Crest-trough asymmetry of waves generated by high-speed ferries

Abstract

The shape of waves from high-speed ferries in Tallinn Bay, the Baltic Sea, is analysed from the viewpoint of the potential asymmetry of the crest heights and trough depths. Only the waves from the first group of the wake (that usually contains the highest and longest waves) are analysed. On average, wave crests deviate from still water level 1.4 times more than the wave troughs. In extreme cases, the crest height exceeds the trough depth by up to a factor of 3. It is shown that asymmetry is an important parameter of the wakes, the values of which do not necessarily correlate with the maximum wave height in the wakes, a quantity that otherwise characterizes the basic properties of the wakes well. The results for the ratio of the crest height over the trough depth coincide with estimates made using classical cnoidal wave theory. Distribution functions of the wave asymmetry for vessels, operating in Tallinn Bay, show that the most frequent values for the ratio of the crest height over the trough depth lie between 1 and 1.6.

A typical wave wake from high-speed vessels: its group structure and run-up

“…Fast vessel generated waves considerably exceed typical periods and heights of wind waves (Soomere, 2005a;Parnell et al, 2008). The periods of the highest waves are of 8-15 s and their heights are up to 2 m depending on location (Parnell et al, 2008;Kurennoy et al, 2009Kurennoy et al, , 2011). …”

“…All three vessels are large conventional ships with lengths of about 200 m and operational speeds of 30 knots, which are capable to generate largeamplitude, long and long-crested waves in Tallinn bay. However, due to the variability in ship track and its speed along the track, the parameters of ship generated waves may vary, their averaged values are described in Kurennoy et al (2009). Vessel generated waves were recorded using a downwardlooking ultrasonic echo sounder (LOG aLevel®) with a sampling frequency of 5 Hz, mounted on a stable tripod approximately 100 m from the shoreline, 2.4 km from the sailing line at a water depth of about 2.7 m from 17 June till 1 July 2009, and were studied overall and with respect to the type of the vessel.…”

“…Waves induced by high-speed vessels, the depth Froude number (the ratio of the ship's speed and the maximum phase speed of linear water waves for the given depth) of which during the regular sailing regime exceeds 0.6, have become a subject of intensive study in the last ten years after the new generation of large and powerful ships operating at cruise speeds up to 30 knots has been introduced (Parnell and Kofoed-Hansen, 2001;Parnell et al, 2007Parnell et al, , 2008Soomere, 2007;Kurennoy et al, 2009Kurennoy et al, , 2011Torsvik et al, 2009;Rapaglia et al, 2011). It has been demostrated that these waves can be a major contributor of energy to sections of coasts that are exposed to significant natural hydrodynamic loads (Soomere, 2005a).…”

Effect of Tidal Stage on Sediment Concentrations and Turbulence by Vessel Wake in a Coastal Plain Saltmarsh

“…Vessel generated waves in shallow water can impact shoreline stability and habitat structure in many waterways [1][2][3][4]. These impacts are linked to sediment transport processes, which are associated with dissipation and turbulence generation similar to wind waves, tides, or other energetic forcing mechanisms.…”

The Failure of Fast Ferry Catamaran Operations in New Zealand and Hawaii

“…With the growing market and operation of high-speed vessels around the globe, environmental concerns are rising, especially in regards to wave wash and emissions due to significantly high fuel consumption [36]. The massive growth in exhaust emissions per passenger-mile and the great increase in external noise and waves generated by large high-speed ships are the major concerns of environmental studies [37][38][39].…”