A more thorough explanation:

A seaman's will is a type of will made by a sailor or someone in the military while they are at sea or in active service. It is similar to a soldier's will. These types of wills are usually informal and may not follow the usual legal formalities required for a will to be valid. However, they are still considered valid if the person making the will was in active service at the time.

For example, if a sailor writes a letter to his family while at sea, stating how he wants his property to be distributed in case he dies, this can be considered a seaman's will. Even though it may not be written on official legal documents or witnessed by a lawyer, it can still be considered valid if the sailor dies while in active service.