Substantial wetdeck slams on a 96m INCAT wavepiercing catamaran have been identified for wave heights in excess of 60% of the wetdeck tunnel height. The relative motion between wetdeck and water surface in each slam has been determined using wave radar and accelerometers and an averaged profile of clearance as a function of time derived for an average slam. This data has been used to establish similarity criteria for drop testing of two-dimensional models representing the double arch section of the wetdeck in the bow region. It is found that hull sections in which the top of the arch is located further outboard from the centre line produce lower slam forces as a broader centre bow gives rise to an outward tangential flow around the arch top. Whilst the tests models did allow venting of the air inside the arch, it was found that the slam forces arising during sea trials reached 31% of the slam forces predicted by extrapolation from the two dimensional model drop tests. This outcome is likely to be influenced by local detail of the water surface/hull interaction during the largest slam observed and the extent of the zone over which the observed slam was distributed on the hull. Also, it is by no means certain that the largest slam observed over a total of 2.5 years of ship operations was the largest possible slam load for the relative motion conditions pertaining to that slam.
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