The thing under the sailboat refers to the bottom part of the boat, which is usually called the bottom of the boat. Normally, the bottom of a sailboat requires special design and structure to ensure the stability and speed of the hull. Generally speaking, the bottom of a sailboat is relatively smooth, and a special coating needs to be applied to prevent marine organisms from adhering to the bottom of the boat and affecting the navigation of the sailboat.

In addition to paint, some common sailboat bottom equipment also includes underwater lights, sonar, depth gauges, paddles, propellers, etc. These equipment can improve the safety and efficiency of sailing boats. Among them, underwater lights can help the crew observe the underwater environment; sonar and depth gauges can help the crew judge the water depth and underwater conditions; paddles can help the crew paddle when needed; and propellers can help sailboats gain greater speed.

At the same time, there are also some special bottom equipment for sailboats, such as splints, pulleys, winches, etc. These equipment are mainly used for the contraction and expansion operations required when sailing. For example, when a sailboat enters a port or is berthed, the crew needs to use pulleys and winches to help the sailboat dock or secure. When the sailboat is close to cables, shores or other obstacles, the crew also needs to use plywood to protect the bottom and hull of the boat.