Is there a limit to the size of ships that can have hydrofoils (would an aircraft carrier work)? Would there be cavitation if the load was high enough, and to what extent would using larger foils help, and would they stop providing any advantage over non-hydrofoils at some point?

  • 2
    $\begingroup$ Hydrofoils turn engine thrust into lift in order to reduce the friction on the hull. At some point, it becomes a question of just how much thrust you can economically produce, and whether the reduction in the amount of power lost to friction remains greater than the other losses in the system. $\endgroup$
    – Dave Tweed
    Sep 5 '16 at 17:44

There is no hard limit on the size of an airfoil/hydrofoil. A ships hull is a hydrofoil. This is how a sailboat sails into the wind for example. A keel is a large hydrofoil used in addition to the boats hull for directional stability or to counteract the force of the sails on a sailboat.

Hydrodynamic lifting of vessels for higher speed and higher efficiency is possible too, and have some very promising applications. However, like everything, there are economic/practicality constraints, especially when going big.

Adding hydrofoils to an aircraft carrier, for example, would require:

  1. Lots of engineering, prototyping, money, more money, and risk.
  2. Multiple long cord (maybe 10ft) hydrofoils added 20ft below the lowest part of the hull. They would be designed to lift half of the hull or maybe even all of the hull out of the water at cruising speed.
  3. More exposed hull at cruise speed; more vulnerable.
  4. Can the structure withstand failure of one or multiple hydrofoils at cruise speed.
  5. Deep hydrofoils limit traversable depth at lower speeds.
  6. Hydrofoils would be more easily damaged in a combat situation and would need to be discardable, or other emergency provisions.

Benefits of this would be:

  1. This would reduce power consumption at top speed
  2. Increase top speed with current powerplant.
  3. Better rough water stability at cruise speed if hydrofoils have a computer controlled leveling system.

While such an aircraft carrier might be advantageous to current designs, it comes with significant opportunity cost. Would that money be better spent on higher performance jets, better nuclear power systems for ships, or even peace-making efforts ;-)

These engineering efforts may make more sense for more cost conscious industries such as bulk transportation. Again, lots of details to contend with. Some new ships use bubbles to reduce drag; so there are opportunities in this area.

  • $\begingroup$ would it be less efficient than non-hydrofoils at some point? $\endgroup$
    – ntno
    Sep 6 '16 at 19:41
  • $\begingroup$ It would be less efficient at low speeds because the hydrofoils would contribute to drag but would not be lifting the hull. Low speed has relatively low power consumption though so it isnt too big of a concern. Provided the system is properly engineered, I don't believe a hydrofoil would ever be less efficient when comparing identical cruise speeds. $\endgroup$
    – ericnutsch
    Sep 6 '16 at 23:07

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