A little frozen water in the bilge wouldn't even get my attention. I did put a full gallon of -100f antifreeze in the empty bilge before I left it. The problem is that water comes down the mast in remarkable quantity and fully overwhelms the bilge and dilutes the AF. The boat does have a full cover on it. It has not been uncommon for me to come and handpump 20 gallons of water out of the bilge each month. The level is probably twice that high now, but frozen solid.
The water starts to back up across bilge compartments and has now penetrated the genset locker. The frozen water in the genset has covered some hoses and insulated electrical wiring and is just about to be high enough to get into the genset cabinet itself.
The primary bilge pump is well above the bilge itself, with only an intake hose down in the bilge. The backup pump is fully submerged under the ice. That cant' be good.
Rock salt seems like it would leave corrosive residue behind. I will have to look into a non-corrosive chemical deicer.
Another suggestion I received was to heat up or boil some -100f antifreeze and pour over the ice. It would melt, mix and keep all from refreezing while I pump overboard. First, I have to check to see if heating antifreeze is a good idea and it isn't flamable. Secondly, that will get expensive as it will take dozens of gallons that will just go straight overboard.
Thanks for the ideas.