Draft Marks are numbers found at the bow of the ship (near ship’s stem) and stern (near stern post) of a ship which indicates the ships draft.
It is very important to know the current ship’s draft before engaging navigation, ship or vessel must never be over-loaded, and in order to know if she floats balance from her port and her starboard side too, and basing to the deep level of water according to navigational map or may suffer constraint on her ability on draft when passing shallow waters.
One of the reasons why a ship or vessel may easily sink duringbad weather or rough seas is due to overloading, and to identify current ship’s draft is a must.
Plimsoll Mark or Load Line Disc are a disc marked amidship below the deck line which is 12 inches in diameter and intersected by a horizontal line 18 inches in length and 1 inch in breadth, the upper edge of which passes through the center of the disc.
Summer load line is indicated by the upper edge of the line which passes through the center of the disc and also to the line mark “S”.
Winter load line is indicated by the upper edge of the line mark “W”. It is one fourth inch per foot of summer draft lower than “S”.
Winter North Atlantic is indicated by the upper edge of the
Tropical load line is indicated by the upper edge of the line mark “T”. It is one fourth inch per foot of summer draft higher than “S”.
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Or click the link to read next page regarding formulas, and some problem and solving Minimum Fresh Water Freeboard and Deduction in Freeboard http://expertscolumn.com/content/seamanship-minimum-fresh-water-freeboard-and-deduction-freeboard-formula-problem-and-solving
Fresh water load line is indicated by the upper edge of the line mark “F”. The difference between the fresh water load line in summer and the summer load line is the allowance to be made for loading in fresh water at the other load line.
Tropical Fresh Water Load line is indicated by the upper edge of the line mark T F.
The authority to which the load lines are assigning may be indicated by letters measuring about four and one half inches by three inches mark alongside the disc and above the center line.