Diploma in International Shipping & Logistics Devron S. Newman - GSK 9/6/2018 Diploma in International Shipping & Logistics General Ship Knowledge ML 301.1(3.0)

Unit 4 – Draft and Loadlines Devron S. Newman - GSK 9/6/2018 Lesson 1: Displacement Lesson 2: Displacement Calculations Lesson 3: Trim, Hogging & Sagging Unit 4 – Draft and Loadlines

Devron S. Newman - GSK 9/6/2018 Lesson 1: Displacement We discussed displacement in Unit 3. Now we will go further with the concept so that we can understand how the calculations are done and how we can determine how much cargo is to be loaded or discharged at a particular time during the cargo operation. But first, we must understand the principle of displacement.

Devron S. Newman - GSK 9/6/2018 Displacement - know Displacement is based on Archimedes Principle of Flotation. It states that… “…the apparent loss in weight of a body immersed in a fluid is equal to the weight of the displaced fluid”; or a floating vessel displaces a volume of liquid, the weight of which is equal to the weight of the vessel.

Devron S. Newman - GSK 9/6/2018 Density Another term that we must understand is density. The density of a liquid is its mass per unit volume. In this context, and for calculation purposes, we will use kg/m³ as the units. Typical examples of densities are: Sea water: 1,025 kg/m³ Fresh water: 1,000 kg/m³ Dock water: 1,019 kg/m³

Devron S. Newman - GSK 9/6/2018 Relative Density Relative density is the density of a liquid relative to the density of fresh water. It means therefore that relative density has no units because it is the ratio of one liquid to another. For example: density of dock water = 1019 kg/m³ Density of fresh water = 1,000 kg/m³; therefore the relative density of dock water is 1019 kg/m³/1000 kg/m³ = 1.019

Longitudinal section of a vessel Devron S. Newman - GSK 9/6/2018 Draft Longitudinal section of a vessel

Devron S. Newman - GSK 9/6/2018 Draft The draft of a vessel is measured from the bottom of the keel to the water line. It has to be measured at the fore and aft of the vessel. Some calculations require that we find the mean draft. Simply put, the mean draft is the mean of the two readings. Therefore we just add both values and divide by 2. We must however, be careful with our calculations depending on the whether we are using metres or feet and inches.

Devron S. Newman - GSK 9/6/2018 Draft and Draft marks In order for us to read the draft marks the forward, mid and aft parts of the vessel must be graduated in the respective units so that the drafts can be read.

Devron S. Newman - GSK 9/6/2018 Draft Marks Draft marks in metres

Vessel alongside showing draft marks Devron S. Newman - GSK 9/6/2018 Vessel alongside showing draft marks Draft marks on the bow of a ship

The Stern of a Container Vessel Devron S. Newman - GSK 9/6/2018 The Stern of a Container Vessel

Draft marks Draft marks in imperial units Devron S. Newman - GSK 9/6/2018 Draft marks Draft marks in imperial units

Devron S. Newman - GSK 9/6/2018 Loadlines Loadlines are line cut into the side of a vessel to indicate how far down a ship may be loaded in a particular season. They are marked on both sides of the vessel at midship.

Loadlines and their Dimensions - know Devron S. Newman - GSK 9/6/2018 Loadlines and their Dimensions - know

Lumber Loadlines Viewed from starboard side Devron S. Newman - GSK 9/6/2018 Lumber Loadlines Viewed from starboard side

Midship – loadlines and draft marks Devron S. Newman - GSK 9/6/2018 Midship – loadlines and draft marks

Lesson 2: Displacement Calculations Devron S. Newman - GSK 9/6/2018 Lesson 2: Displacement Calculations Tonnes per centimetre (TPC) means the number of tonnes required to change the mean draft by 1cm whether by loading or discharging. TPC = 1.025Aw /100; where Aw is the waterplane area in salt water. In general; TPC = (density)(Aw)(0.01) TPC = density (V1cm ) (remember that mass = vol. x density)

Devron S. Newman - GSK 9/6/2018 TPC Sinkage: The inverse of TPC is sinkage and is expressed in cms. It is the number of centimetres that the mean draft of a vessel would sink whenever cargo is loaded. Sinkage = W/TPC

Devron S. Newman - GSK 9/6/2018 Form Coefficients In deepening our knowledge of displacement, draft and loadlines. We must know a little about two types of form coefficients. Waterplane coefficient, and; Block coefficient

Waterplane Coefficient Devron S. Newman - GSK 9/6/2018 Waterplane Coefficient The waterline coefficient is the ratio of the area of the waterplane of a vessel to the area of a rectangle having the same overall length and breadth (or beam). This coefficient is denoted by Cw ; where Cw = Aw/LxB

Block Coefficient of Fineness Devron S. Newman - GSK 9/6/2018 Block Coefficient of Fineness The block coefficient is the ratio of the underwater volume of a vessel and the volume of a block having the same overall dimensions. It is denoted by Cb and Cb = Vu/LxBxd

Block Coefficient Diagram illustrating block coefficient Devron S. Newman - GSK 9/6/2018 Block Coefficient Diagram illustrating block coefficient

Freshwater Allowance (FWA) Devron S. Newman - GSK 9/6/2018 Freshwater Allowance (FWA) This is the amount by which the draft of a vessel will reduce when she moves from freshwater to salt water. FWA = Disp/40 TPC cm

Dockwater Allowance (DWA) Devron S. Newman - GSK 9/6/2018 Dockwater Allowance (DWA) This is the amount by which the draft of a vessel will reduce when she moves from brackish water to salt water. DWA = (change of RD)/.025 x FWA cm

Devron S. Newman - GSK 9/6/2018 Class Exercise A ship with displacement 4,500t; L 85m; B 18m; waterplane coefficient 0.67 is floating in SW at a mean draft of 3.5m. Calculate: TPC for the present mean draft. If the vessel loaded 180t at midship on her centreline, calculate the change in her mean draft. Displacement after loading DWA if the vessel had sailed to a port with relative density 1.015.

Lesson 3: Trim; Hogging & Sagging Devron S. Newman - GSK 9/6/2018 Lesson 3: Trim; Hogging & Sagging Trim is the difference between the aft draft and forward draft. A vessel is said to be trimmed by the stern if the aft draft is greater than the forward draft and trimmed by the head if the forward draft is greater than the aft draft. If both drafts are equal then the vessel is said to be on even keel.

Devron S. Newman - GSK 9/6/2018 Trim by the stern Longitudinal section of a ship shown trimmed by the stern

Devron S. Newman - GSK 9/6/2018 Trim by the head Longitudinal section of a ship shown trimmed by the head

Devron S. Newman - GSK 9/6/2018 Hogging A vessel is hogging when the midship draft is less than the mean of the forward and aft drafts. Hog is the mean draft minus the midship draft.

Devron S. Newman - GSK 9/6/2018 Sagging A vessel is sagging when the midship draft is greater than the mean of the forward and aft drafts. Sag is the midship draft minus the mean draft.