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Old 02-01-2007, 22:27   #1
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Oil and heavy seas

New to the world of sailing and have read in a few accounts of cruising narritives that cans of oil were/are taken along for heavy seas. Is this jargon or is there really a legitimate reason for this and if so, how, why??


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Old 03-01-2007, 05:19   #2
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This is really from the olden days. When I first went to sea all the lifeboats use to have a canvas bag and a can of oil. The idea was that it could be used to stop seas breaking when lying ahull or hove to. Don't know if it works, luckily never had to test it. Nowadays you'd probably get a ticket if you used it before being rescued.

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Old 03-01-2007, 05:38   #3
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I'm sure an expert in fluid dynamics could give a more scientific explanation - the oil sits on top of the water in a thin layer; the wind is only able to drive what it is in contact with, so the oil, being so thin, creates very small waves. You could say it reduces friction between the air and the sea. It doesn't reduce swell, only wind-driven breakers, wavelets and spindrift.
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Old 03-01-2007, 07:28   #4
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Surface tension

Oil has surface tension vastly greater than water and therefore when on top of the water prevents/lessens the formation of breaking waves. Breaking waves being dangerous because of the large amounts of energy and simple 'mechanical advantage' they (mathematically) develop as single waves.

The high surface tension of the oil prevents the formation of high/steep 'peaks'. So, when wave amplitudes 'over-run' one another and the peaks/amplitudes of two or more waves becomes additive, the high surface tension oil tends to promote the formation of 'rounded' peaks instead of sharply formed 'monsters' that cant support their own weight (failure of surface tension) and simply the steep peaks fall-off of the top/break.
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Old 03-01-2007, 12:53   #5
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I don't know much about the science, but I've use oil on the sea in a gale in the north Atlantic when I was ocean-walloping in my little 20 footer,(Many years ago.) You need to be hove-to so that the boat more or less remains in the slick, and its amazing how far a little will go, and it does have a calming effect on breaking seas. Traditionally, one would hang an oil filled canvas bag over the side and prick it a few times with a sail needle so it could leech out. In my case, I dribbled a little down the galley sink where it exited the boat via the skin fitting.
Memory has dulled a little but I recall it as being a very messy operation and of perhaps dubious benefit, in my case at least.

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Old 03-01-2007, 14:13   #6
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oil and heavy seas

I have heard that putting out oil works very well in subdueing rough seas but the hard part is keeping your boat within the slick.
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Old 03-01-2007, 22:45   #7
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The question, then, is how much oil do you need and how far should it extend from your boat? Do you dump a whole 5 gallon / 20 liter jerry can of diesel overboard? Are you trying for a slick 100 meters or 1000 meters long?
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Old 04-01-2007, 02:12   #8
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Wouldn't the oil need to be dropped upwind so that it can calm the sea before it reaches the boat?
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Old 04-01-2007, 03:05   #9
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From: ”The Venturesome Voyages of Captain Voss”*

”... I may say that I believe in oil to calm breaking seas. I have always used it freely when in sealing vessels during heavy storms for the protection of the boats. For if our boats had been broken we would have been robbed of the means of carrying out our enterprise. It is advisable, however, not to attribute too much efficacy to oil, as the following incident goes to show.
On March 19th, 1911, while three hundred miles to the south-south-west of Cape Lopatka in the seventy-five-ton schooner Chichijima Maru, from Yokohama, we were hove to in a heavy gale. When oil was administered it froze as soon as it came in touch with the water. Notwithstanding this, and despite the vessel being loaded down to the scuppers, we did not sustain the slightest damage to ship, boats or outfit. But we were readily hove to and thus safe from shipping seas, which proved to be a sufficient safeguard ...”

* The Venturesome Voyages of Captain Voss ~ by John Claus Voss
ISBN: 0246135158

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