What is indicated at the 13 mark on a lead line?

The 13 mark on a lead line is indicated by three strips of leather. Lead lines are used to measure the depth of water beneath a vessel, and specific markings are placed at intervals to denote various depths. The leather strips are used as physical indicators that can be easily identified and counted, providing a quick reference for personnel using the lead line. Each marking corresponds to a specific depth, and in this case, the three strips signify a depth of 13 fathoms. This system assists sailors in navigating safely and assessing water depths, which are crucial for avoiding grounding or collision in shallow waters.