How do you winterize your boat? A lot depends on what kind of boat you have, now large it is, and whether you leave it in the water or not. Trailerable boats can be easily hauled out and stored on shore, often at the owner's home so they are easily accessible for cleaning, maintenance, and upgrades.
Many aspects of winterizing a boat are similar to winterizing and RV. First of all, drain or freeze-proof all water systems (fresh water tanks, lines, and fixtures, waste water lines and tanks, and engine cooling systems). Remove all perishable foods, sundries, and supplies. Inspect all hatches and thru-hull fittings to ensure they won't leak.
If you have a trailerable boat, or have your boat hauled out for the winter, you may want to shrink wrap it to protect it from the elements over the winter. Doing it yourself can be a lot of work but there are companies that perform this service and are well worth it if it is within your budget. Covering your boat with a tarp will provide some level of protection, but it won't be as secure as shrink wrap and wind may wear holes in the tarp and/or damage the finish on the boat where it contacts hard surface. Custom fit boat covers provide a safer, more secure way of covering your boat but they can take time and can be quite expensive.
While you have your boat out of the water is a good time to clean and inspect it. Hulls often collect algae, mollusks, and other unwanted growths that can inhibit performance and, quite frankly, look like crap! It would be a very good idea to thoroughly clean your boat, top and bottom, inside and out, before you put it into storage. Carefully inspect the deck and hull to determine if they need painting or other maintenance before you put the boat back into service next year.
We have a trailerable Macgregor 25 sailboat. Each winter we pull it out of the lake and bring it home. This saves several months of mooring fees, avoids risking damage from being banged around the docks by winter storms or icing, and keeps the boat in our yard where we can keep an eye on it. We built a shelter for our boat using a PVC pipe frame and a large, green farm tarp. The PVC bends enough to form bows over the boat to hold the tarp up, preventing possible damage to the tarp and the finish on the boat and allowing us access to the deck and the cabin for inspection and maintenance. It looks like a big green covered wagon over the boat. We drive 3/8" rebar into the ground as anchor points for each of the PVC pipes supporting the frame. We used 1/2" schedule 40 PVC pipe. For our 25' boat we use three horizontal pipes -- one at the ridgeline and one alongside each lifeline. We use 4-way (cross) connectors every 2' to run bows and legs from the ground on one side up over the boat to the ground on the other side. Then pull the tarp over and tie it down securely with bungie cords. You might want to glue the framework together or secure each joint with cotter pins or bolts, but I just use a press fit so I can easily replace any parts that my get damaged from snow loading and can disassemble it when it is time to launch the boat.
To minimize tear down and set up time we keep as much of the framework intact when we remove it each summer. If you glue it together be sure to leave enough room on each side to pull the whole boat and trailer assembly out and put it back in next season. If you choose to glue it together and use it as a semi-permanent structure you might want to consider using larger PVC pipe. We went with 1/2" pipe for flexibility and ease of handling as well as lower cost. We managed to break down our framework into about 6 pieces this last time and it took us less than 2 hours from start to finish to install the cover this year. The "covered wagon" style cover also allows us easy access to the boat for inspection, repairs, cleaning, maintenance, and upgrades over the winter while providing good protection from the elements.
We kept our original 1970 Macgregor Venture 24 sailboat after it was totaled by the insurance company when it fell off the trailer on the way to the lake last summer. It makes a fun playhouse for the grandkids and one day, with luck, we might find a new swing keel and mast to repair it and make it seaworthy again. We covered it with a tarp to protect it against winter weather and keep soggy leaves from staining the deck. I used sections of the broken mast to make a ridgepole down the centerline so that rain mostly runs off. Fortunately the tarp doesn't really contact any painted or gelcoat surfaces that might be damaged by chaffing, but it is already wearing through where it contacts the tops of the stanchions along the lifeline.
The more you protect your boat for the winter, the less work you will face before launching it again next spring and the less chance there is of unwanted visitors making nasty nests or messes in or on your boat.
Keep it protected!