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post #11 of 14 Old 04-30-2009
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For the scientific explanation see:

The calming effect of oil on water

American Journal of Physics -- May 2007 -- Volume 75, Issue 5, pp. 407-414

Issue Date: May 2007

The calming effect of oil on water has been known since ancient times. Benjamin Franklin was the first to investigate the effect, but the underlying mechanism for this striking phenomenon remains elusive. We used a miniature laser interferometer to measure the amplitude of surface waves to a resolution of 5 nm, making it possible to determine the effect of an oil monolayer on the attenuation of capillary waves and the surface dilational modulus of the monolayer. We present attenuation data on pure water, water covered by olive oil, water covered by a fatty acid, and a water-acetone mixture for comparison. From the attenuation data at frequencies between 251 and 551 Hz, we conclude that the calming effect of oil on surface waves is principally due to the dissipation of wave energy caused by the Gibbs surface elasticity of the monolayer, with only a secondary contribution from the reduction in surface tension. Our data also indicate that the surface-dilational viscosity of the oil monolayer is negligible and plays an insignificant role in calming the waves.


Those ol' salts of yester-year weren't so dumb afterall.
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post #12 of 14 Old 04-30-2009
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The older narratives frequently discuss "bags" of oil, which argues for a thick or rubber-lined sack from which oil would drip fairly slowly. We've all seen how even a teaspoon of spilled diesel can cover a bedroom-sized surface of a calm harbour, but how this would work in a foaming sea is beyond my experience.

The forereaching boats hove-to in the older stories (pre-1970!) actually describe their hulls as leaving a "slick", so the connection between a upwind zone of relative calm and the quasi-Biblical injunction to pour oil over troubled waters seems to have a long pedigree.

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post #13 of 14 Old 04-30-2009
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Thanks for the tip. I might try it.

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post #14 of 14 Old 05-01-2009
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Originally Posted by sailingdog View Post
The boat drifts when hove-to... the oil slick remains behind... and forms a protective slick upwind of the boat, as it drifts downwind... It works better on old shoes than newer, more modern designs, as they tend to forereach more than the older designs.
As usual SD - right on the money. I have never spread oil on the water because I doubt its effectiveness and don't carry any oil or means of spreading it (Although we could probably rig something up to spread what little cooking oil we do have) but I can attest that the Pardeys are correct about the effect of a boat drifting downwind while hove to and it is obvious to me that hanging an oil bag over the windward side would, indeed, spread a slick up wind.

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