Whenever something moves through water—whether it's a submarine, a sonar system, or a seismic streamer—it has to deal with water resistance. This resistance, known as hydrodynamic drag, affects not only the towed equipment but also the cable that connects it. That drag can slow things down, cause wear, or make it harder to reach the desired towing depth.
To counter these effects, engineers use something called cable fairings. These are smart add-ons that improve the flow of water around the cable, making operations smoother, faster, and more efficient. In this article, we’ll break down what cable fairings are, how they work, and which types might be right for your specific mission.
A cable fairing is a physical modification applied to an underwater cable to manage the way water moves around it. Think of it as streamlining the shape of the cable so it slices through water with less effort. Fairings reduce drag and prevent vibrations that could damage the cable. This results in better performance, less energy consumption, and lower maintenance costs.
Fairings come in several varieties and can be tailored to the environment, the depth of tow, and the mechanical setup of the system. But no matter the type, they all serve one primary purpose: helping your cable perform better in water.
You’ve probably experienced drag without even realizing it. Stick your hand out of the window of a moving car. If you hold your hand flat against the wind, it pushes hard against you. But tilt your hand so it slices through the air, and suddenly the resistance drops. Water behaves much the same way—except it’s denser and heavier than air.
A bare cable is like a flat hand—facing constant pushback. But a cable with fairings is like a tilted hand—streamlined and efficient. By reshaping how the water flows around the cable, fairings reduce drag and eliminate many of the problems caused by turbulent flow.
Drag increases significantly with speed. In fact, if you double the speed at which a cable is towed, the resistance can become four times greater. On top of that, water pressure at deeper depths makes things even harder. That’s why reducing drag isn’t just a ‘nice to have’—it’s essential for deep-sea operations.
But drag isn’t the only problem. As water flows around a round object like a cable, it can form little whirlpools called vortices. These vortices form in a repeating pattern and can cause the cable to vibrate side to side—a phenomenon called strumming. Strumming wears down cables over time and can even lead to failure if not addressed.
Different fairing types address drag and strumming in different ways. Some reduce drag dramatically by streamlining the shape of the cable. Others, like hairy fairings, intentionally disrupt the flow pattern to break up the rhythm of vortex shedding.
It might sound counterintuitive, but in some cases, adding small amounts of controlled drag with a hairy fairing is better than allowing chaotic, damaging vibrations to occur. Preventing strumming extends the life of the cable, reduces risk, and ensures more reliable performance under pressure.
Let’s take a closer look at the different types of fairings, each with their own strengths and weaknesses.
These fairings consist of soft, hair-like fibers that are braided into the cable. They create a bit of turbulence on purpose, breaking up the water flow and preventing the organized vortices that lead to strumming. Because they are flexible, hairy fairings can fit between cable rings on a winch drum without requiring any changes to the system.
However, the added fibers increase the overall cable diameter slightly and may introduce more drag than other fairing types.
Hard fairings are robust, teardrop-shaped covers that are clamped onto the cable at intervals. These components rotate freely to stay aligned with the direction of water flow, minimizing drag and preventing sideways force.
They are ideal for high-speed and deep-water towing, such as in defense applications or with variable depth sonar systems. DeRegt’s own SeaFin 23 hard fairing has been used successfully in real-world VDS projects. The trade-off? They’re trickier to install and can limit how the cable is wrapped on a winch drum—usually only a single layer is possible.
Foil fairings resemble airplane wings in shape, offering a streamlined profile that reduces drag effectively. Unlike hard fairings, they are more flexible and can be wrapped multiple times around a reel, making them easier to handle.
They don’t reduce drag as effectively as hard fairings and are somewhat less durable, but they’re highly versatile. Foil fairings are commonly used in seismic applications such as lead-in cables for streamers.
Canvas fairings are made from soft, flexible materials that are stitched or welded around the cable. Their big advantage is flexibility: they’re easy to wrap, store, and deploy. However, that flexibility also means their shape isn’t as stable, and they provide less consistent drag reduction than harder or more rigid fairing types.
Whether your goal is deeper towing, lower fuel consumption, or longer cable lifespan, fairings can make a measurable difference. But there’s no universal solution—each type of fairing has its trade-offs.
To choose the right fairing, consider your operational goals, towing speed and depth, cable management system, and budget. If you're unsure, the engineering team at DeRegt is always happy to help you evaluate your needs and find a fitting solution.