Results of a ReFRESCO CFD calculation of the dynamic sinkage and trim of two identical 110m * 11.40m inland ships. One ship sailing at 14 km/hr overtaking the other one at 12 km/hr. Draught of both ships 3.5m, water depth 4.55m.
Squat research for inland ships Wytze de Boer
w.d.boer@
marin.nl
Recent periods of low water highlight the importance of understanding the squat (sinkage & trim due to ship speed) of inland ships for a single ship in a fairway, and for ships in traffic situations. This is addressed in a joint research project initiated by the Directorate-General for Public Works and Water Management (Rijkswaterstaat) and MARIN.
There are several empirical formulas to estimate the squat of a ship. Previously, MARIN has assessed methods for inland ships in confined waters (ref ). The interaction between ships also has an impact. In the figure, speed and sinkage at the bow were measured on a loaded 110m*11.45m inland ship (draught 3.45m) when it encountered a tanker of 135m*17.6m in the Amsterdam-Rhine Canal (depth of 6m). The tanker had a draught of 3.1m and speed of 13 km/hr. During the encounter, the maximum sinkage increased by more than 100% with respect to the single ship, to approximately 0.45m.
Inland ships have to cope with low water conditions and at the same time, the energy transition impacts ship designs, resulting in higher deadweight and/or space requirements. Design options to cope with these conflicting requirements are weight reduction, more and smaller propellers, and an increased beam. At a given ship length and speed, an increased beam will increase the squat and decrease the under-keel clearance (UKC). This impacts the safety margin for the UKC in the shallowest parts, and could reduce the payload.
In confined waters, sailing closer to the shore and traffic situations result in more squat, and as a result, in less UKC. MARIN analysed a situation when a 110m inland ship was seriously damaged sailing upstream to the German border. The ship was loaded with a small trim bow down and the draught at the bow was 2.3m. While overtaking another ship, the bow hit the bottom. The combination of increasing the
speed to pass the ship and the interaction between the two ships resulted in a squat at the bow of over 0.7m.
In low water periods, extra squat should therefore be taken into account during overtaking and/or encountering other ships to prevent bottom contact. Further research focuses on overtaking and encountering situations by CFD simulations (see video).
Speed sinkage and trim of a 110m inland ship during an encounter report 23
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