In view of the SALTO JIP (Safe Arctic Logistics, Transport & Operations) a pre-study started to develop a probabilistic model for icing due to spray water over the bow of a ship. The investigation has two stages:

  • a probabilistic model for volumes of spray water (and the break-up in droplets) rising above the freeboard and,

  • a probabilistic model for the ballistic and thermodynamic process of these droplets when falling and freezing to the ship.

The present paper concerns the first stage. The calculation model uses a novel combination of ship motions and wedge impact modelling, taking into account the above water hull shape and non-linear effects in the wave. For droplet break-up empirical spray nozzle modelling appeared useful to derive mean droplet diameters and size distribution.

The results from the calculation model seem realistic when comparing to the scarce validation data. Spray is normally no problem, so the subject has seen little interest. Also -due to scaling problems- model test results are hardly applicable and full scale measurements virtually impossible. The present modelling takes realistically into account the effect of sea state, bow shape, speed, freeboard and ship size, i.e. it reflects that marine spray is a threshold phenomena, with sharply increasing volumes if a given condition is exceeded.

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