Problems caused by low temperatures can be to mechanical organs, such as engine and systems, or to interior furnishings, with mold growth. Damage usually results, rather than from frost, from condensation that forms due to temperature changes.
In order to have the boat always in good order, one must, of course, prepare it for winter and try to go and check it periodically. One of the most immediate effects of cold weather is the accelerated self-discharge of batteries. For this reason it is worthwhile, to turn on the engine periodically and give it a recharge. Otherwise, if you cannot boat frequently, it is a good idea to disconnect the battery terminals before winter or even better, disassemble them and take them to an electrician who will keep them in good condition.
FUEL AND WATER
As far as the engine is concerned, it is generally difficult for the fuel to freeze, but a winter additive can only do good. On the other hand, it is important to leave the diesel tank practically full, especially if it is metal. This eliminates air inside and consequently decreases fuel oxidation and sludge formation. Instead, on the contrary, drain the water tanks, emptying the system completely, including the boiler system.
Beware that condensation is also the main cause of deterioration of on-board furnishings. Dunnage timbers, become waterlogged and moldy, even more so if before winterization they have not been washed with fresh water removing all the salt. Cushioning fabrics also absorb all the moisture and deteriorate inexorably, so if you cannot empty the boat before winter and take the furnishings to a dry garage, it becomes necessary to ventilate the interior periodically by sponging the bilges and drying where it is wet. If this is not possible leave the wind sleeves or tannoys open. If it is any reassurance, on deck, cold damage is quite limited. Again, condensation can be the main enemy, an example being classic mold in the anchor locker. Before winter rinse it with fresh water, including the chain, and remove it if possible. Not only does salt water accelerate rust on the links, but you also risk oxidizing anchor windlass motor cables, which are usually inside.
This, and many other useful tips, you can find in the special issue of Sailing devoted to Practice and DIY: a volume, this special one, designed to keep on hand, at home and on the boat, to take away doubts or brush up on your knowledge at any time. YOU CAN PURCHASE IT HERE