Spatial variation in high-speed ferry wakes in the Tallinn Bay area

Abstract

A large number of high-speed ferry crossings occur in the Tallinn Bay area during the summer season. It is well known that the wakes from such ferries constitute a considerable additional wave load to the coastal region, with different properties from wind generated waves and waves from conventional ships. Waves in this area have been studied with the use of pressure sensors at particular locations, and provide valuable data for assessing the ship wave component of the wave load. Recent numerical simulations show that there is considerable spatial variation in the wave load at the coast due to topographic effects and ship maneuvering. This results in wave focusing and shadow areas on different parts of the coast. It is therefore believed that the previous studies may have missed some ldquohotspotsrdquo for the coastal wave impact. We analyze spatial patterns and far field properties of the long-wave part of wakes of fast ferries in Tallinn Bay with use of the Boussinesq-type shallow-water model COULWAVE forced by realistic ship motions. The calculated heights of ship waves exhibit substantial spatial variability. The largest waves were created when the ship sailing to Tallinn entered into supercritical regime when moving over the coastal slope. The maximum wave height eventually reached 3 m whereas along other sections of the track the wave height was about 1 m. The highest waves hit the area of Pirita Beach that apparently has much larger ship wave loads than the adjacent sections of the Viimsi Peninsula.