Fast-ferry generated waves in South-West Tallinn Bay

Kurennoy, D., Parnell, K.E. and Soomere, T., 2011. Fast-ferry generated waves in south-west Tallinn Bay. Journal of Coastal Research, SI 64 (Proceedings of the 11th International Coastal Symposium), ��� – ���. Szczecin, Poland, ISSN 0749-0208 Waves generated by high-speed ferries sailing at near-critical speeds (depth Froude number ~1) may substantially affect the coastal zone. As typical for large-amplitude waves in shallow water, waves from fast ferries frequently have a substantially nonlinear nature and are often able to seriously damage the coastal environment. We report wake characteristics of fast-ferries sailing in Tallinn Bay in June 2009. Waves were measured using an echosounder in the nearshore at Pikakari Beach at a depth of 2.7 m, 2.4 km from the sailing line. The record contains ~150 wake events for which primary wake parameters as the maximum wave height, wake energy and its flux were estimated. The shape of the highest vessel waves was analyzed in terms of cresttrough asymmetry. Maximum wave heights (up to 0.7 m) occurred exclusively for the longest waves with periods ~10 s. These waves are substantially nonlinear with wave crests exceeding wave troughs typically by a factor of 1.3. Incoming ferries generally excited smaller waves compared to a previous study of outgoing ferry wakes in north-west Tallinn Bay. This apparently reflects the high spatial variability of wake waves along the impacted coastal sections and is not an evidence of an overall decrease in the ship wave intensity.