Dry Docking Stability Part 2 | Water Lines, Virtual Loss of GM and Residual GM | Chief Mate Exam

In this video, we continue our Chief Mate MMD Ship Stability preparation with an important topic, DRY DOCKING STABILITY. The lecture explains how vessel stability changes as the water level inside the dock gradually falls. TOPICS COVERED Water Lines 1 to 5 Change in draft and buoyancy Change in KM and GM P3 Upthrust and Virtual Weight Virtual Loss of GM Residual GM Free Surface Effect Trim during dry docking Critical Period Final Hydrostatic Draft Maintaining Positive GM WATER LINE CONCEPT Water Line 1 represents the vessel entering the dry dock while supported by water. As the water level falls, the vessel approaches the dock blocks and begins transferring weight from the water to the blocks. Water Line 3 is an important stage where P3, Upthrust or Virtual Weight becomes relevant for stability and trim calculations. Water Line 4 represents a critical condition where the vessel may approach zero or negative GM depending on the vessel's condition. Water Line 5 represents the final stage and the resulting stability condition. IMPORTANT CALCULATIONS P3 UPTHRUST OR VIRTUAL WEIGHT P3 is used to determine the effect of the vessel taking weight on the dock blocks. This is important for trim and stability calculations. VIRTUAL LOSS OF GM As the vessel takes weight on the dock blocks, the effective displacement supported by water reduces. This changes the hydrostatic condition and results in a virtual reduction in GM. RESIDUAL GM Residual GM or RGM represents the remaining stability after considering the virtual loss of GM and applicable Free Surface Correction. PRACTICAL NUMERICAL The instructor demonstrates the calculations using a vessel with a length of 84 metres and displacement of 3000 tonnes. The example covers P3, Virtual Weight, Change in Trim, Virtual Loss of GM, Free Surface Correction, Residual GM and Final Draft. CRITICAL PERIOD When the vessel starts taking weight on the dock blocks, the effective buoyancy supporting the vessel changes. During this period, the vessel can experience a significant reduction in GM. Maintaining adequate positive stability throughout the critical period is essential. The lecture explains why entering dry dock with a small initial trim can help control the docking process and minimise the critical period. WHY THIS MATTERS FOR CHIEF MATE MMD Key concepts include Displacement, Draft, Trim, KB, BM, KM, KG, GM, P3, Virtual Weight, Virtual Loss of GM, Residual GM, Free Surface Effect and Hydrostatic Particulars. WHO SHOULD WATCH Chief Mate MMD Candidates Second Officers preparing for Chief Mate Deck Officers and Merchant Navy Officers Maritime Students and Cadets Seafarers preparing for Ship Stability EDUCATIONAL DISCLAIMER This video is intended for educational and examination preparation purposes. Actual dry docking operations must follow the vessel's approved docking plan, company SMS, shipyard procedures, class requirements, stability information and applicable regulations. For MMD preparation, always refer to the latest applicable DG Shipping and MMD requirements and approved study material. ABOUT SAILOR RIDER Welcome to Sailor Rider, A Voice for Every Seafarer. Sailor Rider provides practical maritime knowledge, education and real shipboard information for the global seafaring community. Topics include Chief Mate MMD Exam Preparation, Ship Stability, Dry Docking, Grounding, Trim, Navigation, COLREGs, Cargo Operations, Shipboard Safety, Maritime News, Marine Engineering and practical shipboard knowledge. Our mission is to make maritime education simple, practical and useful for seafarers, officers, engineers, cadets, maritime students and shipping enthusiasts worldwide. Sailor Rider A Voice for Every Seafarer CHAPTERS 00:00 Introduction 00:40 Water Line 1 to Water Line 5 06:30 Water Line Stability Concept 12:45 P3 Upthrust and Virtual Weight 17:00 Virtual Loss of GM 19:40 Residual GM and Free Surface Effect 29:59 Importance of Initial Trim 32:50 Critical Period During Dry Docking 33:35 Numerical Example 40:00 Dry Docking Stability Calculation 48:15 Final Hydrostatic Draft CONNECT WITH SAILOR RIDER YouTube    / @sailor_rider   Facebook   / 19imzynlrp   Instagram   / sailor_rider   Threads https://www.threads.com/@sailor_rider SEARCH KEYWORDS dry docking stability, dry docking chief mate, dry docking MMD exam, chief mate stability, chief mate MMD stability, dry docking numerical, virtual loss of GM, residual GM, dry docking water lines, P3 dry docking, upthrust dry docking, virtual weight, free surface effect, critical period dry docking, ship stability, MMD stability, chief mate exam preparation, merchant navy stability, dry dock calculations, hydrostatic draft, hydrostatic particulars, maritime education #ChiefMate #MMDExam #ShipStability #DryDocking #MerchantNavy