There are four things that should be done to a boat to insure it will be ready for the cold temperatures. All these steps are done to rid moisture from the motor and the outdrive so that they do not freeze and crack. The four steps you'll need to complete will be draining the water from the cooling system of the motor, changing out the engines oil and the outdrives oil. The last step would be foging the engine with foging oil.
Step 1: Draining the Cooling System
Start by locating all the drain plugs located on bottom portions of the motor. there will be anywhere from three to five plugs. Common spots are under each exhaust manifold, on each side of the engine block and on the bottom of the engine block. Today's boats are commonly equipped with either a GM motor or a Volvo motor. Volvo's commonly have a valve that you open and the GM motors have a blue plastic plug with tabs like a wing nut. Weather you have a Volvo or GM motor take caution in the drain valves or plugs when releasing the water. You do not want to break them as this will cause a lot more work. once the water is out of the motor you can close the drains. Put lubricant on each one before closing. Some WD40 for the valves and some pipe dope for the plugs. Once all the drains are closed remove a hose on the top end of the cooling system and fill the system with the pink RV antifreeze. Once the system is full put the hose back on and your done.
Step 2: Changing Engine Oil
All engines have a drain plug on the bottom of the oil pan. Most of the drain plugs are hard to reach let alone get a drain pan under the motor. For this step a oil pump and some small plastic tubing are needed. There are a number of different kinds of oil pumps. There are hand pumps, electric pumps, and drill pumps. The drill powered pump is the most affordable and easiest to find. Find a plastic tube that will fit inside the oil dipstick line. Make the tube long enough to reach the bottom of the motor. attach the tube to what ever oil pump you choose with a hose dumping the used oil into a container. Once all the oil is out, change the oil filter remembering to lube the new filter with oil before installing. Next fill the engine with oil to proper level. Now start the engine and let the engine run for no more than ten seconds (to avoid damage). This will allow the new filter to fill up with oil. Once again fill the engine to the needed oil level.
Step 3: Changing the Outdrive Oil
Start with removing the plug on the bottom of the outdrive near the prop draining oil into a pan. Once the plug is removed, locate the vent plug. remove the plug to allow air into the drive case and allow the oil to drain faster. To refill the outdrive with oil it must be refilled from the bottom at the drain plug, not the vent plug. This can be a challenge depending on the method used to fill. The cheapest way is to buy more oil than you need and fill the case by holding the oil bottle in the drain and squeezing it to force the oil in. This method can make a very big mess so take caution. It takes some work and costs more money but you can buy an adapter to hook a plastic tube up to the drain and pump the oil in. This may cost more but it makes far less mess. with either method, fill the case to the needed level and place the vent plug into the vent hole to slow the oil from escaping while you install the drain plug.
Step 4: Foging the Motor
Foging an engine is the simplest step to ensure that your motor will not loose power to cold temperatures and moisture. remove the air intake filter and have one person controlling the engine while another person sprays the oil into the intake. continue to spray the oil until you hear the engine start to bog down and begin to stall then shut the engine down at that point. This will lube the heads and pistons with oil to keep them in good condition for the spring.