Depth effected by wave height

[Web Monkey]

Does anybody know if the pressure of the water on a diver changes because of wave height?

For example, if I'm at 60 feet and a tsunami causes a 60 foot wave that passes over me, am I now at 120 feet (as far as gas calculations go)?

Terry

 

[H2Andy]

dunno... but am thinking that would never happen unless you are very close to shore

in the open ocean, the wave would not be very large at all (3-5 feet), and it would only get "big" as it hits the shallows approaching land and the waves slow down, thus
"packing" higher and higher

i remember some divers diving off Thailand who were underwater when the tsunami
struck. they didn't notice anything. when they came up, they were like "What on
Earth????"

http://www.timesonline.co.uk/article/0,,3-1418741,00.html

but there are also reports of divers seeing very "milky" water, and being
shaken as if in a washing machine. other divers felt a "sucking" force
taking them down, and one guy said he ended up 45 feet deeper than he was
to begin with.

so i guess it depends on your depth and/or location

 

[Kim]

I'm not sure which thread it was but I read one a couple of days (yesterday??) ago where someone said that their computer did react because of waves passing over head. It created the impression of a saw tooth profile.
Tsunami waves though only become high when they hit the shallow run up to the beach. In open water they aren't that big. Also with a tsunami there are only a couple of waves moving very fast above you. The situation in the other thread was to do with a large swell situation - so many changes.

 

[Rick Murchison]

Because pressure comes from all directions, the effect of waves on that pressure (which we measure as depth) diminishes the deeper you get. The depth to which this effect is measurable depends a little on wave height, but much more on the wave period. That is, waves that are very close together effect depth readings at any given position less than waves of the same height that are far apart.
As an extreme example (to illustrate the point), imagine a choppy sea of two foot waves... on the bottom 50 feet below the surface the pressure (and therefore measured depth) would be essentially unaffected - no change in depth would ever show or be measurable with any diving depth gauge. If that two foot wave is that very long period wave we call the tide, however, we'll show a two foot difference down at 50' between the crest (high tide) and the trough (low tide) of the wave.
In general, if you can feel the surge from the waves above, you'll be able to see the "sawtooth" profile when you download your computer after the dive. (If you get a sawtooth profile without any surge.... well, you can't blame the waves )
Rick

 

[ScubaDadMiami]

Where this would have the greatest real world relevance is in conducting your shallow stops at the end of your dive. On days with big waves, when you are at twenty feet or less (especially for those that elect to make their final stop at ten feet), passing waves can cause depth changes, which is not what one aims for when trying to maintain a constant depth.

 

[Rick Inman]

In general, if you can feel the surge from the waves above, you'll be able to see the "sawtooth" profile when you download your computer after the dive. (If you get a sawtooth profile without any surge.... well, you can't blame the waves )
Rick

I've had my computer beep at me for rapid ascent every time large swells pass over. Kind of disconcerting thinking about the pending shore exit...

 

[miketsp]

As Rick points out, the percentage pressure change will be less, the deeper you are.
The shallower you are the more you will be affected.
There are documented cases of ear trauma to divers swimming shallow under 2.5m waves.

 

[miketsp]

..snip..
In general, if you can feel the surge from the waves above, you'll be able to see the "sawtooth" profile when you download your computer after the dive. (If you get a sawtooth profile without any surge.... well, you can't blame the waves )
Rick

Whether you see the sawtooth on the download will depend on your sampling interval.
During the dive the display is in real-time or near real-time, normally less than 1 second for depth.
The memory however will be recorded at some interval , anything from 1 second to 1 minute depending on the model and chosen setting. At the moment mine is set to 20 seconds recording which makes it hard to see waves after the download.

 

[Web Monkey]

Nice explanation! Thanks!

Terry

In general, if you can feel the surge from the waves above, you'll be able to see the "sawtooth" profile when you download your computer after the dive. (If you get a sawtooth profile without any surge.... well, you can't blame the waves )
Rick

 

[The Kraken]

My question would be, would the passing of the wave, given that the action takes such an insignificant amount of time, be of any real consideration with respect to the dive profile and/or the depth of a safety stop.

How long does it take for a large wave to pass, 6 or 7 seconds???