If you read many reports from the CW era or before, or naval fiction (Patrick O'Brien et al.), you've probably come across the term "hull down," referring to a ship sighted at a long distance. If the weather is clear, you can see well beyond the horizon, and other vessels beyond that point will have their lower parts hidden behind the curve of the earth; sometimes only the sails would be visible. This is known as being "hull down" to the observer. I took this photo today, that illustrates the phenomenon. These are ships anchored in the Gulf of Mexico off the beach at Galveston, probably waiting for a space to open in Houston, Texas City, or Baytown. In this case, all three ships are beyond the horizon as viewed from my vantage point. At my elevation, about 17 feet, the horizon is about 4.43 nautical miles (5.1 statute miles) distant. But you can see plainly how only the upper part of the farthest ship, the Tanja Jacob, is visible. Tanja Jacob is "hull down."