A PFD, or personal flotation device, is one of the most important pieces of equipment to have with you when in the water.
It acts as a safety precaution and should always be nearby when you are on deep or open water.
Water safety is not something that you should ever overlook.
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What is buoyancy?
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?
The first thing you should check is the fit of the device.
It should be snug all of the way around you, so that there is no chance it flies off in the water.
It should be comfortable to wear, as a poor fit will cause you to wiggle and lose buoyancy.
You should be fully confident in your knowledge of all of the safety features and where they are located.
While wearing your personal flotation device, walk slowly into shallow water until it covers your shoulders.
Check to see if your PFD shifts in position as you do so.
If it does not move, it fits you correctly.
If it moves, tighten the straps or try an alternate PFD.
Once you have ensured the PFD doesn’t move, lean back in the water.
Your head should remain above the water’s surface so that breathing is easy and comfortable.
Make a note of your freeboard.
This is the amount of space between the water’s surface and your mouth.
If this space is small, you may wish to try a PFD with a higher PFD rating (see how to correctly store PFDs).
This will minimize your chances of inhaling and swallowing water.
A more technical method involves the use of a short rope, a 10kg weight, and a luggage scale.
Attach the weight to the rope and submerge it in the water.
Use the luggage scale to measure the weight.
Add your PFD to the weight and submerge in water again.
Allow all air to escape from the PFD and then take a weight measurement again.
Subtract the second measurement from the first to give a weight in kilograms.
Multiply this number by 9.8 to give the buoyancy of your PFD in Newtons.
The official standard for adult buoyancy aids is 50 Newtons.