Page 50: of Maritime Reporter Magazine (July 2003)
Dry Dock Structural Integrity with Computers
By Jonathan M. Ross, P.E.
Overloaded dry docks are not a pretty picture. They crack, buckle, flood, sink, damage the ships they are trying to lift - and sometimes even cause accidental deaths. Dry dock accidents are not common, but they do happen, usually resulting in dramatic photographs and disastrous physical and financial consequences.
With past docking failures in mind, prudent dry dock operators strive to avoid overloading, normally through a set of manual calculations, but in certain cases through more sophisticated methods.
A case in point is the AFDL-23 ADEPT, a rigid, one- piece. welded steel, floating dry dock that was built during WWII (principal particulars of the dock are pre- sented in Table 1).
Table 1 - ADEPT Principal Particulars
Length, (o.a.) 288 ft.
Width, (o.a.) 72 ft. (21.9 m)
Depth to top deck 34 ft. (10.3 m)
Depth of pontoon at centerline 9 ft. (2.7 m)
Pontoon deek crown 0.3 ft. (0.09 m)
Lightship 1.275 LT
Certified lifting capacity 1.777 LT
Maximum allowable keel load 10.47 LT/ft.
Throughout the last 50 years, corrosion has caused structural wastage throughout the dock with some structure being renewed with plating and stiffeners that were not in accordance with the dock's plans. Other modifications to the dock include two cranes and a hydraulic power pack mounted to the starboard wing wall (half-inch plating was added to increase deck strength). Also, the original diesel generators and their associated equipment have been removed. ADEPT is leased from the Navy by Gulf Copper Ship Repair,
Inc.. and is located at Aransas Pass (Inglesidel. Texas.
VSTEP Allows "Walk Through" in Planning
VSTEP launched its latest virtual walk-through technol- ogy to visualize new vessels and optimize the design process. The launch followed successful pilot projects with leading shipyards and opera- tors. Circle 88 on Reader Service Card
AutoShip Releases Production Manager
Autoship Systems released Production Manager, a major component of Autostructure. Production
Manager functions include: part subdivision; weld shrinkage compensation; plate nesting; extrusion nest- ing; stock definition; inventory management; remnant management; part tracking. Drawings are exported to
AutoCAD via a programming interface. Both input and computational results are incorporated in the system database. If a part is nested and then changed in the design program, the nesting is flagged as invalid.
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DNV Software Debuts Hull Life Cycle Manager
DNV Software announced Hull Life Cycle Manager (HULC), a class independent software solution based 52 "We use ADEPT to dock Navy minesweeper and mine counter measure Ships - MHCs and MCMs." says Gulf
Copper Dockmaster. Jim Booker. "One of the many requirements included in our Facility Certification
Report is to operate the dry dock within the allowable deflection limits, so our primary concern is always to adhere to NAVSEA operational limits." Gazing at the dock, placid at its pier-side mooring, he continues. "This dock grounded in Guam during a typhoon in the 1970s, and after the repairs, it had a permanent sag on the starboard side. Unfortunately, the dimensional uncertainties of that sag prevented us from knowing what our limiting longitudinal deflection readings should be. We were getting readings of 1.5 in., and the
Navy limit was only 0.8 inches. The block loads seemed okay, and the dock wasn't breaking, but our instruments were telling us we were way out of spec.
We were uncomfortable, and so was our customer. We needed answers."
To find those answers, Gulf Copper turned to Anteon
Corporation's Proteus Engineering Division, and its structural design, analysis and optimization program.
MAESTRO. Kevin Stone, senior principal naval architect at Proteus noted. "MAESTRO is well respect- ed by the Navy. It's been used on lots of combatants on new Microsoft technology for managing inspec- tions and capturing detailed hull condition data consis- tently for the entire fleet. HULC is designed provide transparency and efficiency in administration of inspection routines.The program is due out 3Q 2003.
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Deltamarin Joins Safety at Sea, Markku Kauriala
Deltamarin has joined forces with Safety at Sea Ltd. from Glasgow and Fire Engineering Consultants
Markku Kauriala Ltd. from Turku to provide a variety of services to the shipping and shipbuilding industry.
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HVAC Featured In ShipConstructor2004
Scheduled for a 3Q 2003 release, a major revision of the 3-D product modeling software for shipbuilding and offshore platforms from Albacore Research Ltd..
ShipConstructor2004, will include a full HVAC mod- ule. HVAC is a fully integrated member of the
ShipConstructor suite of Structure, Automatic and
Manual Nest. NC Code generation. Outfit. Pipe.
Fairing, and Lofting tools. To facilitate automatic report generation. HVAC makes full use of
ShipConstructor's SQL Server product database.
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MAESTRO image of ADEPT onto his computer screen. "MAESTRO can automatically evaluate 25 different stress and buckling failure modes - that's unique to this program." Stone's MAESTRO model of ADEPT considered plate and stiffener corrosion of pontoon deck, bottom plate, side shell, and wing tanks.
The analysis showed that the dock structure is satisfac- tory for MHC and MCM dockings, with longitudinal deflections (adjusted to take into account the perma- nent sag) of 0.039 and 0.170 inches, respectively.
MAESTRO was also exercised to determine the maxi- mum safe load for the dock. Figure 1 shows the results, which indicate a limit of longitudinal deflec- tion (again, adjusted for the permanent sag) of 1.27 inches with a 1.7 factor of safety against stresses of 20.000 psi and a 1.25 factor of safety against buckling.
Proteus recommended an operational limit of 1.25 in. for longitudinal deflection.
Both Gulf Copper and the Navy concurred with the
MAESTRO results, and are now confident in the abil- ity of ADEPT to safely dock Navy minesweepers.
About the Author
Jonathan M. Ross. P.E.. is Director of Engineering at
Anteon Corporation. Proteus Engineering Division.
Reference "Analysis of the Maximum Allowable Deflection of the "Adept" (AFDL-23)." Prepared for Gulf Copper Ship
Repair. Inc. by Anteon Corporation, Proteus Engineering
Division, March 22. 2001.
SENER Upgrades FORAN
SENER has partnered with think3. Inc., a global provider of integrated product development solutions, to incorporate its technology in order to improve and upgrade its own CAD/CAM software FORAN. think3 technology will enable SENER customers to reduce the time-to-market of new products and speed up sig- nificantly the product development cycle by allowing the full integration of 2D-3D and PDM.
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Neilsoft Outfit Steel Module Reduces Design Time
The Neilsoft Outfit Steel
Module is a new modeling tool for the Tribon M2 Shipbuilding system enabling designers to easily, quickly and accurately create and place outfit steel objects into the Tribon Product
Information Model (Tribon PIM). The outfit steel objects available are Walkways, Ladders, Staircases,
Equipment Foundations and Masts. This module will be marketed and sold by Tribon Solutions. In fact, last
October, Tribon Solutions and Neilsoft signed a devel- oper co-operation agreement.
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