The Dockmasters Journal - Volume 2, Issue 2
February 2025
Editor: Waleed (Wally) Sayed, P.E., M. ASCE
A publication focused on Dry Docks presented to Dock Masters, Dry Dock Engineers, Operators, and Owners.
Our mission is to focus on the diverse world of dry dock facilities, showcase their successes and unique capabilities, disseminate industry specific knowledge, and share lessons learned from the dry dock incidents with a positive presentation.
In this month’s edition:
⦿ A Note from the Editor
⦿ Questions for the Editor
⦿ Main Article: Floating Dry Dock Deflection Monitoring and Pumping Plans for Floating Dry Docks
⦿ Community Highlight
⦿ So, this one time, I was on a dry dock...
A Note from the Editor:
“A ship in dry dock is safe, but that’s not what ships are meant for.”
Made in the USA No More? The Fight to Save American Shipbuilding
As the US strives for excellence in the maritime industry, our pursuits appear to be stymied by forces greater than all of us acting independently. Our shipbuilding industry is strained to its limits and cheaper foreign built equipment has flooded our domestic markets. I will note that there is a difference between cheap and cost effective. Once upon a time ago “Made in the USA” was a mark of premium design and quality the world revered and was willing to pay for. As others have attempted to mimic our capabilities, we have been deprived of those longstanding attributes that set US Built apart from the rest. I hope that we find our strength and resilience collectively as we work to regain our longstanding dominance in the maritime industry. Since the dawn of marine history, before the Greeks and Phoenicians, those who ruled the seas ruled the world.
Questions for the Editor:
Q) What is the difference between a Rennie and a Sectional Floating Dry Dock?
A) In a way a Rennie type floating dry dock is a sectional dry dock, with a significant difference. In a Rennie type each pontoon is separate and independent, designed as a flat top barge, with the port and starboard wingwalls designed as a continuous structure.
A sectional dock is designed with multiple short lengths, or sections, of a dry dock with independent pontoons and wingwalls. Assembly to create a reasonably infinite length dry dock requires alignment of the individually assembled sections to be joined with splice joints welded to join the individual sections. The splice joints must be designed to carry the shear and moment developed due to longitudinal bending of the dock.
In both cases, when fully assembled with multiple pontoons, the dock can be fully dewatered and then one pontoon flooded and disconnected from the wing wall, allowing for self-docking and repair of a single pontoon.
Deflection Monitoring and Pumping Plans on a Floating Dry Dock
A floating dry dock is essentially a floating beam continuously supported by the water it’s floating in. To change the draft of the dock, the displacement must change. Given that the lightweight of the dock is fixed, the variable at hand is ballast water, which must be added or removed affecting the displacement which affects the draft. If ballast water is not distributed according to the load distribution of an empty or loaded dry dock, trim or list, and/or hog or sag may develop. [Hog is longitudinal bending with upward deflection and sag is longitudinal bending with downward deflection.]
On a floating dry dock, an engineered pumping/ballast plan is calculated for each of the five phases of stability [Phase 1-Maximum Submergence, Phase 2-Draft when Vessel Contacts the Keel Blocks, Phase 3-Water at The Top of the Keel Blocks, Phase 4-Water at the Pontoon Deck, Phase 5-Operating Dock Draft] to ensure the dry dock remains in a neutral condition (i.e. no bending). To ensure proper ballasting of the dock in accordance with the pumping plan requires a console in the control room with Tank Level Indicators (TLI) and Draft Level Indicators (DLI). While there are several methods for designing a deflection monitoring system, the most common and simplest method consists of a transit, several sighting targets and a backsight located on the weather deck. This visual method ensures that during ballast operations the dock does not exceed its allowable deflection limits determined by engineering analysis of the dock’s longitudinal bending strength.
A properly designed control room will include inclinometers oriented longitudinally to detect trim and transversely to detect list which assist the operator in monitoring the attitude of the dock, a control console with tank and draft level indicators, and either a visual sight for deflection monitoring or a radio to hear the personnel assigned to monitoring the deflection from a fixed transit.
On a dry dock designed to ABS Rules for Building and Classing Steel Floating Dry Docks, there should be a method for detecting deflections which are defined as being tank and draft level indicators to monitor the ballast water levels and draft and/or an optical/visual deflection monitoring system. On floating dry docks less than 200-feet long, a properly designed dock will be very stiff with minimal deflection that renders an optical system as ineffective. In docks over 200 feet, the stiffness over the length is such that deflections are observable, and it is generally highly recommended to have both a TLI/DLI system and a visual system in use. The necessity for both systems is due to the reality of a live docking operation versus a calculated plan. There are many variables that may impact the pumping of the dock that renders the calculated plan as the desired operation, but the optical system reflects the actual operation and should control decision making to deviate slightly from the pumping plan. Examples of variables consist of time to open and close valves and varying lengths of ballast piping. Extreme variations from the calculated plan should alert the operator that the operation has significantly deviated from the plan and should be cause to stop operations until the source of the error is determined. For example, if the plan indicates the ship will land on the blocks with 15-feet of water over the pontoon deck and it lands at 16-feeet of water over the pontoon deck the operation should stop because it may be an indication that the vessel has landed on a hull protuberance or a keel/side block has tipped over.
In dry dock design analysis, the longitudinal bending strength, or section modulus must be determined. Classification societies such as ABS provide minimum requirements for the longitudinal section modulus and moment of inertia. From these calculations, the maximum bending limits are determined. It is to note that the use of corrugated bulkheads comes with a design penalty which in most every case renders them ineffective when determining the longitudinal and transverse bending strength.
In floating dry dock analysis, the centroid is located just above the pontoon deck, with the weather deck becoming the critical longitudinal bending section most likely to experience compression buckling. (Buckling of the pontoon deck is due to transverse bending.)
The following sketches provide an overview of floating dry dock ballast operations and a typical setup of a visual deflection monitoring system. In the Loaded Dock Neutral Condition, the following details should be noted: Unloaded sections are not differentially ballasted, the loaded sections are ballasted according to the load supported. Non-proportional ballasting refers to unequal transverse ballasting of each longitudinal tank group.
The above picture is an “Example of Floating Dry Dock Ballast Operations with a Visual Deflection Monitoring System”
Triton Dry Dock is a premier dry dock engineering firm with extensive experience designing, modifying, analyzing and certifying dry dock facilities. This includes the development of customized pumping plans as well as design, calibration and training on deflection monitoring systems. You can trust Triton Dry Dock to provide your shipyard with the most effective and efficient dry dock solutions.
Community Highlight
Wenonah Hlavin is a maritime professional with a career focused on the weight and stability of vessels, especially regarding the drydocking of commercial and naval vessels. She has extensive experience as a weight and stability engineer and as a Dock Master.
A graduate in Ocean Engineering from Virginia Tech, she has worked in naval and commercial shipyards over her 21 year career, supporting inclining and drydocking of CVNs, LHDs, tugs, barges and yachts.
She is currently the principal engineer for Von Schmidt Maritime, a dry dock consulting company, where she provides third party planning for naval combatants related to stability and weight control for pierside and drydocking operations.
So, this one time, I was on a dry dock...
So, this one time, I was on a dry dock…Performing an operational inspection on a floating dry dock. With the dock at full submergence and holding for leak checks on the safety deck, the odor of burnt wire became overwhelming. Just as the source of smoke was found to be emanating from the high-voltage switchgear, the switchgear caught fire and exploded and the entire portside went dark except for the emergency lighting! The head electrician quickly determined that the high-voltage breaker had failed and rendered the portside panel entirely inoperable which also rendered the operational emergency diesel generator as useless. As the electrician worked to repair the system for operation, he found that one of the two spares was defective. While waiting for the repairs to be completed, the dock drafts began to visibly decrease. The only reasonable conclusion was that if the ballast pumps are inoperable then with the falling tide the dock had run aground! With repairs made and the dock pumped to light draft the internal ballast tanks were inspected for damage. The forward end of the dock had experienced minor damage with several localized indentations where the bottom plate had landed on loose rocks in the submergence pit. The lessons learned were to maintain situational awareness and check that spare equipment is operable on delivery. This also highlighted an interesting design anomaly-while many systems such as the ballast system have redundancies, there are some systems such as the high-voltage gear that may become single points of failure. A rigorous assessment should be made to determine if your dock system has any single points of failure and develop an action plan.
Next edition:
✅ Steel Eating Bacteria (Yes, seriously, it is a very real problem for everyone.)
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📩 Reach out to Wally at wally@tritondrydock.com—we’re looking forward to hearing from you!
Disclosure: Waleed Sayed, P.E. is a co-author of “ASCE Manuals and Reports on Engineering Practice No. 121, Safe Operation and Maintenance of Dry Dock Facilities” and a co-author and voting member of “ASCE/COPRI Standard 77-22, Dry Dock Standard”. Mr. Sayed is not compensated for presenting any information related to these publications. This publication was developed and produced without any assistance from Artificial Intelligence (AI).
Disclaimer: The information provided in this publication is general in nature and not prescriptive to any specific dry dock facility. Always consult a qualified professional when developing any site-specific plan.
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