Wave Period/Distance/Math Guru Needed

Jokani

Jokani

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My daughter is struggling with calculating wave distance , and as it is sailing related she came to me, but it is beyond me!

Lots of info Googling, mostly on sail/surf sites, but nothing that really helps.

Looking for info on how to measure wave distance please.
 
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This sounded amusing to me. So I couldn't resist. But first a disclaimer: I am no expert. This might well be all wrong but does seem to use all data....

Also sorry if I give too much detail, but you can decide how much to tell your daughter.

Since the buoy is in open ocean we can assume the waves are "deep water waves" and so the wave speed is given by

c = (g/(2 pi)) P

where P is the period of the wave, g is the acceleration due to gravity and pi is 3.141..... (see for example slide 4 in https://www.soest.hawaii.edu/oceano...ructors/Carter/SP2016/waves2_2016_handout.pdf)

So the first waves to arrive (wave 1) has a period P1 (20 sec) and hence a speed C1 given by the formula above. Three hours later the waves (wave 2) are slower having period P2 (18sec) and a speed C2 computed from the same equation.

Assume the waves were generated by a point storm (!) i.e. a storm that is small in extent compared to the distance travelled by the waves. Then the distance L travelled by the waves is the same. We don't know the time of travel but we assume they started at the same time. So if T denotes the unknown travel time for the fastest waves we know (distance=speed*time)

L= C1 T

The waves measured at the second time arrive at (T+DT) where DT=3 hours (careful with units) and so

L=C2 (T+DT)

Eliminate T and hence determine L. Lets see if we agree!

Now I have to get back to my day job which is currently very boring.
 
Wow, thank you, I'll pass this on, and let you know how she gets on.

Thanks again, really appreciate you taking the time to put that together.
 
Thanks everyone for all the help, really appreciate that.

Took some time to get our heads around it, but in the end, 2 different methods of calculation both arrived at the same result, so pretty confident in the result.

Again, can't thank you enough.

Have a great weekend.
 
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