Comparison of motion sickness incidence of three crew transfer vessels with different hull forms

Abstract

The Crew Transfer Vessels (CTV) which operate near offshore installations rarely sail in calm water. The rough sea conditions produce ship motion such as vertical accelerations that affect people on board. It may cause sea sickness. The increasing number of offshore wind farms in North Sea has increased the number of sea keeping studies to reduce the time transfer even when the weather is bad and avoiding sickness motion. High vertical acceleration peaks could induce voluntary speed reduction and loss of money. A Small Water-plane Area Twin Hull (SWATH), a monohull and a catamaran (CTV configuration) will be compared using motion analysis and the influence on humans. The purpose of this master thesis is to prove that the seakeeping behaviour of the SWATH is better than monohull and catamaran hull forms. My work started during my internship at Abeking & Rasmussen between July and September 2013. There are different indexes to estimate the sea sickness phenomenon, depending mainly on the wave frequency, the vertical acceleration and the time of exposure. The oldest one is the Motion Index Incidence (MSI) to estimate quantitatively the impact of ship motions in the percentage of people that would suffer from seasickness. The ISO rules established the human body limits, function of the duration of exposure. By calculating the MSI index, it is possible to estimate the percentage of sick people in different localization on the deck according to the wave spectrum, ship speed and heading angle. The SWATH is known for its good sea keeping behaviour due to its small water plane area. Physical tests have been done in North Sea in 2000 and 2003; the vertical accelerations and time-domain wave elevations were measured in different localizations on the 25m-SWATH Duhnen. The experimental significant wave amplitude and wave spectrum (frequency domain) were calculated to define the wave spectrum for the two numerical sea-keeping analyses of the monohull and the catamaran. The analyses presented in the thesis are realized with the Seakeeper software, a plug-in of the Maxsurf-naval architectural suite. The 2D-stip theory is used by Seakeeper to calculate the hydrodynamic coefficients. The preliminary design of the comparative hull forms are based on existing designs, recent studies and berthing to the offshore installations. The 33m-monohull has the same displacement than the SWATH and the catamaran the same length. The numerical results will be compared together with the MSI values obtained from the experimental measurements of the Duhnen.