Thread: Non powered boat move upstream

Question: If the hull of a boat was dynamically configurable such that it could take on an airfoil design at will would it be possible for such a boat to move up stream? Using the principles of a sail on a sailboat the hull would allow the boat to propel itself up stream by tacking back and forth.

lift works at right angles to the motion of the current, you can't get parallel motion from an airfoil design.

Oh, gee. What a shock you'd pull that out...

That proposal is similar to the many made for balloons, to 'sail' upwind by tacking. Cannot be done. A balloon drifts in the wind, at the same speed and direction as the wind. Tacking is not possible.

A yacht can tack upwind because it is pushing against the water. The wind provides the energy, but the yacht's keel provides a second force, stopping the yacht simply moving with the wind, and forcing it in the set direction.

The proposal in the OP lacks that factor.

True. There must be a keel, leeboard, or daggerboard/centerboard to prevent the boat drifting before the wind like a balloon. Frequently this has a "foil" section, but it is the sheer area of lateral resistance which is of greatest importance. Sails function much like airfoils as well.

In fact, by definition, sails ARE airfoils

Yes, laminar flow and all that. This is the general case, but is a big spinnaker or a round parachute truly an airfoil? That is why I (perhaps erroneously) qualified the statement. No question that a modern sport parachute is in fact an airfoil, generating lift as well as drag.

Here's a similar fun idea to stretch peoples ideas... a windmill driven boat that can go directly upwind:
Windmill Driven Boat - YouTube