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Tuesday, May 22, 2018

ANCHORING IN STRONG WINDS WITH SAFETY AND CONFIDENCE (PART 2)

Envoy is berthed in Greece's Lefkas Marina while Diane and I are home in Auckland. We're not planning any major Med cruising this year, but hope to visit Lefkas around mid August to check on Envoy and cruise until end October.

Pacific Passagemaker magazine recently published an article we'd written on anchoring in strong winds.
Here's the second of two parts of an edited version of that article.

So Part One has put our vessel into a suitable bay for anchoring.
Much is written about different anchors and their supposed advantages but provided your vessel has a recognised mainstream type of anchor your security will be determined more by your anchoring technique including the weight of chain you have on the seabed.
This article assumes your vessel has totally adequate ground tackle and that is a whole subject in itself. Our main anchor is a 40 kg (88 pound) Delta Setfast with 400 feet of 10.8mm BBB chain and having anchored nearly 2,000 times can only recall Envoy dragging anchor twice (once of which was during a non-forecast 60 knot wind).
A commonly used method to calculate the required length of chain is to add the maximum expected water depth at high tide to the distance from the anchor roller to the water and then multiply that figure by five, six or seven times depending on the conditions. However this formula doesn't work so well in very shallow water or deep water. I prefer to allow for the depth of water plus 30-40 metres of chain on the bottom.

We rarely go into harbours or marinas as it's too expensive when living aboard


In very strong winds we lay out as much chain as possible, even up to ten times total depth while keeping in mind the proximity of other vessels and the consequences of a wind shift. Of course you must be able to monitor how much chain you are paying out using a chain counter or marks on the chain (we use coloured cable ties).
Our anchoring technique is to very slowly motor upwind and stop 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 so that Envoy moves astern no faster than the speed at which chain is paying out. We don't advocate allowing the anchor chain to free-fall until the anchor is on the bottom and reverse movement has commenced as chain can otherwise become tangled around the anchor while it's dropping. However once the anchor is on the bottom, free falling the chain does save wear on the windlass motor. In our experience and observations of other vessels, if too much reverse power is applied immediately on laying the anchor it will often result in dragging the anchor along the bottom, particularly if the bottom is mud or covered in weed. We prefer to first give the anchor time to settle onto the bottom and dig in properly. We then observe whether the vessel is holding and if all is OK after about 15 minutes we motor forward about half the distance of the chain length and then let the vessel drift back with the wind. The anchor will fully dig in when it stops the vessel’s backwards drift and then we apply a little reverse thrust to ensure the anchor holds. When the vessel “bounces back” on its snubbing line (or bridle) you know it's holding. Never do this with the strain of your anchor chain held only by your windlass.

Envoy in superb Zaklopalica, Croatia

In strong winds it is important to use a heavy duty and longer than usual snubbing line to act as a good spring. We set this up with the snubbing fitting just below water level and with several feet of chain hanging on the vessel side of the fitting to add to the spring effect. We also pass a couple of loops of the this line around a substantial part of the hull's bulwark before securing it to a cleat as cleats have been known to pull right out of a deck in extreme gusts.
Now we record our GPS position and activate our anchor and depth alarms to monitor any dragging.
If depth, water temperature and visibility allow we check the anchor using a mask and snorkel to ensure the anchor is well set and not obstructed.
We then 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 that we are able to drop or cut the anchor chain and buoy it in an emergency. 
If there are other vessels nearby we put our buffers in position. 
We prefer to leave our tender in the water in case it's needed, but secure it well close behind Envoy’s stern. Never leave a lightweight tender on its painter behind your vessel in a strong wind as you may lose it or it may flip upside down.

Secure at anchor in Croatia's Loviste


Now is a good time to think what may happen if there is a significant wind shift or a need to move. Check the anchorage using radar and plotter during daylight to know exactly how it looks, because everything looks very different by night. It’s also a good idea for the skipper to get some sleep during the daytime when others can more easily monitor and handle any situation.
Before darkness arrives rig your spotlights, have flashlights to hand, turn the radar on standby, and ensure the engine is ready to start in case of any emergency arising, such as the need to avoid a dragging vessel, or the need to reduce strain on the anchor in very high gusts. As skipper, I also sleep in the pilot house so that I can constantly monitor the situation and 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 two or three feet, even in a sheltered bay with little fetch.
Sometimes your vessel will appear to drag a few metres as the chain straightens out along the seabed, so don’t be in too much of a hurry to move if the position alarm sounds.
Of course there is usually some trepidation and a need to maintain a state of high alert, but by following the above procedures we've safely and comfortably anchored though many blows.
We've never encountered winds above 70 knots and realise that circumstances may be very different in winds of for example 90 knots or more.
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 twice the strength of a 70 knot wind.
We’ll be happy not to experience trying to anchor in those conditions.
Happy and safe anchoring.


Tuesday, May 01, 2018

ANCHORING IN STRONG WINDS WITH SAFETY AND CONFIDENCE

Envoy is berthed in Greece's Lefkas Marina while Diane and I are home in Auckland. We're not planning any major Med cruising this year, but now hope to visit Lefkas around mid August to check on Envoy and do a few weeks cruising.

Pacific Passagemaker magazine recently published an article we'd written on anchoring in strong winds.
Here's the first of two parts of an edited version of that article.

Having done extensive coastal cruising for over 35 years in New Zealand, Australia, and the Mediterranean, we've anchored for literally thousands of nights, most of which have been calm, peaceful and uneventful. But we've often encountered winds over 30 knots (Beaufort 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. Adverse weather conditions and fronts can also bring along thunder storms, which are often accompanied by extremely gusty conditions as well as rapid changes in wind direction. It is probably these changes in direction that represent the biggest challenge to secure anchoring.




There are almost as many theories on the subject of anchoring as there are skippers on the water and these suggestions are mostly based on experience with our Nordhavn 46 trawler, Envoy
With time to prepare, a reliable and tested plan plus some anchoring experience with your own vessel, you can select a suitable location and anchor in strong winds with safety and confidence.
The process starts with awareness and normally there's a period of at least several hours to prepare for arrival of the forecast adverse conditions. Always write down the forecast and subsequent updates so you can accurately monitor how the weather pattern is developing.

In an unexpected storm a serene anchorage can quickly become problematic


This article does not cover the options of continuing a passage (as may be forced upon a vessel far from the coast), or of heading to the closest secure marina or harbour, but is about safe anchoring in a coastal situation.
A safe and comfortable anchorage is dependent on finding an inlet or bay largely protected from the ocean swell and seas. If the wind is forecast to blow directly off the coastal shoreline and there is no significant swell or sea, an option is to simply anchor close to shore, but a major disadvantage of this strategy is the possibility of a wind shift occurring and placing your vessel on a lee shore with waves whipped up by the wind shift. We prefer to pick the most secure anchorage we can find, free of swell or seas, suitable for a possible wind shift and clear of reefs, rocks, moorings or other obstructions. It needs a low tide depth ideally about three to fifteen metres and ideally should also have an easily navigable exit and a nearby alternative bolthole to go to if necessary. The ideal time to find your anchorage is during low tide when minimum depths are known and possible hazards can be more easily identified.

An ideal sheltered bay to weather a blow



This is the same bay during a storm with gusts to 50 knots


Another issue to consider is the placement of other vessels in the anchorage. A safe distance from other vessels must be maintained when anchoring in strong winds because other vessels dragging and fouling your anchor or hitting your vessel is usually the greatest danger to be faced.

Heavy towering clouds like this indicate storms


Before dropping your anchor it‘s a good idea to explore the general area and get a good understanding of its approaches, layout, depths etc. Use this opportunity to record GPS positions, compass courses and a chart plotter track line to assist exiting the bay in case of adverse visibility.
Although some skippers prefer to use two anchors we prefer to use one. A single anchor is easier to deploy and set, avoids issues of one anchor chain becoming twisted around the other during wind shifts when your vessel may turn around several times and is far easier to retrieve in an emergency.
However a situation where I would consider using two anchors is mooring stern-to-shore when the additional anchor helps resist your bow being blown sideways by beam winds (the main cause of problems when mooring stern-to).

Part two will be posted in about a week.