Lesson 4

Pumping the Foil

by Todd Reichert
Pumping the Foil
Milestone #4: Pump the foil to create propulsion, sustaining short runs of powered flight.

Today we get to the crux of the project: learning how to pump the foil so you can extend your glide over the water and eventually sustain continuous flight. It can take between 50 and 500 attempts before you start to really feel what it takes to create propulsion.

Creating Propulsion

Pumping produces the necessary thrust to sustain your forward speed. The diagram below shows how the forces on the hydrofoil produce a net lift and thrust over the course of a pumping cycle. This is the exact same motion as a skateboard on a pumptrack, which provides a really helpful analogy for understanding how to pump effectively.

To pump a foil there are two things that you need to do: Build the pump track, by shifting your weight for and aft, and apply force at the right time to generate thrust.

That's the theory. In practice this is what it looks and feels like:

  • Start the pump by leaning your weight forward. The foil will pitch down and start to pick up speed as it glides downwards.
  • As it accelerates downwards, jump up with both legs. It should feel like you're trying to hop off the board with a quick pop, like when you pop off a ski jump or a trampoline.
  • After you jump, there's not much you need to do. As your body goes weightless, the lift on the foil will cause the board will rise up with you. Then you'll be at the top of your stroke and ready to start again.

Unlocking Progress

At this point, there's a lot going on and understanding what you need to do to improve can be a challenge. Here's a few common roadblocks and breakthrough tips that can help: 

  1. Jump up instead of pushing down. This is the single biggest key to unlocking propulsion. Notice from the force diagram at the top of this page that you can create more thrust by either increasing your force on the downstroke, or by decreasing the force on the upstroke! To decrease your force on the upstroke you need to go weightless. Going weightless also decreases the load on your legs, giving them a brief moment of rest. To do this, focus on popping off the board and visualize that feeling of weightlessness after bouncing off a trampoline. If you focus on the float, the push will come naturally and you'll increase your efficiency substantially.
  2. Lean forward, not backwards, to start the pump. At first, many people  start their pump by leaning back, trying to get the board to rise. But, if you push while you're leaning back you're actually creating drag instead of thrust and you quickly come to a halt. The pump must start by leaning forward to accelerate the board downwards, only once it's accelerating downwards do you initiate the pop.
  3. Push with both feet together. It's common for people to push the nose down with the front foot to initiate the downwards motion, but when you do this there's nothing left to push off of — your jumping platform has just fallen away from you. Instead, initiate the pump with a very subtle lean forward, while your legs are still straight, then jump with both feet together.
  4. Pump hard and fast. This is absolutely critical at the beginning. Speed makes the foil more stable, which makes it much easier to achieve a good solid pump. Speed also gives you a margin for error — if you miss a pump or two, you'll still have the speed to keep going.

Progression at this point just takes a lot of time. Keep filming your attempts and making small changes, and you will progress! Once you're getting to 10 - 20 pumps, it's time to start thinking about turning. If you came to this post looking for more advanced times, jump straight to the lesson on Building Endurance.

Other Resources

There's a few particular videos by Gwen Le Tutour that provide great visuals for some of the points above:

Training Guide