Spatio-temporal variation in sea state parameters along virtual ship route paths

Abstract

The article presents a study investigating the level of variation in sea state parameters encountered by sailing ships crossing the oceans. The sea state parameters have been obtained from a reanalysis, in this case the ERA5. The study is based on the use of different interpolation schemes to compute parameters in geographical positions off the fixed grid. It is shown that the variation in sea state parameters can be significant. Consequently, in case of sailing ships, covering relatively long distances in a short time (30-60 minutes), it is recommended to rely on bilinear interpolation rather than nearest neighbour. The variation in the sea state parameters is, in fact, at a level which means that the normal assumption of a stationary seaway in periods up to 3 hours likely is violated for ships sailing the typical service speed (15 -20+ knots).

Sea state identification using machine learning—A comparative study based on in-service data from a container vessel

“…The main drawback of frequency domain approaches is considered to be the dependency on relatively long time windows, up to 25-30 min as found in this study, for a reasonable frequency resolution. Inherently, this can compromise results due to problems related to nonstationary conditions, emphasizing that even the sea state itself, as encountered from a sailing ship going maybe +20 knots, can vary because of spatial and temporal progression [30,49]. On the other hand, the literature provides promising studies that could be considered for mitigation of the drawback.…”

“…The 𝑅𝑀𝑆𝐸 attributes more weight to outliers or variance and the 𝑀𝐴𝐸 indicates the magnitude of the error without considering the sign. Due to the circular ambiguity in case of the mean encounter wave direction, a similar approach as in Nielsen [49] is…”

Comparison of added resistance methods using digital twin and full-scale data

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How Good Is the STW Sensor? An Account from a Larger Shipping Company

“…ERA5 is a reanalysis database that provides hourly updates of wave spectra in grid points spaced by 0.5 • latitude and longitude degrees. Table 7 presents the features downloaded and later bi-linearly interpolated using the method described in [29]. The sea current velocity vector measurements, combined with the true heading of the ship as given by compass ψ m , one can find the projected speed of the currents on the ship's body-fixed reference frame U COP .…”