Drogues and Sea Anchors
This page is a report of research I did, triggered by a thread in the OPENBOAT Yahoo group. The thread was mostly focused on drogues for dinghies but I found it interesting and wanted to know more.
I had several questions in my mind:
- What are Drogues and Sea Anchors
- What does a Drogue Look like?
- When is a Drogue Used?
- What is the benefit of using a Drogue?
- What are the Problems In Using a Drogue?
- What does a Sea Anchor Look Like?
- When is a Sea Anchor Used?
- What is the benefit of using a Sea Anchor?
- What are the Problems in Using a Sea Anchor?
- I compiled a web page with many of the documents and articles on Drogues and Sea Anchors. It makes for very informative reading
What are Drogues and Sea Anchors
Drogues and Sea Anchors are devices which are used in open water conditions where anchoring is not possible, or in conditions where anchoring is not desirable. Drogues and Sea Anchors help stop the drift of a boat in difficult conditions including high wind or when there are large breaking waves. They can also be useful to help control a towed boat or a boat with damaged steering. They are deployed from the bow or stern of a boat and their effect is due to the drag they have.
What is a Sea Anchor?
A SEA ANCHOR is designed to stop the drift of a boat in open water. Sea anchors are usually deployed from the bow of a ship. They are often shaped like large parachutes.
What is a Drogue?
A Drogue is a device designed to slow down or help control the drift of a boat. It is not intended to stop most of the drift but rather to slow the boat down by pulling from the stern. Deploying a drogue not only has the effect of slowing down the boat and but it also helps keep it properly aligned thus improving control and safety. Drogues are usually deployed from the Stern.
What Does a Drogue Look Like?
There are many different models of drogues which have been tried.
The more common one is a long cone with the narrow end open.
Another common shape is a long rope with a whole series of smaller open bottom cones threaded on. This is a link to Sailrite Youtube Video on making a Jordan Series Drogue from one of their kits.
One also sees several variations of closed pouches and small parachutes and open cones.
When is a Drogue Used
Drogues are often used by fishermen who want to drift slowly without having to motor. They motor upwind to the area they want to fish, stop the motor and let the drogue slow the drift.
Another useful use of a drogue is to help control a boat that is being towed. By adding drag to the stern and resistance to towing, the drogue helps control the sideway motion and potential bounce effect. It is also helpful when towing boats which have damaged or reduced rudders.
A third use of drogues is in high winds when running (with strong following seas) it helps keep the boat pointed downwind and slows its progress so that the wind does not accelerate the boat into the trough and potentially catch the oncoming wave and pitchpole. It is very useful when there is a strong following sea. Many sea going sailing yachts have reported great improvement in steering ability and general responsiveness after setting a drogue.
Deploying a drogue can reduce the angle of yaw and give a smoother ride.
In an emergency a drogue can help steer the boat if the rudder has been damaged. It can also be used to help steer and stabilize a boat when trying to get into a dangerous harbour entrance in poor conditions, in this case the drogue is deployed to winward.
Para-Tech Engineering has a page on drogue use. It's a useful read. They make the Delta Drogue.
What are the problems using a Drogue or Sea Brake
Deploying a sea brake (or drogue) can be tricky. They can get tangled because of the long rode required.
Recovering a drogue can also be difficult since some drogues such as the jordan series drogues, can cause a lot of drag.Trip lines are not always easily used.
Drogues can twist and unwind a rope, for this reason they are sometimes set up with a swivel.
The drag can be quite strong particularly in storm conditions and boat fittings can be damaged or pulled out. Chafe is also an issue.
If the wind shifts suddenly, the pull of the drogue can be from the side and be dangerous. It can drag the boat sideways and cause a broach.
What Does a Sea Anchor Look Like?
Unlike drogues, sea anchors aim to stop the boat almost completely. For this reason they tend to be larger than drogues.
Paratech Sea Anchor Link to sea anchors: paratech sea anchor
There are several design, the most common is in the shape of a parachute. Old army surplus parachute were often employed as sea anchor in the past. These parachute anchors are often quite large and a width of twice the beam of the boat are not unknown.
Jordan drogues are also used as sea anchors by adding cones till the drag is sufficient.
Deployment of a sea anchor is critical and chain plus long lines are used both to keep the anchor positioned under water and to prevent the anchor from skipping out when it is in the trough of a wave.
When are Sea Anchors Used
Sea anchors are deployed when it is necessary to drastically reduce the drift of a boat downwind. If the boat was headed for a lea shore and not responding to controls because of mechanical failure or stormy conditions an anchor would arrest the boat. Note that an anchor drastically slows the drift due to wind and waves, but is not useful against current.
Since sea anchors are usually set from the bow of a boat, they keep the nose into the wind.
Sea anchors are usually set when the sails have been taken down.
Another use for sea anchors and Ship Arrestors are in salvage operations where a ship's drift needs to be minimized. Miko Marine Ship Arrestor.
What are the Problems associated with Sea Anchors
Large sea anchors are tricky and often dangerous to set and retrieve because of their size and shape. They are usually set during rough weather which makes it even more difficult to handle them. People are not safe on deck during gale weather, particularly when trying to deploy large parachute like objects.
Because gale conditions are sometimes quite extreme and changing, keeping the anchor in good position is very important. If the anchor goes too deep it might keep the boat from bouncing on the waves and pull the bow of the boat underwater.
Wind shifts can cause the anchor to pull the boat sideways against waves.
Forces acting on the boat can be extremely strong and pull out the cleats or other attachments. The same forces can cause chafe on the lines.
It can be quite difficult to collapse a sea anchor in order to retrieve it on board. Sometimes trip lines are included in the rigging.
Will I carry a Drogue or a Sea Anchor in either of my boats?
I will not carry a sea anchor. I will however get a series drogue for the Tanzer, and a smaller cone for the Skerry. I believe this would increase the level of safety and give me more options when I get caught in rough weather.
I compiled a web page with many of the documents and articles on Drogues and Sea Anchors. It makes for very informative reading
I try to be accurate and check my information, but mistakes happen.email me if you find mistakes, I'll fix them and we'll all benefit: Christine