I used to keep my boat in Sydney
, Nova Scotia
(Canada), one year it was in the water.
The common practice to prevent the raw water
side of the engine cooling
system from freezing up was to:
-disconnect suction line of raw water
-immerse it in a bucket of household or RV plumbing antifreeze
-run the engine till you see pink fluid in the exhaust
-reconnect to seacock which you leave in the closed position
Then should you need to move the boat quickly turn the seacock and go.
All other lines just disconnect from the seacocks, drain, reconnect and dump in some plumbing antifreeze