If you’ve never worked with buoyancy before these numbers may seem a little confusing. Why is a 15-20lb buoyant life jacket safe for an adult? Wouldn’t a typical adult need 150-200 lbs of buoyancy (or more) to stay afloat?
In this post I’ll answer these questions and more by explaining a little about how buoyancy works.
What Life Jacket Buoyancy Ratings Actually Mean
A buoyancy rating is an indication of how much weight a flotation device can safely keep above water. The weight calculated for buoyancy is based on a calculation of dead weight, which is the equivalent of placing an extremely dense, “heavy” material on top of it, such as rocks or metals.
Standard USCG Types and Buoyancy Ratings
- Type I life jackets must have a buoyancy rating of 22 lbs
- Type II life jackets must have a minimum buoyancy rating 15.5 lbs
- Type III life jackets also must have a minimum buoyancy rating of 15.5 lbs
Why 15 lbs of Buoyancy is Sufficient
If the buoyancy rating is the amount of weight the device can hold, why do we only need 15-20 lbs of buoyancy to remain safely afloat in the water?
Let me answer with a subsequent question: Have you ever noticed you feel lighter when swimming than on land?
This is because the overwhelming majority of the human body is not dead weight, and the heaviness of a person’s body on land is not the same as the weight of one’s body underwater.
We are surprisngly “not dense.” In fact, roughly 90% of our body weight is lighter than or equal to the density of water.
Depending on your individual body size and makeup, you are comprised of roughly 65-75% water (which has no ‘weight’ in water), and an additional 10-20% fat, which is actually less dense and hence lighter than water.
This means that in addition to only needing to account for 10-15% of our weight when calculating buoyancy, we already have a high level of buoyancy built into our bodies to start with!
How Much Life Jacket Buoyancy Do You Need?
For the overwhelming majority of people, the USCG approval ratings are more than enough to sustain your body weight.
A person needs at most 10% of his way supplemented with life jacket buoyancy, and this figure is even a little high, and would be for someone who has no capacity to maneuver in the water.
The result is that, along as the vest is USCG approved, you don’t really need to worry too much about buoyancy. Click here for more information on choosing a life vest.