Stern Twin-Propeller Effects on Harbor Infrastructures. Experimental Analysis

Anna Mujal-Colilles,Toni Llull,Xavi Gironella,Xavier Martínez De Osés,Marcel·La Castells

doi:10.3390/w10111571

Abstract

The growth of marine traffic in harbors, and the subsequent increase in vessel and propulsion system sizes, produces three linked problems at the harbor basin area: (i) higher erosion rates damaging docking structures; (ii) sedimentation areas reducing the total depth; (iii) resuspension of contaminated materials deposited at the seabed. The published literature demonstrates that there are no formulations for twin stern propellers to compute the maximum scouring depth. Another important limitation is the fact that the formulations proposed only use one type of maneuvering during the experimental campaign, assuming that vessels are constantly being undocked. Trying to reproduce the real arrival and departure maneuvers, 24 different tests were conducted at an experimental laboratory in a medium-scale water tank using a twin propeller model to estimate the consequences and the maximum scouring depth produced by stern propellers during the backward/docking and forward/undocking scenarios. Results confirm that the combination of backward and forward scenario differs substantially from the experiments performed so far in the literature using only an accumulative forward scenario, yielding deeper scouring holes at the harbor basin area. The results presented in this paper can be used as guidelines to estimate the effects of regular vessels at their particular docking location.

Highlights

The significant growth experienced by regular shipping lines and the marine transportation industry over the last 20 years is producing severe problems for old marinas designed to host smaller vessels with lower docking frequencies
The former is originated by the vicinity of the front wall. The former is originated by the direct impact of the jet flow at the sediment bed, whereas the latter is produced by the returning flow direct impact of the jet flow at the sediment bed, whereas the latter is produced by the returning flow with a clear vertical component towards the sediment bed due to the existence of the docking wall
The present contribution introduced the use of twin propeller experimental results and the description of the consequences and erosion evolution of the sediment bed when incorporating back-and-forth scenarios

Summary

Introduction

The significant growth experienced by regular shipping lines and the marine transportation industry over the last 20 years is producing severe problems for old marinas designed to host smaller vessels with lower docking frequencies. Bigger and more powerful propulsion systems and deeper draft vessels are needed nowadays to satisfy the demands on marine traffic. This increase in propulsion system and vessel sizes is affecting the docking infrastructures and the operability of the entire harbor. The main problem is the change in bed morphology of the harbor: entrance channels suffer high rates of erosion and the changes on harbor basins seafloor combine both erosion and sedimentation. If the erosion is located at more central areas of the harbor basin, a problem arises with the deposition of the eroded sediment along the harbor basin, Water 2018, 10, 1571; doi:10.3390/w10111571 www.mdpi.com/journal/water

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