Shift of Ship's Center of Gravity (Part2) when Adding Weight ll Calculate Final KG

Summary

In this video, Captain Ron explains the effect of adding or loading weight on a ship's center of gravity (G) and its impact on the ship's vertical center of gravity (KG) and metacentric height (GM). The tutorial covers scenarios including cargo on the upper deck, cargo in the lower hold, and ballast water in wing and double bottom tanks. Viewers learn to calculate the vertical shift of G using a clear formula and determine the final KG, with practical exercises illustrating the calculations. The video emphasizes understanding weight placement for ship stability, while horizontal movements and free surface effects are noted for separate discussions.

Takeaways

• 😀 The video explains how a ship's center of gravity (G) shifts when adding or loading weight on board.
• 😀 Vertical movement of G is the main focus, while horizontal movement is covered in another video about ship listing.
• 😀 Loading weight on the main deck increases KG and decreases the ship's initial metacentric height (GM).
• 😀 Loading weight in the lower hold decreases KG and increases GM, improving stability.
• 😀 Filling ballast water in wing tanks increases KG and decreases GM.
• 😀 Filling ballast water in double bottom tanks decreases KG and increases GM.
• 😀 The vertical shift of G (GGV) can be calculated using the formula: GGV = (weight added × vertical distance) / (ship displacement + weight added).
• 😀 When adding weight, the final KG is found by adding or subtracting the vertical shift (GGV) depending on whether the shift raises or lowers G.
• 😀 The ship’s sounding table is used to determine the KG or VCG of liquids in tanks.
• 😀 Free surface effect of liquids is not included in the examples and requires separate calculation for accurate stability assessment.
• 😀 Understanding KG shifts when loading or adding weight is essential for ensuring the ship's stability and safe operations.

Q & A

What is the main topic of this video?

The video explains the effect of a ship's center of gravity when loading or adding weight on board and how to calculate the vertical shift to determine the ship's final kg.

How many parts is the full video divided into, and what does each part cover?

The full video is divided into three parts: Part 1 covers shifting a weight already on board, Part 2 covers loading or adding a weight, and Part 3 covers discharging a weight.

In this video (Part 2), what type of movement of the ship's center of gravity is considered?

This video focuses on the vertical movement (G vertical shift, GV) of the ship's center of gravity. Horizontal movement is not considered here.

What effect does loading weight on the main deck have on the ship's center of gravity and GM?

Loading weight on the main deck causes the ship's center of gravity to move upward, resulting in an increase in kg and a decrease in the initial metacentric height (GM).

What is the effect of loading weight in the lower hold of the ship?

Loading weight in the lower hold moves the ship's center of gravity downward, decreasing the final kg and increasing the initial metacentric height (GM).

How is the vertical shift of the ship's center of gravity calculated when loading or adding weight?

The vertical shift (ggv) is calculated using the formula: ggv = (weight added × vertical distance between ship's G and weight's G) ÷ (ship's displacement + added weight).

What does filling ballast water in the wing tank or double bottom tank do to the ship's kg and GM?

Filling ballast water in the wing tank increases kg and decreases GM, while filling in the double bottom tank decreases kg and increases GM, depending on the tank's vertical position relative to the ship's center of gravity.

Can you provide an example calculation for the final kg when loading cargo on the upper deck?

If 2000 tons of cargo is loaded on the upper deck with a vcg of 11.2 m, the ship's initial displacement is 18,000 tons and initial kg is 8.75 m: ggv = (2000 × (11.2 - 8.75)) ÷ (18,000 + 2000) = 0.245 m. Final kg = 8.75 + 0.245 = 8.995 m.

How is the final kg calculated when adding ballast water in a double bottom tank?

If 80 tons of ballast water is added with vcg 1.8 m, ship displacement 4500 tons, initial kg 4.25 m: ggv = (80 × (4.25 - 1.8)) ÷ (4500 + 80) = 0.043 m. Since the shift is downward, final kg = 4.25 - 0.043 = 4.207 m.

Is the free surface effect of ballast water included in the kg calculations in this video?

No, the free surface effect is not included in these calculations. A separate video is suggested to cover the effect of free surface on fluid kg and GM.

Why is horizontal movement of the ship's center of gravity not discussed in this video?

Horizontal movement is not discussed because this video focuses only on vertical movement (kg). Horizontal movement is related to ship listing and is covered in another video.