Basic electrical system upgrades and repairs (such as: How Can I Save Battery Power With My Refrigeration System? and Using LED lighting on your boat) are one of the most common do-it-yourself projects we undertake as boat owners, writes Gary Reich.

Ratcheting crimper

This ratcheting crimper places a precise amount of pressure on the crimp fitting while also making two crimps—one on the wire and one on the wire jacket—at the same time. Photo by Gary Reich.

And while most folks start these projects with the best intentions, many of the materials they use are often ill-suited for life in the marine environment. With that in mind, let’s take a look at one area where using the wrong parts is a recipe for disaster: electrical terminal fittings.

Electrical crimp terminals do exactly what the name implies—they provide an attachment point for a wire where it terminates. Good examples include a ring terminal where a wire is screwed to a fuse block, a spade terminal connecting lead wires to a removable depthsounder or fishfinder, or a butt connector joining two pieces of wire. These terminals are crimped down on the wire using a tool engineered for that purpose, and provide a good connection between the wire and its termination point.

So why not just use the cheap terminals found at your local car-parts shop or hardware store? Three words: corrosion, vibration, and moisture.

Let’s start with corrosion. The crimp terminals you generally find at your local car-parts shop are what you might call “mystery meat,” meaning it’s difficult to know what type of metal they’re made of. I’ve seen them made of anything from mild steel to zinc, and neither of those materials is good at much of anything electrical, save for sacrificial zinc anodes.

Tin-plated copper terminals are what you’ll want to look for at your marine store. Tin is highly resistant to corrosion, and copper is an excellent conductor of electricity. In tandem, they make for a great marine-grade electrical terminal. Plain copper terminals with no tin plating can be found on many boats, but they’re all susceptible to that funky green corrosion that can cause connectivity issues in the future.

Marine terminal

A double-crimp, ring-style marine terminal installed on a section of 10 AWG wire. Note the double crimp points as illustrated. Photo by Gary Reich.

Moisture and corrosion-resistance go hand-in-hand, especially if your boat operates in a saltwater environment. Tin plating will definitely help suppress this corrosion, but if you really want to nip it in the bud, use not only tin-plated marine terminals, but tin-plated marine terminals with integral heat-shrink tubing. This integral tubing often is lined with sticky adhesive that melts and seals out the end of the termination when heat is applied. Alternatively, you can apply your own heat-shrink tubing, cut it to size, and shrink it on the connection yourself. If the electrical work you’re undertaking is in a bilge, underneath a center console, or in any location where there’s a remote possibility of water contact, it’s absolutely essential to use these high-quality marine-grade terminals and heat-shrink protection.

Marine ring terminals

An assortment of ring-style marine crimp terminals. Photo courtesy of Ancor.

Vibration is an electrical system nemesis we don’t generally think about, but a nemesis it is. Engine and drivetrain vibrations, shock waves from wind and waves, encounters with docks and pilings, bumps and bangs caused by hatches and locker doors — all of these  bad vibrations (not like the good ones the Beach Boys were singing about) can make a terminal fail at its connection with the wire, causing circuit failure or a fire.

To battle these connection failures, a good marine terminal uses not one crimp, but two, and is aptly called a “double crimp” terminal. Look for terminals labeled as such. A double-crimp terminal makes one connection onto the bare wire, and another on the wire jacket, which provides excellent strain relief and resistance to the effects of vibration.

Last detail: Make sure you use the proper tool when installing double-crimp terminals. There are many different types of tools out there, but I like ratcheting double-crimp tools. Not only do they release when the proper amount of pressure is applied to the fitting, but they also crimp the terminal fitting to both the wire and the wire jacket in one motion. You also can use a standard strip-and-crimp tool, but make sure you crimp at both the wire and the wire jacket.

So there you have it. Next time you’re elbow deep in marine electrics – rewiring a VHF radio or installing a new navigation light –, spend the time to find the right terminals for the job. In the long run, you won’t be sorry you did.

Here’s a video that walks you through the steps of how to install a heat-shrink terminal:


For more DIY advice, see: 10 free and cheap boat improvements, or How to prepare and apply antifouling.