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The electrical system on a marine vessel is probably the most neglected. Think about it, if you have a leak in your plumbing system, you notice it and you fix it. If your engine is not running properly, you notice it and you fix it. Exploiting potential flaws and problems with a typical electrical system on a marine vessel is the purpose of this article.

Some electrical problems are more commonplace than others. For example, your engine cranks but slowly ceases cranking. Your automatic assumption is that you have a bad battery, you buy a new battery, and your problem is temporarily fixed. When I say temporary, I mean for 1 month to 1 year. You have a light bulb that has burned out; naturally you replace the light bulb. Later on in the article I will go into detail with these more common problems, which most people notice with their electrical system.

Let’s start with the basics. In order to understand electricity and how it works you must know the basics, at least for the sake of having rudimentary troubleshooting skills and a core knowledge base to start with.

Ohm’s law states that the current (Amps / I) that flows through a conductor between two points is directly proportional to the potential (Voltage / V) difference across two points, and is inversely proportional to the resistance (Ohms / R) between them.

The formula for Ohms law is:

Power, as defined at, is “work done or energy transferred per unit of time,” and is represented by the symbol P. In electronics, power (P) can be thought of as the amount of energy given off by a resistance, or load, when current is passed through it. Power is measured in watts (W). One watt is equal to one joule.

The formula for Power is:

Now that the basics are covered let’s get down to business; I mean, let me help you understand the so called “unknown” problems and mysteries with your electrical system.

Along with the batteries on your vessel, the battery distribution cables are the heart of your system. You can have brand new top of the line batteries that are fully charged, and if you cannot distribute/transport that power then the batteries are useless. Imagine the batteries being the engine of your truck, and the cables being the transmission of your truck. It doesn’t matter if you have a brand new engine because if you have a bad transmission, the truck will not move. Hopefully the average mariner is starting to connect the dots with the previously stated analogy. Problems that affect the power distribution are corroded or loose battery terminals, corroded battery cables, improper cable size, improper crimping methods, and loose connections.

Saltwater environments significantly increase the rate of corrosion of copper conductors. Just because you use a wire brush and clean the exposed cable terminal does not mean that your battery cables are okay. Older manufacturing techniques did not employ adhesive lined heat shrink to ensure a waterproof connection of your cable terminals. If you were lucky, they covered your cable terminals with electrical tape. Electrical tape only disguises what is happening beneath it. If you or your technician really takes pride in what you do, than you would apply the tape nice and neat as if Picasso was painting a portrait (hopefully you sense the sarcasm). A REAL MARINE ELCTRICIAN DOES NOT USE ELECTRICAL TAPE!!! Except for a few exceptions which include but is not limited to, marking wires for identification, taping wires to a fish tape… etc., but definitely not for sealing wire or cable terminals.

The pictures that are shown to the left are pretty typical of a marine vessel. I’ve heard thousands of customers in the past say, what’s wrong with these cables? And they say something along these lines; “They are the original cables that came with the boat, last year my technician replaced the factory copper cable terminals with tin-coated cable terminals. Look there isn’t even any corrosion on the terminals. So you’re saying I need new battery cables? I think your pulling my leg.”

Keep in mind that just over the past 10 years, tin-coated copper conductors and tin-coated cable terminals have become more common. Although in the recent years some (and I mean some) manufacturers have started using this premium tin-coated copper conductors and cable terminals, along with the adhesive lined heat shrink. If you plan on having your electrical system last your lifetime, than it is absolutely imperative that these materials are used in your electrical system. Tin is a non corrosive metal in its natural form. It is also conductive as well. That’s why tin is the preferred choice when it comes to coating copper conductors with a non-corrosive material.

Heat shrink is a sleeve that you slide over the end of a wire to cover the exposed difference from where the terminal was crimped on. At some point in time, they decided to line the heat shrink with adhesive. So when you apply heat to the heat shrink the adhesive kind of oozes out of each end to create a waterproof connection.

Now that you understand the purpose of tin-coated copper and adhesive lined heat shrink, take a second look at some pictures of the exact same cable that I previously showed you.

After peeling back the “inappropriate” cable insulation you can see how heavily corroded the copper conductor is. This is the part that the customers cannot see, and is also the part that affects your whole electrical system. It is not uncommon for cables to look like this for several feet. Remember it is the heart (transmission) of the system. Let’s go back to the basics for a second. Voltage is similar to the pressure in a pipe. Current is similar to the amount of water flow in a pipe. However water flows inside of a pipe, while current flows on the outside of a conductor. There you have it, I have solved myth No. 1 for you. The reason I mention this is because customers have told me in the past that a little bit of corrosion will not hurt anything because the current flows through the wire. These are the same customers who know what they are talking about, who has been a mariner since they were knee high to a grasshopper, and also have a friend/neighbor who is an electrician.

Below are a few pictures of properly terminated cable terminals with adhesive lined heat shrink, Tin- coated copper cable, and Tin-coated cable terminals. Also, I have dissected it to show you what it should look like between the conductor and the insulation.

Ohm’s law variables are directly proportional. With that being said WHEN VOLTAGE DROPS CURRENT INCREASES!!! Don’t forget that simple rule. A few reasons you have voltage drops are because of corroded or loose battery terminals, corroded battery cables, improper cable size, improper crimping methods, and loose connections. INCREASED RESISTANCE CREATES VOLTAGE DROPS. Are you starting to put the pieces together? The most common cause for additional incurred resistance is corroded conductors and loose connections.

Corroded battery cables alone can reduce life expectancy of a brand new battery by up to half or more. If you are really absorbing the knowledge within this article, you would have made a direct correlation with what I said about the “temporary” fix with the new batteries and engine that slowly ceases to crank. I wish I had a tenth of the money I have seen customers waste on batteries because they “thought” they could fix the problem their selves. When in all actuality their batteries were fine, but their cables were corroded. It’s understandable, it’s psychological. The customers cannot see the corrosion between the conductor and the insulation so they do not see a problem.

Low voltage damages electric motors, pumps, alternators, generators, starters, and voltage sensitive components. As I said with batteries… Low voltage can reduce the life expectancy of electrical components by up to half or more. Remember? WHEN VOLTAGE DROPS CURRENT INCREASES. When current increases it creates Heat (resistance). When this happens it creates additional carbon that builds up on the brushes of the electrical motors. Once the carbon becomes too much, it will create an open in the circuit, and electricity will not be able to flow. Also the added resistance, if there is enough of it, will begin to break down the insulated coating on the stator and rotor of the electric motor. When this happens, it will create a “dead short” internal of the motor and become scolding hot to touch. And if your circuit is not properly protected, it will definitely start a fire. A more common reference to an electric motor is the starter on your engine, and, let’s say a water pump. Hopefully you are starting to put all the pieces together.


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