Question: I have heard that when a sailboat is sailing against the wind, it operates on the principle of 'lift'. I am unable to understand the explanation, based on Bernoulli principle, completely. My question is, when it says 'lift', it literally means that the boat is being 'lifted' out of the water? Like when we throw a stone across the lake and it skims and hops on the water?

Answer: 
Unfortunately the link is broke with no forward link. However the effect is the same as an airplane wing, where lift is generated on the upper or slightly rounded surface. This in effect "Pulls" the aircraft up at a constant rate of assent as long as the upper surface continues to receive the "flow" at a constant rate. Now imagine the airplane wing sitting im the vertical position. The air flow will do the very same thing to the wing as it does to the sail. Now to make matters more complicated, Airplane wings have "airflow disrupters called ailerons, which disrupt the air flow in a certain section of the wing. Now if the flow remains constant, then the disturbed air will cause an area of increased or decreased pressure which causes certain areas of the wing to either slow down or speed up depending on the pressure flow. 

The Wikipedia article on [wingsails](https://en.wikipedia.org/wiki/Wingsail) explains the use of a fixed wing/sail and the way airflow flowing around the wing creates the force needed to push the boat. These are essentially airplane wings that have been turned from a horizontal position to a vertical position. The effect is the same because the sailboat with a center keel assumes the characteristics of a plane. The lower centerboard or keel act as a wing in the same way as the fixed wing above decks.

This explains the relation between the Bernoulli principal and how a boats sail works. Aviators are trying to build a stunt plane with both horizontal as well as vertical wings for never before seen stunts. (See [this gizmag article](http://www.gizmag.com/vertical-winged-aircraft/21206/) for more information)
Well, [according to this](https://physics.stackexchange.com/a/295/85020) Bernoulli effect is NOT the cause of lift.

> 
> Basically planes fly because they push enough air downwards and receive an upwards lift thanks to Newton's third law.
> 
> 
> 

It is clear that blowing over a piece of paper pulls it up ([video](https://youtu.be/025lsG3VHKM?t=74)).
Here: fast air => lower pressure => paper pulled up. Right.

But that IS NOT the case for sails and wings. Wind arriving to a sail/wing goes ALL of it at the SAME speed. The air above the wing / on leeward of a sail does not spontaneously accelerate up. It gets speeded up by a a lower pressure in that zone. Thus, the "fast air" is not the cause but THE CONSEQUENCE.

What does it cause the low pressure zone above a wing / on leeward of a wing?

What is for sure is that wings/sails deflect air. Then for wings and sails:

Main cause: air deflection => change of pressure => changes in air speed.

That's it.

Don't get confused by the fact that Bernoulli equation can be effectively used to measure lift. It's perfectly right to estimate the real cause (air deflected downwards) by a direct effect (change of pressure).