A drogue (or sea anchor) is towed from the stern of a vessel in severe conditions in order to reduce its speed and hold its stern to the oncoming seas. This allows for better steering control and helps to prevent the boat being caught broadside on to the seas and possibly broaching, or potentially rolling or pitch-polling.
Yachts venturing offshore are well advised to consider equipping the vessel with a drogue, and racing boats in AYF category 3 and above are required to have a means of deploying one. (Depending on the brand chosen, this can also fulfill the emergency steering requirement under AYF racing rules.)
The drogue line needs to be strong enough to withstand significant force and shock-loading. Thimbled eye splices are generally recommended and a length of chain is usually required to submerge the drogue to an adequate depth. The other factor to consider is the method of attachment to the stern of the vessel; some form of bridle may be required to spread the load over several cleats or winches.
Ocean Rigging can advise, supply and assemble the line and drogue to the recommended specifications (including the splicing, thimbles, chain, line and any bridle system that may be required).