The Mechanics of Personal Flotation

Thanks to Archimedes, we know that an object immersed in fluid is buoyed upward by a force equal to the weight of the fluid the object displaces. In other words, when your body is in the water, it floats because the weight of the water it displaces is greater than the weight of your body.

What does that mean for paddlers? Well, because the human body is made up mostly of water, the average adult weighs between about 10 and 15 pounds submerged in freshwater. Body fat is less dense than bone or muscle mass, making it quite buoyant. Therefore, just because someone is heavier doesn’t mean they require more flotation.

That’s a lot of science, but stick with us here. If we trust the cute kid from Jerry Ma­guire when he says a human head weighs around eight pounds, then in order to keep the most important parts above the water, somewhere in the neighborhood of 15 to 20 pounds of flotation is required. Phew!

A PFD, which stands for personal flota­tion device, is anything used to keep you afloat and includes everything from a seat cushion to a life saving ring to a vest.

A lifejacket on the other hand, is specifi­cally designed to keep your head above the water should you become unconscious. These are usually either keyhole-shaped, like you might find on a cruise ship, or vests that have flotation flaps behind where your head would go. True lifejackets must also be red, yellow or orange, one-size-fits-all and reversible so they’re easier to don in an emergency.

This is an important distinction—most paddling jackets are PFDs, not lifejack­ets. Designing for comfort and mobility has won out over the necessity to keep a paddler’s head above water should he go unconscious.

Okay, back to the science.

Any flotation device worth its salt has been approved by one of a number of agen­cies depending on its type and your loca­tion. Most vest and waist belt PFDs de­signed with paddling in mind currently fall into either Type III or Type V U.S. Coast Guard ratings, or Type III or Special Use ratings in Canada. The dis­crepancy in regulations has created some difficulty for consumers. But all that is about to change.

An initiative to har­monize standards across North America has been underway for the past five years and a resolution is likely to come sometime in 2013. Flotation devices will soon go through the same testing in both countries so that they will no longer be sub­ject to separate certification processes in or­der to meet legal requirements. The hope is that this will reduce confusion for users, put more options on the market and increase innovation since the barriers to releasing a new product into both U.S. and Canadian markets will be fewer.

Among other things, these ratings mean that the PFD offers a minimum level of buoyancy. Currently, for Type III that’s 15.5 pounds in a buoyant foam device and for Type V or Special Use ratings, it’s anywhere between 15.5 to 22 pounds, depending on its intended use.

Why the extra flotation? In choppier con­ditions, like coastal paddling or whitewater environments, it’s nice to have a little extra clearance above the water. Aerated water like the stuff found in rapids and surf is less dense than water, requiring even more flotation to keep a swimmer afloat. Another important factor is whether or not a pad­dler intends to perform rescues with the vest. If you’re towing another person or boat, once again, more flotation will help keep your head above the water.

Many paddlers opt for inflatable devices that use a cartridge or lungpower to blow up the device. Belt packs are espe­cially popular for standup paddlers. These are handy as they don’t interfere with your strokes (or your tan) like a traditional vest will. They don’t, however, offer the same degree of pro­tection as inherently buoyant foam-packed paddling jackets because they require the ex­tra step of inflation to become buoyant.

The consequence of a well-used paddling jacket isn’t just faded nylon and a worked-in feel. All inherently buoyant PFDs will lose flotation over time as the foam breaks down. Keep your jacket stored out of the sun so UV rays can’t break down the ma­terials. Allow it to dry fully so mold and mildew can’t accumulate. And resist the urge to sit or kneel on it to maintain its effectiveness. If you attend a pool train­ing session be sure to rinse out your PFD as chemicals can break down its compo­nents. It’s also a great idea to check for worn stitching and weak points to ensure that the jacket will do its job during an emergency or rescue situation.

To test out a new PFD or to check the effectiveness of an older one, try it out in the water. Relax your body and let your head tilt back. Make sure your PFD keeps your head out of the water and that you can breathe easily. If not, check the label and go for something with a couple more pounds of flotation or retire your old one. For average users, replacement every five to seven years is a safe bet, more often if you’re on the water every day.

Competent paddling shops will only sell PFDs that are approved, making most of this technical stuff less vital informa­tion. That frees people up to focus more on style, fit, comfort and whether the col­ors match. The flotation offered by your device will come into play in more adverse conditions and rescue situations. At the very least, now you understand the label in your paddling jacket and have some great conversation for your next cocktail party.


This editorial originally appeared in the 2013 Paddling Buyer’s Guide. Download our free iPad/iPhone/iPod Touch App or Android App or read it on your desktop here.  


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