Variability in spatial patterns of long nonlinear waves from fast ferries in Tallinn Bay

Abstract

Abstract. High-speed ferries are known to generate wakes with unusually long periods, and occasionally large amplitudes which may serve as a qualitatively new forcing factor in coastal regions that are not exposed to a sea swell. An intrinsic feature of such wakes is their large spatial variation. We analyze the variability of wake conditions for the coasts of Tallinn Bay, the Baltic Sea, a sea area with very intense fast ferry traffic. The modelled ship wave properties for several GPS-recorded ship tracks reasonably match the measured waves in terms of both wave heights and periods. It is shown that the spatial extent of the wake patterns is very sensitive to small variations in sailing conditions. This feature leads to large variations of ship wave loads at different coastal sections with several locations regularly receiving high ship wave energy. The runup of the largest ship wakes on the beach increases significantly with an increase in wave height whereas shorter (period <2-5 s) waves merge into longer waves in the shoaling and runup process.

Identification of ship wake structures by a time–frequency method

“…The length Froude number is therefore not very large for these ships, F L 0.34. The water depth along parts of the sailing line lies between 20 and 40 m, particularly for north-bound ships, hence the depth Froude number can potentially be in the range F d ∼ 0.72-1.0 within these regions (Torsvik et al 2009). The analysis presented here focuses on single events that could be reasonably identified and that occurred on days with little wind-wave background.…”

“…The wake events we analyse are generated by large passenger ferries for which we can assume that F L 0.5, but where F d can reach values of ∼0.7 along certain sections of the route, hence some shallow-water effects can be expected. However, as F d varies considerably along the ship route due to local depth variation (Torsvik et al 2009), and we do not know the exact points of origin for the wake components that we record, we have performed the analysis based on deep-water linear wave theory which is invariant with respect to the water depth. This paper is a continuation of the work presented in Didenkulova et al (2013).…”

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

“…This, together with near-critical and supercritical speeds, leads to high loads on the coastal environment [39]. This has been confirmed in a series of studies conducted at Tallinn Bay, Estonia [37,39,[42][43][44].…”

Ship-induced solitary Riemann waves of depression in Venice Lagoon

“…3). None of the recorded depressions had an elongated almost horizontal trough that is suggested by weakly nonlinear simulations [15,16]. This suggests that the depressions had strongly nonlinear nature.…”

“…It is at times present at fairly low Froude numbers (down to 0.13 [13]) but is much more pronounced at moderate and high depth Froude numbers. It becomes often evident as a region of depression of nearly uniform depth [14][15][16], causes the draw-down effect (squat [17][18][19][20][21][22]) usually restricted to the navigation channel and may form structures similar to undular bore [23][24][25].…”