Unfortunately, the boating season only last a few months in many parts of the country and then the awful task of winterizing your investment becomes a reality. Winterizing a boat reminds me of the old commercial that says "pay me now or pay me later." The time and effort you spend now will have a definite effect on your boat's performance, or lack of it, and certainly save you time, effort and money come spring. You should remember that your insurance policy may not cover damage done by lack of maintenance or neglect.
The best place for your boat to be during the winter is out of the water, under cover, in a climate-controlled boat storage area. This, however, can be expensive. If you don't have this option perhaps you should consider shrink-wrapping your boat. This, too, is a little expensive but provides a very protective cover. Short of these two items, make sure that your boat is well covered with a tarp or some other sturdy cover.
Your first step in winterizing should be to make a checklist of all items that need to be accomplished. Check the owner's manual of your boat and motor(s) for manufacturer's recommendations on winterization. If you are a new boat owner, perhaps you should employ the assistance of a friend with experience in winterizing or hire a professional to do the job. The following is a generic outline of areas which should be of concern to you, however, there are many resources on the Internet with more detailed and specific information.
Inboard Engine(s) - You should run the engine(s) to warm it up and change the oil while it is warm. This tends to allow impurities to be drained away with the oil. You should also change the oil filter(s). Flush the engine(s) with fresh water. You should circulate antifreeze through the manifold by using a pickup hose from the water pump to a bucket of antifreeze. Start the engine and allow the antifreeze to circulate until water starts to exit the exhaust. This process will vary slightly depending on whether you have a "Raw Water" cooling system or an "Enclosed Fresh Water" cooling system. While you're in the engine room you should also change the fluid in your transmission. Remove spark plugs and use "fogging oil" to spray into each cylinder. Wipe down the engine with a shop towel sprayed with a little fogging oil or a WD-40 type lubricant.
Stern Drive(s) - You should thoroughly inspect the stern drive and remove any plant life or barnacles from the lower unit. Use Captain Gary's BARNACLE REMOVER & HULL CLEANER if necessary. Drain the gear case and check for excessive moisture in the oil. This could indicate leaking seals and should be repaired. Clean the lower unit with Captain Gary's OUTDRIVE / LOWER UNIT CLEANER and water. If your stern drive has a rubber boot, check it for cracks or pinholes. Grease all fittings and check fluid levels in hydraulic steering or lift pumps. Check with your owner's manual for additional recommendations by the manufacturer.
Outboard Engine(s) - Flush engine with fresh water using flush muffs or a similar device attached to the raw water pickup. Let all water drain from the engine. Wash engine down with Captain Gary's OUTDRIVE / LOWER UNIT CLEANER and water and rinse thoroughly. Disconnect fuel hose and run engine until it stops. It is important to follow a step by step process to make sure that all fuel is drained from the carburetor to prevent build-up of deposits from evaporated fuel. Use fogging oil in the cylinders to lubricate the cylinder walls and pistons. Apply water resistant grease to propeller shaft and threads. Change the gear oil in the lower unit. Lightly lubricate the exterior of the engine or polish with a good wax such as Captain Gary's MARINE BOAT POLISH.
Fuel - Fill your fuel tank(s) to avoid a buildup of condensation over the winter months. Add a fuel stabilizer by following the instructions on the product. Change the fuel filter(s) and water separator(s).
Bilges - Make sure the bilges are clean and dry. Use Captain Gary's BILGE CLEANER, hot water and a stiff brush to clean up any oil spills. Once the bilges are clean, spray with a moisture displacing lubricant and add a little antifreeze to prevent any water from freezing.
Fresh Water System - Completely drain the fresh water tank and hot water heater. Isolate the hot water heater by disconnecting the in and out lines and connect them together. Pump non-toxic antifreeze into the system and turn on all the facets including the shower and any wash-down areas until you see the antifreeze coming out. Also put non-toxic antifreeze in the water heater.
Head - Pump out the holding tank at an approved facility. While pumping, add fresh water to the bowl and flush several times. Use Captain Gary's Marine Head & Toilet Cleaner or whatever your owner's manual recommends that will not harm your system and let sit for a few minutes. Again add fresh water and pump out again. Add antifreeze and pump through hoses, holding tank, y-valve, macerator and discharge hose. Again, check your owner's manual to make sure that an alcohol-based antifreeze won't damage your system.
Interior - Once you have taken care of the system you should remove any valuables, electronics, lines, PFD, fire extinguishers, flares, fenders, etc. Over the winter these items can be cleaned, checked and replaced as necessary. Open all drawers and lockers and clean thoroughly. Turn cushions up on edge so that air is able to circulate around them or, better yet, bring them home to a climate controlled area. Open and clean the refrigerator and freezer. To keep your boat dry and mildew-free you might want to install a dehumidifier or use some of the commercially available odor and moisture absorber.
Out of Water Storage - Wash hull using Captain Gary's ALL-PURPOSE BOAT SOAP with POLISH or Captain Gary's HULL CLEANER, clean barnacles off props and shafts, rudders, struts and trim tabs. Clean all thru-hulls and strainers. Open all seacocks to allow any water to drain. Check the hull for blisters and if you find any that should be attended to you might want to open them to drain over the winter. While you're at it, why not give the hull a good wax job? Use Captain Gary's PREMIUM GRADE BOAT POLISH. It is probably best to take the batteries out of the boat and take them home and either put them on a trickle charger or charge them every 30-60 days.
In Water Storage - Close all seacocks and check rudder shafts and stuffing boxes for leaks tighten or repack as necessary. Check your battery to make sure it is fully charged, clean terminals, add water if necessary and make sure your charging system is working. Check bilge pumps to ensure they are working and that float switches properly activate the pumps and that they are not hindered by debris. Make sure either to check your boat periodically or have the marina check it and report to you. If in an area where the water you are docked or moored in actually freezes, you should have a de-icing device or bubbling system around your boat.
By following some of the above suggestions, you should be in good shape for the winter. Do not, however, neglect to consult your owner's manuals for manufacture's recommendations on winterizing your boat and other systems. If you have not done a winterization job before or don't have an experienced friend to rely on seek out a professional to do the job for you.