stability

Keep the outside wet, and the inside dry?

That depends on the country/state in which you live. However possible additions to a registration number could be insurance, a working marine radio, a certificate of seaworthiness, a licence, and a certified captain.

Chinese junks are ancient sailing ships used in East Asia for trade and travel. They have distinctive sails and design features, such as a flat bottom and a rudder that can be raised. Chinese junks were known for their seaworthiness and were widely used in maritime trade until the 20th century.