Flight Component - A hydrofoil is simply another name for a wing. In our context, a hydrofoil is a board that you stand on with a wing (or foil) underneath it. Similar to a plane taking off, as the board travels faster and faster through the water and water flows faster and faster over the foil it increasingly generates lift. When the foil has produced enough lift to offset the weight of the rider and the board, you break free of the water and begin to fly.
Drag Component - When any boat, kayak, or board travels through the water, there is surface tension between the water and the vessel that generates the drag. (The amount of drag generated is called your drag coefficient and varies based on hull shape/size.) This drag limits your speed and increases as you go faster through the water. When you introduce the foil and begin flying above the water, this surface tension goes away and your drag coefficient goes virtually to zero. With zero drag, your speed and maneuverability increase, and it takes considerably less force to make you go. This is why hydrofoils are so efficient and fun to ride.
The best analogy for riding a hydrofoil is that you are on a “balance board” along two axes: forward and aft and laterally side to side. Like being on a balance board, if you put too much weight on one foot along an axis, you will fall in that direction. When you ride a hydrofoil the key is keeping your weight centered on the board providing continuous input to keep you balanced on both axes. If you put load on the back foot, you'll rise out of the water/rise higher into the air. If you put load on the front foot, it will cause you to come down lower to the water/put the board back on the water. If you put too much load on the back foot it causes the foil to clear the water and you wipe out. If you put too much load on the front foot it causes you to bury the nose of the board into the water and you wipe out. As you go faster and faster, the board becomes more and more stable and you can fly along sustained with minor inputs.
A hydrofoil is made up of four components: board, mast, fuselage, and wings (or foil). The wings attach to the fuselage, the fuselage attaches to the bottom of the mast, the mast attaches to the bottom of the board, and then you stand on the board.
Board - The board is the platform you stand on while riding. Boards can range in size from extremely small and light with no flotation (volume) to full on paddle boards with lots of flotation that are extremely stable and allow you to stand. The shape, size, and weight of the board has a big effect on how a hydrofoil performs.
Mast - The mast is a hydrodynamically (think aerodynamic, but for water) shaped foil that runs vertically and attaches to the bottom of the board and the fuselage of the foil wing. The height of the mast determines how much “ride height” you have above the water with different heights being optimal for different sports.
Fuselage - The fuselage is a tube to which the front and back foil wings and the mast all attach to. It should have a hydrodynamic shape and is what ties the whole setup together. A longer fuselage will provide more stability but also more drag
Foils (or Wings) - Hydrofoil wings on a board have a front and back wing. The front wing is what generates the lift on a foil and the rear wing is used for trim to provide it stability.
Aspect ratio on a hydrofoil determines how the foil performs in the water. While it sounds complex it is actually quite simple. Find out more details on the breakdown here.
Purchasing a hydrofoil comes down to a few key questions: aspect ratio, mast height, material type, board type, and new vs used.
Should I buy a high aspect or low aspect foil? - Like anything in life, there are tradeoffs and the right foil for you depends on where you are in your learning and what you want to do with the sport. If you go with a purely low aspect surf foil, it can generate too much lift for kiting and be clunky and slow. If you go with a purely high aspect race foil, it can exacerbate your learning curve and will probably be obsolete for racing by the time you’re ready to race. We recommend compromising by purchasing a foil somewhere in the middle, closer to low aspect. Most of all - we recommend purchasing a modular foil that allows you to swap wings to suit your progression and riding.
Looking for more information? Check out our guide to buying a hydrofoil.