Maybe you’ve seen them. Those crazy looking surfboards that rise out of the water and hover as they move across the waves. This illusion is the result of hydrofoil technology. The hydrodynamic outcome is the appearance of a flying or hovering watercraft. This maritime marvel isn’t only available for adventurous watersports. Many ferries employ hyrdofoil technology to make their passages faster, more comfortable, and more fuel efficient. Hydrofoils can be found in recreational boating, too.
Let’s Take a Look at Hydrofoils
Hydrowhats? What, exactly, is this mechanism that can lift and propel a surfboard (and a boat) out of the water?
This is where physics and aerodynamics take center stage. Motorboats with hydrofoils still need a motor. Sailboats can use hydrofoils, but they need to be fast enough to reach a speed appropriate for the hydrofoils to deliver lift. Motorboats need a motor with enough horsepower to get the hull moving through the water. But the motor will not have to work as hard as a result of the efficiency that the wing of the mechanism offers. The physics behind the mechanism are somewhat complex, but let’s look at a short breakdown.
Hydrofoils work by reducing resistance. That can apply to a myriad of watersports, as well as boat hulls. The wing of the hydrofoil creates an upward force that raises the hull out of the water, reducing the hydrodynamic resistance of the payload.
If you’ve seen a hydrofoil surfboard in action, you may have noticed that it didn’t displace any water, in other words, there were no divergent or transverse waves following the object. This lack of water friction is another reason the hydrofoil technology is so efficient.
How Does Hydrofoil Technology Translate to Boat Hulls?
Traditionally, boats required a significant amount of engine power to gain enough speed to lift a boat onto a plane. A hydrofoil aids in this process with a cleverly constructed angled wing that deflects the water downward, thereby creating upward force that pushes the vessel out of the water.
Watercraft movement is subject to a few basic forces: gravity, resistance, and buoyancy. Historically, to make a boat increase in speed, more thrust was added in the form of more engine power. Watercraft speed is increased by either increasing thrust or reducing resistance.
Getting a boat, like a dinghy, up on a plane, is a good example of increasing speed by reducing drag. If a boat can plane, it will go much faster and use less fuel. It does this by reducing water displacement—by raising itself up out of the water: “planing”—which decreases resistance and friction.
What Do They Do For Boats?
Hydrofoil technology works with the engine thrust required to get a boat up on a plane. The wing underneath the hull lifts the boat up and out of the water by deflecting water downward. The boat engine paired with hydrofoil technology can be smaller, requiring much less thrust to provide speed.
Different Types of Hydrofoils
The types of hydrofoils can vary by manufacturers and in accordance with their intended use. You will find trimaran hydrofoils, monohull hydrofoils, catamaran hydrofoils, hydrofoil boards, wingfoiling hydrofoils, and more.
Hydrofoils come in several shapes and configurations, each optimized for different performance characteristics. Some of those include:
- T-foils are shaped like a T with a horizontal wing at the bottom of a vertical strut. They are common in high-performance racing boats and hydrofoil boards because of their substantial lift and stability.
- L-foils are shaped like an L and are mounted at an angle that provides lift and lateral stability. They are particularly useful in multihull racing sailboats.
- S-foils are shaped more like an S, a unique curvature that provides versatility in lift and substantial stability. They are less common but can be found in custom hydrofoil designs.
- C-foils are shaped like a C. Such a curvature allows for a combination of vertical lift and lateral stability. This is especially useful in rougher waters. C-Foils are more adaptable in varied sea conditions, as they can lift the boat partially out of the water, reducing drag without fully lifting like T-Foils.
What Are Their Strengths?
The basic advantage of hydrofoils is the hydrodynamic performance boost provided by their unique engineering design, rather than fuel-based engine thrust. Hydrofoils reduce fuel consumption, reduce emissions, and minimize environmental impacts.
What Are Their Limitations?
Hydrofoils do have a few limiting factors.
For one thing, they can be damaged easily by debris in the water. Similarly, they can become entangled in netting or stray fishing lines. Also, since they protrude below the surface of the hull, they become a problem in shallow water.
Another limiting factor is cost. Hydrofoils are very complex, which can lead to higher production costs.
Finally, weight distribution must be managed appropriately on a boat that utilizes hydrofoil technology. Too much weight can inhibit the ‘lift’ capability of the vessel.
What Extra Care Do Hydrofoils Require?
A little extra care is required to maintain hydrofoils’ optimal performance.
You must clean them regularly to minimize drag, especially if you do your boating in saltwater. Scrape any barnacles off them as often as needed. That timing will differ in individual saltwater environments. Consider using corrosion protection if your metal hydrofoil is spending prolonged periods in saltwater.
Inspect hydrofoils regularly for damage. They are often exposed to impacts due to their long mast/strut.
To prevent a decrease in performance ability, definitely protect hydrofoils’ edges. Use protective covers and take extra care during transport.
Real-Time Implementation
I mentioned that hydrofoil technology can be costly. Sometimes the cost outweighs the benefits, but that’s up to each buyer to decide. The cost of hydrofoil engineering is one of the reasons it has been somewhat limited in watercraft implementation. It has come and gone in waves of experimentation in the last century.
Recently, advancements in materials and technology have led to a resurgence of the mechanism. Boatbuilders such as Candela, Princess Yachts, SEAir, and Iguana are all currently utilizing this technology.
SEAir specializes in foiling RIBs (rigid inflatable boats). I find this technology to be especially useful. Having lived on a sailboat, I used an inflatable dinghy every day. The only way to get from our anchorage to shore in an inflatable dinghy in a timely manner, was to get up on plane. That can be tricky depending on the size of the motor and the weight in the dinghy. Sometimes, it just wasn’t possible. An inflatable dinghy that uses hydrofoil technology to plane could be an asset to a lot of sailors.
Iguana Yachts has ventured into hydrofoil technology with the Iguana Foiler. This contemporary design features folding foils and retractable caterpillar tracks, allowing it to operate both on land and sea. This is modern technology at its best. A boat that can hover over water and crawl on land.
The upside of hydrofoils is significant for the appropriate styles of recreational boats. Widespread implementation is still a long-term consideration, as is the case with any disruptive technology. Still, boats that “fly” are fun to imagine.
