General Discussion Triathlon Talk » IMKY Swim - effect of the current Rss Feed  
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2008-11-16 6:31 AM

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Subject: IMKY Swim - effect of the current

For IMKY first timers wondering about the effect of the current in the Ohio River, here are some numbers.  The swim goes up-river against the current for about 1/3 of the swim and then down-river with the current for the remainder of the swim.  Obviously a strong current will hurt your up-river time but will help your down river time.

So the question is, it is more advantageous to have a strong current or a weak current?

In 2007 and 2008 I took my splits at the turn-around buoy.

2007 total swim time: 01:30:04 Turn-around buoy: 38:39 (strong current)

2008 total swim time: 01:32:55 Turn-around buoy: 33:00 (weaker current)

So in 2008 the weaker current allowed me to swim up-river much faster than in 2007 but the down-river swim time in the slower current resulted in an overall slower swim time.

Conclusion: The stronger the current, the faster your swim time will be.

Maybe this conclusion was intuitive to some since you swim with the current twice as long as your swim against it....but now you have some empirical data to support your intuition.

Disclaimer: Your mileage may vary.  I'm a 'slow and easy' swimmer.  My pool time for 2.4 miles was pretty much the same as my river time.

One more thought.  I totally enjoyed the swim in the Ohio River!  After months of swimming 25 yds and stopping and changing direction over and over and over, it was so nice to just get out and swim.  The water temp was great and it was so fun just to swim and relax and let all the pre-race stress wash away.

~Mike



Edited by Rogillio 2008-11-16 6:51 AM


2008-11-16 6:39 AM
in reply to: #1810801

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Subject: RE: IMKY Swim - effect of the current
Mike, you have a graph / diagram demonstrating the effect of the current as well?
2008-11-16 6:48 AM
in reply to: #1810805

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Subject: RE: IMKY Swim - effect of the current

kaburns1214 - 2008-11-16 6:39 AM Mike, you have a graph / diagram demonstrating the effect of the current as well?

 

Yeah, but it's on a logarithmic scale and when you take the first derivitive of the velocity vectors to get the tagental acclerations and covariance, you get spurious data that you don't really care about.  So I'll spare you the graphs.  :-)

~Mike

2008-11-16 7:38 AM
in reply to: #1810801

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Subject: RE: IMKY Swim - effect of the current

But if the current is faster than your swim speed, you'll never make it to the turn around buoy.  That would be a bad start to the day.  Better pack the flippers just in case.

 

2008-11-16 9:35 AM
in reply to: #1810828

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Subject: RE: IMKY Swim - effect of the current
wiky - 2008-11-16 7:38 AM

But if the current is faster than your swim speed, you'll never make it to the turn around buoy.  That would be a bad start to the day.  Better pack the flippers just in case.

 

 

You joke but in 2007 two days before IMKY the current was so strong in the river that people were being taken down river on the practice swim despite their best efforts to swim up river.  This was when they decided to move the swim start to the estuary and shortend the up-river swim.  By race day the current had died down considerably....I think also the corps of engineers slowed the current some on race days via the dams.

Flippers are only allowed in IMFL (IM FLippers).  :-)

 

~Mike

2008-11-16 9:38 AM
in reply to: #1810809

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Subject: RE: IMKY Swim - effect of the current
Rogillio - 2008-11-16 7:48 AM

kaburns1214 - 2008-11-16 6:39 AM Mike, you have a graph / diagram demonstrating the effect of the current as well?

 

Yeah, but it's on a logarithmic scale and when you take the first derivitive of the velocity vectors to get the tagental acclerations and covariance, you get spurious data that you don't really care about.  So I'll spare you the graphs.  :-)

~Mike

Yep...that's what I thought too...and we all know that too much spurious data= potential thread yankage. 



2008-11-16 10:03 AM
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Subject: RE: IMKY Swim - effect of the current

I'll defend Mike on this one. Worthwhile info. I am doing IMKY and was curious on how the swim course was setup.

I know the IMKY website is SO indepth with a wealth of info but still had questions like...course maps???

I wondered what kind of advantage the current "could" be but know seeing you swim with it more than against it answers my concerns.

Now back to more prerace dinner questions and graphs from Mike Wink

2008-11-16 10:38 AM
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Subject: RE: IMKY Swim - effect of the current
What about the cureent relative to the closeness to the shore.  I heard something of a small island too.  Any advantages or disadvantages to the distance from these?
2008-11-16 1:20 PM
in reply to: #1810939

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Subject: RE: IMKY Swim - effect of the current

mikep - 2008-11-16 10:38 AM What about the cureent relative to the closeness to the shore.  I heard something of a small island too.  Any advantages or disadvantages to the distance from these?

The swim start is in a channel between the bank and a small island.  The width of the channel is maybe 50 ft and people were pretty spead out in the channel.  After about 1/4 of a mile, you end up in the main river (still swimming up river) and the buoys get further and futher out from the bank.

Here is a lesson learned.  After you round the buoy, start angling back toward the south bank.  If you just head down river without really thinking about it, the current will tend to take you toward the center of the river.  Now I guess in theory the current is fastest in the middle of the river but when you consider the river is probably 3/4 of a mile wide...and you eventually need to end up at the south bank, you need to start heading back toward the south back right after you round the buoy.  I'm not sure I'm explaining this very well but I just remember looking around on the swim and realizing I was nearly dead in the middle of the river.  So maybe the lesson is simply, pay attention to where you are in the river and try to avoid swimming to Indiana and back.

~Mike

2008-11-16 4:42 PM
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Subject: RE: IMKY Swim - effect of the current
this is great information..thanks I`ve been thinking about this over the past week
2008-11-16 5:01 PM
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Subject: RE: IMKY Swim - effect of the current
Thanks for this thread!  I was just wondering about this the other day.  One thing that I've wondered is (and this relates to the fact that the IMKY website doesn't have a lot of great info for us) do you think it is necessary to go scout out the course prior to being in Louisville in August or do you wait until the week of to check it out?


2008-11-17 8:19 AM
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Subject: RE: IMKY Swim - effect of the current
I am hoping that some crazy force of nature changes the current as I hit the 2 differant areas. That is what I am banking everything on. Or hitching a ride on a gigantic flat head catfish.
2008-11-17 9:03 AM
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Subject: RE: IMKY Swim - effect of the current

For all those freaking out.

Course Map

IMKY swim

The Channel between Louisville and Townhead Island.  From the end of the boat dock.

channel

My favorite pic of the swim course.  I took this on Thursday before the race..... after a brief rain.  Great motivation to swim faster.

ohio river

 

I agree with Mike once you round the last up stream buoy head back toward the island.  I swam by myself for 15-25 minutes.  As I passed a kayaker I stopped and asked where is everyone?  And he pointed to the middle of the channel and said swimming to Indiana.  The closest swimmer was probably 50 feet away from me.

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