This is to be avoided wherever possible! But if you do have to anchor in a coral atoll, Dan Bower has some tips for the sixth part of our ocean cruising series
Anchoring in coral is illegal in many places and should certainly be avoided if at all possible. A nice patch of sand is better for holding, better for your ground tackle and considerably better for the environment.
However, there are places and anchorages where you simply don’t have an option – and believe me you wish you did!
I am not talking about anchoring in the middle of a pristine reef, but many South Pacific coral atolls are strewn with small coral heads in the anchorage, so even if you manage to land your anchor in a nice sandy patch, the chances are you may get your chain wrapped around one or many, and if the wind is changeable you can tie the chain in all sorts of knots.
These coral heads usually stick up around a metre from the seabed and it can be difficult to distinguish the height. This is further complicated because many of the anchorages are deep and so it’s hard to see what is going on.
There are several problems with this. Coral is hard and can seriously chafe your anchor rode – a rope stands no chance and even chain can take a beating, all the while making a graunching noise which can be felt through your snubber and resonate through the boat to ruin your night’s sleep.
With every wrap or snag you effectively shorten your scope, and therefore the catenary effect, or spring, in the chain is diminished. This is what usually absorbs the load when a gust hits the boat or you’re anchored in a swell – as the yacht pulls back or the bow rises, the weight of the chain lifting off the seabed takes the brunt and prevents any snatch loading.
The problem with coral snags is that the chain can get so caught and wrapped that the pull becomes straight down. A firmly wrapped chain is very secure and unyeilding, but a gust or swell can apply too much shock loading, which can cause real damage and, since the coral is strong, the damage is to the boat. Depending on your ‘weak link’, you can snap the snubber or the chain, rip out a cleat or bow roller or, worse, the windlass!
Getting the anchor up can be a real challenge. We have been in anchorages in the Tuamotus and watched (and helped) yachts for up to two hours trying to raise their anchor. In some cases where the water is shallow or clear enough a look below with the snorkel can map out your chain’s path and help the helmsman unwind the chain. Otherwise keep someone in the water to watch and guide you or if it’s really stuck and unclear, a dive may be required to free it off.
In the tradewind areas, the times the wind is likely to be really shifty is either when it’s very light airs (when it’s less of a problem) or when a bigger system is approaching. Despite being in a protected lagoon, if the wind blows the wrong way there can be quite a chop.
Rangiroa lagoon, for example, is 40 miles long, the second largest in the world, but most are bigger than the UK’s Lake Windermere, so there is plenty of fetch to create a nasty chop and this is when being wrapped around the coral heads is likely to be a serious problem.
The only sure solution is to have plenty of chain in the locker and keep letting more out as you feel your scope is getting shorter or each time there is an appreciable windshift. Once the weather has improved, work can be done to untangle the knitting. Another option is to use an extra-long rope snubber to bring back some elasticity – a boat length or two of anchor warp tied to the chain and taking the weight would be a last resort.
Buoying the chain
One method that seems to work very well, and has helped us, is to place floats along the anchor chain. These should be just buoyant enough to keep the chain off the bottom and high enough to clear the snagging coral heads, or at least reduce the area affected.
The principle is that you drop your anchor in as clear and sandy a patch as possible; the first 2x the depth is lying on the sea floor, the rest of the scope is then buoyed to lift the chain off the ground. The Skyelark formula is to put one buoy every 1x the depth of water up to a scope of 5-1.
So in 10m our procedure is drop 20m of chain, then attach a float at 30m and 40m. We stop the chain at 50m.
You must use something fairly sturdy as a float – it is going down to near the seabed and there is a fair amount of pressure at 15-20m. A water bottle will just collapse. We choose the marker floats that are used regularly for fishing buoys and can be freely obtained by picking up the many that litter the windward reefs in the South Pacific from the pearl farms.
Another option is to use your fenders – Skyelark’s are so oversized that they are too buoyant, but it’s worth an experiment to see what works for you. We have our buoys on short tethers that you tie to the anchor chain, but an improvement on this would be some quick release carabiners or snapshackles.
Buoying the chain is not completely failsafe, but it will help. The first of the scope is still on the sea floor and may well still get wrapped on a coral head. If you suspect this has happened, you can clip on another buoy and let out another water depth of chain.
Do’s and don’ts
√ Do use floats that won’t compress at depth.
√ Do use a heavy-duty ‘springy’ line for your snubber (anchor plait works well).
√ Do Do snorkel on the anchor after setting and before raising.
x Don’t anchor in coral at all if it can be avoided.
- Don’t force the chain free with the windlass or excess engine use. Take it slowly and if it gets caught, let out more chain and manouvre in a different direction. Be patient!
Dan and Em Bower
Dan and Em Bower, both in their thirties, are lifelong sailors. Six years ago they bought Skyelark of London, a Skye 51 by American designer Rob Ladd, built in Taiwan in 1986, and have been sailing and chartering her ever since, making some 12 transatlantic crossings and covering around 60,000 miles.
It may be rare, but the consequences of having a man overboard when sailing rapidly away under spinnaker are so serious that Dan Bower dedicates Part 7 to his advice
12-part series in association with Pantaenius