time we rounded up. The sails would have to be stowed properly. I considered streaming warps, but we had neither enough in terms of length nor could they be got at safely because the cockpit locker lid was massive and we had no means of lashing it safely open for one person to delve in it without risk of serious injury in that sea and motion.

At last I handed over to Joyce. The boat was running in a series of wild glissades, burying her bows deeply, wave-surfing dizzily between times with the foam bursting and blowing ahead of her in streamers. Harnessed I crept forward. I had taken the lanyards off three fenders to provide tiers and with these I lashed down the heads of both sails and the bunt of the mainsail. I started the engine.

My plan was to attempt to hove to under engine half bows-on at the minimum revs necessary. The working jib I felt was much too big - I was also disinclined to try setting it as I might have done in normal seas. I rounded her up between waves. It was a repetition of the first attempt. We were thrown violently down under a solid weight of breaking water, propeller threshing air and the motion had a whip-lash force that left us in danger of being flung straight out of the cockpit. I tried again and again to bring her up to an acceptable angle but I was tiring and I had no doubt that we would be too exhausted to hang on much longer. I came off on the run again.

After a while the wind fell to gale force. the visibility cleared enough to be able to make out coastal details occasionally and I handed over the helm. Ahead of us there was a headland though and beyond it a deep bay and that was where we must reach. I had found by then that it was our speed which was the saving of us and the reason why we had not broached so I had left the engine in gear to maintain it during this slight lull. Now I could see a black line of cliffs some two miles away with seas bursting and climbing palely up the face of it. I altered course to port for an offing. Plainly I must keep in visual touch with the headland and be ready to alter hard to starboard as soon as it came abeam in order to get into a lee before we went tearing past downwind. The second white squall burst upon us, the log had stuck again at 10 knots plus. I timed our distance on my watch; I gave it six minutes and then brought the sea on our starboard quarter.

Perhaps four minutes went by and then suddenly, almost magically the seas decreased. We had a sudden glimpse of rocks, a white tower, a cove with small boats and all at once we were under the lee.​

 

[rgarside]

But that happens on every sea in the world. It seems to be only in the Mediterranean that we get these aggressive, steep little waves. We do also have many complex swells, in the Dodecanese largely from the SW but with reflections and diversions caused by islands they can finish up coming from a variety of directions.

Wind against tide in the Wallet does a pretty good job too.

 

[Hydrozoan]

... All I was able to come up with was that surface tension is indeed a factor in the generation of 'capillary waves', but these are typically less than 2cm in length (such as cat's paws?). The process of generating larger waves goes way beyond this, and no measure of surface tension seems to figure in it.

Any thoughts?

My (albeit old) understanding was that capillary waves provide the surface roughness which enables the wind to 'get a grip' on the water, and thus lead to gravity wave formation (for a slightly more formal explanation, see e.g here https://books.google.co.uk/books?id...&q="capillary waves" "wave formation"&f=false). So presumably anything which affects surface tension and thus capillary wave formation could affect gravity wave formation in turn - but it seems a lot on which to hang the steepness of Mediterranean seas!