Another major problem with a vessel in the marine environment is corrosion and rust. Corrosion is a result of non-ferrous metals (such as Copper and Aluminum) oxidizing. Rust is a result of Ferrous metals (such as Steel and Iron oxidizing. Marine vessels have a mixture of Ferrous and Non-Ferrous metals.
The reason boat manufacturers use Stainless Steel, is just that. According to Wikipedia the description for Stainless Steel is as follows:
In metallurgy, stainless steel, also known as inox steel or inox, is defined as a steel alloy with a minimum of 10.5% or 11% chromium content by mass. Stainless steel does not stain, corrode, or rust as easily as ordinary steel (it stains less, but it is not stain-proof). It is also called corrosion-resistant steel or CRES when the alloy type and grade are not detailed, particularly in the aviation industry. There are different grades and surface finishes of stainless steel to suit the environment to which the material will be subjected in its lifetime. Common uses of stainless steel are cutlery and watch cases and bands.
Stainless steel differs from carbon steel by the amount of chromium present. Carbon steel rusts when exposed to air and moisture. This iron oxide film (the rust) is active and accelerates corrosion by forming more iron oxide. Stainless steels have sufficient amounts of chromium present so that a passive film of chromium oxide forms which prevents further surface corrosion and blocks corrosion from spreading into the metal’s internal structure.
If you have ever crawled around your boat, you will notice that just about every piece of metal is painted. General exceptions to this rule are Stainless Steel hardware and fixtures, brass, bronze, and high grade aluminum. Usually what is not painted, is either rusted or corroded. The reason everything is painted is to prevent rust and corrosion.
Using a quality rust and corrosion inhibitor is always an excellent idea. Generally speaking I spray just about everything in the engine room with either WD-40, CRC 6-56, or LPS-1. Each product serves its own unique purpose. If you make this a standard practice while maintaining your boat, it well help you increase the longevity and maintain the quality of all your metal components.
Thru-Hull fittings (and there associated valves) are normally made of bronze which is an alloy that consists primarily of copper and tin. Depending on the application, it will sometimes contain other materials. Thru-Hulls are the life line to your boat. They can either help you (generally this is what they do) or at worst, put you in a life threatening situation.
The thru-hulls are the life of your engine (s). They allow the engine (s) to pump water into the engine to help keep it at a safe operating temperature as well as getting rid of the harmful exhaust fumes. Also they provide access for you to desalinate water to make it suitable for drinking while you are on extended voyages. Discharging waste is another feature that thru-hulls allow you to do. While they help you in so many more ways than I have listed; they can also sink a boat in a matter of minutes. This reason alone is what makes it so important to maintain the various metal components on your boat. All it takes is a wire brush and some rust/corrosion inhibitor.
The thru-hull fittings (and there associated valves), should be lubricated and free of corrosion at all times. You should be able to open and close the valve (s) with minimum effort at all times. If you were to spring a leak you should be able to close the valve where the source of water is coming from. Heaven forbid if you cannot close the valve, you take on water, the bilge pumps turn on but cannot keep up… then your boat sinks if you do not get appropriate help in time.
Hopefully you understand the importance of this often overlooked maintenance item. With that being said, lets discuss a few indirect problems with rust and corrosion.
Your fresh water pump usually consists of a steel motor housing and either a plastic or metal pump housing that is attached to it. The motor housing is always painted, usually it is black. The motor housing is usually sealed with some sort of gasket between the pump and motor housing, along with another gasket between the motor housing and the end cap. Herein lays the problem. These gaskets are not designed for the engine room environment where they are normally installed. After time (a year or two) they begin to dry-rot and crack. When this happens, moisture is able to infiltrate the motor housing, and sooner than later your pump will stop working.
The pictures above depict an ordinary pump that you would find on almost any vessel. By looking at the first two pictures, you would not think that anything is wrong. The motor is painted, and there is no corrosion on the pump housing. This is the point that I am trying to make; Its what you don’t see that causes all of the problems (remember the previous page, when I discussed about corroding wires). That’s why making it standard practice to maintain all of your metal components is so important.