ANCHORING IN STRONG WINDS

This is an abridged version of our article published in Pacific Passagemaker.
During 30 years of boating we’ve frequently anchored in sheltered positions with winds over 30 knots (Force 7), and occasionally encountered gusts up to 70 knots. Remember that the Beaufort Scale registers the mean wind speed, for example Force 7 represents a mean wind speed of 28-33 knots, while gusts of up to about 45 knots (or greater) can be expected. In particular thunder storms are often accompanied with extremely gusty conditions, as well as rapid changes in wind direction.
There are numerous theories about anchoring, and we base our suggestions on experience with our Nordhavn 46, assuming your vessel has adequate ground tackle - a major subject itself.
Envoy’s main anchor is an 88 pound Delta Setfast with 400 feet of 10.8mm BBB chain. The only time we have dragged anchor in recent years was in unexpected wind gusts up to 55 knots with insufficient chain deployed.
We’re also assuming there are no safe marinas or harbours available, and anchoring is therefore a necessity – we generally prefer to go into a marina in anything over Force 7.
The process starts with awareness of an adverse weather forecast, and normally there is adequate time to prepare for the conditions. Always write down the forecast and subsequent updates, so you can monitor how the weather pattern develops.
If the wind is forecast to blow directly off the shoreline and there is no significant swell or sea, an option is to anchor close-to-shore, but a disadvantage is the possibility of a wind shift placing you on a lee shore.
A safe, comfortable anchorage depends on finding an inlet or bay largely protected from the ocean swell and seas, suitable for a possible wind shift, and clear of reefs, rocks, moorings or other obstructions. The ideal anchorage also has an easily navigable exit and an alternative nearby bolt hole to go to if necessary.
Explore the general area before anchoring to understand its approaches, layout, depths etc., and record compass courses and gps positions for exiting the bay in poor visibility. Use your radar and plotter during the day to compare exactly how the anchorage looks in reality and appears on screen, because everything looks very different by night.
Consider the placement of other vessels in the anchorage, because them dragging and fouling your anchor, or hitting you, is usually the greatest danger.
We prefer to use just one anchor, as it’s easier to lay and set, avoids issues of anchor chains becoming twisted in wind shifts, and is much easier to retrieve in an emergency.
Our technique is to slowly motor upwind to stop Envoy in the position where we want our anchor to sit, pay out chain until the anchor is almost to the bottom, and then give a short burst of reverse thrust to move Envoy astern at the same speed chain is paying out. We don’t allow the anchor to free-fall, as chain can become tangled around the anchor, or cause damage if obstructed in the anchor locker while falling.
A common method to calculate the required length of chain is adding the maximum water depth at high tide to the distance between the anchor roller and the water, and then multiply that figure by five, six or seven times, depending on the conditions. In very strong winds we lay out as much chain as possible (even up to ten times), keeping in mind the proximity of other vessels and the consequences of a wind shift.
Applying reverse power immediately after lowering the anchor often results in dragging it along the bottom, so we first let Envoy set the anchor using her own weight, allowing the anchor time to settle onto the bottom and dig in properly.
If all is OK after about 15 minutes we motor forward about half the distance of the chain length and let Envoy drift back with the wind to fully dig the anchor in.
We record our GPS position and set our position and depth alarms to monitor any dragging.
In strong winds it’s important to use a heavy-duty, longer-than-usual anchor rode to act as a good spring. We set this up with the snubbing fitting just below water level and several metres of chain hanging on the vessel side of the fitting to increase the spring effect.
If depth, water temperature and visibility allow I check the anchor using a mask and snorkel.
We make preparations for the coming blow, ensuring all gear on deck is securely lashed down, buffers are readily available in case of another vessel dragging into ours, and having a means to cut the anchor chain in an emergency. We leave our tender in the water in case it’s needed, but firmly secure it in the lee of Envoy’s stern.
Now is a good time to plan actions in case of a significant wind shift or a need to move. It’s also a good idea for the captain to get some sleep during the daytime, when others can more easily monitor and handle any situation.
Before dark we rig spotlights, have torches to hand, the radar on standby and ensure the engine is ready to start quickly in case of any emergency arising, such as the need to avoid a dragging vessel or to reduce strain on the anchor in very high gusts. In such conditions I stay in the pilot house, catching a little sleep where possible, but constantly monitoring the situation to react quickly.
When the strong wind arrives it’s usual to see sheets of spray lifted off the surface of the water and wind waves up to about 2-3 feet even in a sheltered bay with little fetch.
Naturally there is some trepidation and a need to maintain a state of high alert, but by following the above procedures we have safely and comfortably anchored though many blows. We have not encountered winds above 70 knots and realise that circumstances may then be very different - the “strength” of wind does not increase in a linear way relative to wind speed, but dramatically more so as the square of the difference. For example to compare the strength of a 40 knot wind with a 20 knot wind:
20 knots squared = 400
40 knots squared = 1600
So a 40 knot wind is 4 times as strong as a 20 knot wind.
Similarly a 90 knot wind is nearly 1.7 times the strength of a 70 knot wind.
I’ll be happy not to experience trying to anchor in those conditions.