A text by Johannes Erdmann
At anchor: Suddenly the ship rolls
The anchor drops in the shelter of the high mountains of Martinique, behind which it is completely silent. Calm, smooth sea, peace. Into the bunk. But what is this? In the middle of the night, as if out of nowhere, the yacht begins to roll. There is still no wind around the ship, but the rocking is getting wilder and wilder. The wind has probably shifted a little to the south on the Atlantic side of the Caribbean island. Far enough for the waves to run along the coast and into the lee behind the island.
Pots and plates clatter in the galley. Lee boards are needed at the anchorage to prevent falling out of the berth. The ship rolls 20 degrees to each side. How can that happen? The berth is wonderfully sheltered by a headland.
Headlands do not always protect against waves
The fact is that such a headland often protects against wind, but not always against swell and swell. Both follow the coast and can therefore hit the ship in a different direction than the wind. To prevent the yacht from rolling at anchor, it is therefore important to know the behaviour of the waves at headlands, in shallow water and at breakwaters (see also the diagrams on the next page).
If you still cannot find a sheltered anchorage, it is useful to master certain anchoring techniques and the use of aids to prevent rolling at anchor.
Depth contours show wave behaviour
Information about the suitability of an anchorage in the prevailing conditions can usually be obtained from the nautical chart. If the yacht anchors behind a headland in the hope of protection from swell, for example, it is also worth taking a look at the depth contour. Waves generally reduce their speed as soon as they reach water depths that are less than half their length from wave crest to wave crest.
When the waves approach a coast and enter shallow water, they are therefore broken by the slowing of their speed, deflected and from then on run parallel to the coast. This is why a yacht can lie protected from the wind behind a headland, but still offer its full broadside to approaching waves. The ship is then continuously pushed sideways by the waves and set into a rolling motion. However, if the water is consistently deep, the direction of the waves does not change when travelling along a headland and the yacht can find a sheltered anchorage behind a headland.
Breakwaters: Not always as protected as hoped
Every skipper would also expect a protected anchorage behind an artificially constructed breakwater made of concrete or piled stones. However, the breakwater can create a similar effect to a headland in shallower water: small waves are created at the seaward end of the breakwater by the rising and falling of the sea, which radiate into the supposedly protected area behind the breakwater. Here too, the yacht is caused to roll sideways by the waves, even though the wind is coming directly from the front.
When waves play "over the edge"
Rocks or concrete walls can also deflect waves. If the sea is playing "overboard", reflected waves can suddenly appear from the side at the supposedly protected anchorage. Although reflected waves are smaller and shorter, they can still be unpleasant.
Tides and currents: The underestimated factor
Anchoring in tidal areas is a special case, where the influence of the current can cause a risk of rolling - for example, if so-called eddies form when anchoring in small bays near a tidal current or river. These are whirlpools that are accompanied by corresponding turbulence. Normally aligned waves then overlap with a turning movement. In most cases, the yacht then aligns itself with the current and receives wind and waves from the side.
Anchormen anchored in a strongly flowing river or tidal current should be aware that the situation can change radically. For example, if the yacht is still lying with its bow in the wind and in the direction of the waves when the water is running out, it may be pushed across the wind and waves by the current when the water rises and then begin to roll. If the current is stronger than the wind (as is often the case in Brittany), the yacht will orientate itself in the current and can be made to roll again and again by the wind and waves.
At anchor: the current as an ally
However, strong currents can also be beneficial. When waves run against a current, they encounter a weaker secondary current at its edge, which offers less resistance to the waves than the main current. The waves can therefore suddenly move faster there and turn back into the current - they cannot leave it. Another rule is that when waves run against the current, the outer edges of the current act as breakwaters. This is why anchorages with few waves are often found next to strong currents.
Reefs and sandbanks as natural wave dampers
Reefs or sandbanks can also create sheltered anchorages. In contrast to deep water, where current-against-wind situations usually create confused, high, short seas, reefs or sandbanks in shallow water have the greatest wave-smoothing effect when the current is against the waves. What sounds illogical is easy to explain: A current does not create waves, but rather focuses the energy of existing waves. When a current runs over a sandbank or through a strait, the water current is accelerated in the eye of the needle and creates a more turbulent sea behind the sandbank - where it meets the approaching waves - because it amplifies the waves. Conversely, the waves upstream are shallower and calmer.
Anchoring techniques against rolling
Rolling at anchor can be an ordeal. In any case, pitching is more pleasant if the bow, or if necessary the stern, is directed against the wave. As described in detail, this can be achieved either by choosing a suitable place or by using special anchoring manoeuvres.
American Jessica Johnson, 33, has been sailing around the Atlantic on her Sabre 34 "Serendipity" since 2012 and has had to drop anchor several times in the hundreds of anchorages on her journey in suboptimal locations - but she found solutions: "In some anchorages, the rolling was almost unbearable. To remedy this, we attached a second line to the anchor chain and winched the ship into the waves with the bow"
What the location of the anchorage reveals
The triangle trick and other tricks
A similar effect can be achieved with a trick that is popular among long-distance sailors. A long line is hooked into the chain and led aft onto the sheet winch. A triangle is formed between the bow fitting and the sheet winch. The ship can now be positioned against the direction of the waves. Even if the current and wind change direction and strength, regular readjustments can be made.
The use of a stern anchor deployed to the side works according to the same principle. Both anchor chains and lines are now hauled in and lowered until the bow is in the direction of the waves. Incidentally, this can sometimes be achieved in current waters simply by laying and fixing the rudder.
The mainsail as a support sail
If it is not possible to hold the bow against the waves, the effects can at least be minimised. To do this, the main is set so far at anchor that it has the effect of a support sail. In this way, the rolling movements are dampened.
Mechanical aids in a practical test
There are also a number of accessories and skipper tricks for avoiding rolling. In contrast to hydraulic stabilisers on large ships and mega yachts or even luxury systems such as the Seakeeper automatic gyro roll stabiliser, only mechanical auxiliary systems can be used on sailing yachts without a generator. And there are physical limits to their efficiency.
A test at anchor with the Contest 33 "Maverick too", 9.83 metres long and 3.15 metres wide, should provide more precise information.
The impact gun: an old trick with moderate effect
First attempt, an old sailor's trick: a lowered bollard tied to the foot rail. This roll brake proved ineffective in the test. The movements of the bailer under water are obviously too small, as is the resistance, so that the rolling of the boat is not reduced.
However, a variation of this measure actually has an effect: deploying the bucket. Sunk three metres away from the ship on the spud pole, the bucket on the long lever produces a certain damping of the rolling movements when it moves up and down under water. However, there is no noticeable improvement in living comfort on board.
Extended dinghy: effective, but risky
Another home remedy at anchor is to boom the dinghy from the main boom. As the boat rolls, it is repeatedly lifted out of the water and set down. The rolling movements of the yacht are actually reduced noticeably, but the alternating load on the boom and fittings caused by the 60-kilogram inflatable boat is so great that it cannot be used as a permanent solution under any circumstances.
Rocker stopper in practical test
There are two main commercially available solutions to the problem: "Rocker stopper" from Davies and the stainless steel stabilisers from SwiTec.
The rocker stoppers (16 euros/each) look like flattened pylons, have a diameter of 33 centimetres and should be tied to the side of the boat and lowered into the water to minimise rolling. For the test boat, four pieces are recommended per ship's side, which should be attached to a line about 44 centimetres apart and fitted with a 2 to 4 kilogram weight at the end. The test shows that the effect is similarly modest to that of the impact bollard.
SwiTec stabilisers: Installation determines the effect
The set of two stabilisers from the Swiss blue water mail order company SwiTec costs 322 euros, is far larger than the rocker stoppers and is said to be suitable for ships weighing up to ten tonnes. The design is simple but functional: the base is a solid stainless steel frame onto which two large hard rubber flaps are screwed. The frame can be attached to the ship's side using four lines that converge in an eye. When the ship rolls at anchor, the stabiliser is pulled downwards by its own weight. The rubber flaps open to create less resistance. If the ship rolls to the opposite side, the flaps of the stabiliser close - the result: it creates resistance in the water and slows down the rolling movement of the ship.
During the test, both stabilisers are first attached to the side of the boat as described by the manufacturer and lowered into the water. There is almost no noticeable reduction in the rolling motion. This is presumably because the stabilisers are simply too close together with a boat width of 3.15 metres.
In the next experiment, the stabilisers are attached to two spinnaker poles and swung outboard - a mounting solution similar to the deployment of the jib, but which the manufacturer does not mention. With the distance between them increased to around seven metres, the effect of the stabilisers is now far greater and the roll is significantly reduced. Whereas the ship previously rolled about 15 degrees on each side, it now rolls about 7 degrees on each side.
Little helpers
Conclusion: the choice of seat is crucial
Complete roll damping at anchor is not possible even with the most expensive accessories, as the practical test shows. The SwiTec stabilisers must first be lifted about 20 to 30 centimetres upwards on each side by the rolling movements of the boat before the flaps close completely and the stabilisers show their function through their resistance.
As far as rolling movements are concerned, the following applies: A mistake made when choosing the anchorage cannot be compensated for by the usual accessories.
Anchor tricks
More about anchoring:
