The first question：
（1） Why is one section of anchor chain 27.5 meters long?

Many classification societies have defined the single section length of anchor chains as 27.5 meters or slightly less in their regulations. Where did this 27.5 meters come from? This can be traced back to the old British Empire. Although Portugal and the Netherlands were once dominant, the empire that spanned the oceans for centuries was still the Sun Never Setting Empire. In this era of great navigation and naval cruising, Britain accumulated rich experience. And navigation is an industry that places special emphasis on tradition and inheritance, so many ancient habits and requirements have been passed down from generation to generation.

Everyone knows that Britain is a country that uses imperial units, which is incompatible with the metric system invented on the European continent. Although the mainstream today is to use international metric units, the imperial units represented by the United States and Britain still thrive.

The length of a single section of an anchor chain is derived from the British unit 'Xun', also known as' Tuo ', which is a unique unit of length used at sea. One Xun is approximately 1.8288 meters, which is the length of a person's (of course, a white European) arms spread out (measured above the sea, similar to the origin of feet). One section of anchor chain is taken as 15 Xun, which is more than 27.43 meters. When converted to the metric system, the last digit is erased and 27.5 meters are directly taken. So it was conventionally agreed upon and continued to be passed down.