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Mooring System Designs for Floats, Breakwaters, and Vessels

A mooring system is a network of structures or elements that secure a float, breakwater, or vessel in place. Mooring systems have also been called anchor systems because they typically involve the use of anchors. There are several types of mooring systems commonly used in the marine environment including rope - anchor systems, chain - anchor systems, timber pile sytems, and steel pile systems. Each application has a specific use, including benifits and drawbacks to be considered prior to deciding which mooring system is best suited for your harbour.

Types of Mooring Systems

Rope - Anchor

Rope and anchor mooring systems are typically used in waters deeper than 5 metres, estpecially in the marine environment where daily tidal fluctuations make mooring structures difficult. Rope anchor mooring systems are flexible and long lasting. These systems have been used to secure large scale marinas such as Rushbrook in Prince Rupert and the floating breakwaters in Lund and Cowichan Bay. Rope systems are subject to abrasion if care is not taken during installation and their is abuse from locals in the harbour. However, unlike chain, the lifespan of a rope - anchor mooring system is 10 times that of a chain mooring system, and can be installed without the use of heavy machinery in many cases.

Chain - Anchor

Chain and anchor mooring systems are typically used in waters deeper than 5 metres. Chain systems are ideal for senarios where draft adjacent to a float located in deep water is required. The chain will arch and achieve depth quicker than a rope mooring system due to the weight of the steel. There are several drawbacks with chain - anchor mooring systems. Most chain systems will only last up to 10 years before they require replacement, but many only last 5 years, due to corrosion and abrasion. The cost to install chain is also expensive due to the weight of the steel. These systems are also difficult to tension without expensive equipment. They also place excessive loading on the floats requiring more floatation.

Pilings

Pilings are typically used where the seabed will allow pile penetration and the water depth is shallow enough for pile drving. Piles offer secured moorage points that are better at holding floating structure in place, however, require maintenance of pile wells where abrasion occurs. In addition, the piles themselves require anodes if steel, or creosote if wood. If worn, timber piles may loose their creosote layer lending them suseptable to attach from marine borers. Timber and steel piles are very common in shallow waters around the world. Typically they are installed with a crane from a pile driving barge. Typicall costs are around $1,000 per pile.

Pile Design Resources

Prior to installation of a mooring system, proper permits must be secured. Typically agencies such as the Department of Fisheries and Oceans - Habitat Enhancement Branch will require a biophysical survey of the seabed to ensure that beds of eel grass or other regionally significant biological systems are impacted by the proposed works. In addition, for pile driving, pressure wave measurements are often required during environmental monitoring to ensure local fish are protected from pressure waves.