R o l l - O n / R o l l - O f f And Container Carriers
A N e w Concept In M a r i n e Transport Is Seeded Only In Times Of Economic U p h e a v a l And Bears Fruit Only If It Is A d a p t a b l e To Economics Of A C h a n g i n g Pattern The most c h a l l e n g i n g and unique problem the naval architect faces when developing the design of a new vessel is that of combining the best technical know-how with the best economic analyses, then adding a bit of magic forecasting and talent.
From the technical know-how of the past dozen years or so, many specialized vessels have evolved. If one includes in a comparison the tankers and bulkers and their many combinations, but excludes such unique vessels as passenger and cruise ships, one can perhaps distinguish the following basic types of cargo ships: 1. LASH, SEABEE or barge vessels of different types.
2. Container and pallet ships which move cargo to and from the ship "over the rail." 3. Ferries, train carriers, auto carriers and roll-on roll-offs which transport or allow movable and wheeled vehicles to carry cargo to and from them.
4. B r e a k b u l k cargo carriers which may carry any cargo, including containers and wheeled vehicles, by utilizing self-contained suitable lifting equipment and moving all cargo over the rail.
5. B u l k e r s , tankers, etc. designed to carry uniform or nearly uniform goods in quantities and in bulk.
The first three types fall into the category of what the authors would call specialized types of ships. Historically, the oldest type of these specialized carriers must be the ro ro vessel.
The container vessel, on the other hand, was slowly emerging in the maritime arena in the 1950s.
The 1960s saw its emergence in the more competitive international trades.
Somewhat later, but in an almost parallel development, LASHtype vessels were developed for special routes, carrying non-selfpropelled barges.
Meanwhile, the ro/ro vessel was slowly emerging. Ferries in some parts of the world began carrying more than passenger vehicles and started looking at heavier cargo and trucking as a paying proposition. Figure 1 shows an artist's impression of a modern deepsea ro ro, clearly indicating cargo access and transfer equipment onboard.
A ro ro vessel is not the answer to all problems and in many cases the adaptability of the ro ro to a specific area or service may not be clear-cut and may be weighed one way or another by many parameters and special situations.
Design Parameters It may be worthwhile to consider some design philosophies and parameters in the selection of a ro ro and container carrier.
Basically, "a horizontally wide open" vessel is desired. No transversal obstructions in the form of bulkheads can really be tolerated in the main cargo spaces, and pillars or other deck supports must be kept to a minimum. In this respect, it becomes obvious that, below the freeboard deck, a double-skin construction must be utilized for strength as well as for damaged stability reasons.
A stern ramp is a necessity. It must suit the requirements of the trade as much as possible, without l i m i t i n g the utilization of the ramp or vessel too much. In larger ships, a ramp that can be operated in at least two directions is the minimum acceptable. A slewing ramp, which allows operation in three directions is the most desirable but may be prohibitive in cost, Figure 2.
Containers must be carried in all decks. The standard unit, known as the TEU (20-foot equiv- alent) is the basis of all studies, but 40-foot boxes must not be disregarded.
The movement of containers over the stern ramps of ro/ro/container vessels is done in several forms. TEUs are moved in an athwartships attitude by large forklift trucks or they are placed, several together, on low "bodies" in systems such as MAFI and LUF. Forty-footers are moved on truck bogies, MAFI or LUF units, or with shore cranes over the rail on accessible decks. The use of specialized bogies is cumbersome and expensive, requires special tractors that are not always available, and severely limits inclination of ramps within and without the vessel. It is therefore felt that TEUs can move by forklift trucks and 40-footers should be loaded and discharged by shore cranes.
Whenever a 40-footer is utilized in quantity, it usually means sufficient facilities ashore are available.
The odd 40-footer moving in and out of undeveloped ports can still be handled by a truck bogie and stowed inside the vessel by a forklift with a top spreader.
Some of the specific design parameters for a ro/ro/container carrier are: Stern ramps and internal ramps: The gradient should be no more than 1 to 7 and with approach slopes on both ends of about 1 to 9. A width of at least 7 meters will allow athwartships carriage of TEUs and double-lane truck traffic. A quarter stern ramp will have to be wider at the entry to the vessel to allow unimpeded movement of trucking without backing and filling for turns. Axle loads of about 65 tons for forklifts and 45 tons for trailer trucks must be allowed. Total loads per 12.19-meter-long unit is about 80 tons. The tire print pressures are 12 kilograms/square centimeter.
The maximum permissible load on the quay (fully laden ramp) is limited to 2 tons/square meter.
Heights must allow clear passage of the highest vehicle expected, keeping in mind movement envelopes of tractors and bodies. The tidal ranges for stern ramps is from plus 4.0 to minus 2.5 meters.
Stern ramps of a minimum twoway utilization, preferably threeway, are recommended. Internal ramps should preferably be of the movable type to conserve cargo space, except perhaps in very large vessels.
Stern doors: Stern doors must have a clear height of at least the maximum expected for any vehicle plus the envelope of the body when passing through the maximum gradient of the ramp. Stern door width should be somewhat more than the width of the ramp and they should, of course, be watertight.
As both stern ramps and stern doors are, in many cases, the only shore access equipment onboard oceangoing ro/ros, it is imperative that alternative means of opening or closing them be provided.
Elevators: E l e v a t o r s should have minimum lifting capacities of 80 tons in large ro/ros and no less than 40 tons in any ro ro except the smallest ones. They should not reduce clear heights at any deck and, if flaps are used for their loading approaches, vehicle movement envelopes and slope limitations should be observed.
Elevator lengths should be about 18 meters. If the vessel is expected to trade heavily in the European Economic Community area and is to often carry rigid trucks with trailers, then their length should be 18.5 meters to accommodate this type of vehicle.
Widths should be at least sufficient to accommodate the width of a forklift truck (3.20 meters).
They should be capable of loading from one side as well as from front or back to allow placing of containers on them by forklift trucks. Axle weights should be equivalent to the maximum axle weight of the decks. Speeds should be about 7 meters per minute for normal loads, with minimum 4 meters per minute for maximum all-up capacity. If an elevator is the only means of transporting cargo to and from a deck, alternative means of operation must be considered.
Car decks: Car decks should be stowable to the overhead and lockable with a minimum amount of lost space. Heights under stowed car decks should be sufficient for stowing two 8-foot 6-inch TEUs with forklifts, and under lowered car decks enough to allow the unimpeded passage of a 4.11-meter-high truck. Space between car deck and overhead, when lowered, should be minimum of 1.7 meters and possible 1.85 meters to allow small truck stowage.
Tie-down points should be spaced half a meter apart. Deflection of car decks, when loaded, must be considered. Finally, cardecks should be in suitable panel sizes and port and starboard sections.
Each section and panel should be independently lowerable or hoistable.
Decks: Decks obviously must be designed to withstand the maximum load (axle and unit) expected to travel over them. All decks should be capable of supporting a forklift truck carrying a fully laden TEU (high cubage), and deck heights must be for two high-cubage containers, plus stacking cones and quick-locking devices between containers, plus lifting clearance for a forklift truck with side or front spreaders lifting a TEU on top of another, both of the 8-foot 6-inch type.
Decks should also be equipped at regular intervals with tie-down devices for trucks and wheeled cargoes (minimum four per side of a 12.19-meter-long body) placed in line between lanes. Lanes are usually assumed to be 2.9-meters wide, allowing a clearance of 200 millimeters per side per truck.
F r o n t and back clearances of 12.19-meter bodies or truck unit (15 to 18-meter total length) is usually 100 millimeters each end.
Hatch covers: Hatch covers are another cargo access equipment of an oceangoing ro, ro ship. The uppermost deck must be fitted with hatch covers that are watertight and flush with the deck.
Pontoon covers are the most logical answer as they can be lifted with shore cranes that would lift containers, but hydraulic cleating would be necessary to minimize releasing and stowing time. Sizes of covers must be such as to allow unhindered vertical loading of containers 40-feet long and a multiple (plus clearance) of 8-feet in width. Strength of the covers must be the same as the rest of the deck.
There are, of course, many other parameters and design philosophies to be considered and each study will have an individual character of its own, molded around the trade route considered, the size of the vessel contemplated, and the type and amount of cargo which the original studies indicated to be available.
Cargo transfer equipment: Having arrived in very general terms at the "optimum" size of vessel required for the route and having established the basic factors, parameters and design philosophies, the naval architect must now decide on the number and type of ro ro equipment and other cargo access equipment that is to be incorporated in the design. At this point, it may be worthwhile to call in for consultation the experts of the trade and listen attentively to the advice they can give.
Maneuverability: The oddity of the lines of a ro/ro/containership creates unusual results in turning circle, crash stop, zigzag, and maneuvering.
Good maneuvering demands the incorporation of a bow thruster(s).
Some designers also favor the inclusion of a stern thruster. The authors believe that machinery rooms of these vessels are crowded enough without such additions, which, if controllable-pitch propellers are used as main propulsion, would have a doubtful degree of utilization. The authors feel that the inclusion of controllable- pitch propellers is almost a must.
Shallow-water maneuvering and speed characteristics are expected to be affected by stern and run aft flatness, but no tests have been conducted, and operational experience is insufficient to establish the degree of afterbody shape influence.
Rudder areas must be increased over conventional cargo vessel areas to compensate for these lower than standard maneuvering characteristics. A t o t a l rudder area of 1.65 percent of immersed underwater lateral area at scantling draft should be sufficient.
Finally, it is true that a vessel which is over-complicated relative to the technical environment in which she is expected to work represents a poor investment. The designers' constant aim should be to obtain the least expensive ship in the long run and the one that would bring the best secondhand price. This means maximizing simplicity and reliability, compatible with fitness for the purpose intended.
Other stories from June 1980 issue
- L i t e r a t u r e A v a i l a b l e On Schoellhorn-Albrecht Capstans, Deck Fittings page: 4
- $18-Million Drill Rig Contract Awarded To Ingalls Shipbuilding page: 4
- Seminar O n Shipping F r a u d Prevention Slated For N e w York June 2 6 - 27 page: 6
- Ed w a r d Kaune To Be G e n e r a l M a n a g e r Of Todd-San Francisco page: 6
- Brochure Available From AAT Communications On Wesmar Products page: 7
- Miami Car/Passenger Ferries Designed By Nickum & Spaulding page: 8
- E.K. Arndt Discusses Fuel Conservation At Riverman's Conference page: 8
- Atco Marine Appointed U.S. Agent For Peabody Inert Gas Systems page: 8
- Blount Marine Delivers Offshore Supply Vessel page: 10
- Norshipco Appoints Two N ew Officers, Promotes Five Others page: 10
- Literature A v a i l a b l e On C r a n e Packing's N ew Package Seal Design page: 10
- Gotaverken Signs Contract For $85-Million Semisubmersible page: 10
- Bulk Carrier Delivered By Naikai Zosen Setoda Yard page: 11
- R o l l - O n / R o l l - O f f And Container Carriers page: 12
- Hitachi Awarded $13-Million Contract For Diesel Conversion page: 12
- Levingston Launches U.S.-Flag Bulk Carrier 'Pride Of Texas' page: 12
- Shipbuilding Technology Transfer Discussed By New York SNAME page: 12
- Mini-Tanker 'Dagwood' Delivered By Delaware Marine Shipyard page: 14
- Brochure Available On Columbia Offshore Technical Services Ltd. page: 14
- Executive Changes At O h i o Barge Line And A f f i l i a t e d Companies page: 16
- Floating Drydock Delivered By St. Augustine Trawlers page: 16
- D.M. Surgenor Named VP/General Manager Of Nickum & Spaulding page: 16
- $ 1 9 5 . 4 - M i i l i o n Contract For Three Frigates A w a r d e d To Bath Y a rd page: 17
- A $lS5.4-miIlion contract for c o n s t r u c t i o n of three FFG-7 class guided-missile frigates was awarded by the U.S. Navy recently to Bath Iron Works Corporation, a Congoleum company. The award raises to 16 the. number of the versatile s page: 18
- d m i r a l Kidd Guest Speaker At H a m p t o n Roads SNAME M e e t i ng page: 18
- Passenger/Supply Vessel Delivered By Mississippi Marine page: 18
- Ray Tsuneyoshi Named Vice President For Pacific Towboat page: 18
- GE Wins $11-Million Spanish Ship Control System Contract page: 20
- Bell-Halter To Build Four SES 'Dashboats' For Command Marine page: 21
- Bruce McAllister Named Deputy To Assistant Secretary Of Commerce For Maritime Affairs page: 22
- Brochure Available On 'Sea Fence' Oil Containment Boom page: 22
- Promet Y a r d In Singapore Launches Jackup Barge page: 23
- Zesco W i l l Represent Camar Inert Gas Systems Division page: 23
- R o w a n To P u r c h a se T w o ' G o r i l l a ' Rigs F r o m M a r a t h on page: 24
- Davie Will Build Two Drill Rigs At Total Cost Of $70 Million page: 24
- New Pall Filter Assembly Is Bi-Directional— Literature Available page: 24
- Three N e w VPs A n d Three Promotions Announced By Halter M a r i ne page: 26
- C r o w l e y M a r i t i me Announces Three N ew M a r k e t i n g Appointments page: 26
- McDermott And Dominion Bridge To Form Joint Venture In Canada page: 26
- Executive Changes Announced At Stanwick page: 26
- New Worthington Pumps Feature Energy Savings —Literature Available page: 26
- Propulsion System For Product Carriers Discussed At P h i l a d e l p h i a SNAME page: 28
- Coast G u a r d Sets Up N e w N a v i g a t i o n Office page: 28
- $2.34-Million Navy Contract Awarded To Sperry Division page: 28
- Literature Available On National Marine Service Master Clock System page: 28
- N e w Low-Stretch Rope Announced By S a m s o n - L i t e r a t u r e A v a i l a b le page: 30
- G.T. F l a n a g a n N a m ed N o r f o l k General M a n a g er For McAllister Bros. page: 30
- Harbor Supply Vessel Completed By Delaware Marine page: 30
- ASNE Delaware Valley Section Hears Paper On Large Gas Turbines page: 30
- McDermott S.E. Asia Subsidiaries Receive $ 6 0 M i l l i o n In Contracts page: 33
- McAllister Begins New Container Feeder Service At Baltimore page: 34
- Auxiliary Oiler For U.S. Navy Christened At Avondale Shipyards page: 34
- Ronald L. Stone Named To Maritime Aids Post page: 36
- MARCO Christens Its First Refrigerated Seawater Trawler page: 36
- Wall Shipyard Completes Custom Sand Barge For RJM page: 36
- Admiral Edwards Receives Shepheard Safety Award page: 39
- FMC Yard Lays Keel For Puget Sound Lines Barge page: 40
- McDermott Shipyard G r o u p Expands Into Mississippi page: 40
- K.K. George A p p o i n t ed O p e r a t i o n s Comptroller At Bethlehem SB Div. page: 40
- F.T. Shaver Appointed Washington Director For Sun Ship page: 40
- M a r a t h o n M a r i n e A w a r ds Contracts For 2 Barges —Will Purchase 2 Tugs page: 42
- Shell Literature Details Benefits Of MVI Lube Oils In Marine Diesels page: 42
- New Garlock Bulletin Presents Wide Variety Of Sealing Devices page: 42
- Canadian And U.K. Companies Form Joint Venture page: 43
- New Control Valve Introduced By Leslie —Literature Available page: 43
- M a r A d Approves Title XI C o v e r i n g $ 3 6 - M i l l i on Conversion Of 'Lurline' page: 44
- M a r i n e Transmission Bulletins A v a i l a b le From T w i n Disc page: 44
- Blount Marine To Build Mini- Liner For Explorer Cruises page: 44
- Advanced Gas Carrier Launched By Moss Rosenberg page: 44
- N e w Drydock Added At McDermott Yard page: 45
- R.H. Cleary To Head N e w York Operations For Systems Engineering page: 45
- More Offshore Orders For Gas Turbines Awarded To Rolls-Royce page: 46
- Drill Rig Commissioned At Bethlehem-Beaumont page: 47
- Neville Jordan To Manage Magnavox London Operation page: 47
- New Phoenix Dispenser Protects Welding Rods- Literature Available page: 47
- NASSCO Will Build Six Tankers At Total Cost Of $ 3 0 0 M i l l i on page: 48
- Robert C. Engram Joins Ryan-Wals h Stevedoring As Vice President page: 48
- $ 2 . 5 - M i l l i o n Expansion Planned For Cargo Carriers' Barge Yard page: 50
- Literature Available On Peabody Holmes Limited Inert Gas Systems page: 50
- W.A. Snell Appointed To Marketing Staff At J.J. Henry Company page: 51
- Senator Daniel Inouye Named 1980 Recipient Of AOTOS Award page: 51
- Port Of A l b a n y A w a r ds $ 5 . 5 - M i l l i o n Contract page: 52
- A l a n Hobbs Joins I M O D C O ' s London Staff page: 52
- J.R. McKenzie Elected Executive VP At SCNO Barge Lines page: 53
- N e w Corporation Formed By Halter M a r i n e And Bell Aerospace Textron page: 53
- F.L. Hamons A p p o i n t ed To H e a d M a r y l a nd Port Development page: 56
- B&W Licenses Y a rd In U r u g u a y To Build Stern Trawlers page: 56
- McGoidrick Elected To Board Of Directors At Barber Steamship page: 57
- Federal Barge Announces Four Executive Promotions page: 58
- Fifth N a v y LHA Commissioned At I n g a l l s S h i p b u i l d i n g Y a rd page: 59
- Crew/Supply Vessel Delivered By Progressive Shipbuilders page: 60
- SNAME Chesapeake Section Examines Propeller Design page: 60
- P.T. V e l i o t i s Elected To Board Of Directors At General Dynamics page: 61
- Ron H. W r i g h t N a m ed V P - E n g i n e e r i n g For Sperry Gyroscope page: 61
- USCG A w a r d s Contract To O f f s h o r e Devices For O i l Spill Recovery System page: 62
- Derby N a m e d M a r k e t i ng M a n a g e r For Crowley's C a r i b b e a n Division page: 62
- Four Assistant VPs N a m e d By I n t e r n a t i o n al M a r i n e Coatings page: 62