Melted Log Transducer

[Macruairidh]

Hi. I have a C&C 44 with a Nexus Classic Log, Depth and Wind package. About mid summer something happened following a thunderstorm I cant quite figure out. My Log and Depth instruments stopped working. Tried pulling them but they would not budge. Whe I pulled the boat for the winter I thought my log was encrusted with barnacles however on closer inspection I realized the the impellor had melted. My first thought was a lightning strike however everthing else still works. My question is - On a 12 volt system what would cause a surge powerful enough to Melt the Log Transducer Impellor under water with out blowing the wiring insulation off as well.