James Casey has started to post bits from his Coach Casey Club calls on his YouTube. Just saw the first one today. Yes, the video is essentially a commercial, but it’s free tips that might be useful for you guys that are into downwind.
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I never knew about wave energy moving from one to the one behind it until I started thinking about considering planning to get stuff to downwind. I see it all the time now in whatever waves I see. It’s like there’s a sandbar that moves downwind at maybe less than half the speed of the waves. I think boat wake does it too. Anyone know why?
Go watch the casey catchup with Matt Costa on youtube. He has computer graphs that explain what waves are doing and how they continue to cycle on themselves.
Or just message him on instagram https://www.instagram.com/foil.me.harder/ and he’ll quote you the text books to read and learn about it.
Oh and he has something in his stories right now actually.
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The difference you are talking about is the group vs the phase velocity of wave system.
In deep water, an individual wave moves at twice the speed of the group.
The why of this always seems to get into some ugly calculus and I still haven’t managed to wrap my head around it properly. The closest I’ve come is basically this quote from the above article:
“Loosely speaking, different frequency-components of the wavepacket travel at different speeds, with the faster components moving towards the front of the wavepacket and the slower moving towards the back. Eventually, the wave packet gets stretched out.”
So basically the different frequencies making up the wave (no ocean wave is a pure sine wave, big long long swells get the closest) go in and out phase with each other as they propagate. When in phase, you see the wave moving along and when they drift out of phase the wave seemingly disappears.
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I had a good text book called ‘processes and landforms’ by clowes and comfort’ … it had a good chapter on wave motion …
It reckoned that as (let’s say) 1/2 the wave energy is kinetic (motion) and 1/2 is potential (due to wave height), the total wave energy would only move 1/2 as fast as the wave front …
I often thought about this when windsurfing … Gybe onto the best looking wave out back only to reach the breaking zone to discover the one behind was ‘the one’ …
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We got the great Riggs on the forum!!! Stoked. And thanks for the tips!
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Here is the link, it’s really interesting, about 5min long
Links from the clip
http://galileoandeinstein.physics.virginia.edu/more_stuff/Applets/wavepacket/wavepacket.html
Takeaway - catch the later waves in the group
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The only time I’ve ever stopped my car and then switched to the youtube version so that I could watch a podcast.
Matt just did 58 minutes on foil in the surf zone this week on Oahu.
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