Repairing freeze damage takes time and all too often involves a complete engine replacement.
In The Boater’s Guide to Winterizing, you’ll find the list of items that would have prevented more than 95 percent of the freeze claims handled by the BoatUS Marine Insurance Program in the past decade.
To protect the engine against damage from freezing, run antifreeze through the engine. For the best protection use marine engine grade antifreeze, either one rated to -60 or -100 degrees. Do not dilute the antifreeze or it will not perform correctly.
To protect the inside of the engine until spring you must fog the engine to protect its moving parts. You can spray them into the carburetor while the engine is running or apply it through spark plugs holes while the engine is turned over.
Winterization starts with prepping the fuel supply long before the day you haul out for the winter. The engine’s fuel supply should be treated for storage during the last week or so of your boat’s in-water use. Neumann says they used to tell customers to fill the gas tank and add a stabilizer. However, he adds that ethanol in today’s gas is not good for boats at all. It breaks down the gas and gums up the engine in a short time. Now he tells customers to drain the tank as empty as possible and stabilize the rest. If a tank is empty there is no need for a stabilizer.
If your boat is small enough, simply disconnect the batteries and bring them home. Add distilled water and charge them occasionally.
For larger boats, disconnect the batteries, add distilled water and then periodically reconnect and charge them using shore power.
There is a benefit in removing batteries and storing them in a warm environment. The cold saps the juice out of batteries, providing less cranking capacity. The other benefit is that the cable connections get cleaned when the battery gets put back.

To double the life of a battery, there is a charger, called a battery tender, available that you can leave on the battery all winter. It will not overcharge the battery, sensing the level of charge, only working as needed.
The old chargers would overcharge and ruin the battery if left on all winter. Plus, batteries have gone way up in price, so it makes sense to keep yours maintained properly.
Winterize the hull and interior of the boat. First, do a thorough examination of the hull, keeping a careful lookout for blisters in the gelcoat.
Also check for stress cracks which most often occur near the bow. Finally, pressure-wash the hull to remove dirt and debris.
Fall/winter is a perfect time to put the shine to your boat’s gelcoat, restoring or maintaining your boat’s shiny finish. By washing and waxing the boat before it goes into storage you will have less work to do when spring arrives.
Storing your boat outdoors in shrink-wrap or indoors each has their own advantages and disadvantages. If you store your boat outdoors, be sure to choose a sturdy boat cover and support structure to withstand heavy snow.
If you want to keep mice from causing trouble keep your boat away from buildings, including indoor storage areas. Neumann adds he has tried everything to keep them out but nothing seems to stop them, even mouse poison or shrink wrap.
The work you do at the end of the boating season will extend the life of your craft and is well worth the time (and money) to do it right.