The concept of tandem anchoring is very popular amongst the boating community. On internet message boards, the topic seems to be raised nearly as often as discussions on anchors themselves. This article is intended to provide an overview of tandem anchoring.
Using multiple anchors on boats is fairly common, and various well recognized arrangements exist for handling particular situations. For example, a bow-and-stern arrangement may be used to hold a boat into a swell in order to minimize rolling, or a Bahamian Y moor may be used to deal with frequent 180 degree veers such as when anchored in a tidal area.
A tandem anchor set-up is intended to simply maximize holding power. It does not deal with complex situations for which another rig may be more appropriate, and works best at dealing with strong winds from a single direction. There is one point that should be strongly emphasized, and that is the fact that any multiple anchor rig introduces a complexity to an anchoring set-up and may complicate retrieval.
Your primary anchor should be sized to be good enough on its own for most all situations – if it is not, reconsider your choice of that anchor. Tandem anchoring is for extreme situations, in which a single anchor large enough alone would not be practical for daily use.
Let’s pause to reiterate this. It is a mistake to think to tandem anchor regularly. You must have a primary anchor of a good size and type for your boat.
Throughout this article, we are assuming that a single anchor on its own, for whatever reason, is inadequate. Clearly there is no point in using a tandem rig if a single pick will do the job. While this might seem obvious, it is important to point out, as it implies that a single anchor of any multiple anchor rig will drag if all the load on the boat is applied to that one anchor. This is a situation which frequently needs to be considered.
Overview and Terminology
A tandem anchor rig is where two anchors are somehow connected in line with each other, on a single rode which is deployed from the boat. “Rig” refers to the entire system deployed in the water, i.e. anchors and rode, including shackles and/or swivels.
There is no standard for this, but for this article the terms will be defined as follows. The primary anchor is the aft-most anchor, i.e. that closest to the boat. The tandem anchor is the forward most, i.e. that out in front of the primary.
The rode is split into two sections, the primary rode and the tandem rode. The tandem rode is either attached to the back of the primary anchor or is simply an extension of the primary rode.
Figure 1: Basic elements of a tandem anchor rig
In a situation where the holding is poor, for example volcanic ash, loose sand, small gravel or sloppy mud with a hard base below, the length of chain connecting the two anchors need only be around 3m in length.
The second or tandem anchor should be of a type that is not the same as the primary. For example if your primary is a Rocna or similar then a Danforth or Fortress anchor as the tandem would be suitable.
In situations where holding is not the primary problem but perhaps a busy anchorage with limited swing room then a modified tandem can be used in the same way as you’d use a kellet. A Kellet is a weight attached to the rode to aid catenary. This allows less scope to be laid out as the weight keeps the pull on the anchor much flatter.
In this situation you could attach the tandem to the primary with say 20m of chain and use an anchor similar to the primary.
In both cases above it’s a good idea to attach a rope between the primary and tandem to facilitate recovery.
Scenario two can also be used in deeper anchorages to reduce the scope required.
To conclude, in situations that require this type of “Fix” the skipper should consider if the risk is worth the reward or if it would be more prudent to find a more suitable anchorage.
If taking any of the options above you should also consider keeping an anchor watch if the wind, current or forecast could potentially cause a problem.