According to Archimedes, the philosopher from Ancient Greece, buoyancy is closely linked to the displacement of water.
To calculate the buoyancy, work out the weight of the object sinking (so the PFD). Subtract from this figure the weight of the water that is displaced.
Buoyancy is the overall effect of 2 opposing forces counteracting one another.
This is the upward force working against the downward force.
What Buoyancy of PFD is Needed?
All personal flotation devices will come with a PFD rating.
This number reflects the number of pounds the personal flotation device can help to keep buoyant.
The higher the PFD rating, the more buoyant the life jacket will be.
Human bodies are already made of 80% water.
This means that an adult will need roughly an extra 12 pounds of buoyancy to remain afloat.
A good rating to look for is around 15 or higher.
Many people believe that overweight individuals will sink faster in the water.
This is a common misconception, as fat actually floats on water.
This means that overweight people are likely to remain buoyant for longer than skinnier people.
What are the Types of PFD?
Type I
Offshore Life Jackets
These personal flotation devices have the highest level of buoyancy and have been designed to withstand rough water conditions for a long period of time.
It is positioned on the upper chest, at the front of the body.
This means that the user is forced to face the sky and will be able to breathe naturally when wearing it.
This is particularly effective when the wearer is unconscious as it ensures they do not drown from being face down in the water.
The ideal PFD rating for this type of PFD is 7 for babies, 11 for children, and 22 for adults.
Type II
Near Shore Buoyant Vest
As the name indicates, this is commonly used close to the shore line.
The water in this region tends to be calmer and the flotation devices cannot hold the wearer up for as long.
These tend to be used on calmer bodies of water, such as lakes.
Here you are likely to be noticed and saved in a short period of time, meaning that the buoyancy does not need to be as great.
The ideal PFD ratings are 7 for babies, 11 for children, and 15.5 for adults.
Type III
Flotation Aid
This is more commonly referred to as a life jacket.
People wear type III flotation devices when doing activities like water skiing and kayaking.
They are best used when you are close to the beach or land, so your chances of rescue are high.
For adults, you should find a PFD rating of 15.5.
To extend their lifespan as much as possible, hand wash your life jacket after each use and hang it up to dry, out of direct sunlight and heat.
Type IV
Throwable Devices
These are the flotation devices that you see mounted onto the side of boats.
Typical examples include floating cushions, rings, and buoys.
They come into use when lifejackets are not used or fail to be used correctly.
These devices are thrown into the water and the person being rescued approaches them and cling on.
They are never used alone, and only utilized as part of an ongoing rescue mission.
Depending on the specific device used, you should look for a PFD rating of between 16 and 16.5.
Type V
Special Use Devices
These are used for people who are employed to spend a large portion of time in the water primarily.
This could be people such as paddle boarders and white water rafters.
These devices can take many forms, including belts, harnesses, and deck suits.
These personal flotation devices have special properties such as heat and chemical resistant.
Depending on the style, you should look for a PFD rating of 15 to 22.
What Is The Best Way To Check The Buoyancy Of Your PFD?
When preparing to use a personal flotation device (PFD), the fit and proper function are crucial for your safety in the water.
Here are the essential steps to ensure your PFD fits correctly:
Check the Fit: The first thing to do is check the fit of the device. It should be snug all the way around you, preventing any chance of it flying off in the water.
Comfort is Key: Ensure the PFD is comfortable to wear. A poor fit could cause you to wiggle and lose buoyancy.
Know the Safety Features: Be fully confident in your knowledge of all the safety features and where they are located.
Test in Shallow Water: While wearing the PFD, walk slowly into shallow water until it covers your shoulders. Check if the PFD shifts in position during this movement.
Adjust if Necessary: If the PFD does not move, it fits you correctly. If it moves, tighten the straps or try an alternate PFD.
Ensure Head Above Water: Lean back in the water to ensure your head remains above the water’s surface for easy and comfortable breathing.
Check Freeboard: Take note of the amount of space between the water’s surface and your mouth (freeboard). If this space is small, consider trying a PFD with a higher PFD rating to reduce the risk of inhaling and swallowing water.
Technical Evaluation: For a more technical assessment, use a short rope, a 10kg weight, and a luggage scale. Measure the weight, then add the PFD to the weight and measure again after submerging it in water.
Calculate Buoyancy: Subtract the second measurement from the first to give a weight in kilograms. Multiply this number by 9.8 to determine the buoyancy of your PFD in Newtons.
Check Standard: The official standard for adult buoyancy aids is 50 Newtons, which is recommended for most situations.
By following these steps and ensuring a proper fit, you can enjoy your time in the water with confidence, knowing your personal flotation device will keep you safe in any aquatic activity.
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Igor
Hi, I’m Igor, Skipper of S/Y "The Hooker". A decade ago, I conquered my childhood dream: to be a sailing skipper, own a sailing yacht. Yes, it knocked dullness out of my urban life — Read more →
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