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Heavy weather sailing - drogues and para-anchors
By Duncan | August 12, 2008
Plan for the worst and hope for the best - probably the best basis on which to plan long ocean voyages. While hoping for 15-20 knots of wind at TWA of 140 degrees, we do need to plan for conditions of 40+ knots of wind and serious seas, so onto the ‘fun’ task of planning for more ‘exciting’ times…
In heavy weather sailing the main risk is capsizing, the now infamous Fastnet of 1979 demonstrated the necessity of proper drogues in a rather macabre fashion with 23 boats abandoned or sunk, and the tragic death of 15 sailors. For modern day sailors the lessons learnt as a result have been invaluable, and advanced the quality of yacht safet gear immensely, not least through the lesson of always stepping up into a liferaft and never down. However here I am focussed on the avoidance of capsizing.
Keel yachts are clearly not designed to capsize, and it takes a rather extreme set of conditions to cause this, well, I can think of 2 conditions:
- Loss of keel
- Big breaking waves
Now, losing the keel will generally only be the result of poor design or damage as a result of impact causing delamination of the matrix, so let’s discount this for now and focus on big breaking waves. The exact mechanics associated with capsizing boats is complex, and I haven’t sudied them in detail, rather focus on the simplified summaries from RORC and US Coastguard studies. Essentially if a boat is beam onto the wave, it can be rolled relatively easily, so the key is to keep to boat inline with the direction of travel of the wave. Up to a point, this can be acheived through sailing and helm control, however there can come a point where the speed of the water rushing down the face of a breaking wave will accelerate a boat to speeds in excess of 40 mph before it crashes into the trough of the wave. This is generally considered to be a bad thing.
Therefore there is a need to slow the boat to a controllable speed. This is acheived through throwing stuff over the bow or stern to act as a drag on the boat - whatever you throw over can be referred to as a drogue, though modern day parlance tends to refer to conical shaped devices thrown off the stern as drogues and parachute style devices deployed off the bow as para-anchors. From the research we have done, there seems to be 3 main types of drogue:
- Classic / admiratly type drogue
- Series drogue
- Parachute anchor
The classic drogue is a single conical shaped unit deployed from the stern. The series drogue consists of 107+ 5 inch diameter cones attached to up to 80 metres of double braid nylon deployed from the stern. The parachute anchor is a heavy duty parachute deployed from the bows. The classic and series drogues are both designed to slow the boat and keep the stern pointing into the waves and bow pointing down. The parachute anchor is designed to keep the bows pointing into the waves, up the slope. The parachute anchor is the most expensive option, and seems to be preferred among many of the yachtsmen I have spoken to. It is also the hardest to recover.
In terms of reviews or drogue performance, the best research I have found on performance was prepared by the US Coastguard in 1987 following RORC research based on learnings from the 1979 Fastnet, you can find it on the Jordan Series Drogue website here. For simplicity I have quoted the conclusions from this report below:
“This paper documents the investigation of the use of drogues to prevent small sailing yacht capsize in breaking seas. The following conclusions were reached:
1. In many and possibly most cases, a properly engineered drogue can prevent breaking wave capsizing.
2. For fin keel sailing yachts the drogue should be deployed from the stern, not the bow.
3. A series type drogue provides significant advantages over a cone or parachute type drogue.
4. A full-scale series drogue demonstrated satisfactory handling and durability characteristics under simulated storm conditions and in actual breaking wave conditions.
5. A recommended design specification including design loads is presented for cone, parachute and series type drogues.
There are no patents or proprietary information associated with the series drogue. It is hoped that some sailors who venture offshore will construct a series drogue using the recommendations contained in this report. As experience and knowledge are gained, this device could become part of the standard safety gear used on yachts. Preventing capsize, and its subsequent damage to the boat and potential loss of life, will be the ultimate benefit.”
I have read the whole report, and the paragraphs above summarise it very well. Essentially it seems the series drogue is the best option, coupled with the fact that there are no copyrights associated with it, and it can be made by anyone with a sewing maching and the ability to splice double braid rope (or be able to find a rigger that can) makes me wonder why these aren’t more common.
The more common parachute drogue can cause the boat to lie beam across the waves when the line goes slack and then get hit violently when a wave hits causing a significan shear on the boat/para-anchor system, potentially causing damage, the Coastguard report referenced above has the following to say on para-anchors:
“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
For my part, I am embarking the construction of a series drogue. While you can buy these, the simplicity of design and fabrication means I would rather spend the time making one, than spend $1200 or so on a fully completed unit. Now I must confess, when I say “I am embarking…” what I actually mean, is that my lovely mother has said she isn’t totally averse to sewing up 107 cones…stay tunes, updates of progress, and (hopefully) videos of the construction will follow….
A useful guide to building your own Johnson Series Drogue can be found here.
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