Cooling for power electronics in leisure vessels has so far been based in the use of forced air, even though such vessels are surrounded by water which can ultimately be used to dump the heat developed by power electronics converters and electrical machines. Some of the reasons to avoid the use of sea water for cooling are the need to deal with biological-fouling, salt water, corrosion, and condensation. We propose to apply a new concept where pre-filtered seawater is used to cool down power electronic modules in order to significantly reduce the size of the cooling system. A new type of cold plate with direct flow of seawater has been designed considering the mentioned challenges. The cold plate will cool down a 5kW (10kW peak) power electronics module. Such module consists of a 3 kW 3-phase AC-DC rectifier, a 2 kW (10kW peak) full-bridge DC-DC converter and a 5 kW (10 kW peak) DC-AC single phase inverter.