Unlike ordinary anchoring, a permanent mooring system is designed for leaving your boat unattended for long intervals. A mooring, in many cases, is the safest and most cost-effective way to leave a boat in the water, whether riding out a storm or leaving it until next weekend. The following is a guide to building your own mooring; it provides an outline of common practices, including recommendations from maritime authorities such as Chapman's and various harbormasters. Whenever installing a mooring, it is absolutely necessary to first check with the local harbormaster. Before purchasing gear, find out the ground tackle requirements in your harbor.
The anchor weight and type is crucial to holding strength on any mooring. The more exposed a mooring site, the rougher it will be during storms. For exposed moorings go supersize. Exposure to open sea or fetch allows wave and wind strength to build enough force to drag gear around. On the other hand, protected inlets require less hefty ground tackle. In general, permanent moorings are designed with less scope than traditional anchors, thus forming a tighter swing radius. The compromise, shortened scope, means a more effective anchor is required. Therefore, a permanent mooring anchor must be significantly heavier than your everyday use anchor. Mooring scope from anchor to end of pennant should be at minimum 3 times the depth of water at highest tides. Your local harbormasters will specify type and weight of approved mooring anchors in the harbor.
The following is an example taken from Town of Chatham, MA, mooring regulations. Notice the difference in tackle size between protected and exposed mooring fields.
In general, a mushroom anchor is the most common, great for softer seabeds. As the mushroom anchor digs in, it buries and creates suction. For effective holding power, the mushroom must remain embedded in mud or sand, otherwise storms with wind direction opposite the prevailing will cause the anchor to "spin out" and drag. For estimating the mushroom weight, multiply the boat length by 5-10 times as a good rule of thumb. On hard or rocky bottoms, heavy dead weight anchors such as massive concrete blocks are the norm. Since a blocks holding power relies on shear weight, dead weight anchors must be significantly heavier than mushroom style. Density is also a consideration, more concrete is needed than comparably denser cast iron for equivalent weight in water. Block style moorings are set with a barge and crane. A third option is the Pyramid anchor, for sand or hard bottoms.
An approved professional mooring installer can set the whole rig for you for a fee. Most towns have a list of approved installers in the area. Professionals installers can also offer more than just the traditional anchors. Helical screws driven into sand bottom seabed with a hydraulic tool have superior holding power. Pioneered by oil rigs decades ago, sand screws leave only an exposed eye to connect tackle. Along with better holding power, sand screws are less likely to foul, but they're also easy to lose should the gear part. Newer Hazelett Elastic Mooring Systems also offer amazing forgiveness in extreme weather with their elastic technology, but the gear can be a significant investment. Other areas may require several anchor points connected in a bridle system. Whenever setting up a mooring for the first time, ask around to find what works best in your harbor of choice.
A standard mooring setup consists of 2 lengths of chain. Heavy ground chain on the bottom, connected to a lighter chain up top. Bottom chain length should be 1.5 times the maximum height of water (i.e., spring high tide). The heavy weight helps lay mushroom on its side. Length of lighter top chain should equal the maximum height of high water. The diameter of both chains depend on size of vessel.
Why chain? Aside from its strength, chain acts as a shock absorber: as the boat rides up a wave it uses energy to lift chain weight. This, countered with force to submerge large mooring buoy act like shocks, sapping the jolt before chain gets bar-tight. This is especially apparent on a rough weather day.
Add a swivel to correct for boat spin. The boat will spend its anchored life whirling around that one point. Think of all the wind shifts and tide swings. As chain twists, it loses break strength. The swivel prevents twist, thus maintaining chain strength. Always use mouse shackles with locking wire or zip-ties to prevent pin from backing out.
Best chain for moorings
Aside from unavoidable corrosion, chain's biggest wear comes from continually brushing the bottom. The sand abrades the metal over time, making those unseen links near the bottom precariously thin. Be sure to have a certified mooring inspector periodically inspect the integrity of chain. (Annual inspection is the standard.) It is commonplace to replace chain every 3 seasons or so in salt water. Wider diameter chain has thicker metal per link to wear away, thus it should last longer. Chain diameter is measured by the thickness of the wire forming each link, not the opening of the link (link opening measurement is coil size).
When selecting chain, there are 3 basic considerations: grade (metal tensile strength), diameter (thickness of chain) and coil (opening size). A secondary concern is finish for corrosion resistance. For moorings Proof coil, preferably with hot dip galvanized finish, is the most common and economical.
Proof coil, also known as Common Coil chain, is the standard commercial quality regularly stocked by hardware and industrial supply houses. Proof coil is grade 30 chain, a general purpose chain for pulling or restraining applications. Proof coil is not for overhead lifting or where maximum tensile nor impact strength is crucial. Basic carbon steel metal composition makes it the go-to chain for log chains and towing. This metal can look different depending on finish. Standard Finishes may be plain, colored, bright zinc or hot dip galvanized. Because tolerances aren't as tight for inconsistencies in link size and diameter with proof coil, the cost is less than precision chain such as BBB for windlasses.
Chain link openings vary, too. We offer chain with elongated link size called Long link. This is a practical choice where connections must fit mid chain, not the end link. With the longer links, shackles bolts fit anywhere along it's length, whereas standard coil sizes may only fit shackles on end links. Long link also makes the chain lighter than equivalent length of standard chain. Another variation is studded chain, also called tugboat chain. Studded link means the wire forming each link also spans across the middle of link opening, making it extremely heavy and strong. Studded is for large diameter chain. If you have a boat 60 feet or above you may used studded link on the ground tackle for added weight and strength.
Grade refers to the tensile strength of the metal. The grade number used by manufacturers is an indicator toward the ultimate break strength of chain. The higher the grade the greater the break strength. With galvanized chain it basically boils down to how much carbon is in the steel. Grade 30, aka proof coil, has less carbon and is good service duty chain. Grade 43 (aka Grade 40) has higher tensile strength and abrasion resistance and comes with a higher price tag.
|The grade refers to the tensile strength of the chain. This is expressed in newtons per square millimeter (a newton is approximately 0.224805 lbs). The tensile strength is calculated by multiplying the grade times the area of the two cross sections of a link (see above).
(Area) 157.08 mm2 x 800 n (Grade)=125,664 newtons ultimate breaking strength
125,664 newtons x .224805=28,250 lbs ultimate breaking strength
125,664 newtons/1000=125.66 kn (Kilonewtons)
When it comes to metal finish, "hot dip" galvanized steel works best in salt water. While stainless steel is preferable on deck, it's not best for below the water. Stainless steel needs oxygen to breathe. Constantly submerged, the lack of oxygen is thought to cause stainless steel to corrode. Steel that is "hot dip galvanized" into a bath of zinc at over 800° yields a very corrosion-resistant metal. But even so, wear is unavoidable, meaning you will need to replace any chain after a few years mooring service regardless. Even the best stuff will wear away with time so it's more cost effective to replace less expensive chain frequently. For all the above reasons, the most common chain for mooring use is a hot dipped galvanized Grade 30 proof coil.
The mooring buoy serves a dual function. It floats all that heavy chain to the surface, and also increases holding power by absorbing the shock of heavy weather waves and wind. USCG regulations require standard white with blue stripe mooring buoys. The chain should thread through the center of the buoy before connecting to the pennant. Stopper rings cut like washers from old tires are a good provision to prevent the shackle from pulling through and crushing buoy core. Taylor Made makes a heavy duty steel mooring collar for this exact purpose. Quality mooring buoys are made with a hard plastic shell filled with closed cell flotation foam. This ensures sufficient buoyancy, even if shell integrity is compromised.
A lighter pickup buoy at the end of the pennant makes hooking up to the mooring easy. A small float does the trick. For boats with higher freeboard, a mast buoy is a huge help, making pickup easy without a boat hook.
The pennant ties the boat to the mooring. Choose the largest diameter that reasonably fits through the bow chocks and around the mooring bit or cleat for best bet. Easy splicing 3 strand line is most common, made from nylon for shock absorbing stretch. Equivalent diameter double braid polyester offers more strength than 3 strand. Either should include some kind of chafe gear sleeving to prevent abrasion. To connect the pennant to chain use an eyesplice around a galvanized thimble and a heavy-duty galvanized shackle. Some larger, heavy tonnage vessels opt for stainless steel wire pennants for maximum strength and chafe resistance.
Please sign in to leave a comment.