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Estimating wave height

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Created by FRP 1 month ago, 12 Sep 2019
FRP
334 posts
12 Sep 2019 8:18AM
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I am reading a marvelous little book entitled "How to Read Water" Clues and Patterns from Puddles to the Sea by Tristan Gooley. In Chapter 11, "Reading Waves", he describes an "easy" and "dependable" method for gauging the height of approaching waves.

"All you do is walk up or down the beach, away or towards the sea, until the tops of the waves are in line with the horizon. Then the height of the wave will be your height plus or minus the difference to the level of the main backwash. In other words, if your feet are still dry, the breakers must be taller than you, and if you need to get into the water to line up the tops with the horizon, they must be shorter than you."

Perhaps you all knew this, but it is new to me and I have been trying it out the last few days. It seems to work. Previously I have been sometimes surprised to find that I have paddled our into waves that are well beyond my pay grade.

Cheers

Bob

LucBenac
282 posts
12 Sep 2019 10:22AM
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Thanks for the tip. I just checked and this book is available on my Amazon membership so I can read it for "free".

pumpjockey02
258 posts
12 Sep 2019 9:11PM
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Arrghhh the dreaded wave height dilema, I think the consensus in the 90's went a little like this. If the wave was always taken on the size of the rider on the wave trimming along, up untill 6ft. So if you could fit into the barrel you knew it was over 4ft. From 6ft to 12ft it was measured by how long it took you to paddle up the face, From 12ft to 20ft the time you spent in seconds before pulling the bottom turn.
Hawaii was always measured from the back of the wave.
Tahiti, was usually 3-4ft extra as the wave dropped below the reef.
Every year past the most epic session of the year increased by at least a foot, so if it was ten years ago the wave went from inside 4-6ft barrell to an outside 14ft monster ten years after the event.

colas
3422 posts
13 Sep 2019 12:42PM
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With the progress on wave forecasts, i must say I look more and more at the wave energy amount (in KiloJoules) rather than pure height. Whereever you are now, there is a forecast available. It also factors in the period, and is a much more accurate scale to estimate the wave actual power. Two waves of the same height may not require the same "pay grade" depending on the period.

For instance, at ms usual spot, I know that under 30KJ is not surfable, 100 to 300 KJ is a fun wave size, and over 500KJ it begins to close out depending on the tide.

hilly
WA, 4854 posts
13 Sep 2019 1:16PM
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Select to expand quote
pumpjockey02 said..
Every year past the most epic session of the year increased by at least a foot, so if it was ten years ago the wave went from inside 4-6ft barrell to an outside 14ft monster ten years after the event.


Yep and then some bastard gets a video of it and it was really 2-3ft.

FRP
334 posts
13 Sep 2019 3:02PM
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Select to expand quote
colas said..
With the progress on wave forecasts, i must say I look more and more at the wave energy amount (in KiloJoules) rather than pure height. Whereever you are now, there is a forecast available. It also factors in the period, and is a much more accurate scale to estimate the wave actual power. Two waves of the same height may not require the same "pay grade" depending on the period.

For instance, at ms usual spot, I know that under 30KJ is not surfable, 100 to 300 KJ is a fun wave size, and over 500KJ it begins to close out depending on the tide.


Thanks Colas,

Yes I agree and use the energy forecast a lot in deciding what beach to head to. I find the wave height forecasts to be unreliable. Once at the beach however I have on occasion paddled out into waves that were far bigger than anticipated and I am now trying to use this simple method described to get a sense if the waves are significantly over my head. Around head high is my maximum comfort level. Double that and fear becomes the dominant emotion and I tend to wish I was somewhere else.

Cheers

Bob

ghost4man
315 posts
14 Sep 2019 4:59AM
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Currently in Hawaii and been to Waimea Bay.

What you would call 10 foot is about 4 to a Hawaiian ??????

FRP
334 posts
14 Sep 2019 8:35AM
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ghost4man said..
Currently in Hawaii and been to Waimea Bay.

What you would call 10 foot is about 4 to a Hawaiian ??????


Yes! In Hawaii they clearly do not measure wave height from shore. But you could use this method if you want to decide if it is a good idea to paddle out. I just wouldn't tell anyone that I chickened out because the waves were waist high!

Bob



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