We wondered a lot about anchoring among coral reefs before taking off from Mexico… and we’ve heard the question a few times since going through the experience ourselves. Jamie put together this response.
South Pacific anchorages add a new dimension to parking the boat. Coral heads snag anchors, tangle and abrade anchor chain, and chew up nylon rode. This is not helpful to the common illusion of what South Pacific cruising is supposed to be like; nor is it good for living coral, in my view the most spectacular of all living things.
First, it’s important for the uninitiated South Pacific cruiser to understand the difference between boobies and bommies. The former refers to what you saw at Isla Isabella and hope to see in French Polynesia. The later is the common reference to coral heads (derived the Australian Aboriginal word bomboras, loosely meaning isolated reef). So while the meanings of both words share a certain aesthetic beauty, bommies differ in that they can wreck your boat.
Among bommies, the “floating chain” anchoring technique is not new. It’s also not well known or practiced. It does reduce coral damage caused by anchor gear; and minimizes anchor chain on coral macramé events. The basic concept is to attach floats, usually boat fenders, to anchor chain thereby keeping sections of the chain above bommies.
Technique notes from Totem:
- Depth: we measure anchoring depth as being from the bottom to the bow roller at high tide.
- Scope: commonly 4:1 but varies widely based on local variables.
- Floats (boat fenders are perfect): we used fender measuring approx 8” x 30”. Occasionally we used larger fenders (12” x 32”) in deep anchorages or around very tall bommies.
- Attaching fenders to chain: use about 2’-ish of line between chain and float. Tie to chain with a rolling hitch or clove hitch AND with an extra half hitch to “lock” it, as current/chain/boat movements keep the fenders working.
- Safety: mind the finger/toes/etc once the float is tied and more chain is let out! Make sure the float will not foul on the way over the side.
- Anchor drop: pick a clear spot to drop anchor (very challenging sometimes). The anchor drags before setting (varies with type), so account for drag distance as well.
- 1st float: about 1.5 x anchoring depth
- Additional floats: Very loosely, spacing equals 1 x anchoring depth. Amount varies with how much or little you want to control anchor chain droop between floats.
- Setting the anchor and use of snubber is no different than without floats.
- Communication: Is a must, especially when windy/choppy. When attaching the first float it is incumbent on the person at the wheel/engine controls to keep the boat from sliding backwards much – or you’ll find the unset anchor will end up on or to close to a bommies.
- Hauling anchor: The cautions mentioned above are especially true when raising the anchor in rough conditions – fingers/toes/boat position. It’s also a good idea to take advantage of the clear water and get a good picture of the section of chain that is on the bottom because floats don’t eliminate minor bommie wrapping. Slowly motor forward in the direction of the chain to reduce the chance of destroying coral and to reduce the chance of pulling the anchor back into coral, causing bigger problems.
The catenary question: catenary we all know is the curve in the chain rode between the two fixed ends. More curve means better holding because of a dominate shear force (horizontal on the anchor) instead of peel force (lifting anchor from bottom); and because the curve acts as a shock absorber (in conjunction with the snubber) so that a pitching bow doesn’t jerk the anchor out. Floats do affect the catenary. In the first case, the first float lifts the chain and thereby makes the pull on the anchor more vertical – less good. In our experience on Totem, this never once caused us to drag; although different anchors may yield different results (we have a 33kg Rocna). In the second case, the shock absorber affect is not affected by the floats because they do not cause the chain to be straight between the 2 fixed ends.
The opposite is true if you don’t use the float method. Because the chain will wrap around a bommie (more or less dramatically) the anchor pull angle parallels the bottom so holding is very good. The problem is that the effective scope is reduced to the distance from bommie to bow roller; thus reducing chain weight and catenary, reducing the shock absorber affect. In a bouncy anchorage this can cause shock loading that stresses the chain, bow roller and/or snubber. Also, chain wrapped on bommies wears through galvanizing very quickly, can cause loading perpendicular to the chain link (much weaker), and causes loud scraping sounds as the boat moves around.
So in terms of holding power, anchoring both with and without floats poses issues to be aware of around bommies. The real benefit of the float method is that you are much less likely to delay your departure from an anchorage due to a need to untangle chain. This process can literally take hours or be demanding in rough conditions. And you cause less damage, or no damage, to the living coral that we all want to see.
Pacific destinations where Totem used the float method:
- Marquesas – Tahuata (Hanamoenoa Bay), Ua Huka (Haavei Bay), Nuka Hiva (Anaho Bay, Controller Bay)
- Tuamotus – Makemo (all anchorages) Fakarava (all anchorages)
- Societies – Moorea (Opunohu Bay), Huahine (all anchorages), Tahaa (Baie Hurepiti)
- Cook Islands – Suwarrow (Anchorage Island)
- Tonga – Vav’au group (Hunga, Kenutu, Vakaaeitu)
- Fiji – Yasawa and Mamanuca groups
- Vanuatu – NW side of Lelepa Island
- New Caledonia – N side of Lifou Island in the Loyalty group