SPECIAL REPORT
When my toes get cold, I know the wind has piped up. The dorade over the foot of our bed only seems to move air when it’s blowing over 20 knots, and that night it was working overtime. As the wind howled through our rigging, I pulled the blanket back over my feet and struggled to fall back asleep as Agàpe was battered by high winds and driving rain.
The next morning, after three days confined to the boat with 35+ knot winds, I finally decided I'd had enough. I would escape for a swim under the pretence of checking our anchor, but as I swam forward, my anxiety for the safety of our boat grew. I could see that even though we had a scope of 7:1 out, all of our 10mm chain was suspended in the water column.
I'd always believed that the weight of our chain was instrumental in our anchor’s holding power, but now, watching as the wind gusted into the high 30s, the boat pulled the chain taut, and any assistance of a catenary effect added by the chain’s weight was lost. But still, the anchor did not move. Even when the full length of chain was lifted off the seafloor, the anchor would not budge. As I watched for several minutes, I quickly realised that it was not the weight of our chain, or any catenary effect that it might provide, which was responsible for holding our boat, it was almost entirely the angle at which the anchor was being pulled.
Sailors tend to love formulas, and certainty. A quick glance at a Nigel Calder, John Vigor, or Danial Spurr book will reveal calculations to find the correct anchor size, scope, catenary angle, and so on. What we often fail to take into consideration though, is how much force the wind puts on our boats, and that our chains’ perceived weight is less when submerged.
A 42ft cruiser like Agàpe presents a little over 115ft2 of surface area to the wind, but since boats typically sail around at anchor, we double this to account for the larger surface area of our beam, the bimini, mast, and rigging. The wind force is roughly 3lb/ft2 at 30 knots, and grows exponentially, meaning the same square foot will have 13lb of pressure at 60 knots.
In 30 knots, Agàpe can pull on her anchor with almost 700lb of force, not including waves or current. It’s no wonder then that the 200ft of chain that we had out for the blow was pulled tight. All 200ft of our 10mm chain weighed in around 320lb, less than half of the force applied to the boat. In lighter winds, having an all-chain rode – or at least some chain – does help greatly, as the weight of the chain will be more than the force of the wind and will therefore reduce the angle of pull on the anchor. This is when the catenary effect comes into play!
We have safely ridden out more than 50 knots, where the force on the chain was enough to distort the grab hook on our snubber. I could have played our anchor chain like a guitar string, it was pulled so tight, and we had almost no chain on the bottom. The majority was attached to floats, keeping it suspended in the water column, safely away from the corals that threatened to entangle it.
It’s because of all these forces at play, that
over the last eight years we found it is less about the added weight of chain that keeps us sleeping soundly, but more the correct angle of pull, or scope that is important – particularly when the wind picks up. This is especially true when the substrate we are anchoring in is less than ideal.
ENVIRONMENTAL IMPACT
Losing a yacht because of dragging is not only devastating to the owner, but also the beach, reef, or coastline that it comes to rest on. As our ocean conservation awareness increases, so too does our realisation of the environmental effects of cruising. Whether we're aware of it or not, every time we anchor the boat we affect fragile marine ecosystems. In some regions, like the South Pacific and Caribbean, this has led to heated debates on how local governments should handle the increasing number of yachts. As cruisers, we love the element on which we live and the creatures that call it home, and we should strive to have as little negative impact as possible.
Over the years of cruising, we have visited increasingly remote areas where perfect sand bottoms are few and far between. On Agàpe, we have had to learn how to set the hook in boulderfor strewn bottoms, around thick kelp beds, avoiding coral bommies, and in fields of slippery eelgrass. Our first priority is to make sure our boat – our home – is safe. But, we also want to have the slightest impact on the marine environment we travelled so far to enjoy.
Everywhere on the seafloor, life flourishes, from the gobies and garden eels of the sand bar to the sea stars and urchins of the kelp forests. There is life even in the benthic substrate of the mucky, muddy river bottoms. Each time we set our anchor deep into the bottom, we are disturbing some little creature struggling to make a life for itself, and over the years we have become increasingly picky about where we drop our 25kg Rocna wrecking ball.
So, how can we anchor more responsibly, in a way that does minimal harm to the environment and also ensures our yacht’s safety?
Talking about anchoring techniques is often like talking about politics, religion, or money: people tend to hold strong opinions and debate can be heated. It's not my intention here to convince anyone of how to do anything. Instead, I'm going to outline three techniques that we have successfully used on Agàpe.
THREE POINT PLAN
First and foremost, we take our time. Sometimes it can feel like a competition, or a boost to our cruiser’s pride when we can sail into an anchorage, come to an open spot, stop, drop and call it good.
But I challenge myself to take an extra minute or two to look over the side and see what is below. Perhaps take a lap around the anchorage to find a place that is already scarred from previous anchors. Back down a little slower to help give our anchors a chance to dig in, instead of ploughing a trench in the bottom a boat length or more. Backing down slowly is also a great technique for anchoring in silty, mud bottoms, or eelgrass.
It helps when possible to know what the bottom is comprised of ahead of time. If you know you are going to a bay with abundant seagrass, think about dropping a little deeper, in around 30ft; much less seagrass grows at these depths so you'll greatly reduce your chance of damaging it.
Second, we set with adequate scope, not an exorbitant amount. Yes, more scope will lead to better holding, but more is not always better when taking into account life on the sea bottom, or when it’s a crowded anchorage. Agàpe almost always rides on 5:1, so if it is 15ft deep, we have 75ft out. If the bottom is foul or in rocks, we might put out a little more with the addition of a float or two. By not putting out 7, 8, or even 10:1, unless it is needed for really high winds, we keep the excess chain off the bottom and away from the fragile ecosystems living there.
Just as important – if not more so – is backing down to ensure the anchor is well set. We can have 10:1 out but if the anchor is fouled and
cannot properly set it's of no use.
Third, and our favourite technique, is floating our chain in order to protect it and the bottom. To do this properly can take some time and practice but, once you get the hang of it, the technique can ensure the beautiful corals are there for others to enjoy long after you have come and gone. This practice works because as the wind picks up, the force applied to the chain will pull the floats down, giving you the same angle of pull as if the chain would have been on the bottom to start. When floating our chain, we leave some on the bottom, preferably equal to the depth of the water, then we begin to add our floats, roughly 30ft apart. I try to stagger the floats, leaving less and less chain between them, so they float at different levels in the water column. This helps to ensure that when the wind is light the floats and chain do not become tangled. Floats need to be robust enough that they won’t compress at depth – there are usually lots of discarded fishing floats lying around the shoreline which do the job.