What Determines the Effectiveness of a Life Jacket? Life Jackets #3
3: What Determines the Effectiveness of a Life Jacket?
Different Boaters May Benefit from Different Features
“Safety Moments, in support of the Culture of Safety”
By Chuck Hawley, San Francisco Station, 1/1/2025
The underlying reason to wear a life jacket is to provide buoyancy to keep the wearer’s mouth above the water to prevent drowning while awaiting rescue. With that relatively simple goal, why are there so many life jacket designs, and why are some more effective than others? One reason is that boating is quite varied, from calm water kayaking to waterskiing to crossing oceans on catamarans. Different boaters may desire hypothermia protection, or rough water survival, or freedom of movement, over other attributes. Unfortunately, it’s not always possible to ascertain the technical properties of a life jacket from the information available to the consumer that’s provided by the manufacturer, but general observations can paint a picture of the pros and cons of a particular model.
NOTE: The new life jacket labels which are appearing on the new generation of life jackets are far superior to the acres of tiny text that used to be the norm. We’ll have an article on those labels in the future. A sample of the new label design is embedded in this article.
Total Buoyancy
Total buoyancy can be thought of as the amount of weight that it takes to completely submerge the life jacket. However, all items weigh less due to the water they displace when submerged in water, so it may be easier to think of the amount of force it would take to press a lifejacket completely under water. Not including children’s life jackets, life jackets are available from about 11# (50 Newtons) of buoyancy to 60# (275 Newtons). (Technically, the 11# models are not legally life jackets, but rather buoyancy aids.)
More buoyancy generally relates to more airway freeboard and a shorter heave period and it will be of benefit in short, choppy seas. Heave period is described in more detail below, but simply it is the time that it takes to get back on the surface of the water so you can breathe.
Reserve Buoyancy
Reserve buoyancy refers to the volume of an item that is above the waterline, and available to “pop” the person (or ship) to the surface when it is forced farther under the water. A water skier may wear a vest that is barely visible in still water: the buoyancy of the life jacket is “at work”, lifting the skier’s head out of the water. But as the wake from a nearby boat travels past the skier, the skier will bob up and down (and the airway will be submerged) because there’s no reserve buoyancy.
Alternatively, a sailor wearing a high buoyancy inflatable life jacket may have ⅓ or more of its total volume above the waterline. The reserve buoyancy is obvious because it can be seen around the sailor’s head and shoulders. If a wave passes by the sailor and he bobs up and down in the water, the reserve buoyancy will temporarily be submerged and will lift him back to the surface quickly. That’s one of the reasons that while a person may only need 15 or so pounds of buoyancy to keep his mouth above water in calm conditions, the same person may require 35 pounds in choppy conditions.
More reserve buoyancy generally corresponds to a shorter heave period.
Freeboard
Freeboard in the life jacket sense is analogous to freeboard in yacht design. With life jackets, it’s the distance between the “waterplane” and the person’s mouth. Think of the waterplane as being the surface of the water surrounding the life jacket wearer when it’s calm.
Most approved life jackets will provide about 1.5 to 4.5” of freeboard. Putting it another way, a person can breathe without treading water in calm water with an approved life jacket.
Freeboard can be increased by the wearer if s/he uses leg straps to pull the buoyancy (the inflated chamber or possibly the foam material in the life jacket) down into the water. If you immerse more of the buoyancy, you will rise in the water. Presuming you could take the entire life jacket and put it between your legs, with none of it showing above the waterplane, you’d rise out of the water as far as possible. Increased freeboard is one of many performance improvements that leg straps offer.
Righting Ability
Ideally, a life jacket would turn you face-up if a wave rolled you over, or perhaps if you were too cold or exhausted to maintain a face-up attitude by yourself. In general, life jackets can “right” you, or keep you face-up, if they have more flotation in the chest area than the back. This is obvious with most inflatables and many high-buoyancy inherently buoyant life jackets.
A small detail is that many life jackets that used to be categorized as “Type I” with 22-24# of buoyancy had asymmetrical construction. If you look at them closely, one side of the front of the life jacket has more foam than the other. This was done to force the wearer to rollover due to the incremental rolling force on one side of the chest.
What types of life jackets fail the righting test? In general, those life jackets with nearly equal buoyancy on the chest and back side will float the wearer as easily face-up as face-down. It takes swimming effort on the part of the wearer to maintain a face-up orientation.
What kind of boater stands to benefit most from a life jacket with good turning performance? There are several categories, but overall, if there’s a chance of being unconscious in the water, you want the life jacket to turn you face-up.
- If there is a chance of being knocked unconscious due to a high speed impact (think jet ski or drag boat).
- If the water is so cold that you could be overcome by hypothermia.
- If you need to reduce your heat loss in cold water and assume the HELP posture (can’t hold the HELP posture with a dinghy vest).
- If you lack the swimming skills to maintain a face-up attitude.
Inclination Angle
We define the inclination angle as the line down through a person’s trunk compared to the surface of the water. Someone who is vertical in the water is said to have a 0 degree angle of inclination, while someone on his or her back has a 90 degree angle of inclination. Neither is ideal.
Generally, it’s accepted that the ideal angle of inclination is around 45 to 60 degrees. This does several positive things for the wearer:
- It provides good visibility for possible rescuers or to anticipate waves.
- It raises the wearer’s freeboard by tilting his head back to lift his nose and mouth.
- It allows the wearer’s head to be cradled by the flotation behind their neck.
Leg straps are helpful because they allow the wearer to have some control over their inclination angle. When pulled tightly, leg straps roll the wearer back in the water, putting him/her more on their back. When released, the wearer becomes more vertical in the water.
Impact Protection or Dynamic Strength Testing
Until recently, life jackets were given a rating in miles per hour (MPH) that indicated how secure the life jackets were on the body of the wearer when smacking into the water at high speeds. This is mostly of interest to water sports enthusiasts (e.g. waterskiers, wakeboarders, tube riders) as well as boaters in either Personal Watercraft (PWCs) or fast open boats (like bass boats). The term Impact Protection was replaced by Dynamic Strength Testing, and finally was dropped by the most recent life jacket standards.
The ratings used to be 30 MPH, 50 MPH, 70 MPH, and 100 MPH. To do the 70 and 100 MPH tests, a test torso was dropped from a helicopter to see if the life jacket remained on the torso.
Why go to all this trouble? Let’s say you’re in a 13’ RIB with a 30 HP engine, and you’re zipping around, exploring, while the mothership remains anchored in a pretty cove. You hit a wave and fly out of the RIB, hitting the water at about 30 MPH. Your loosely adjusted life jacket slips off, and lands about 20 feet away, but carried by the wind, it floats away from you faster than you can swim. The RIB, too, has stopped about 50’ away but the wind is carrying away as well. You have no one to blame but yourself because you adjusted the life jacket for comfort . The lifejacket must grip your body tightly enough to NOT come off, regardless of what its strength rating is.
So how do you identify life jackets with the ability to stay on in high speed accidents? They have to have at least two encircling belts that run around your chest and then buckle. An additional method of closure is also required, consisting of either a buckle above the belts (but not necessarily encircling) or a zipper under the belts.
Hypothermia Protection
While this may not be a “rated” attribute of a life jacket, hypothermia protection varies widely in different types of flotation gear. If you were to rank the heat loss reduction of various types of flotation, they might end up in a list something like this:
- Immersion suits, a.k.a. “Gumby Suits”
- Cruiser’s suits with insulated jackets and pants or one-piece coveralls
- Float coats with a “beavertail” (best) or no “beavertail” (good)
- Foam lifejackets that fit tightly around the torso
- Inflatable life jackets
- Everything else
How important is this to the average sailor? It obviously depends on the air and especially the water temperature where you’re sailing. A sailor who is dry, wearing quality layered clothing under a quality suit of breathable foul weather gear may be very comfortable, presuming they stay on deck. As soon as the same sailor is immersed in cold water, the clock starts ticking on the way to cold incapacitation. That’s when the insulating properties of a “cruiser suit” or other insulating garments that can limit the amount of cold water that contacts your skin is vital. Water conducts heat away from your body 25X more quickly than air of the same temperature.
Heave Period
Heave period can be thought of as the time it takes to get back on the surface of the water so you can breathe. Imagine that you’re in a body of water with closely-spaced wave crests, and you’re trying to avoid inhaling water. The wave crests and troughs pass by you, and you settle into a harmonic immersion cycle where your mouth is underwater for a portion of each cycle. Life jackets with a short heave period will lift your body back to the surface more quickly each time it immerses. This aspect of a life jacket combines multiple qualities that we’ve discussed, but primarily total buoyancy and reserve buoyancy.
A short heave period won’t entirely eliminate mouth immersions, but it will make them shorter in duration, allowing a person in the water to spend more time on the surface where they can breathe.
So what should I look for based on my use?
Offshore Sailing: high buoyancy inflatable life jacket with harness
Offshore Powerboating: high buoyancy (35#) inflatable or inherently buoyant life jacket without harness if you don’t regularly clip-in, or a high buoyancy inflatable if you do clip-in.
Kayaking, dinghy/shoreboat use, small boat sailing: low buoyancy (15#) inflatable or low buoyancy foam vest (“dinghy vest”)
Cold air, cold water: Gumby suit, cruiser’s suit, one-piece flotation coveralls.
High speed powerboats and watersports: inherently buoyant life jacket, 15#, rated for high speed boats and sports with encircling belts.
Author’s Note: My great thanks to Dr. Gordon Giesbrecht from the University of Manitoba for his helpful comments on this article. Dr. Giesbrecht is a renowned expert in thermophysiology and is the author of “Cold Water Boot Camp” and other videos on hypothermia.
The Cruising Club of America is a collection of accomplished ocean sailors having extensive boat handling, seamanship, and command experience honed over many years. “Safety Moments” are written by the Club’s Safety Officers from CCA Stations across North America and Bermuda, as well as CCA members at large. They are published by the CCA Safety and Seamanship Committee and are intended to advance seamanship and safety by highlighting new technologies, suggestions for safe operation and reports of maritime disasters around the world.
