Efficiency is the key

I stumbled upon efoils just today and tried to research if i can build one myself.
After reading on this board and googling i come to the following conclusion:
You can build a very cheap wooden foil if its passive. (without propulsion)
If you want to build an active efoil its all about energy efficiency. The more efficient your design is the less money and time you have to spend on building your efoil. If you want to build an efficient efoil you need to specify your goal because your foil and prop has to be optimized for a velocity range. After getting your specs, you need to decide for a foil design for that velocity and weight. After that you need to get an efficient propulsion system. and then everything else.
Of course foil and prop are the hardest things.

  1. specs
  2. foil
  3. prop
  4. motor
  5. electrics
    Other observations:
    People seem to overvalue weight. Not that important for an efoil.
    Another foil between board and foil seems to be a good idea. So you get more lift during takeoff and reduce drag at top speed.
    Maybe a triangle foil like here is a good idea: https://keyassets.timeincuk.net/inspirewp/live/wp-content/uploads/sites/18/2018/07/Enata-Marine-Foiler-©Guillaume-Plisson-_180684482_271447381-630x364.jpg
    as your speed increases drag reduces and too much lift is prevented
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You want to keep weight down for two main reason. Maybe three following your own arguments.

  1. A heavy board is not as manuverable as a light one. As you get more good att foiling you want a agile efoil because it is more fun to ride.

  2. A heavy board is a hustle to carry around With about 30-60 minutes riding time it is a lot of handling between rides (charges)

  3. A lightweight board (but still optimal in other aspects) is more efficient.

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I know, i still think its overvalued.

Each of these Jfoils if reduced would represent the surface (therefore the weight) of one of our setups (1 mast + 2 wings)
Not sure whether you can turn shifting your weight.

Firstly welcome to the forum…
However your statements completely contradict each other. First you say its all about energy efficiency, and then you go on to say that weight doesn’t matter?
In reality the heavier a setup is, the less efficient it will be. It will sit deeper in the water before take-off, it will need more speed to take-off, you’ll need a bigger wing to take-off and then once on the foil that wing will use more power because its more resistant to propel forward.

The triangle foil is designed for a boat because of how the boat turns. The foils we use turn in a very different manner and as a result we don’t need the extra wingspan. As a foil increases in wingspan, it also reduces the manoeuvrability, so we want a happy medium between this.

In the world of efoils there are some very basic cores to the system that if they are achieved start the baseline for a very good setup. These are:

  • Board, keep it as light and strong as possible with a nice large hatch so there isn’t a space issue when selecting components. You also don’t want to have a board that is too long as once you can stand you want it as short as possible.
  • Foil Mast: get a mast that is strong, light and can run decent diameter wiring as well as a tube for water cooling. You also want a setup that can attach to multiple wings.
  • Motor: get a motor that can drive both slow and fast foils and that will not need you to “pump” the board to get it up.

Ultimately, once you have a solid foundation you can start to experiment with all the other options like different electronics, props, foil wings etc.

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i agree, still think youre overvaluing.

If you just want a “look it rides and does a few turns” efoil, yes sure I am overvaluing it.
If you want a fantastically efficient high performance efoil that’s also safer and easier to carry, then no I’m not. I’ve had multiple setups, so I know just where the frustrations are…

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When you’ve got to carry it for 200meters weight does matter :slight_smile:
Regarding efficiency yes weight is not the first aspect to consider, first is motor prop combo, then foil

I think you forgot : building skills and riding skills , you may end up with a completely different board

While weight is an issue, mass and its distribution within the design is equally critical.

Anyway, a search on “Active Foil” showed me this thread.

Several teams seek to make use of this research to create biomimetic primary drives for fish-like drones.

I am a minimalist in philosophy and in lifestyle, and my interest in this form of personal hydrofoil is personal enjoyment of course but also building a series of a test mules, precursors to greater load capacity vehicles.

For that I need an extremely efficient, highly adaptive strut and foil system, creating a submerged foil system that efficiently navigates across a spectrum of speed regimes, thus transcavitating sub to super (base-ventilating and or aerating), adapting many of the theoretical concepts and experimentation of aeroelastic wing design with synthetic muscle actuation.

While some technicologies cannot scale because their effect is predicated on their specific scale, my research is exclusive to design factors that are scaleable. I am a proponent of Cooperative Problem-Solving, commonly termed Action Research, Design, Development, though in practice I chose to view it as more Cooperative/Collaborative Action Exploration, Experimentation, Design, Development, and of course down the line Delivery.

Hydroelastic Foil Shape and Articulation informed by nature . . .
Journal of the Royal Society
Three-dimensional scaling laws of cetacean propulsion characterize the hydrodynamic interplay of flukes’ shape and kinematics
Fatma Ayancik, Frank E. Fish and Keith W. Moored
Published: February 26, 2020
Subjects: biophysics, biomechanics
Keywords: scaling laws, biological fluid dynamics, bio-propulsion, swimming

This is somewhat dated prior-art but still informative in framing the historicity of high-speed supercavitating foil as a concept. This is a rough scanned to pdf of a circa 1963 report from Grumman Marine during their development and testing of the USS High Point.

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