What the US Coast Guard Reports say
In U.S. Coast Guard Report CG-D-20-87 it is noted that most storms, even severe ones, do not create dangerous breaking waves. It also points out that those who have survived such storms typically concluded that the tactics they employed, such as heaving to, lying ahull or running off, were adequate to prevent capsize but that this is usually a serious mistake. It is reported that there is very compelling evidence to show that while a well-found boat will likely survive a storm in non-breaking waves, none of the above tactics will prevent a capsize during a breaking wave strike.
The same Coast Guard Report documents the investigation into the use of sea anchors vs series drogues to prevent sailing yachts from capsizing in breaking seas. The following conclusions were reached:
- In many and possibly most cases, a properly engineered series drogue can prevent breaking wave capsizes.
- For fin keel sailing yachts a drogue or sea anchor should be deployed from the stern, not the bow.
- A series-type drogue provides significant advantages over a cone or parachute-type drogue or sea anchor.
- A full-scale series drogue demonstrated satisfactory handling and durability characteristics under simulated storm conditions and in actual breaking wave conditions.
- A recommended design specification including design loads is presented for cone, parachute and series type drogues.
Why the U.S. Coast Guard thinks series drogues are better than parachute anchors in a storm.
The US Coast Guard Report cites the series drogue as simple and safe to deploy under the difficult conditions experienced during a storm as the drogue is simply payed out over the stern where it gradually builds up the load as it is fed into the water, unlike a parachute anchor which suddenly tensions up when it inflates. This is assuming that the series drogue is deployed while the boat is moving slowly. Any vessel that is moving at great speed should first be slowed down by heading into the wind or heaving-to briefly while the drogue is deployed as otherwise it may run out too quickly to manage safely. A series drogue, however, is also almost impossible to foul or entangle enough to make it ineffective.
A major advantage of the series drogue is that it rides beneath the waves and is not affected by a following sea, even when a wave breaks in the wave that the drogue is buried in. Also, as some of the cones in a series drogue are nearer the vessel where there is relatively little stretch in the line, the load on these cones builds up faster than the load on a single parachute at the end of a line. In fact a computer study has shown that two seconds after a wave strike the series drogue develops 40% more load than an equivalent single parachute does. The series drogue can also build up a load much more quickly than a parachute can when a wave strikes at an angle to the line. This is important because the drogue must be able to catch the boat quickly to prevent a broach from occurring.
The Coast Guard Report also highlights how the tests demonstrate just how much more durable the series drogue is than a parachute anchor due to the loading on the individual cones being so low and complete failure not occurring, even if several cones failed.