Multiple anchor rigs
Techniques using the deployment of more than one anchor have evolved over time for various reasons, some of which were necessary to compensate for the failings of old generation anchors. The rationale viewed from a modern perspective can often be that 'two wrongs make a right' – in theory. We start with this note in order to point out that one good anchor and one good rode set-up is the ideal. Lighter and stronger chain, which permits a larger and more effective anchor in the first place, can be a much more sensible and practical approach.
However, a number of specific circumstances can require that multiple anchors are deployed at once, either to hold the boat in a certain orientation that cannot be achieved by a single anchor and rode, or for the benefits of cumulative holding power. With regard to the latter objective, it is important to reiterate that the primary anchor should be selected and sized so that it is adequate on its own in practically all conditions – if it is not, then it needs to be upgraded. Routinely using multiple anchors to gain the required performance is seriously and strongly advised against.
A "Bahamian moor" is a deployment of two anchors which is designed to minimize the boat's swinging circle, and place essentially unidirectional pulls on each anchor. This has a number of benefits but is a hassle to deploy in normal circumstances, and requires that other anchored vessels in the proximity are using the same techniques (closely moored boats must swing from their anchors or moorings in the same manner).
It is common and should be familiar to any crew for use in areas where there are predictable wind or tide reversals. It will for example allow a boat to anchor on the side of a river, bow always facing the predominant wind or tide, but restricted from drifting out into the main channel.
Bow and stern
Stern anchors may be deployed in addition to bowers for any number of reasons. A tight bow-and-stern deployment will keep a vessel rigidly in one location, appropriate for close quarters anchoring or a narrow channel where no swinging whatsoever may be tolerated. Or, a stern anchor may keep a vessel facing the predominant swell, regardless of wind or tide, for reasons of comfit.
Because a stern anchor restricts a vessel's orientation, some attention should be paid to the ramifications of this. An unexpected strong wind from the beam will almost certainly drag both anchors, as the increased windage profile and leverage on both anchors will be too much for them to handle. Or, rough waves from the stern could cause problems for small vessels, particularly those with low freeboards.
The V arrangement, whereby two anchors are deployed from the bow at equal angles and scopes, is one which may be used to assist a single anchor if it is considered inadequate. However, this arrangement is specific to one direction of wind or tide, and does not handle veers well. A 180° reversal will require both anchors to re-set themselves without error, and a partial veer will probably require the anchors to be manually redeployed.
One of the advantages this set-up does provide is a resistance to lateral forces, and a dampening on "sailing" at anchor. The peak forces on an anchor, those likely to cause problems, tend to come when the boat is taking up on its rode, an event which is repeated and a force which is amplified if the vessel is excitedly veering first to one side then the other. If your boat has a tendency to engage in this behavior, a V deployment can keep it in check, and so reduce the peak loading on the anchor.
A tandem anchor is one which is connected directly in front of another; i.e., two anchors are used in series on the same rode.
|The topic of this section is supplemented by an article at the Rocna designer's personal website.
To read this article, click here: Two to Tandem: Rigging Dual Anchors to Maximize Holding Power
Tandem anchoring is a complex topic, as the presence of the second anchor has many ramifications for the primary. In the course of developing the Rocna, its designer Peter Smith carried out a fair amount of practical testing with regard to this technique. The Rocna is the sole anchor available today which features a dedicated tandem anchor attachment point (on the models 10 and above).
In general this is recommended as a superior alternative to a V or Y deployment, as the two anchors work together more efficiently, the load always being evenly shared. (In a V or Y configuration, load tends to move from one anchor to the other, always concentrated on just one, meaning that the overall capability of the system is defined essentially by the single least capable anchor present).
Nb.: Most boaters should never have cause for tandem anchoring. For most boats, the primary anchor should be sized so that it is adequate on its own in practically all conditions – if it is not, then upgrade.
To avoid duplication, this topic will not be covered further here. If you intend to make use of this rig, please read carefully the comprehensive article on Peter's personal website linked to above.