The tide is a wonderful force, at which many are awed. Truth lies behind that awed feeling when one thinks of the dangers that go with the tides. For everything in nature that is beautiful is dangerouse. As you know, the world isn't some large ball of water that flows with the moon, it has continents, and more, shallow spots, bays, rivers, ans straits in which the water must flow. The water not only goes up and down, but side to side, and frequently, with great speed. The side to side, or horizontal movemnt is called tidal current. In normal cases, the tide flows in one direction for six hours and in the opposite direction for the following six and so on. Some condition one might call dangerouse are whirlpools, or maelstroms. Mael means to grind, and strom means a stream, a grinding stream... enough said. In books published for navigators, details are given on where the most vicious of all conditions are. Those conditond lie on the northwest coast of Norway. It is called "Saltens' Maelstrom because the whirlpool forms near a town named Salten. Here the tides have to flow through a skinny little channel, in and out of a big bay, and the tide can rise to about 90,000,000 gallons of water. As I've stated the tide direction changes every six hours, try and picture 90,000,000 gallons of water flowing through a thin little channel in six hours, the speed can reach up to thirty mph! This channel is only navigable during specific times in the day, when the tides are about to change direction, you see now, haw being able to predict the tides is important. Honestly, this window of time is not great, and even maneuvering a ship through, at what they call "slack water" when it's slower, is difficult, and must be handled carefully. Ships caught in a swirl of water can be hurled against the rocks at a high velocity, and crushed to pieces.