Determining wave height

B

baz

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Fluid Motion Model
C-24 C
I hope this question does not cause too much laughter...

When on the water with wave action how does one determine the actual wave height?

I would assume one way would be note where the wave crest is relative to ones horizontal eye sight looking forward when the boat is positioned in the wave trough. If the crest appears to be level with the eyeball then the wave height would approximate to the distance from the water line to the eyeball.

So what do others do to figure out wave height when on the boat ? Is there a handy gadget that magically displays wave height for you ?

Thanks.
 
From the "Mariner's Learning System"

Height of eye or freeboard – With the boat in the trough and on a level and even keel, any wave that obscures the horizon is greater than the height of a person’s eye. One can also compare a wave to the deck edge or a structure such as the handrail. The wave face is observed while bowing into it and in the trough on an even keel. This is also generally the best method for judging surf.

Thy offer a couple of ways to judge wave height here:

http://blog.marinerslearningsystem.com/ ... -wave.html
 
Wave height is entirely boat-dependent: if you are on a small boat with low freeboard, a 3 foot wave is 6 feet high. If you are on a 55 foot boat with a lot of freeboard, a 3 foot wave is "light chop, about a foot and a half."

😉 Note: the above definition is mostly tongue-in-cheek. :lol:

Driving excursions boats, I hear a lot of wave height estimates. Coming from NOAA or the NWS, I usually figure the numbers are close, but vary according to local conditions. Coming from other boaters, it varies: most of the time, I take the wave height estimate and divide by 2. If it's coming from someone I know and trust, I divide by 1.5. :mrgreen: Well, there is one captain friend that drives a big, heavy boat - I take his estimates and multiply by 2. :twisted:

Yeah, that probably didn't help at all. Unless it's just flat out ugly out there, it's often worth poking out to see what the conditions feel like. Then, use your bow height to help determine your estimate of wave height. The period is just as important as the wave height estimates... when I hear the period in seconds is less than the wave height in feet, I know it is going to be a lousy ride.

Best wishes,
Jim B.
 
Thanks for the responses... I appreciate your time.
 
This is what Wiki calls Wave Height, "the wave height of a surface wave is the difference between the elevations of a crest and a neighbouring trough." Now, if you run out to the bow with your tape measure real quick.... 😉 😎 :lol:
 
In Australia the marine forecasts give figures for seas and swell. The combination can create big waves. The weather forecasts always warn that actual height can be up to 30% more. Fortunately my little EC21 is very seaworthy and can take swell quite easily and seas above the pulpit.
Ogger
 
Observation, if you are worried about wave height while in it, no need to measure, go to safe harbor. My rule of thumb is winds over 18 kts or seas reported at over 6 feet stay at port. These are my minimums, but others may feel comfortable with higher minimums.
 
My primary reason for my OP was to figure out how people were estimating the wave height when posting their topics saying something like... "the wave height was X feet". Many members state wave height so I was wondering how they arrive at their number of feet.

In summary, it seems to me it's guess work based on an individuals experience. There seems to be no scientific method being employed.

Thanks. 🙂
 
There are scientific ways of determining wave height and it depends upon who you are as to how it is to be determined. Search the wiki for wave height and it will give you some ideas. Search NOAA and you can really get into it. I like to keep it simple. The wiki definition says from the bottom of the trough to the crest of the wave. If you know the measurements of your boat, then you can estimate wave height. For example, on my R21EC, it is 3 feet from the water line (the white line) to the bow. The handrail is another 2 feet above the bow. The last time I was in heavy seas and my bow was at the bottom of the trough, I had waves coming approximately 2 feet over the handrail. So, my guess is 7 foot waves. You get a better idea of wave height when you are plowing into a wave than observing it from a different angle/attitude.

That is the actual approximation of one wave. I think NOAA uses an average of three waves, or something like that in their formula. I don't remember. Like I said, I like to keep it simple.

Now if you are talking about "swells", that is another story.
 
Thanks Rick for that additional info... 🙂
 
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