If commerce is “war by peaceful means,” as has been said, than many of the principles from this classic U.S. Army manual will ring true today.An excerpt from Port Construction and Repair, updated in 2013 from the 1990 edition.
Successful port construction requires careful planning based on detailed reconnaissance, which continues until actual occupation. Planning may appear complete before occupation, but last-minute factors may necessitate a major change in plans.
FACTORS INFLUENCING SEAPORT LOCATIONS
A seaport should lie near sheltered waters. Shelter comes in any of the following ways:
- A bay or river forms a natural location for a seaport.
- Engineers create shelter by increasing the length or height of natural formations, such as land arms, rocks, reefs, islands, or other barriers.
- Engineers build breakwaters or jetties as protection for the inner water.
PLANNING PRIOR TO OCCUPATION
Before occupying a port, planners must consider estimated logistical requirements and both the current and expected physical condition of the port to be occupied. Planning prior to occupation covers a long period of time. Operation orders then give construction assignments, facilities required, and target dates for development.
The theater commander must evaluate ports according to the possible quantity and nature of cargo and personnel they will handle. Often this phase of planning depends on the first reconnaissance. The commander examines previous plans critically in view of the physical condition of the port. Priorities in the operations order may change in light of the port’s actual physical condition. The commander coordinates indicated changes and their impact on logistics through Army engineer, transportation, and other command channels, as well as with naval units engaged in clearance, dredging, and other harbor projects. Planning and scheduling depend on meeting all immediate needs and making all work contribute toward meeting final requirements.
During final development, planning depends on a full knowledge of the theater-wide logistical situation. Planners study the relative value of rehabilitation and construction, and the value of specific facilities to the construction effort required. Selection of the best sites for development depends on need for dispersion, location of logistical requirements, time and effort needed to move construction units, locally available material, and civilian or prisoner- of-war labor. Similar factors determine the best development within a port.
STANDARDS FOR ESTIMATION
The following terms establish standards for estimation:
- Port capacity. The estimated amount of dry cargo, containerized cargo, and bulk and roll-off equipment. It is usually expressed in weight, measurement tons, or number of containers per day that can be discharged onto the available piers, wharves, quays, jetties, moles, and beaches of a port.
- Standard minimum width. The wharf width for deep-draft, non-contain ships using one-side discharge is 60 feet, or 90 feet for two-side discharge. Container ships require 80 feet, and lighterages either 35 or 42 feet.
- Minimum required depth below mean low water. The depth required by the draft of a ship. For deepdraft non-container ships, the minimum required depth is 30 feet. For high-speed container ships, it is 40 feet. Shallow-draft crafts require a minimum of 12 feet.
- Wharf systems. Wharves include any extensions built from shore to water of minimum required depth to provide direct contact for handling cargo between deep- or shallow-draft ships and shore. “Wharves” also include structures described as quays, piers, or marginal wharves.
Engineer responsibility. Port-capacity requirements are estimated by Headquarters, Transportation Command (TRANSCOM) or by the TASCOM ACS,M. The construction engineer usually makes an independent estimate of the capacity of the port under various alternative methods of construction, repair, or rehabilitation. This estimate is used to determine priorities for engineer projects. The person doing this estimate must understand how the capacity estimates of TRANSCOM and TASCOM work with respect to military loads. The engineer recommends schedules for repair and maintenance of port cranes and other equipment and facilities, roads and railways within the port area, and storage and marshaling areas.
Wharf facilities. Rehabilitation, construction materials, and plans affect wharf capacity.
Discharge rates. Port capacity estimates depend on the discharge rates of ships either at the wharf or in the stream. Priority goes to expedient methods that allow ships to discharge quickly. Construction coordinated with transportation units cuts interference with the discharge of ships.
Anchorage available. Sheltered anchorage allows for discharging cargo while deep-water wharves are constructed or repaired. Continuous lighter craft usage allows the following:
- Continuous dredging of the deep-water approach channel using the shallow-draft approach with discharge outside the dredging areas.
- Use of the shallow-draft parts of wharves while some of the deep-water wharves are under construction.
- Unloading the shallow-draft vessels over deepdraft wharves when removing obstructions that prevent deep-draft use
Other factors. Base periods of time, such as the 2-shift, 20-hour working day or a specified number of days in a month, allow engineers to consider bad physical conditions peculiar to the location in preparing time estimates. For example, they can estimate time needed in some harbors to work in ice during winter.
Extreme range of spring tides may bear upon work. Where heavy seasonal rains, snowfall, icing, severe winds, fog, and heat or cold exist along a coastline, engineers modify their estimates to allow for these conditions.
DETERMINATION OF WHARF REQUIREMENTS
Standard wharfage requirement estimates match only the specifications for non-container ships, but only an 80- by 900-foot wharf is sufficient to support the latest container vessels. Total estimated container wharfage is the basis for up-to-date wharf layout.
Characteristics. A quay (figure 3-1, (1), page 3-4) is a marginal wharf supported by either the shore itself or by solid fill. Quays are used in water with minimum required depths. A piled marginal quay is supported by shore bracing and piling. The linear feet at the face of the quay is the length of berth accommodations.
- Stability and bearing strength of the solid fill supports the load, especially when handling cargo in containers.
- Accessibility of the upshore work area.
- Use of surplus fill.
- Moving earth or other material to provide fill requires equipment and personnel.
- Berth length is limited to the length of the wharf face, unless mooring dolphins extend the usable length.
Characteristics. A square pier (see figure 3-1, (2)) has berth accommodations at the sides as well as at the face. It is supported by solid fill or piling. Usually the area of the deck is so great that it precludes all-pile construction. For this reason,
this type of pier is rarely adaptable for new construction. For linear feet of berthing space per 1,000 feet of shore front, see table 3-1, page 3-3.
- Solid fill offers stability and bearing strength.
- Upshore areas are accessible for storage and traffic circulation.
- Side berths add to berthing accommodations.
- Moving earth for fill requires equipment and personnel.
- Requirements for fill or piling are great compared to usable space on the deck.
- When on fill, the square pier changes the natural current system.
OFFSHORE MARGINAL WHARF SYSTEM
Characteristics. An offshore marginal wharf (figure 3-1, 8 and 9) is located offshore but parallel to the shoreline. Causeways are used to connect the wharf to the shore. The wharf provides deep-water berths at its outer face. Shallow-water berths often lie along the causeway section and shoreward face. The wharf is either floated or supported by piles or solid fill. Causeways are solid construction resting on piles or floating. U-type causeway and wharf arrangements allow truck traffic to circulate.
- The layout allows many construction methods. Navy pontoon gear normally supplies needed floating wharfage.
- Moorings for shallow-draft craft range along the sides of the causeway. When multiple causeways are used, a movable section can provide access to space(s) between causeways for mooring or unloading vessels of suitable draft.
- Along rocky shores, offshore construction is likely to save costs.
- If only a single causeway is available, unloading or traffic problems may occur.
- The large area of the wharf structure not tied to shore anchorages requires moorings that are not supported by the wharf structure.
Characteristics. The pier-and-slip system (figure 3-1, (3), (4), and (6)) provides alongside-berthing space perpendicular to the shore. Commercial ports generally use this system. The piers are long enough to accommodate the ships and wide enough to provide adequate working space for cargo handling. The slip should provide depth for the ships and width between two berthed ships at adjacent piers for floating cranes and other harbor craft and equipment. Piers are usually built on piles, but may have solid-fill mass support.
Pier construction is obviously impractical in water that is too deep for the available piling. If water depths cause large unsupported piling lengths, dump rock fill after the piles are driven.
- Advantages Offers more linear feet of berthing for a given length of shoreline.
- Pier work space is directly accessible from the shore area
- Limited space between piers causes dense navigational traffic in and around the piers.
- Piers are an encroachment on the restricted waterway.
- Pier- or bulkhead-limit may affect the line set to ensure adequate channels or anchorage.
ANGLED PIER-AND-SLIP SYSTEM
Characteristics. The angled pier-and-slip system (figure 3-1, (5) and (7), page 3-4) provide alongside berthing, but the piers are not placed at right angles to the shore. This type of system is frequently used where strong currents or strong prevailing winds would adversely affect perpendicular piers.
- This layout fits narrow shorelines where the perpendicular- pier layout cannot be used or where the pier system is located on a narrow waterway, with insufficient room for a ship to make a 90-degree turn to enter the slip.
- With normal current and wind conditions and adequate approaches, ships berth and moor more readily in slips with a 90-degree layout.
- Construction is difficult and requires more material
- Abnormal currents or winds make the use of tugs critical.
Characteristics. The finger-pier (figure 3-1, (10), page 3-4), like the pier-and-slip system, provides alongside berthing space. If built wide enough, finger-piers can accommodate vessels on each side. A simple causeway of pile construction or solid fill, or a floating causeway is used to connect the pier to the shore.
- Adaptable to many types of construction. It may be built using piles, floating wharfage, or the steelspud or spud-type barge.
- Shallow-draft craft can discharge onto the causeway.
- Pier can serve in marshes and mud flats
- Where tides fluctuate, the finger-pier causeway can extend out into deeper water to ensure an adequate depth, regardless of the tide.
- The single causeway may result in unloading and traffic problems.
- Separate moorings, which are not supported by the wharf structure, may be required for mooring ships at the wharf.
Lighter wharves and basins. Lighters are shallow- draft craft used for loading or unloading larger vessels. They may be either self-propelled or towed. The controlling depth for lighter crafts is the same as that of the tugs which use them, usually 12 feet. However, at lighter wharves, extremely shallow water or breaching on the soft bottom is possible. Self-propelled lighters, especially those with outboard engines, need more depth than their actual draft to prevent fouling of their cooling systems while navigating over the soft bottoms. Required slip width is based on the beam of the craft and navigational requirements.
Floating wharves, typically fabricated from Navy pontoon gear, can be assembled in almost any size layout. Use hinged joints to avoid long, rigid structures. A typical floating wharf for a single non-container cargo ship has a 43- by 431-foot deck with two or more pontoon bridge approaches. Existing designs and equipment specifications will require modification and strengthening to support container operations.
- Floating wharves can be moored in water that is too deep for pile driving. They are good in areas with very high (30 feet or more) tides.
- Pontoon cube bridges or sections can be assembled elsewhere and towed into place, reducing in-port assembly time.
- These wharves permit quick assembly, movement, and disassembly. Piecemeal disassembly during replacement by a fixed wharf is also possible.
- Initially light maintenance requirements may later become heavy because of weakened connections and corrosive effects of salt water.
- Equipment will not support the large deck loads of containers
- Operations using floating wharves must stop during high seas.
Jetties, breakwaters, and moles. Jetties and breakwaters are usually designed and located primarily to protect the harbor and its channels. When favorably located and furnished with a vertical face on the protected side, both structures may serve as tie-ups for ships and, when surfaced, as wharves. When used this way, a breakwater is called a mole.
Bulk petroleum handling facilities. Facilities consist of wharves, dolphin moorings, ship-to-shore pipelines, and shore pumping stations and storage tanks. For fire protection, these facilities must be a safe distance from other structures and storage areas. Terrain barriers, ground slopes, and current charts are used to keep gasoline from flowing overland or floating on water. If the port is small and congested, an outside location at a protected cover or roadstead is preferable. Coordination with the Quartermaster Corps, Transportation Corps, and Navy helps in selecting locations.
Marine railways and graving docks. Engineers allocate space not needed for wharfage navigation, or onshore facilities to provide for marine railways. They allow space for the marine railway from the piling that marks the deep-water end of the railway to the winch, or other equipment, handling the cable on shore.
• A marine railway consists of a platform with a cradle. It operates on a railway from deep water to shallow water or dry land. Small vessels are secured to the cradle on the platform and hauled ashore. • A graving dock is a basin into which a vessel is floated. The basin is then emptied to do work on the underwater part of the hull. After completion of the work, the basin is flooded and the vessel floats back into service.
Republished from Marine Construction Magazine Issue IV, 2022