Para anchor vs series drogue

                                                                                                                          

 


 

Series drogue, para anchor, heaving to, lying ahull or running off are options for survival in storm conditions, which is best? Only you can evaluate your boats handling peculiarities and use this knowledge to choose the right storm tactics suited to your yacht.

Heaving to, Lying ahull, or Running off
It is important to note that most storms, even severe storms, do not create dangerous breaking waves. Sailors who survive such storms may conclude that the tactics they employ, such as heaving to, lying ahull or running off, are adequate to prevent capsize. This is a serious mistake. There is very compelling evidence to show that while a well found boat will survive a storm in non-breaking waves, none of the above tactics will prevent capsize in a breaking wave strike.
U.S. Coast Guard Report CG-D-20-87 sec1-1

Columbia River Bar, Coast Guard testing site for Series Drogue

Sea anchors and Para anchors
The sellers of para anchors promote these items as bullet proof protection in storm survival situations, we question the veracity of this description.

Para anchor positives
A vessel disabled, in danger of closing with land or other hazards can hold station, until the problem is fixed or help arrives.

In moderate weather, before seas begin to break dangerously, parachute anchors are effective at helping boats hold station. Many of the users whom we have interviewed speak well of their experiences in moderate gale conditions
Steve Dashew

Fishing boats with hulls designed to sit parallel to anchor lines, sit well to a para anchor, they are widely used by squid fishers, to hold station while fishing.

Para anchors - what the experts say
Many yachts yaw and sail at anchor, and even more on para anchors, this phenomenon is called shearing. If a wave hits the bow in this shear cycle the boat can be forced backwards, resulting in :-


____i)Damage to rudder.
____ii)Breaking rode.
____iii)Rolling over.
____iv)Forcing water thru exhaust system under extreme pressure and into the engine.
____v) All of the above


In the trough of a wave/swell the para anchor rode goes slack, the yacht will commence to yaw wanting to lie ahull, leaving it partially or totally beam to sea with the possibility of being knocked flat or rolled.

Even with a large sea anchor the bow of a modern yacht will tend to yaw away from the wind when the towline goes slack as it will when the boat passes through the trough of the wave. For these reasons the use of a sea anchor deployed from the bow is not recommended
U.S. Coast Guard Report No CG-D-20-87 sec 6-6

Anecdotal evidence - para-anchors in storms
Para anchor users interviewed all find their parachute anchors extremely difficult to retrieve in other than moderate wind and sea.
A major factor regarding both personal comfort and ones use of parachute anchors in breaking seas is the boats tendency to sail at anchor. As stated earlier, if your boat sails on the hook, the odds are it will sail around even more fiercely while lying to a parachute in the middle of the ocean. This oscillation creates extreme loads, presents the bow at a wide and dangerous angle to the sea, and is extremely uncomfortable.
There are two ways around this. One is some form of riding sail or backstaysail as weve discussed. The other is to bridle the parachute off the bow, as advocated by the Pardeys. The bridle is used with a reefed trysail or deeply reefed main to increase resistance to rolling. A key feature of this approach for the Pardeys is the creation of a slick off their keel, which - theoretically, at least - calms the seas. This is a major safety issue, because without the slick, the boat is now lying at an angle of 50 deg or 60 deg to breaking crests, quite vulnerable to a knockdown or worse. I have no doubt that the Pardeys Seraffyn did in fact create a slick to windward in its day, but I have never seen this myself, and I have interviewed only one other sailor who claims to have been able to crate this type of beneficial slick and have it work as advertised.
In furiously breaking seas, the situation worsens dramatically. An excellent example of problems encountered comes from the experience of the Burman family aboard Freya, a Stan Huntington-designed, heavy displacement, full-keel 46-footer. Last spring, Freya was caught in a major storm off the coast of New Zealand. Rather than close with a lee shore in difficult conditions, Bruce Burman decided to deploy his 18-foot Para-Tech sea anchor. This was attached to a 450 foot piece of New England Ropes three-strand nylon. The rode was new, right off the spol, had never before been used, and was the size recommended for this vessel.
Dry breaking strength on the rode was 16,700 pounds (wet, about 20 percent less). The Para-Tech anchor was good for roughly 10,000 pounds of load, and then would start to blow panels, which in turn would relieve the load on the rode. The rode was attached to a heavy bronze cleat, fastened with four 5/16 stainless steel bolts, recently replaced and beefed up with a backing-plate under the deck. The four bolts and cleat would probably bear 12,000 pounds or more of load. Bruce Burman eased the rode out a couple of feet every two hours. The rode went through a bronze chock, and no sign of chafe was observed.
During the first evening of the storm, Freya was knocked down and rolled while lying to the parachute anchor. Because the wind had developed from a compression zone between vigorous high and low-pressure systems, the wind direction was relatively steady. Data from the helicopter pilot who eventually picked up the Burman family confirmed that there were no crossing seas from wind shifts or other conflicting storm systems.
Either during the knockdown or just before it, the rode parted about 10 feet off the bow in what appeared to be a tension failure. While the failure was unfortunate for the Burman family, it provides a valuable data window for the rest of us - an opportunity to get a handle on the loads involved.
Steve Dashew

 


U.S. Coast Guard conclusions - series drogue vs para anchor.
This paper documents the investigation of the use of drogues/sea anchors to prevent small sailing yacht capsize in breaking seas. The following conclusions were reached:

i) _____In many and possibly most cases, a properly engineered drogue can prevent breaking wave capsizing.
ii)___._ For fin keel sailing yachts the drogue/sea anchor should be deployed from the stern, not the bow.
iii) ____A series type drogue provides significant advantages over a cone or parachute type drogue/sea anchor.
iv) ____A full-scale series drogue demonstrated satisfactory handling and durability characteristics under simulated storm conditions and in actual breaking wave conditions.
v) ___._A recommended design specification including design loads is presented for cone, parachute and series type drogues.


U.S. Coast Guard Report CG-D-2087 sec 7-0


Columbia River bar

Why the U.S. Coast Guard thinks the series drogue is better than a para-anchor in storms.


The two conventional drogue configurations are the cone drogue and the parachute drogue/sea anchor. Both types have been used successfully in a variety of applications. A third type of drogue called a series drogue has been developed as part of this investigation. The series drogue is intended to provide near optimum performance under storm conditions and to avoid some of the problems encountered with cone and parachute drogue/sea anchor.


The series drogue offers the following desirable features:
If pre-rigged and coiled down into lazeret, the drogue is simple and safe to deploy under difficult storm conditions. The boat, under bare poles, will be either running off lying ahull. The anchor can be slipped over the stern and the line payed out. The drogue will build up load gradually as it feeds out.
It is almost impossible to foul it or entangle it enough to make the drogue ineffective.
The drogue ride-s beneath the waves and is not affected by the following sea even if a wave should break in the vicinity. There are cases on record where a cone drogue has been pulled out of the face of a following wave, and even instances where the drogue has been catapulted ahead of the boat. It is difficult to weight a cone or parachute drogue so that it will ride at a sufficient depth to avoid the wave motion. As discussed previously in this report, a weight causes the drogue to collapse when the towline goes slack.
When the boat is in the trough of a large wave, the towline tends to go slack thus permitting the boat to yaw. With the series drogue, the anchor sinks pulling the drogue backwards and taking some of the unwanted slack out of the towline.


When a breaking wave strikes, the drogue must catch the boat quickly to prevent a broach. The series drogue, since some of the cones are near the boat where towline stretch is low, will build up load faster than a conventional cone or chute at the end of the towline/bowline. A computer study shows that two seconds after wave strike, the series drogue will develop 40% more load than an equivalent cone or chute. Similarly, if the breaking wave strikes at an angle to the towline rather than directly astern, the series drogue will build up load much faster than the conventional types.


The series drogue is durable as demonstrated by the testing described in this report. The load on each individual element is low. No single failure can make the drogue ineffective.
The series drogue can double in function as a spare anchor line and can use the boat's regular anchor as a weight. All 90 cones weigh only four pounds.
U.S. Coast Guard Report CG-D-20-87 sec 6-5

More Para-anchor thoughts.

To reiterate our feeling on the subject of parachute anchors in particular and storm tactics in general - there is no magic bullet. There is no single piece of gear or any specific tactic which works for all boats in all conditions. If you are caught in dangerous weather, the tactics employed - regardless of whether they are passive or active, must be modified to suit the sea state, wind, and navigational issues as they change. Obviously crew and vessel capabilities have a lot to do with what approach has the lowest risk factor.
We have nothing against parachute anchors per se, and in moderate conditions, where seas are not breaking dangerously, properly deployed, they can do a good job of holding you in position. But then, so can heaving to.
The difficulty arises in breaking seas. When we were doing our research for Surviving the storm, we did not find a single positive experience in these conditions using para anchors. And the unmistakable conclusion for us from this is that in dangerously breaking seas, tactics other than a parachute anchor have a higher chance of success - for most situations.
Steve Dashew

Series Drogues and boat design

With a series drogue deployed, a well-designed and properly constructed fibreglass boat should be capable of riding through a Fastnet type storm with no structural damage. Model tests indicate that the loads on the hull and rigging in a breaking wave strike should not be excessive.
Many sailors are reluctant to deploy a drogue from the stern because they fear that the boat may suffer structural damage if the breaking wave strikes the flat transom, the cockpit and the companionway doors. The model tests do not show this to be a serious problem. The boat is accelerated up to wave speed and the velocity of the breaking crest is not high relative to the boat. The stern is actually more buoyant than the bow, and will rise with the wave. However, the boat may be swept from the stern. The cockpit may fill and moving water may strike the companionway doors. The structural strength of the transom, the cockpit floor and seat, and the companionway doors should be checked at a loading corresponding to a water jet velocity of approximately 15 ft./sec.
When a boat is riding to a series drogue no action is required of the crew. The cockpit may not be habitable and the crew should remain in the cabin with the companionway closed. In a severe wave strike the linear and angular acceleration of the boat may be high. Safety straps designed for a load of at least 4g should be provided for crew restraint. All heavy objects in the cabin should be firmly secured for negative accelerations and drawers and lockers should be provided with latches or ties which will not open even with significant distortion of the hull structure.


U.S. Coast Guard Report CG-D-20-87 sec 6-4



Broaching yacht 1

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Broaching yacht 2

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Broaching yacht 3

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Broaching yacht 4

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Broaching yacht 5

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Broaching yacht 6


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