PFD Buoyancy Code Broken!

| May 6, 2009 | 0 Comments

Some of you may be wondering what it means when a PFD has 16.5 lbs. of flotation, or wondered why manufacturers don’t list a PFD weight limit. I have also wondered myself so I went on a detective hunt…here is a simple answer…Buoyancy is determined multiple factors that include body weight, lung capacity (how much air is in the body) and body fat fat percentage.

If you have a Type III PFD that has 16.5 lbs. of buoyancy (the NRS Vista for example), it would be capable of supporting 16.5 lbs. of dense material such as lead, iron, gold, granite, etc. It would not let the material sink to the bottom.

How can this PFD with 16.5 lbs. of buoyancy hold up a 325 lbs. person in the water you ask?

Time to do some math! Take the example of a 325 lbs. person. Approximately 80% of the body is water. Water in the body has no weight in water. So now we are down to having to support only 65 lbs. of weight.

Water in the Body:
325 lbs. x 80% = 260 lbs. of water weight

Actual Supported Weight:
325 lbs. – 260 lbs. = 65 lbs. of actual weight

But the PFD only has a buoyancy rating of 16.5 lbs. How can it hold up 65 lbs.?

On average our bodies also contains between 15% and 20% fat and fat is actually lighter than water.

Lbs. of fat:
325 lbs. X 15% = 48.75 lbs. of fat

Weight Supported
65 lbs. minus the  48.75 lbs. of fat = 16.25 lbs. of weight that needs to be supported

So for another example, using the same math, a 200 pound person only weighs about 10 pounds in water. The 16.5 lbs of buoyancy in the PFD is more than enough to keep the person afloat.

Steve

PS – United States Coast Guard (USCG) certified Type III PFDs must contain at least 15.5 lbs. of flotation.

Category: Kayaking, Knowledge, Resources

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