Boot Key Harbor
"Marathon- the Heart of the Florida Keys"

An On-Line Cruising Guide for the Florida Keys & Cuba
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Guide to predicting Fully Developed Seas (FDS)
(wind/wave discussion below tables)

*Note: 10% of the waves will be 1.29 times the Significant Wave Heights (SWH) listed here. The average seas will be 0.64 times this SWH, and the tallest waves will be twice the SWH.
Source: Nov 2000 article in Cruising World Magazine by Michael Carr. Faculty Maritime Institute of Technology & Graduate Studies in Linthicum Maryland.
(See the related discussion of Marine Weather Definitions and Significant Wave Height)

Table for Beaufort force 4. Wind 11-16 knots. Stops at maximum FDS fetch/time.

Fetch (miles)	Time (hours)	Height (significant wave ht)	Period (seconds)
50	12.4	4.0	3.8
100	20.0	4.0	4.4
200	33.5	4.3	5.6

Table for Beaufort force 6. Wind 22-27 knots. Stops at maximum FDS fetch/time.

Fetch (miles)	Time (hours)	Height (significant wave ht)	Period (seconds)
50	9.1	9.8	4.8
100	15.1	11.4	6.0
200	25.4	12.2	7.1
400	42.2	13.5	8.6
600	56.3	13.8	9.5

Table for Beaufort force 8. Wind 34-40 knots. Stops at maximum FDS fetch/time.

Fetch (miles)	Time (hours)	Height (significant wave ht)	Period (seconds)
50	7.7	15.7	5.6
100	12.8	20.5	6.9
200	21.5	23.5	8.5
400	35.6	26.0	10.2
600	47.7	27.5	11.3

Table for Beaufort force 10. Wind 48-55 knots. Stops at maximum FDS fetch/time.

Fetch (miles)	Time (hours)	Height (significant wave ht)	Period (seconds)
50	6.4	23.0	6.7
100	11.0	32.0	8.1
200	18.1	40.0	9.8
400	30.2	47.5	12.0
600	40.3	50.0	13.3
1000	59.3	52.0	15.3

Wave height is determine by wind strength, duration and effective fetch. The maximum height of a wave assuming unlimited fetch and duration is called a "fully developed sea" (FDS). The fetch determines how long it must blow to attain FDS so, for example in a Force 8 wind with a 400 mile fetch, it will attain maximum height in 35.6 hours and be 26.0 feet.

This 26.0 feet is the significant wave height. This is the average of the tallest third of all waves and is what is reported on marine weather.

Forecasts are available on NOAA's web site. There is also a Wave Period Chart that uses NOAA's new Wave-Watch III model and shows peak wave period for both locally generated seas as well as dominant swells. Details can be found at http://polar.wwb.noaa.gov/waves/wavewatch .

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