STABILITY AND TRIM FOR THE SHIP'S OFFICER, 4th Edition, by William E. George

Fundamentals of Trim and Longitudinal Stability
Source Material:  pages 187–189, 192–193

I. Longitudinal Stability Foundations (Pages 187–188)

• Longitudinal Stability: The vessel’s resistance to being longitudinally inclined about its transverse axis.
• Longitudinal Metacenter (ML​): Formed by the intersection of lines of force through B before and after a small longitudinal inclination.
• Stability Scale: Because a ship’s length is significantly greater than its breadth, the Longitudinal Metacentric Height (GML​) is enormous compared to transverse GM.
• Metacentric Radius (BML​): Calculated as BML​=IL​/∇, where IL​ is the moment of inertia around the transverse axis and ∇ is the volume of displacement.

II. Professional Trim Definitions (.Pages 187–189)

• Trim: The physical difference between the drafts Forward and Aft.
• Drag: A term used on tankers and in USCG License Exams meaning Trim by the Stern.
• Even Keel: A condition where the drafts are identical at the Bow and Aft.
• Change of Trim: The algebraic sum of the initial and final trims.
  • Rule 1: If trims are both by the head or both by the stern, subtract the lesser from the greater.
  • Rule 2: If trims are different, add the two values.

III. Trimming Moments and the LCF (Pages 188–189)

• Trimming Moment: Created whenever a weight is moved longitudinally or is loaded away from the tipping center.
• Longitudinal Center of Flotation (LCF): The tipping center or fulcrum of the vessel; the center of gravity of the water plane at a specific draft.
• Calculation: Trimming Moment = Weight × Distance from the LCF.

IV. Trimming Constants: MT1 and MTC (Pages 189, 192–193)

• MT1 (Moment to Change Trim One Inch): The foot-long tons required to change trim by exactly one inch.
• MTC (Moment to Change Trim One Centimeter): The meter-metric tons required to change trim by exactly one centimeter.
• Derivation of MT1: Formula is MT1=(GML​×Δ)/12L.
• Empirical "k" Formula: For license examinations: MT1=k×(TPI)2/B, where k is a constant based on the block coefficient (e.g., k=30 for 0.75).

V. Technical Figure References

• Figure 9-1 (Page 188): The geometric relationship of ML​,B,G, and the scale of GML​.
• Figure 9-2 (Page 189): Examples for determining Change of Trim.
• Figure 9-3 (Page 193): The geometric evolution of the MT1 formula.

Produced by William E. George and Powered by Google's

Become a supporter of this podcast: https://www.spreaker.com/podcast/stability-trim-for-the-ship-s-officer--4180737/support.