How long should sailors know the weather at sea before going out to sea?

Three days. You should check the weather forecast for three days before and after the day of going to sea in advance, and don't choose to go to sea under bad weather conditions, especially after the relevant departments have issued warnings of meteorological disasters such as typhoon, rainstorm, lightning, strong wind and fog. Weather forecast, also known as meteorological forecast (measurement), refers to the use of modern science and technology to predict the state of the earth's atmosphere in a certain place in the future.