Most sailors are familiar with Thor Heyedrahl’s adventures aboard his balsa raft Kon Tiki. Some may remember the self-rescue line that they dragged behind the boat. Since the raft travelled so slowly, this last chance line gave a fit sailor a sporting chance to haul himself aboard.
The difference, of course, is that modern boats are much faster than the glacially slow Kon Tiki. As documented in our four-volume Practical Sailor ebook Man Overboard Prevention and Recovery, the challenges of making contact and getting the person in the water back on board are complex. Although we’ve heard of self-rescue lines on cruising boats, we found little evidence that these sailors had actually tried their inventions. So we set about doing this.
Pondering the problem, it seemed obvious that for such a system to reliably work with a modern cruiser, we’d need to also stop the boat.
What We Tested
Our focus here is on smaller sailboats, typically less than 27 feet, because this is the size of boat for which a last chance line is often suggested. These small cruisers are frequently singlehanded, and because of their narrow decks, MOB prevention through the use of tethers and jacklines is often more difficult. Finally, they are generally slower and lighter, which gives these strategies the best possible chance of working. Do not attempt to transfer any of this testing to larger boats.
First, we timed swimmers falling off a boat and estimated the time required to reach and firmly grab a trailing line. We then established drag data for a person in a Type III personal floatation device (PFD) at a range of speeds. Finally, we rigged a boat brake from a trailing line, parachute sea anchor, and nylon climbing rope and tested it by allowing a swimmer to trigger the device.
How We Tested
Our test boat was a Corsair F-24 trimaran. Though capable of speeds in the mid to high teens, we focused our testing at around 7 knots, the maximum probable speed of boats in this class. Our swimmer wore a Type III PFD place of foul weather gear, the water was warm, and we felt this might reasonably simulate the drag of a rainsuit with a slimmer manually inflatable PFD. Because a PFD will inhibit your ability to swim and climb back aboard, you will want to delay inflation until after the last chance line failed.
The drag of a body was measured using a load cell. The effectiveness of the braking system was evaluated on a variety of courses, both upwind and downwind, using working sails and a reacher, as well as under power at wide open throttle. Test speeds ranged from 5-7 knots.
We tested only in light to moderate winds and only during the day. At night finding the rope would take a miracle, and rough weather introduced too many safety hazards.
The tester was a reasonably fit 57-year old sailor. Fitness is important; unless you can swim a few laps of the pool at a good pace and do 10 pull-ups without blinking, this may be difficult or require a different design.
Observations
Grabbing a line dragging through the water is tough, and pulling yourself 100 feet or more back the boat at speed is a serious workout.
About 3.5 knots was the greatest speed we could reliably grab a 7/16-inch nylon double-braid line. With a 3/8-inch double braid polypropylene line, the fastest speed our tester could still grab the line at was 3 knots.
Getting back to the boat requires much slower speeds. About 2.5 knots was the practical upper speed for hauling oneself, fully clothed, back 100 feet to the boat. At this speed, the ordeal was extremely difficult, on a par with 20 pullups.
About 1.5 knots is probably the maximum practical speed for pulling yourself up the line. The effort required is akin to hoisting a sail hand over hand 150 feet or more without stopping.
Clearly the longer the trailing line, the better, but there has to be some limit. We settled on a length of 150 feet. In our best trials, with an aware victim who knew what was coming, it took 10 seconds to react, begin swimming, and reach the rope to grab it. At seven knots an object can travel about 120 feet in those 10 seconds. In fact we were often close to the end of our 150-foot trail line when we reached it.
Finding a floating line in rough water or at night would be more difficult, if not impossible. You may not feel the line while wearing foul weather gear and gloves, making the operation akin to catching spider silk with a baseball mitt. In the rain or at night, the chances of success are very low. Thus, our minimum length of 150 feet.
Boat Brake Design
The system includes a 150-foot floating grab line with a 4-inch float on the end. This is attached to the apex of a five-foot diameter parachute, the bag it is stored in, and the attachment of the parachute. The drag created by the grab line reduced speed by about one-tenth of a knot.
There is a recovery float attached to the apex of the chute on a 6-foot line; this is standard rigging for sea anchors, and keeps them near the surface and eases recovery. The parachute was then attached to a stern cleat via 100 feet of 11-mm nylon climbing rope (UIAA certified).
The parachute, recovery float, and nylon rode are stored in a long nylon stuff sack that is secured to the aft deck with a bungee cord. When the floating line is given a light tug, the parachute is pulled from the stuff sack and deployed, similar to the action of a ripcord on a skydiving parachute. As soon as the floating line is given a tug, it no longer pulls away from the victim, since the boat brake is now floating back toward the victim.
When the nylon line draws tight, the parachute fully deploys, the boat slows from 7 knots to 1.4 knots in about 5 to 8 seconds. Needless to say, the line should terminate at a well-reinforced cleat or strong-point on deck. Measured peak impact forces ranged from 240-480 pounds, about the equivalent of the loads imposed on an anchor cleat in storm winds.
Self-Rescue
As soon as you fall off the boat, swim over to the line on the float and give it a firm yank. This should take no more than 15 seconds. The floating line will then go slack; you should take this time to reel in as much of the floating line as possible, as this will minimize the distance you have to pull yourself back to the boat.
Once the chute reaches full extension, the boat will slow to about 1.4 knots. It is then reasonable to pull yourself up to the boat, hand over hand. Presumably, you have a boarding ladder that can be released from the water. Alternatively, a webbing ladder could deploy with the parachute rode.
It took about 10 seconds to reach the line. This could obviously take longer. The bag pulled off the transom promptly when the floating line was tugged.
In our tests under power, the 9.9 horsepower engine bogged down as the boat decelerated from 7 knots to 1.4 knots in about 5 seconds. It then took the better part of two minutes for the tester to pull himself on to the boat. The effort was somewhat vigorous, but not by any stretch exhausting, depending on fitness.
Any eyes for joining or terminating lines were made using figure 8 knots, which were never difficult to untie. This reinforces our belief that the actual loads on the rig and boat hardware are not excessive, well within the 740-pound working load limit of 7/16-inch nylon climbing rope.
Estimating Size
The design of the system must be matched to the boat. Kinetic energy of the boat is given by:
Ek=1/2MV^2. If mass is in pounds and velocity is in knots, Ek = 0.04MV^2 in foot-pounds.
Thus, to slow our 2600-pound boat from 7 knots to 3 knots required dissipating 4,200 foot-pounds of energy. Our climbing rope could safely absorb 100 foot-pounds per foot, so a minimum of 42 feet of rope is required. We used 100 feet, safely extending our stopping capacity for the test boat to 10 knots.
Additionally, the parachute will dissipate considerable energy opening and tearing through the water, about equal to the energy absorption by the rope. As a result, the actual forces we measured in our test were far lower than energy absorption by the rope alone would suggest.
Nylon rope is weakened about 15 percent when wet and loses about 40 percent of its maximum dynamic braking ability. There are other considerations that can vary by boat, and as you put together your own system, it would be best if an engineer reviewed the design.
Although we used a 5-foot diameter parachute sea anchor and testing, it may be practical to use any number of commercial drogues, including a drogue that might be used to control the boat in heavy weather. If the boat brake were rigged from a bridle, this could conceivably be dual-purpose equipment. That said, the advantage of a chute is that it provides the most stopping force in the smallest package; a Seabrake or Delta Drogue of sufficient size to slow the boat to 1.5 knots would be enormous.
Other Ideas
What about systems that stop the boat by turning the engine off, disengaging the autopilot, or pulling the tiller hard over? These have potential, but none are complete in themselves.
There are wireless systems to cut the engine, which we will explore in a future article, but they don’t stop the boat and they don’t bring it back to you.
Some boats don’t stop if the tiller is put hard over; our last test boat would tack, but then continue to plow ahead at 4 to 5 knots.
What about just releasing the tiller and letting the boat shoot into irons? If the boat is reaching, with large head sails, it may just keep going. Even the most complex autopilot tie-in may not bring the boat under control. And in all cases, the trailing line will still be required to get yourself back to the boat.
We will be exploring these options in a future article. But if it was that easy, MOBs would always be recovered in minutes and no one would be lost. We think it is not that simple.
Rather like killing ants with a hammer, the parachute brake approach assumes nothing about course, sail selection, or if the engine is running. Force meets force. Higher speed, more sail area, and larger boats present more challenging the engineering.
Calculations must be made and strengths confirmed. But being able to simply stop presents interesting possibilities, even with crew.
Ideally, every crewmember on your boat should be familiar with MOB recovery techniques (see PS January 2010), but if the crew is injured or otherwise unable to manage a Quick Stop under sail, the brake is an option.
In this case, someone could deploy the parachute anchor, drop the spinnaker, clear up the lines, start the engine, and then cut the drogue loose if necessary for rescue. The ability to quickly brake prevents the boat from going farther downwind in the process.
Or perhaps the swimmer is tethered but drowning in the bow wave. If we can hit the brakes, stop the boat in 10 seconds, and then haul him back aboard with the boat heeling but more stationary. We leave it to you to discover the right application.
Conclusions
There is no practical chance of hauling yourself back to the boat, along a floating line while going 7 knots. We doubt it’s a realistic plan above 3 knots, and probably not above 1.5 knots if the water is cold.
The parachute sea anchor stop worked every time. We’ve been testing drogues and sea anchors in this way for years, throwing them off the back at speed to apply test loads. We’ve never experienced a failure to deploy or any gear damage. But even after we were sure of our systems, with crew in control on board, watching the boat sail away made even the most jaded tester slightly queasy. Something could foul, a line could break, and you can miss the floating trip line.
This is not offered as an engineered solution. It is intended only to provoke thought regarding safety systems for single-handed sailors.
Use short tethers, stay low, and stay on the boat. The difficulty in finding the rope in challenging conditions is reason enough for us to Not Recommend this method as a primary MOB prevention system.
It can also be deployed a glued loop line attached to winch so you can go back to the boat with minimum effort, a pulley system could be attached too.
Also two lines attached to tiller by both sides to control steering should help
This type of system should be mandatory and regularly practiced