Single point moorings are often provided by port authorities and marina operators as a facility for visitors at locations where there is poor holding ground, deep water, insufficient slips at docks, or where there is a requirement to moor boats more densely than can be achieved using the yachts’ own anchors. In addition, at some locations, anchor damage to sensitive seabed ecology can be minimized by the provision of moorings. Finally, at some locations, visiting yachts are an important contributor to the economy. If these locations are exposed, the difficulties of anchoring or unsafe conditions means that many yachts will not visit unless secure moorings are provided.
There is a lack of clear guidance for several aspects of single point yacht moorings. Therefore, PIANC Working Group 168 (WG 168) was formed to provide guidelines for the design, installation and maintenance of these type of moorings to designers and operators.
The presentation will provide a description of the work performed by WG 168 and an overview of the guidelines, which focused on the following aspects of single point yacht moorings:
- Design Principles
- Type of Mooring Systems
- Components
- Design
- Installation
- Maintenance
- Case Studies
There are several types of yacht mooring systems but, regardless of type, all must be designed following similar design principles. These include functional, regulatory, environmental, constructability, operational, maintenance, and economic principles. The WG 168 reviewed these principles, and provided designers and operators with guidelines that would achieve designs that balance all these principles.
Single point yacht mooring systems such as catenary, conservation and trot systems are described and application areas discussed. In addition, to offer a perspective and alternative systems, two-point and pile mooring systems are also reviewed.
Mooring systems have several components and the capacity of the system is often limited by the resistance or ability to perform of one of its components. Anchors can drag; chain links, ropes, shackles and swivels can break; buoys can sink; biofouling can increase loads and corrosion of metal components that can weaken the system. WG 168 reviewed typical mooring systems components and provided descriptions of alternative designs, application areas, standards and materials.
Just like for design of any structure, the design of mooring system requires a basis for design. As is typical in marine infrastructure, the basis for design would include the characterization of the site from various perspectives such as bathymetry, bottom conditions, wind, waves, current and water levels. The basis for design would further include the definition of yacht parameters in terms of type (sailing or motor yacht) and the estimation of loads. WG 168 reviewed practical guidelines to characterize the site, from the collection of existing information and anecdotal evidence to detailed field investigations and numerical modeling, as well as simplified formulations for the estimation of loads. A description of the working principles of catenary and elastic moorings is included in the guidelines, along with methods for the estimation of mooring offsets and loads, and swing circles.
Just as important as design, are installation and maintenance. These would depend greatly on the type of mooring system and site conditions, contractor experience and equipment. The WG 168 guidelines describe the typical equipment and methodologies for installation, critical items for inspection and frequency to achieve an adequate maintenance of the system.
Finally, case studies that describe the implementation of the guidelines are presented.