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Sea Monsters??

09/30/2006 4:58 PM

Here's something I came across while working on a fast sailboat design. In this particular design, the side force on the boat, when going fast (40 knots and above) would actually exceed the total weight of the boat and crew. Therefore, the airfoil-shaped centerboard (a type of keel that can be retracted) would have to generate an amount of lift (directed sideways) roughly equal to the weight of the boat. Structure was one concern, hydrodynamics another.

So, suppose I did a test of two competing foils, with one facing one way and the other facing the opposite, mounted from a fast motor boat. With their lifts canceling (more or less) the boat could go in a straight line (more or less) instead of being pushed sideways as would happen if I tested one foil at a time. I didn't actually do this at night, but I might have, just for fun and additional thrills. Suppose while testing, I saw blue light emanating from the water. Aside from the obvious – hallucinations – what other causes might there have been for by seeing blue light? Could I look for something on the foils to prove (or strongly suggest) that the light occurred for the reason you propose?

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#1

Re: Sea Monsters??

09/30/2006 5:05 PM

I just noticed that Shyam probably knows the answer to this. Therefore, I think he should wait a day or two to give others a chance to come up with a few theories.

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#2

Re: Sea Monsters??

10/01/2006 7:40 AM

I think your blue light was phosphorous in the water, which only shows at night.

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#5
In reply to #2

Re: Sea Monsters??

10/01/2006 11:11 AM

Seems like a plausible explanation, although the glow seemed to come only from the area around the foils and not elsewhere. Also, the test was performed in Skaneateles lake in upstate New York -- one of only a couple lakes in the US that is triple A rated for water quality. It's crytal clear, and you can pump drinking water straight out of it without having to treat it in any way. So I think that the phosphorous content would be too low to see.

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#3

Re: Sea Monsters??

10/01/2006 8:26 AM

Maybe the blue light was the local harbor police who are now patrolling the water with subs in order to be more stealthy.

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#4

Re: Sea Monsters??

10/01/2006 11:08 AM

I believe that it is plankton and other little one and multi celled creatures.

The are naturally phosphoescent.

They especially give off light when agitated.

In Puerto Rico, there is Phosphorescent Bay, where

the waves and breakers light up.

Personally, i have seen small jelly fish do this when touched or

sand was drizzled on to them in the water.

They light up a beautiful green.

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#6
In reply to #4

Re: Sea Monsters??

10/01/2006 2:14 PM

Another good possibility, although the testing was done in crystal clear cold fresh water where few of such things live. So I don't think it was that sort of creature. In fact, I suspect it might not have been due to any lifeform, but instead to some sort of mechanical (physics) effect.

I also ruled out a K-mart Blue Light special, because the nearest K-mart was many miles away.

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#7

Re: Sea Monsters??

10/01/2006 4:24 PM

How about sonoluminescence, caused by cavitation?

I am in the process of studying for an exam, so I will leave a detailed description for later.

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#8
In reply to #7

Re: Sea Monsters??

10/01/2006 5:58 PM

Hmmm. Cavitation. I think I had my teeth checked not too long before the test. But nevertheless, I await your detailed descitption.

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#9
In reply to #8

Re: Sea Monsters??

10/02/2006 1:42 PM

Sonoluminescence

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#10

Re: Sea Monsters??

10/02/2006 8:56 PM

Simple, Planckton, its hapen very offen,

be in the Sea more offten affter 9:00pm,

you will see again...

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#11
In reply to #10

Re: Sea Monsters??

10/02/2006 10:08 PM

See post #6. There were no plankton around.

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#12

Re: Sea Monsters??

10/02/2006 10:29 PM

Posts 7 and 9 are correct. When cavitation (the formation of tiny vapor bubbles as a result of low pressure) occurs, the bubbles quickly and violently collapse. (It is a little like steam hammering, where what was once taking up a lot of space as a vapor suddenly condenses and takes up a tiny bit of space.) These bubble collapses are so violent that they emit bursts of blue light. The effect is called sonoluminescence.

I asked if I could look for something on the foils to prove that the light occurred because of sonoluminescence. These violent collapses can damage hydrofoils (propellers, turbines, etc.) by causing small pits to form on the surface of even very tough materials, like stainless steel.

As I was researching foil shapes that would resist or lessen cavitation at high speed, I came across an article on sonolumiscence -- and at first thought it had been written by a science fiction writer.

Cavitation has long been a potential problem with hydrofoil-borne watercraft. The problem occurs at high speeds, when the pressure on the low pressure side of the foil gets so low that the water boils. It is a problem distinct from ventilation, in which air from the surface is pulled into the same low pressure region. The two terms are often confused -- probably partly because the common outboard motor "cavitation plate" does not prevent cavitation, but does reduce ventilation.

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#13

Re: Sea Monsters??

11/12/2006 2:37 PM

I believe cavitation will reduce the efficiency of the parts concerned....it would be interesting to see if when air is introduced (to fill the vacuum bubbles called cavitation) if the effects of the foils still work as designed....

I spent a good deal of time once trying out a trimaran (model only) to see if the effects that you are looking for actually helped the boat to point up better with less skidding when hard on the wind. My carreer prevented me having the time to carry out full tests.

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