Over the course of hundreds of hours per year, ports experience the influence of wind on nautical and terminal operations. This influence is increased by the global trend of ever increasing vessel sizes and the movement of ports to deeper water near or even beyond the coastline. The influence of wind and possible solutions to this problem are discussed in this article.
Wind is an uncontrollable source of disturbances, reducing efficiency of port operations and sometimes even causing downtime. Because of the increase in scale, the movement further towards sea and also stricter regulations, the impact of wind continues to increase.
Wind can be characterised by speed and direction. Unfortunately in the working environment of ports there is confusion about Beaufort scale (Table 1) and wind speed. The wind speed of the Beaufort scale is ‘the average wind speed taken over the ten minutes preceding the time of observation at 10 m’ (J. Weringa en P.J. Rijkoort Windklimaat van Nederland, KNMI) or mean wind. Sometimes however, a wind regime at Beaufort 6 is wrongly interpreted as gusts of wind with speeds varying between 10.8 and 13.8 m/s.
By definition of the European standard for Crane design (European standard EN13001 Cranes – general design) the gust wind is the average three-second wind. Table 2 shows the relation between the maximum wind speed and the measure time interval. The table shows that wind speed increases with decreasing interval time. The maximum gust wind at Beaufort 6 is therefore not 13.8 but 13.8*1.5=20.7 m/s!
Increase of wind velocity
To handle vessels with deep draught the international trend is to construct new ports closer to the sea, while older docks near city centres become less important or are even closed. The difference in wind speed between the coast and the open sea is indicated by the Royal Meteorological Institute of the Netherlands (KNMI) as: “under equal circumstances … it is concluded that potential wind on sea is 12% stronger than on open terrain on shore only because of the difference in roughness. However, most experiments reveal a difference of 20% or more mainly because the shore terrain is not open but rugged.”
This is also confirmed by our own research where we found that 30 km off-shore the mean wind speed is up to two m/s higher than on shore, while for wind gusts, the difference can be even four m/s. If we assume that moving five km towards sea (from Maasvlakte I to Maasvlakte II) increases mean wind speed with one m/s, the amount of hours with troubling winds and loss of productivity on a container terminal due to wind will double. Increase of wind pressure The increase in world sea trade causes an increase in port equipment and vessel size. For example, the 9500 TEU container vessel commissioned in 2005 is almost ten times the capacity of the first generation container vessels of 1962. This also affects the size of the cranes. The effect of wind increases due to larger wind surfaces of cranes and vessels, but the effect is also augmented because of the extra wind speed at higher altitudes. Besides the affects on vessels and cranes, high investments in quay strength are also needed, in order to support the high corner pressures of a 110 m high stowed crane, which is exposed to storm winds (Figure 1).
Over the years society has become str icter in ter ms of accepted pollution and hazard level. An example of this increased attention is the str icter inter pretation of wind pressure due to wind gusts in the new European crane design standard EN13001. Wind pressure on cranes is now explicitly dependent on wind gusts, while previously in National Standards (Din 15019 teil 1 Krane, Standsicherheit; NEN 2018 Hijskranen) only the wind categories ‘light, normal, and heavy’ were defined. Further more, ter rain roughness factors account for higher coastal winds, while wind loads no longer depend on countries, but rather on a wind map where Europe is divided into wind regions (A to F) based on measured data (Figure 2).