Effects of freeboard and bow height on green water loads for a general purpose cargo ship

A series of experiments were carried out on a model of a modern cargo ship in high sea states, to measure the loads on the deck as a function of the sea state, the draft and the freeboard of the vessel. The measured loads were compared to the values required by the 1966 International Convention on Load Lines (ICLL).
The experiments show that the ship motions and the relative motions at the bow can be predicted by linear theory in severe sea states until large amounts of green water are shipped over the bow. Shipping green water over the bow appeared to occur very often. The pressures on the hatch cover appeared to be very high; the required values of the ICLL were exceeded in high sea states. The loads on the forward hatch covers are higher than the loads aft.
Increasing the bow height appeared to be very effective in reducing the maximum loads on the forward hatch cover. Installing a breakwater on the fore deck showed to have a negative effect; the loads on the forward hatch cover were much higher than without the breakwater.
An approximation formula is derived for this specific vessel which links bow height exceedance to maximum pressures on the deck. Using this formula, exceedance levels of 1/hr are drawn in a wave scatter diagram. These diagrams show that the ICLL pressure of 1.75 m water column can easily be exceeded. This illustrates that the 1966 ICLL values for minimum bow height and water height on the hatch covers need to be adopted.