I've researched a number of 1830-40's ship logbooks and have seen one of thwo things recorded in numerical form such as that you indicate. 1) soundings 2) Weight (tonnage) of supplies loaded aboard.

The latter of course is not the case if the vessel was not in port on that day.

Another consideration is they might have been involved in a coastal survey & were travelling a straight line while determining distance offshore, or in some manner, the elevation of the bluffs.

Kenneth