When swimmers cross a channel or participate in an ocean swim, they tend to most vividly remember the extremes of their swims. That is, the swimmers wax poetically about their swims over the tranquil beauty of a flat ocean especially when the sun sets or sun rises and their challenges across the roughest, toughest turbulence that is thrown in their way. The slight chop that lies somewhere in the middle of these two extremes is relegated to the deeper recesses of their memory.
They prefer to write and talk about those extremes where beauty and challenge are at their maximum.
So how do mariners, surfers and open water swimmers measure waves? Traditionally, the wave height is measured from the trough of the wave to the the crest. I’ve come across a term new to me: significant wave height, that gives us a clue in the exaggerated heights. Here is the article: http://en.wikipedia.org/wiki/Significant_wave_height In the article it says to use the MEAN of the highest THIRD of all the waves to estimate the height. Then it mentions the exceptions under the section statistically distribution: 1 in 1000 can be twice the height. Plus (not mentioned in this article) are anomalies caused by superposition of waves when wave fronts from two different waves intersect, their heights add together. I’m sure it’s the large wave the observers remember.
However, it seems there are issues in how to measure the height of just a single wave front. The easiest metric to obtain is the wave period (time from wave from crest to crest). If you refer to my power point lecture from 2011 at Columbia, slide 17, I dicuss waves and provide a formula the allows you to calculate the speed of the wave C by dividing the Lenght L of the wave by the period, T. Deriving the height from this data is a bit more complicated and has been given over to computer software.
Mariners at sea use the Beaufort scale as it provides an estimate of the wind speed from a discription of the state of the sea surface and gives you a height. See: http://en.wikipedia.org/wiki/Beaufort_scale. This is a useful scale that has been developed and refined over the centuries since it was first developed and you can easily see when to pull the swimmer. Plus, marine stores sell card charts with this information on it and any well-equipped escort vessel should have some source (book) that includes this information. Skippers usually practice their wind estimation and gauge their accuracy by the observed wave height. So observers would do well and learn a lot by asking the skipper what they think the wind speed is. If their vessel is equipted with a wind speed indicator, there can’t be any doubt if the device is working properly. So their swim report record should include a spot to mark wind speed as estimated or instrument derived next to their wave height record.
In shallow, coastal waters the wave height differs from the Beaufort scale from open ocean where the depth is >100 fathoms (600 feet). The height become higher. But the wine doesn’t change thus the Beaufort scale could in shallow, coastal water provide a minimum wave height. I included a discussion on shallow water waves in the power point mention above.
Also, note the information on current generated by the wind on slide 24: you need a wind of 100 knots to pick up a current of 1 knot. I validated this information indirectly: I was in the English channel is 16′ seas, the boat has a wind speed indicator on it showing 39 knots, taking current measurement and they were spot on with the predictions. Didn’t vary one detectible iota from the predicted current.
Jane and I enjoyed the conference immensely. Let me know if we oue you any money (we had lunch).
Tim
From: headcoach@openwatersource.com [headcoach@openwatersource.com]
Sent: Sunday, September 30, 2012 5:22 PM
To: Vito Bialla email; Lexie Kelly email; David Holscher email; Zach Jirkovsky email; Patti Email; kimberley chambers; Phil Cutti email; Joseph Locke; Forrest Nelson email; Dave Van Mouwerik email; David Clark email; Marcy MacDonald; Peter Attia; Johnson, Timothy; Dale Petranech email; Lewis Pugh; Angel Yanagihara email; Matthew Mitchell email; Hank Wise email; wineartist@yahoo.com; Rob Webb
Subject: Reporting Wave size in open water swimming
Vito,
In the open ocean (e.g., between Hawaiian islands, Catalina or in the Caribbean), I just ask the skipper what is the height of his boat. Then I compare the maximum height of the swells with the mast of the boat. It is just a very rough estimate of ocean swell size. It is a report similar to a surfer who surfs in “double overhead waves”.
But this is very non-scientific, inaccurate, and is no longer suitable for proper reporting and documentation of our sport.
We must do better but I wonder how to accurately report ocean swell size?
Forrest, Peter, Marcy, Angel, Lewis, Rob, Skip, Tim, Mike, Matty, Hank and Dave,
How do you recommend that we should properly report on the size of waves and swells in the ocean during open water swims?
If we all agree on a standard like many surfers do in the surfing world, this will be very useful to our sport. I have read too many reports about lake swims where media and swimmers report they faced 4-10 foot waves. Almost without failure, swimmers who tackle the Molokai Channel realize that the wave sizes they have reportedly faced elsewhere have been exaggerated, at least to what they face in Hawaii.
Thank you very much all in advance for your input, experience and recommendations.
Steven Munatones
Sent via BlackBerry from T-Mobile
From: Vito Bialla
Date: Sun, 30 Sep 2012 11:37:03 -0700
To: Steven Munatones; Lexie Kelly; Dave Holscher; Zach Jirkovsky; Patti Bauernfeind; kimberley chambers; Phil Cutti; Joseph Locke; Vito Bialla
Subject: Fwd: Wave size
Steve if you look at this one wave take the length of the swimmer exclude his arm and measure 5’11” then measure vertical is that a remote measure to use for wave height?
Vito Bialla cell 415-713-4517 office 415-332-7111 SKYPE vito.bialla www.bialla.com www.signium.com
Begin forwarded message:
From: Vito Bialla
To: Vito Bialla
Subject: Wave size
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