[Skybird]

If he means it as an illustration of principal gravitational attraction between two masses, then he is right in a way, but given the specific details of the example he'd choosen, other (environmental, global, astronomical) effects and variables add to the formula so that the virsible effect, I would expect, is so minimal that you can no longer observe it within a reasonable timeframe.

The example of two matches in a glass of water, if taken as a literal experiment indeed, I would see more as a demonstration of surface tension of water and what it can do, also maybe helped by the coriolis force.

General law of gravitation:

FG = G * ( M1 * M2) / r^2

F = resulting gravitation force
G = Gravitation constant
M1, M2 = two masses
r = distance between the masses' centre

The force of gravitation between two masses is directly proportional to the mass of the two objects. The force of gravitation is in an inverse squared relation to the distance between the two objects: you double the distance, but the force looses 75% in effect.

Both objects in this example'S setup, are object two two much more dominating gravitational forces that interfere with them: that of Earth itself, and the moon.

Summary: while true in principle, I would not expect to see a visible, gravitation-caused effect between two sailing ships that are in sight to each other, but some miles apart on the ocean: at least not within a reasonable timeframe for observation. the likelihood to notice the said effect, would fall rapidly with growing distance between both objects. I couöld imagine that the said effect just becomes evident when both ships (the centre of their masses, that is) are so close to each other that their outer hulls stand in their ways, crankle against each other, and prevent any further movement towards each other.