Basic Ship Structure and dimension of Ships
In Ship Construction, several terms are used.
Ships are made up in various sections. The terms given to them are used to help in understanding how the strength of the ship is affected by effectively using these components.
As an operational level deck officer, you are expected to fully understand, recall and apply these terms.
1. Length Overall
Length overall is the horizontal distance between extreme fore and aft of a ship measured along its greatest length
2. Forward Perpendicular
Forward Perpendicular is a vertical line drawn at a point where the waterline of the ship at the summer load line meets the stem of the ship.
3. Aft Perpendicular
After Perpendicular is a perpendicular drawn at the point where the aft end of the ship’s rudder post meets the summer load waterline. If there is no rudder post then it is taken from the centerline of the rudder stock.
4.Length Between Perpendiculars
Length between perpendiculars is the horizontal distance between the forward perpendicular and after perpendicular measured along the summer loadline.
Midship is a point midway between the forward and aft perpendiculars.
*Refer to the above diagram
Depth is the height of a ship at the midship from the base line to the moulded line of the deck at the ship’s side.
Moulded depth is the vertical distance measured along the shipside from the top of the keel to the waterline.
8. Extreme Depth
Extreme depth is the height of a ship at midship from bottom of the keel to top pf the deck beam at the ship’s side.
Draft is the vertical distance measured along thw shiside from the bottom of the keel to the waterline.
Moulded Draft is the vertical distance measured along the shipside from the top of the keel to the waterline.
Freeboard is the vertical distance from waterline to the upper edge of the deck line measured amidship at the ship’s side.
Statutory Freeboard is the vertical distance from upper edge of the summer Loadline to the edge of the deck line measured amidship at the ship’s side.
Sheer os the rise of a ship’s deck in fore and aft direction, rising from the midship and is maximu at the ends. Its adds buoyancy at the ends of a ship.
Flare is the outward curvature of a side shell of a ship at the forward end of a ship. It increases buoyancy and limits sinkage of the bow in head seas.
Scantlings are the dimensions of the various parts used inn the costruction of a ship. The various parts include frames, stringers, griders, structural strenght members, etc.
4. Base line
Base line is a horizontal line drawn at the top of the kill plate.
Camber is the transverse curvature of the deck from the centreine to the sided. It helps to drain water from the decks and adds to the longitudinal strength of the shipp.
Tumblehome is the inward curvature of the side shells towards the centerline above the waterline. Tumblehome reduces the width of the upper deck. Present day ships rarely have tumblehome.
7. Rise of floor
Rise of floor is the slopping of bottom shell plating above horizontal base line measured at the ship;s side. This facilitates drainage of liquids into the ship’s bilges.