# Drag coeffecient of Jellyfish?



## T34C (Sep 14, 2006)

I have sailed/raced in areas where jellyfish are very prolific in the summer months. I can't help but think these jellyfish in the water must increase the drag on the boat as you go through them. The question is this: Could you gain speed and advantage in a race by avoiding some of the clumps of jellyfish in the water much the same way that you play the wind shifts? Does anyone already have data compiled on this subject? If not, any ideas on how to measure this phenomenon?

Any thoughts on this would be great. I'm trying to really tune up my racing for next season.


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## sailingdog (Mar 19, 2006)

Umm... exactly how would you predict where the clumps of jellyfish were... and of course, the amount of drag they present is dependent on what species they are.


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## T34C (Sep 14, 2006)

Minor issues to be resolved...

Perhaps a scout boat on the course before the race???


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## ReverendMike (Aug 1, 2006)

Are you applying for an 'Ignoranus'? Hmmmmm?


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## Giulietta (Nov 14, 2006)

Actually its pretty serious if you ask my son Fred.

During the Nationals Qualifications, he lost a race, and I asked what had happened. He said that him a few others had struck a whole bunch of Jellyfish.

For a while I was laughing at it, then, a few others confirmed the same problem. They actually slow the Optimists down when you hit them with the dager board and with the rudder.

Fred actually told me he had to raise his dagger board several times during that one race.

He said he could not see them, but he could feel them as he hit them.

So in all this there is some truth....if you can trust the kid, that is...I do.


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## Idiens (Jan 9, 2007)

Was that those Portuguese Man-o-Wars? Nasty!


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## ReverendMike (Aug 1, 2006)

I withdraw the accusation, sorry T.
M

(though I'm skeptical of any effect on a keelboat of any size)


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## T34C (Sep 14, 2006)

ReverendMike said:


> I withdraw the accusation, sorry T.
> M
> 
> (though I'm skeptical of any effect on a keelboat of any size)


Apology accepted.

I have sailed in areas where the jellyfish in the water were pretty dense. I think they wold certainly be dense enough to see from the deck. Since sailboat racing is a game of inches, I think steering around them or tacking away from a known area might help. It would be helpful to know how much they slow you down to help with the decision making process of when to tack away.

I think this idea might have played a part in the AC last summer. If they had spent a little more time looking at (into) the water instead of trying to second guess the wind... who knows??? The Mug could have been moved back to NZ.


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## Libellula (Aug 20, 2007)

I must wade in
I have raced for 35 years and can tell you that short of catching a crab pot or sailing into a hole
Strategic errors lose more races than anything else. I would venture to guess that if attention was paid to the relative position of boats in a race and the relevance of these associated positions analyzed correctly, that a gaggle of jellyfish would not affect the results
So I guess if you have everything else right- then you can worry about jellyfish


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## T34C (Sep 14, 2006)

Libellula said:


> I must wade in
> I have raced for 35 years and can tell you that short of catching a crab pot or sailing into a hole
> Strategic errors lose more races than anything else. I would venture to guess that if attention was paid to the relative position of boats in a race and the relevance of these associated positions analyzed correctly, that a gaggle of jellyfish would not affect the results
> So I guess if you have everything else right- then you can worry about jellyfish


But, you have not measured this "jf affect"????? Hmmmmm???? So we don't really know how much of an adverse affect they have on your boat. Perhaps when you thought your tactics were better it was really that the other boat was being slowed by the jf affect.


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## ReverendMike (Aug 1, 2006)

(Now I think I was right the first time folks, maybe he is just angling for an "Iggy" and Fred's run-in was a bit of 'luck' for his allegedly straight question...)


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## T34C (Sep 14, 2006)

Fred's "run-in" is documentary evidence of the jf affect heretofore refered to simply as JFA. And I for one am sure that the JFA has cost me any number of positions in various races. I'm sure that the two second place finishs I got this past summer should have been First place if not for JFA!!!


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## Giulietta (Nov 14, 2006)

Fred has also lost races to the DSF effect, but not as many as I have lost to the BTDBM effect!!!

because Fred does not have a bow per se, he can't blame it on the BTDBM effect.


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## tenuki (Feb 11, 2007)

puget sound has giant squid, I'm blaming any races I loose on them!


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## blt2ski (May 5, 2005)

I can blame that squid too, along with FA crew members! ack! No names to be mentioned here......................

Altho, usually around here, it is the Giant octopie that screw one up, along with orca's! that is my story, and I am sticking to it.........

Then again, there are a few JF's too!

marty


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## Sasha_V (Feb 28, 2004)

I know of one keelboat that definately suffered due to jellyfish strike...But it wqas a pretty cutting edge design with a foil forward of the keel and that is what the jelly(s) got snagged on. Totally changed the way his boat behaved for the worse. It was a very fast, very light 24 footer.

We ahve personally had a jelly hit the centreboard of our pacer dinghy and bring us to a near stop for a second...then we were suddenly going sideways and wondering what the hell was going on.Looking down revealed that the jelly had actually knocked up the pivoting daggerboard despite the hold-down. I would say we were badly out 10 seconds to fix the issue and more liek 30 by the time we were back on course and up to speed. (We went sideways far enough to reuire throwing in an extra tack).

That's my experience of the damned things.

Sasha


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## tenuki (Feb 11, 2007)

I can't believe not one of you insensitive louts expressed any sympathy for all these jellyfish being hammered by uncaring boaters!!!


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## ceol (Apr 15, 2007)

having sailed in the gulf coast for many years on a nacra. hitting those cannonball jellies will knock you off your trapeze line if you are not paying attention.  then again cannonball jellies are a lot more substantial than most jellies.

G~


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## sailingdog (Mar 19, 2006)

Tenuki-

I can understand why you are so outraged, with them being your direct kin and all... 


tenuki said:


> I can't believe not one of you insensitive louts expressed any sympathy for all these jellyfish being hammered by uncaring boaters!!!


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## blt2ski (May 5, 2005)

no SD, tenuki is a a bit harder than a jelly fish. More like the squids he pictured, a bit bigger, altho still slightly soft in nature! On the other hand, he does look like some of the native octopi too

Tenuki, If you do not know the local race schedule for ECYC< i will be emailing shortly to you and kids!

Marty


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## bobmcgov (Jul 19, 2007)

Big ball of mucus that inflict agonizing stings -- what's not to love? Come give daddy a kiss, Jellybaby.... 

I hear they cause problems in the Antipodes, dozens of them building up on the foils. But those are Aussie jellyfish, so they are probably ten times as big & poisonous as other jellyfish and come with a pouch.


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