# Wave Speed

Hey does anyone know where I could find out the average wave speeds for New Jersey for the past year or so?

5.3424 MPH. Not scientific though. I take one of those Rawlings kids radar baseballs, put it in a ziploc bag and chuck it out into the surf. Then I use a water proof catchers mit to slow the ol’ heater down. I’ve only gotten 1 in 20 back, and \$30 a pop is starting to wear on my bank account, but I will prevail.

Your speed may vary with current, wind, and tide.

-Jay

Wave speed isn’t so much dependent on location as it is on size. A one-foot wave will move in a direction perpendicular to the crest, at the same rate in Tavarua or New Jersey.

or look at:

period vs speed http://members.aol.com/Rosendalhe/somesurf.htm

NJ period today: 11 sec

this was just a quick google search; did not inspect for accuracy

Wave period is what counts. Wave period is proportional to wave speed. Deepwater speed of a wave is 1.5 x the period. 10 sec wave travels @ 15 kts. 20 sec wave travels @ 30 kts. Find the average wave period and you have your average wave speed. Try calling NOAA.

Tavarua and new jersey? same speed? aaaaaaaahhhhhhh? continental shelf considerations are some what different and may affect wave crest speed …where’s Ricky Gregg when he says so I’ll believe it…maybe…ambrose…honolulu, is that you ricky are the waves really 6’ now on the face back plungemetric scanner waimea bouy…Noaa build me an ark…whats a cubit

it’s 13 inches, roughly.

Let’s start measuring wave height in cubits and get away from the whole head-high thing. Man, that wave was 6 cubits at least! (3 cubits Hawaiian…)

http://www.stormsurf.com/gc/gcht/nj_zoom.html - great circle path for Manasquan

http://www.stormsurf.com/page2/papers/Java/Swivel.shtml - Great Circle Distance Calculator and Swell Arrival Calculator

this should help -

Regardless of the explanation, as groups of waves move further away from their source in deep water (a thousand or more nmiles) the group becomes better defined, with waves of the exact same speed traveling together. If the waves in a wave train have sufficient energy (normally a period equal to or greater than 15 seconds), they can continue with little loss of size or energy, for thousands of miles or until they reach land and break. That's because at these periods (or wavelength) all the energy is traveling deep under the oceans surface, and there's little that can stop it (except for shallow water). A wave with a 14 second period reaches down into the ocean about 516 feet. A 17 second period wave at 761 ft, 20 second at 1053 ft and 25 secs to a whopping 1646 ft! So you can see how little impact an opposing wind wave with a 7 sec period reaching down only 129 ft would have on one of these long period deep water swells. Also, wave groups of different heights and periods can pass right through each other with no effect to each. In fact, other than shallow water or land, the only factor that causes significant decay is the surface tension of the ocean itself. The same tension that allows an insect to carefully walk on water has the long term cumulative ability to slowly sap the height out of a long period swell, but only over thousands of miles. Conversly, a short period swell is much more vulnerable to the affects of surface tension and opposing wind and waves becuase of it relative lack of energy.
Eventually the group starts to encounter shallower water. When this happens the group velocity and the individual wave velocity become the same. As mentioned before, a group can have anywhere from 3-8 or upwards of 15 waves in it. In shallow water, this group is known as a [b]'set'. If watching the surf, you will occasionally notice a group of waves break that are bigger than the normal background surf. These 'sets' appear as often as every few minutes to once every half hour or more, depending on how far they have traveled to reach your shore. The further the travel time, the better the organization. In shallow water, the in-phase/out of phase phenomenon is no longer applicable. From a surfers perspective, this is good. It would indeed be difficult to catch waves if they disappeared from under you.
The speed (in nautical miles per hour) of an individual deep water wave is about 3 times it's period (in seconds). That is, an individual wave with a 13 second period travels at 39 kts/hr. Contrary to what you might intuitively think, there is a linear relationship between wave period and wave speed. But because most deep water waves move in groups, the group speed is half that of an individual wave (within the group), or in this example about 19.5 kts/hr. As the wave moves into shallow water, the group speed and the individual wave speed become the same, so the individual wave starts traveling at the group speed, or 19.5 kts per hour. This wave speed formula is approximate, and actually wave speeds are a fraction different, but this is close enough for all but the most detailed surf forecaster.
[/b]

Quote:

Wave speed isn’t so much dependent on location as it is on size. A one-foot wave will move in a direction perpendicular to the crest, at the same rate in Tavarua or New Jersey.

Actually i think its waves of the same period travel at the same speed. one foot short period wind chop travels slower than one foot groundswell.

oops didn’t read on…lots of other oceanographers on the case

from Table 6.3 of Oceanography of the British Columbia Coast: Approx wavelengths and wave speeds for deep water waves with different periods (waves at the beach will be slower):

5 sec period, 128 ft wavelength, 15 knots wave speed

10 s 512 ft 30 kn

15 s 1161 ft 46 kn

20 s 2048 ft 61 kn

25 s 3200 ft 76 kn

Quote:

1. …as groups of waves move further away from their source in deep water (a thousand or more nmiles) the group becomes better defined, with waves of the exact same speed traveling together…
2. …A wave with a 14 second period reaches down into the ocean about 516 feet. A 17 second period wave at 761 ft, 20 second at 1053 ft and 25 secs to a whopping 1646 ft!..
3. …These ‘sets’ appear as often as every few minutes to once every half hour or more, depending on how far they have traveled to reach your shore. The further the travel time, the better the organization…
4. …The speed (in nautical miles per hour) of an individual deep water wave is about 3 times it’s period (in seconds). That is, an individual wave with a 13 second period travels at 39 kts/hr…
5. …As the wave moves into shallow water, the group speed and the individual wave speed become the same, so the individual wave starts traveling at the group speed, or 19.5 kts per hour. This wave speed formula is approximate, and actually wave speeds are a fraction different, but this is close enough for all but the most detailed surf forecaster…

1. The waves do not have exactly the same speed. Waves of different periods can arrive at the same location at the same time since the storm moves and has a fetch. It is this small difference in period and hence speed that gives rise to “sets” of waves.

2. These numbers should be considered as ballpark estimates since the effects of a wave decay exponentially with depth and thus have no distinct cut-off. For example, for the motion to follow that of the “deep water” equations with a deviation of less than 1 percent, the water depth must be approximately 0.42 times or more the deep water wave-length of the wave. For the motion to follow that of the “shallow water” equations with the same accuracy, the depth of the water must be less than 0.010 times the deep water wave-length of the wave. Motions in water depths in between these two values will not be described with this accuracy using either the deep water or shallow water equations. (Reference: “Wind Waves - their generation and propagation on the ocean surface”. Blair Kinsman, 1964. John Hopkins University, Prentice-Hall Pub., Englewood Cliffs, NJ)

3. The number of waves in a set, and the time between sets is roughly related to not only the distance that they have traveled, but also to the effective fetch of the storm that generated them. (Reference: Lecture by Walter Munk, Scripps Inst. of Oceano., LJ,CA)

4. As stated, speeds are in nautical miles/hour. But 1 knot = 1 nautical mile/hour, so knts/hr is an acceleration, not a speed (i.e. just read knts/hr as knots).

5. In shallow water, the speed of progression of the wave (of infinitesimal amplitude) is not constant, but rather proportional to the square-root of the water depth. So the speed of the wave diminishes as it moves into shallower water. Since in deep water the total energy is equally divided between potential energy (wave height) and kinetic energy (motion through the water), if energy is approximately conserved as the wave moves into shallow water, the reduction in kinetic energy must be offset by an increase in potential energy (wave height). Hence the wave generally increases in size as it moves into shoal water. For a wave of finite amplitude, the height of the wave also starts to affect the speed of the wave as that height becomes comparable with the water depth. In this case, empirical studies indicate for a steadily shoaling bottom, the water depth should be replaced by the sum of the water depth and three-quarters of the height of the wave to get the “effective water depth” for computing the speed of the wave. (Reference: “Oceanography and Seamanship”, Wm. G. VanDorn, 1974. Scripps Inst. of Oceano., Dodd, Mead, and Co. Pub., NY,NY)

Pardon my cubit.

There were different kinds of cubits. The common cubit, called the cubit of a man, was about eighteen inches (Deut. 3:11). Clearly, an exaggeration! The king’s cubit was three inches longer than the common one (so what else is new?). The holy cubit, not to be outdone, was a yard, or two common ones. Holy cubits, Batman!

It seems that the length of a cubit is about as precise as wave-height stories. Poor Noah.

messag from god : measure wave heights in cubits …that is all …ambrose…ah to be the real conduit…

Quote:

messag from god : measure wave heights in cubits …that is all …ambrose…ah to be the real conduit…

And Noah said thank you, god, a cubit is in the eye of the beholder.

This thread has some very interesting info on it.

Just for the record a cubit is the distance fron the elbow to the tip of the middle finger. Eighteen inches is approximate for obvious reasons. Using body parts remains the simpilest way to measure length. Knowing how long you stride is, how far it is from the ground to a given part of the anatomy, your reach, a portion of it, the length of a digit or a segment of a digit can save a lot of time when approximate measurements are all that are required.

Nice wave speed formula!

Mahalo, Rich

3.85 miles per hour multiplied by the square root of the wave height, in feet.

Wave height (ft) Wave speed (mph)

3 6-7

10 12

20 17

This is for breaking waves in shallow water, and makes a whole slew of assumptions (wave height when breaking equals water depth, bottom slopes gradually, etc).

In deep water wave velocity is proportional to period, with 20 second period waves travelling 31 knots, or so.

I went surfing yesterday after voting, needing to cleanse my mind. I took off on a wave and in my head was “Let’s see, my personal cubit is 15.5 inches…” When I paddled back out I said to the guy next to me in the lineup, “Fun little 2.5 cubit wave.” The guy looked at me strangely, paddled out past me toward the shoulder, and left me the peak. Relative measurement is apparently a good strategy for success.