Cetacean Season 2015

Ocean Waves (Nov 18, 2015)

Much theory exists in weather books, mariners manuals and sea-going texts on the characteristics if large ocean waves.   Three most important variables regarding wave relationships are the wind on the sea surface, the fetch (the stretch of water over which the wind blows) and the duration, the length of time that the wind has blown.

Blue Waves. Splosh!

Blue Waves. Splosh!

The Beaufort Wind Scale, as described by Rear Admiral Sir Francis Beaufort (1774-1857) during tenure as a Royal Navy hydrographer, allows one to estimate the Beaufort Force (or wind speed) from the appearance of the sea. This wind scale notes the speed of the “Wind” in knots, its’ “Description” and the “Effect at Sea”. Assessing all of these factors, for most of the day we have had a Beaufort 6 (22-27 knots of wind) with a description of “large waves begin to form, the white foam crests are more extensive with a possibility of spray” – not too bad really. We have had two swells, one from the SE of 4-6 m (of 7 second period) and the other from the S of 1.5 m (also of 7 second period). Checking the fetch, with wind from 1330, this breeze is coming all the way from Cape Leeuwin across the Indian Ocean! That’s 1750 nm of fetch!

White Waves. Nice day for white waves!

White Waves. Nice day for white waves!

I love all the theory about waves, such as wave speed C = L/T (where C is the speed of the wave, L is the wave length and T is the time of one wave period), as well wave speed in knots can be calculated as:

                 Velocity (knots) = 0.6 x Length (m)

                                                          Period (s)            

and there are relationships between maximum wave height & fetch, wave speed & fetch, wave height & wind speed, wave speed & wind speed, wave height & duration of wind, wave speed & duration of wind, etc… but, mostly I just love waves.

Tiny Flying Fish. Short life lost in the whosh of water on deck.

Tiny Flying Fish. Short life lost in the whosh of water on deck.

By 5pm, the sea state had gone up a notch, we now had a Beaufort 7 (28-33 knots) but the sea was very confused, most likely due to the ridge at which we are surveying.   Turning straight into the waves, and now heading 1330 proved a good heading in the confused sea – this might be our new course.

More Blue Waves. Did I get wet?  Yep.

More Blue Waves. Did I get wet? Yep.

We shall keep you posted from the middle of the Indian Ocean briny.

 

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