By Frank Lanier
Offshore Magazine (2005)
As successful anchoring is often viewed as something of a black art by many boaters, nothing quite compares with the satisfaction of picking up your own mooring buoy after a hard day’s sail, free from the hassles of dealing with heavy ground tackle or worries over midnight anchor dragging. Setting your own mooring buoy is common practice in many areas and for good reason as it allows maximum usage of protected waters, particularly those where construction of docks for slips isn’t practical.
Unless you’re lucky enough to own waterfront property, the first step in setting a permanent mooring buoy will likely be getting approval from the state, federal, or local entity in charge of the area you’d like to place it. Each will typically have regulations in place regarding construction and setting of moorings and while requirements will likely vary between them, here’s some general installation and maintenance basics that will help no matter where your mooring is located.
A typical mooring system consists of a pendant, buoy, riding chain, ground chain, various shackles and swivels, and finally some means of anchoring the whole system to the bottom. [see illustration below].
Illustration by Jan Adkins
Pendants can be constructed of most any type of rope, however braided polyester probably best meets the requirements of strength and resistance to both chafe and deterioration due to sunlight – elasticity (as in the case of selecting an anchor rode) isn’t an issue due to the pendant’s short length. Each mooring buoy should have dual pendants, one primary and one back-up or safety pendant. Both should be constructed of the same size and type of rope, with the safety pendant roughly 25% longer than the primary. Wire rope or cable should not be used, as they can saw through chocks or fairleads due to the motion of a moored vessel. Boaters sometimes use polypropylene or install a float in the pendant to make it easier to pick up, although some areas don’t allow floating pendants (to reduce the chances of fouled props).
Mooring floats normally consists of a white buoy with a horizontal blue band visible above the waterline, although vertical spars may be called for in some locations. Buoy selection is based on the buoyancy required to support the combined weight of all suspended mooring system components (pendant, riding chain, etc) – buoyancy provided should be around 50 to 100% greater than this total weight.
All mooring buoys should be labeled for identification purposes, either with the owner or vessel’s name, mooring permit number, intended use (as in the case of yacht club moorings for visiting boats labeled “Guest”), or whatever the controlling authority of the water your mooring is located in requires.
Both riding chain and ground chain are sized based on factors such as mooring location, vessel size, and often what is specified by the harbor master or whoever oversees the area you buoy is located. General requirements are that they be heavy enough to both provide minimal vessel movement with reduced scope and be of sufficient size to allow some wearing due to corrosion and abrasion without significant loss of strength. Because of this need for increased chain size, use of galvanized chain is good, but not a critical requirement – most of it will probably be worn off after a season or two anyway.
The key requirement of
remaining rode components (shackles, swivels, float through-bolt, etc)
they be sufficiently sized to meet the intended load you’ll be placing
SINGLE POINT MOORING SYSTEMS
Mooring systems are typically classified as either single point or double point. Single point systems (the focus of this article) provide a single point of attachment (i.e. one buoy and pendant), while double point systems provide both fore and aft mooring – two single point mooring systems set close enough that a vessel’s bow can be tied to one and stern to the other is a good example of this.
The most common single point mooring systems utilize either a mushroom anchor or a deadweight (such as a concrete sinker), although screw-type anchoring systems such as those offered by Helix® are also popular. “Star” moorings utilizing three patent anchors (Bruce, Danforth, etc) set 120 degrees apart (multiple anchor-single point mooring) may be another option in some cases. Each of the above has their own pros and cons, which when coupled with factors such as bottom composition, vessel size, location, etc, will help decide which anchoring system is best for your particular situation. Be forewarned that you may not have a choice in some areas, as many agencies dictate which types they’ll allow in the waters they oversee.
Mushroom anchors are well suited for clay and mud bottoms soft enough to allow the anchor to fully bury itself. Once set, they provide great holding power when subjected to a steady pull (due to both anchor weight and suction of the bottom soil) however it’s possible they may creep if subjected to sharp, repetitive jerks, although a well set mushroom will most likely not pull completely free.
Deadweight anchors can be anything from concrete sinkers to automobile engine blocks (with oil and other such contaminates removed, of course). Pros include cheaper cost and being able to use just about anything heavy at hand to make them, however a deadweight anchor’s biggest advantages are their ability to be used in seabeds where other anchors may have difficulty setting (packed sand, hard clay, etc) and the fact their holding power (unlike mushroom and patent anchors) is not significantly reduced if they begin to drag. Horizontal holding power (for concrete sinkers anyway) can be increased even more by casting rebar “fingers” into the sinker’s bottom to increase drag.
Deadweight anchor selection must be based on “immersed weight” rather than air weight – concrete’s immersed weight, for example, is roughly half of what it weights out of the water, which can translate to requirements for some substantially large anchors. A deadweight anchor will need to be roughly 10 times as heavy to do the same job as a comparable, well-set mushroom anchor. Sufficient scope is important in this regard for both deadweight and mushroom anchors, although not in the same way as for a standard anchor, the goal here being to reduce vertical lifting force rather than provide horizontal penetrating power. Typical recommendations call for providing between four to seven feet of rode per foot of maximum water depth (taking extreme high tides into consideration). You’ll also need to take a look at your vessel’s swing radius while moored, to prevent problems such as hitting nearby boats or possibly shallow water.
Screw type anchoring
just that – the mooring consists of a screw anchor (available in
sizes) that is literally screwed into the seabed.
Holding power is determined by the size and number of spirals
contains and seabed composition. The
holding power attributed to this type of mooring is impressive – Earl
states in his book “The Complete Book of Anchoring and Mooring (Second
edition)” that a properly set 150-pound screw anchor with a 1 ¼” shaft
exhibited holding power equivalent to a 40,000-pound concrete sinker.
Properly constructed mooring systems require relatively little maintenance, however regularly scheduled inspections are crucial. Shackles should be properly moused with stainless steel safety wired, pennants must be regularly checked for chafe and deterioration, and the mooring itself should be pulled annually for a complete inspection (or at least every two years).
During these annual inspections the entire mooring system should be laid out and checked for problems such as wear at connecting items (shackles, chain end links, swivels, etc) and rust or electrolysis damage. Some rust is unavoidable and not a big deal, but be sure to chip it off in various areas to ensure you have enough good metal left to hold everything together. Also, don’t paint the bottom of your mooring buoy floats with copper-based antifoulant paint, which may possibly cause problems with electrolysis.
Unless installing a permanent mooring buoy in private waters (and even then in some cases) the entity in control of the waters your mooring will be located – the town harbor master, marina manager, yacht club, etc – will generally provide you with information on both the type of mooring they require you to use, as well as the size of all components. These will most likely be based on your vessel’s size and whether the mooring is located in areas they consider to be well protected or those more exposed. Below is an example taken from a website for the Town of Chatham, MA.
Recommendations for permanent mooring design loads
available from the American Boat and Yacht Council (ABYC) http://www.abycinc.org/