Winterization Tips

Technical Articles


Whether you winterize your Catalina 320 yourself or have your boatyard do it, the following can serve as a guideline for the work that should be accomplished.


Remember that the primary objective is to prepare your boat for the possibility (or inevitability) of freezing conditions. Fluids must be removed or protected and nothing should be aboard that might be damaged by low temperatures. As always, manufacturers’ instructions have priority. We’ll start with the engine, since that is best winterized prior to haul out, and then assume the other systems are winterized “on the hard”.




Top off the fuel tank, adding a biocide. You’ll want to lay-up the boat with clean engine oil, so this is a good time to bring the engine up to operating temperature and change the oil and oil filter. After you’ve fired the engine back up and checked for leaks, its time to winterize the fresh water cooling system. You’ll need 2 gallons of propylene glycol RV/Marine antifreeze for this task (plus 15 gallons or so for the plumbing later on). Make sure you get the non-toxic propylene glycol NOT ethylene glycol. Start by opening the aqua muffler drain and draining any water contained in the muffler. Close the engine cooling water intake seacock and empty the water from the intake strainer bowl and clean the strainer. Disconnect the strainer’s exit hose. This hose end will be used to suck antifreeze from the jug into the engine. Start the engine and run it only until antifreeze comes out the exhaust. Reattach all hoses but keep the seacock closed.

Unless you plan on replacing your water pump impeller in the spring, you should remove it now for inspection (cracked or broken vanes, abnormal wear). To avoid the vanes taking a permanent set in the pump due to non-use, store the impeller over winter in a plastic baggie attached to the intake seacock (so you don’t forget about it). In fact, it’s a good idea to keep your ignition key there also. Close the fuel line petcock at the fuel tank.

Once the boat is on the hard, open the engine thru hull so as to evacuate any water in the hose between the thru hull and strainer.  If storing in the water, the hose should be disconnected at the thru hull in order to drain the remaining water. 

If you have a dripless packing, you might be worried about water remaining in the bellows. The bellows are reportably designed to expand with freezing and will not rupture.

Lastly, check the specific gravity of the internal engine coolant to make sure you have adequate freeze protection. Any automobile antifreeze checker can be used.



Plumbing and Sumps


Empty the two fresh water tanks. Open the inspection ports on the tanks and remove any residual water and/or debris (a wet vac is good for this). Open the strainer at the fresh water pump, empty the water out and clean it. With the fresh water system pump off, open the hot water taps at both sinks and the stern, and then drain the hot water heater under the sink via its drain tap. Hooking a short section of garden hose to this tap and draining directly into the bilge or over the side will make less of a mess. Opening the high pressure relief valve has been reported to allow more water to drain out.

Now the idea is to displace and dilute any remaining pockets of water in the system with propylene glycol antifreeze. Add 5 gallons of antifreeze to each tank. Open the valves for both tanks, so they are both feeding the pump. Using the cold water faucets only, run each faucet until the bright pink color indicates that the antifreeze has been sucked through the feed lines and the pump, and up to the faucets. Don’t forget the stern faucet. Then do the same for the hot water side. Some owners have reported the ability to connect the inlet and outlet water lines together at the heater, thus bypassing the heater. This makes it easier to winterize the water lines, remember however, the heater still needs to be drained and winterized.

Once you have all the water displaced and antifreeze coming out of the faucets, you have a couple of choices. You can leave it as is or you can use a wet-vac to blow out all the lines. Some owners feel that the latter technique makes it quicker and easier to remove the antifreeze taste the following spring.

By the way, if you have a wet-vac, you may want to try using it to suck the water out of the tanks, water heater, and lines prior to adding any antifreeze. This won’t eliminate the need for antifreeze, but can reduce the usage. This is especially true for the water heater which seems to retain a gallon or so in the bottom below the drain.

In the spring, you want to flush the tanks and lines with fresh water several times BEFORE starting the engine or powering up the water heater since it has been reported that the lingering antifreeze taste is much worse if the antifreeze has been heated.


Start winterizing the head by closing the seawater supply seacock and removing the hose at the seacock. Wet flush the head until the supply line is emptied then dry flush removing as much liquid as possible. Then pump out the holding tank. Stick the loose end of the supply hose into a gallon jug of PG antifreeze and use the wet flush function to draw antifreeze through this line into the head and through to the holding tank. Reattach the seawater supply line at the seacock. I would also add ½ gallon of antifreeze directly through the deck pumpout. This will insure that antifreeze gets down to the hose that is Tee’d to the macerator. Leave about ½ gallon in the bowl and check it frequently during the winter to make sure it either has not leaked or evaporated.  The rationale is that the standing antifreeze prevents back flow of residual odors from the holding tank.


You’ll want to leave all your bilge areas clean of dirt, oil, and fuel, so use a quality, emulsifying cleaner if needed, collecting all contents for proper disposal. Put a gallon of antifreeze in the bilge, and then pump it out using the manual pump. Then put another gallon in the bilge and pump it out using the electric pump.  This way, you ensure both pumps have been winterized. If your boat has a tendency to collect rainwater in the bilge, leave a gallon of antifreeze in the bilge (and you may need to check this during the winter). The sink drains have no traps so it is not necessary to winterize them, just make sure they are clear of water. If on the hard, just open the thru hulls.  If stored in the water, close the thruhulls and dump antifreeze down the sinks until you see it come up in the sink. The refrigerator sump and shower sump can be winterized by adding ½ gallon of antifreeze to each and operating the valve and pump so that all the lines are protected.


If you have A/C on your boat, follow the manufacturer’s winterizing instructions. Some can simply be drained of water while others will need to have antifreeze sucked through the lines. The same goes for any washdown system you may have installed.





Top off the electrolyte in each cell with distilled water, if needed, and use shorepower to bring the batteries up to full charge. A fully charged, healthy, battery will exhibit low self-discharge rates at low temperatures thereby maintaining its specific gravity and freeze protection. However, if you have ANY doubts about your batteries, now is the time to get them off the boat, so they do not freeze, crack, and spill electrolyte.  Disconnect all loads, except the bilge pump, and turn the battery switch to OFF. Pay attention to devices connected directly to the batteries, such as battery monitors, and make sure they are not going to draw down the batteries during the winter. Wash and dry the tops of the batteries to further reduce the potential for self-discharge. You might consider running the battery charger one day per month during the lay-up period, especially in very cold climates and if you have lead-acid batteries.





Remove all clothing, bedding, towels, books, documents, personal belongings, and electronics to the extent practical. Remove all food and perishables. Don’t forget to remove any liquid cleaning supplies that might freeze. Prop up all cushions to improve air circulation, or better yet, take them home and store in a warm and dry environment. Prop open cabin and locker doors and covers, the refrigerator, as well as the removable floorboard over the bilge. Wash and dry compartment interiors, the refrigerator interior, and all hard surfaces. A mild chlorine solution works well and will provide some mildew protection.

Make sure the propane is turned off at the tank and bleed the line of residual pressure at the stove.





As soon as the boat is hauled, wash the bottom of any biogrowth. Most haul outs include a power washing but you may need to use a brush or plastic putty knife on stubborn spots, barnacles, zebra mussels, etc. This is much easier to do before the bottom dries out.

All seacocks should be exercised and lubricated with a waterproof lubricant such as Superlube Teflon Gel, before closing them for the winter. If your boat has an operating seacock after the macerator, you will want to have a bucket ready to catch and contain any residual from that line.

Flush hardware, rigging, and fiberglass surfaces with fresh water to remove salt, grime, and stains. If the companionway boards have any worn or damaged spots, touch them up until you can refinish in the spring.

Remove the sheets, control lines, sails, dodger, and bimini and take home if practical. Make sure any remaining lines (e.g. halyards) are secured to prevent chafe.

If the boat is to be covered, make sure that the cover is installed in such a way to provide adequate ventilation and that the cover is not permitted to chafe against the hull or deck. If the boat is not covered, a well-secured steering pedestal cover and winch covers are recommended to protect the instruments, compass binnacle, cockpit table, and winches. Make sure any covers won’t come loose in a windstorm.

Consider applying a coat of wax to all exposed fiberglass (except the non-skid) if weather (and motivation) permits.



This may seem like a lot of work, but damage from freezing can be quite extensive and expensive. Think of this as preventative medicine! Check on the Association website for a handy winterization checklist you can use at the boat or give to your yard.



Karl Mielenhausen, Hull #690, Silver Lining


by Karl Mielenhausen

Moved up to the C320 from a Catalina 22. We purchased Hull 690 in Sept 2005. I am a retired Quality Assurance Engineer (Eastman Kodak Co.). My wife, Elaine, and I relocated from Pittsford, NY to New Bern, NC in March 2005.

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