Wave Height Estimation

Was on the radio the other day. Another boat asked what an estimated wave height was in a particular area.
I guessed. Someone else guessed something else. And another had another estimate.

Never have been good at judging distances.
Anyone have any rule of thumb or other advice for this wave height estimation?

Measuring waves is subjective and most people over-estimate the height of the wave.

Boating Mag has a good summary here: http://www.boatingmag.com/how-to/measuring-wave-height

Here's the excerpt:

In a boat it’s easy to overestimate wave heights. This is because of a phenomenon discovered by William Froude in 1861. He found that, no matter how your boat is situated on a large swell, what you feel to be “straight down” is actually at right angles to the wave. So when you think you’re looking out on a level line to judge a wave, you are actually looking on an angle, distorting your judgment. The only time to make an accurate appraisal of the waves is when you are at the bottom of a trough, midway between two waves, and you are sitting relatively level. In a small boat your eye might be about four feet above the waterline. If you can sight along several wave tops in a row when in a trough, then the waves are about three feet high, which is what most of us judge to be “six-footers.” Sight along the gunwale, about two feet off the water, to judge smaller waves. Stand up to raise your eyes to six feet or more to judge larger waves.

Take what everyone else is calling it and divide by 2

Good question, I have wondered about that also.

Guessing that at the helm, my eyes are 15 feet from the water (figured that out by total height of the boat and estimating distance from my eyes to the high point). When I think about the angle of distortion, makes sense that it is difficult estimate.

A few years ago I posted a video of the waves in one stretch of the Columbia River. The waves were running about 5'-6' tall in that narrow stretch of the river and were caused by a strong tail wind we had. When I posted it several people claimed the waves weren't that tall until another person reminded them that the video was taken from about 16' above the water and altered their perspective. I hadn't realized how much difference the height above water made.

Why guess?

The USCG has a great app for your phone. part of the app links to NOAA buoys nearest you and it will give you the, wave height, duration, air and water temp, air pres.
has lots of other useful info: boating law by state, safety check requests, review of the safety item needed for your particular boat size, float plan filing, rules of the road, and direct reporting for hazard, pollution and suspicious activity.

Rich

Rich122 said:

Why guess?

The USCG has a great app for your phone. part of the app links to NOAA buoys nearest you and it will give you the, wave height, duration, air and water temp, air pres.
Rich

Click to expand...

You also need to pay attention to the location of the nearest buoy to your location it's usually in the left upper corner of the app or webpage, in our case where we boat frequently the nearest buoy is approximately 18 NM away from our location. It's not unusual for us to be in 10-15 knot winds with 1-3 ft waves with the buoy data being 4-7 knot winds with <1 wind waves gusts to 19 knots or visa-versa. We use 3 weather apps all 3 give a different forecast.

Also in forecasting wind waves 1-3' wave is actually an estimate of the hight of the highest wave estimate.
reference NOAA:

Wind-Wave Height (WWH)
This is the average height of the highest one-third of the wind-waves. Again, it is estimated by the process mentioned under "Swell Height", except that it is the calculated from the energies above the separation frequency.

If your bored here's some good reading from NOAA:
http://www.ndbc.noaa.gov/waveobs.shtml

Measure the height of your bow above the water. It will give you an idea of how the waves are. The frequency between the peaks is more important. The further the Peak to Peak the smoother the ride.

Agree...and once back in the slip with a few beverages down it was 8' - 10' with an occasional 12'.

sfergson727 said:

Those things are always off, saying it's 3 footers when the "real" height is like six feet! :grin:

Click to expand...

I have been using windyty.com quite a bit. Great user interface on PC or Pad.

Question - there are quite a few options for viewing this type of data - windguru, windyty, etc. Are all these apps presentation tools for the same underlying data source (ie Buoy).

What I have noticed on this past trip, AccuWeather Marine app does not present the same picture as windyty. My guess is that is because AccuWeather averages over a larger area???

sfergson727 said:

Those things are always off, saying it's 3 footers when the "real" height is like six feet! :grin:

Click to expand...

I used to think they were always way off too. Windspeed and direction can remain the same but there are areas on the lake that are not consistent with the forecast, especially near shore. I've often moved out a few miles to get away from some rough water.

When it comes to waves we need to understand when they say 3' it means that 6 footers could be there too.

Significant Wave Height
Commonly referred to as Seas in the Marine Forecast. This is the average of the highest one-third (33%) of waves (measured from trough to crest) that occur in a given period. This is measured because the larger waves are usually more significant than the smaller waves. For instance, the larger waves in a storm cause the most beach erosion, or the larger waves can cause navigation problems for mariners. Since the Significant Wave Height (Seas) is an average of the largest waves, you should be aware that many individual waves will probably be higher.

If we take a sample forecast of Seas Beyond the Reef of 2 to 4 feet, this implies that the average of the highest one-third waves will have a Significant Wave Height of 2 to 4 feet. But mariners need to keep in mind that roughly one of every ten waves will be greater than 4 feet; one in every one hundred waves will be greater than 5 feet; and one in every 1000 waves will be greater than 6 feet.

As a general rule, the largest individual wave one may encounter is approximately twice as high as the Significant Wave Height (or Seas).

Note: Seas can refers to the combination or interaction of wind waves and swells (combined seas) in which the separate components are not distinguished. This includes the case when swells are negligible or are not
considered in describing sea state.

I used to try to take pictures of waves but had no success.

I just finished reading a book called Ghost Wave. A great read about the Cortez Bank, along with good descriptions of wave heights, rogue waves, etc. And I agree, people often think waves are higher than they really are. The Hawaiians measure the back of the wave, at least in regards to surfing, so a 6 ft face, is a 3 footer.