This article is excerpted from the Hurricane Preparedness Guidelines for Georgia Marinas, originally published by the Marine Management Company under a grant from the federal National Oceanic and Atmospheric Administration (NOAA).
The manual includes a compilation of policies and practices that are used at marinas around the United States and are generally accepted throughout the marina industry. Much of the content was provided by college programs, state extension services, the international marine institute, private marinas, and from documents produced by marina managers
Design and construction of even the smallest marina is complex, multi-disciplinary and requires a number of considerations combined with a vast array of data requirements. Each facility is site specific, market specific, environment specific, and use specific.
This article is intended as a preliminary introduction to marina planning and design concepts related to significant storm events. This information shall be useful for new design professionals, marine product manufacturers, new or prospective marina owners and others who wish to become familiar with marina planning and design concepts

Basic Planning Considerations
▪ Develop and commit in writing to a specific severe weather operation policy. The design professional should be requested to provide cost/benefit trade-offs during the decision process.
▪ The marina design professional should use the best reasonably available technology and judgment to predict design loads that will actually be applied throughout the marina. The design return period on hurricanes should be balanced against the expected life of the marina, and compliance with local codes and ordinances. Keep in mind that codes are minimum design criteria and increased strength and reliability may be more economical in the long run.
▪ The recommended design period for hurricanes (wind and tidal surge) is normally 50 years (2% probability, in any given year) and 25 years (4% probability in any given year) should be considered the absolute minimum design period. This is true even if the expected life of the offshore facilities is less than 25 years. Operation plans that assume boats will leave the marina are detrimental and unrealistic. Even if boat owners were willing to remove their boats, they may be unable to get to their boats or they may be prevented from moving their boats due to severe weather or channel obstructions. If they do move their boats, passing transients may dock in the empty slips.
Design Factors to be Addressed
• Wind: Velocity, direction and duration are critically important in the design of dry stack facilities, and winds also apply forces to docked boats which translates into forces on docks and pilings and other anchor systems. Potential wind blown missiles include dock boxes, signs, dinghies, sheet metal panels from buildings, and all other unsecured loose objects. Navigation of vessels into or out of the marina or the use of marina equipment such as fork lifts may be severely restricted.
• Waves: Height and period are important because they determine the force on the dock system as well as on the land/water interface (either bulkheaded or riprapped shoreline). Waves affect not only boats moving into, out of or within the marina but may restrict movement of personnel on docked vessels and prevent access to or from vessels on either fixed or floating docks or swing moorings.
• Tides and storm surge: The combination of these provides the base elevation to which waves and required freeboard must be added. Begin with the level of high water (Mean Higher High Water, MHHW, is a good choice), and add the increased water level due to storm surge to get the basic starting water level. For example, a mean spring tide at Ocean City, Md. is +4.2 feet above Mean Low Water plus a 17-foot storm surge similar to that seen in Charleston during Hugo (1989) equates to +21.2 feet. For this extreme example a fixed, pile supported walkway or dock at an elevation of 21.2 feet would be level with the still water level and even 3.0 ft waves would create serious problems for individuals using the facility. In the case of a floating dock, the freeboard of the dock must be added to pile lengths just to keep the dock from floating away! The implications of the combined effects of tide and storm surge on landside facilities at the marina are obvious.
• Currents: Currents have the same effect on boats and docks as the wind except that the force is applied to the portion of the boat below the waterline. Currents may vary in both velocity and magnitude due to changing tides. During severe storm events, currents may carry a significant amount of large debris, which adds additional impact forces to boats and docks when they are struck.
• Soils: Soils must be tested by a licensed soils engineer to determine horizontal bearing capacity relative to the forces applied by wind forces on the boats and through the docks. One boring per 10,000 square feet of area may be sufficient but these must be taken in the fixed pile supported walkways and docks, vertical bearing capacity is required along with the vicinity of the piles offshore, not at an onshore location chosen simply for convenience. For ability of the pile to withstand the buoyant forces of a totally submerged dock system, soil borings must be deep enough to define the total strata that the piles penetrate, plus an additional 5 feet.
• Access: Access is of concern during storms for those desiring to leave the marina or seeking shelter within it. Access will be hindered by high, gusty winds, large irregular waves, and possibly strong currents carrying much debris. Harbor entrance channel widths should be at least 100 feet and even using these criteria movement into or out of the marina may be prevented by other boats sinking in the channel. Bridges may remain closed and may be inoperable after the storm.
Channel Entrance & Wave Attenuation
• Jetties and breakwaters: These aids to navigation may provide sheltered water while entering or leaving the area of the marina but the level of protection they afford and even the survivability of the structure itself may be in question, depending on the severity of the storm. To be of value during a severe hurricane the riprap or armor stone must be of sufficient size to protect the structure from the increased design wave height incurred during the storm and the height of the structure must be sufficient to provide the desired wave attenuation. Consider possible overtopping during the storm surge in defining the height of the structure.
• Wave attenuation: Additional wave attenuation may be required within the marina to maintain an acceptable climate for boaters to move about on their boats in preparation for the storm, especially if long period waves can approach the marina from the open sea by passing straight through the entrance channel.

Inner Harbor Structures
• Basin perimeter: All basin perimeters must be designed for the selected storm recurrence interval. Bulkheads designed by a licensed structural engineer should withstand the oncoming storm as well as remain intact during the receding tide without excessive scour of the backfill behind the bulkhead, which could cause failure of tiebacks and subsequent failure of the entire structure. The inclusion of bulkhead returns and good drainage through filter cloth and weepholes will reduce scour. As previously mentioned, a sloping armored perimeter has several advantages, including reduced reflection of wave energy, but it also requires additional space within the marina and rough surfaces may pose a hazard to boats.
• Fixed docks: The fixed docks must be designed for vertical and horizontal forces. All fixed structures must be designed to withstand upward vertical forces caused by total submersion of the structure and any connected appurtenances. Fixed docks and pile-supported walkways should use split pile caps bolted with double dip galvanized hardware. Pile caps spiked on to piles will disconnect from the piles when submerged due to uplift forces caused by the buoyancy of the decking, stringers, etc. Dock boxes shaped like polystyrene tubs and securely attached to the fixed walkways will provide additional buoyancy and apply an upward force to either separate the walkway from the pile or pull the pile out of the ground.
On fixed, pile supported structures, either a metal connector or adequate lap must be provided in butt and lap joints to prevent the joists from becoming dislodged from the joints. The beam joints should be staggered rather than locating all the joints in a line over the pile cap, which would then act like a hinge rather than a continuous beam. Connection hardware, such as cleats, must be adequately sized for the moored vessel and must be bolted through the dock using appropriately sized galvanized or stainless steel hardware.
• Floating docks: When floating docks are in the plans, they should be designed for full loading unless there are absolute assurances that the boats will be removed. The design must account for hurricane wind load and storm surge simultaneously with a Spring high tide. If the marina is adjacent to critical shipping lanes or vital installations that might be affected if slip the floating docks are damaged or dislodged and boats sunk, serious consideration should be given to increasing the design storm recurrence interval. Commercial dock systems may perform better than locally built, contractor constructed docks. In addition, the owner should be aware that the manufactured systems may also lend themselves to easier repair and reinstallation. Ancillary equipment (utilities, dock boxes, etc.) should be integrated into dock systems that will make hurricane preparation and recovery easier (e.g. removable power pedestals, dock boxes, gangways, etc.). Since most failures occur due to pile failures, a licensed professional should assure that the piles are of adequate diameter, have adequate penetration and are of adequate height to account for the high tide, storm surge, wave heights, and adequate freeboard for the dock. Connection hardware sized adequately for the moored vessel and bolted completely through the dock with galvanized or stainless steel hardware is essential.
• Moorings: If open moorings are used, both bow and stem moorings should be installed to keep boats properly oriented, reduce swing and provide an additional factor of safety. Proper inspection and preventive maintenance of swing moorings may be more difficult than for fixed or floating docks, but is absolutely essential.
• Gangways: High wind loads can make gangways fly horizontally and flap in the wind. The hinge connection on the gangway undergoes torsion and the gangway is subjected to racking forces. Unless gangways are disconnected, the waterside end may be forced above the floating docks and utilities trapped between the dock and the gangway. Utilities should be nested securely under the gangway with a loose loop connection at the bottom to allow movement where the gangway meets the floating dock. The floating dock may be crushed as well but increasing the dock offset may alleviate dock damage.
The gangway hinge should allow for torque from twisting and racking by the gangway during the storm. A better solution might be to put quick disconnect couplings on the utilities and the gangway and remove the gangways just before the storm arrives.
• Dry Stack facilities: The dry stack facilities must withstand the extreme wind forces exerted on the large but lightweight structure. Tremendous uplift forces are applied to the foundation. Failures begin as the metal skin on the sides and roof peel away leaving the remainder of the structure and the racks to independently withstand the wind loads. Special attention should be paid to uplift forces on the roof structure. Rack supported roof structures may require additional design analysis.
• Launch facilities: Launch facilities may become overburdened with boaters attempting to remove their boats during the inclement weather preceding the hurricane. The inclement weather may require extra time for tie downs and boaters may be shorthanded due to limited time available to get help before the impending storm. Therefore, extra staging areas may be required due to additional loading time. Marine travel lifts may also keep the launch ramp busy, and the inclement weather will hinder travel lift and forklift operations. Assume that all operations will be at about one-half normal speed during the period of inclement weather before the storm.
Marina Systems
• Fueling: Fuel pumps should be installed above the high-tide-plus-storm-surge elevation for the selected design storm and fuel tanks must be counter weighted sufficiently so that they will not rise if they become both empty and completely submerged in saturated soil.
• Sanitary system: Landside sanitary holding tanks must be designed and counter weighted so they will not float when empty and completely submerged. The cover should be bolted down during the storm to prevent escape of the sewage.
• Electric and communications: Transformers and utilities on floating docks will be destroyed when the docks are lost and associated items such as power pedestals, gas pumps, lights, pump-outs, dock boxes, etc. will also be damaged and lost. Transformers should be located on land whenever possible and the other items should be removed and stowed. Radio antennas should be designed to withstand the maximum wind velocities expected.
• Hazardous waste: Waste oil, antifreeze, and other hazardous waste should be designed to meet the local, state, and federal requirements. Storage areas should be designed to be above the floodplain.
• Trash and debris: Containers such as dumpsters should be well anchored and secured to prevent them from floating away and becoming hazards. They will be needed immediately after the storm.
Reprinted from Marine Construction Magazine, Issue II, 2024
