How do YOU measure wave height?

I just breezed through the “apology for Coffee” thread, and saw the comment by Schizopak where he says wave height is the distance from dead-center to the peak, or half the distance from trough to peak. That’s the first I’ve heard that. Though it makes sense in a way (the height of the wave = its height above the water’s surface IF the water were flat and level), anyone else I’ve talked to has considered wave height to be measured between the peak and the trough. That makes sense too, since that’s the elevation difference you can actually see.

So how do you folks do this? Is one method “right” and the other “wrong”, or are they just “different”?

Three ways

– Last Updated: May-19-05 1:43 AM EST –

The scientific method - Schizo is right, that is the technical definition of wave amplitude. Sometimes called swell height too, that's the measure buoys give.

Surfers method - measure the wave face, basically peak to trough, using someone standing as the unit of measure. Ankle high, knee high, chest high, head high, overhead, double overhead, triple overhead .... bigger than that they are either at Killers, Mavericks or Hawaii, or lying.

Hawaian Surfer Method, Measure the back of the wave, ocean surface to peak, subtract a little to sandbag and make yourself look modest --- so a three foot hawaiian is a pretty good sized wave to surf. (Just used as a joke around where I live.)

yeppers
backside is the way we do it out here in Oregon.

http://www.parapraxis.com/extempore/heights.html

steve

Don’t you just make up something
that sounds impressive? It seems pretty easy to to find out if someone is full of shit.

Like when someone tells of steady waves twice or three times the magnitude showing up on a bouy. Or when they speak of rogue waves 4 times the height on a bouy 5 miles away. I love stories like that. Lots of big fish out there too.

Each time I head to the ocean I check the bouys. Never have I encountered a wave significantly greater than what was shown on the bouy and almost always find the breaking waves in the surf zone to be significantly less than the bouy data might suggest. Maybe it a new england thing. Just my observations over the last decade. Not saying that rec boats cant stay afloat in 3-4 foot waves or that 11 footers dont pop out of nowhere. Just saying I doubt sometimes.

Backside Measurement Is …

– Last Updated: May-19-05 7:30 AM EST –

the most modest but also likely inaccurate too because you pop over the wave, it's moving away from you quickly. By the time you turn, it's too far to give a good measurement.

I personally like the frontal approach. As soon as I hit the base of the wave I use my eye level as measurement. Am I looking at the crest (around 2'), the middle of the wave, or am looking way up? Anyway, for describing to others, especially newbies, this is probably the best way to give the wave height. This is what they will see (confront) will they paddle out through the zone.

sing

Dunno what’s right but…
I go by rise and fall. If a wave lifts me two feet and drops me two feet, chances are it was a two-footer.

Damn! Bagged Again! LOL!

– Last Updated: May-19-05 6:46 AM EST –

Several weeks ago, we were surfing waist to shoulder easterly sets at Nantasket. One of our group went to Pegotty, a point break, about 15 miles south afterwards. He said the waves were head to slightly plus. Perhaps possible bottom topography stacking up the waves more? I didn't see it so I'll take his word for it.

sing

I have always measured from trough
to crest. Been in some big waves , but that was a powerboat of lake Huron.

I cut my estimate in half
and then i’m only slightly over! Like you stated, I do use the “buoy method” to measure wave height, but it’s hard to be really accurate. What I figure is that if i’m in the trough and have to lift my head upwards to see the crest, it’s probably a 3 footer. If I can see the crest without lifting my head too much, then I figure its a 1-2 footer. Even with this method I’m still off quite a bit. I’d estimate that we were out in some nice 2 foot swells but the more experienced boaters would correct me by saying it was more like 1-1.5 footers. So if I cut my cursury estimate in half, I’m usually semi-close.

Since many of us mentioned various ways of interpreting wave height, is there a kayaking standard? We’re not standing up so the surfer method isn’t as valid although the Hawaiin method seems about right. I’d figure since we’re kayakers and we use a lot of the data from the ocean/lake buoys, that we would start using those as our frames of references.

That is how I always measured…
Trough to crest… Spent every summer on the lake from 3 yrs old to 10 yrs old. After that every summer on Lake Huron till I was 16… Vacationed on the Ausable pretty much all my life.

Never heard of taking the wave height & cutting it in half???

Coffee

i measure
the face from the trough if it’s shoulder high it’s less than three feet, if it’s greater than shoulder height it is probably around three feet, and double shoulder height is probably 5-6.

it should be noted
that mr. kwikle is roughly the height of a large hobbit!

Optical illusion…
The reason the common method of measuring wave height from the back is used is because of the illusion (from the front) that it’s higher than it actually is.

All I know is
last time I was at Nahant I got out there in my C1 and they were over my head, I mean they were huge, I’m saying they were coming down and clobbering me, 6 or 7 footers at least!

Funny, I got back on shore and watched a few boardies for a bit. Didn’t look more than waist high from the beach.

Perception is reality.
Technically speaking, your method is taking the wave height and doubling it. I don’t know if you did trig in school, Coffee, but a sine wave is measured from its mean (dead flat zero if there was no wave) to the maximum distance of oscillation (ie: to peak OR trough, not both). That being said, we see a marine wave as trough to peak because that’s what we physically have to deal with.

down to my wooly toes
i should change my last name to bolger, boffin, baggins, or maybe even brandybuck?..

exactly

So from trough
to crest and half it is considered standard measurement? i understand this will only be a rough measurement.

i guess so
the more I think about it, the more I like the Hawaiian method. As using the backside of a wave is sort of impractical when paddling out in surf, the wave face would be our best reference. The link that flatpick gave is great in terms of the calculation.

From that site:

"(1) take the wave face and divide by two

(2) examine the result, the quotient, to see how many multiples of five it contains

(3) for each multiple subtract one foot.

For example:

How big is a wave with a 20-foot face?

(1) 20 / 2 = 10

(2) 10 / 5 = 2

(3) 10 - 2 = 8

That seems to be the best way to get close. Like I mentioned, I do the face divided by two method and I’m usually slightly over. This method would correct that.

That’s The Trick…
I actually surf quite a bit with boardies around these days. When start using “body” part measurements, then I talking about someone standing up, as in a boardie on his board riding the wave, not in reference to a kayaker sitting down.

Actually, it’s been a year of learning for me in terms of figuring when waves show, best direction and, yes, a somewhat consistent height measurement (in terms of I how I measure it from base to crest).

sing