One of the most frequently asked questions from homeowners contemplating their first fiberglass pool is, "Will these pools "pop" out of the ground?"

At Trilogy Pools, we believe in educating the consumer and letting them make the best decision for their particular application-not-pressuring them with fluff and scare tactics. So, will a fiberglass pool float? The answer is YES! A fiberglass pool will float like a boat. After all, from a manufacturing point of view, it is simply an inside out boat hull that you stuff in the ground. What? We are not afraid to tell you this alarming news? The reason will be quite evident when you understand not will it float, but rather how and why it can float. In fact, you may be surprised that there was an entire fleet of concrete ships that were built during world wars I and II. It became impractical, but yes, even a concrete boat will float.

Let's take a little sidetrack into the science of why pools, people, and even aircraft carriers float. Obviously the first clue is that it does not matter what the object weighs. Certainly an aircraft carrier, like the Harry S. Truman (CVN75), weighing in at 91,209 tons, would be much more difficult to float than a person if weight were the only factor. But as we will see, weight really has little to do with why something floats and this is something that is mysteriously left out of the discussion in the pool store. That mystery item is the technical term, density. You see, every object has a certain weight for a particular amount, or volume, of the material. We know that a bag full of feathers does not weigh the same as that same bag full of bricks. In this sense, a brick is denser than a feather. Not really that surprising or complicated.

Don't be so dense

Now once we understand that concept of density, lets now look at a boat. As the boat is placed in the water, it starts displacing water. You have seen this in the bathtub. When you stand up, the water level goes down. Now, if you could take that amount of water, displaced by your body or the boat haul, and put it on a scale, it would have some weight. If that weight is more than your body or boat, then it will float. If it is less it will sink. We call this upward force "buoyancy" and so you often hear that an object that floats, described as buoyant.

As it turns out, the reason a boat floats is simply that it displaces a volume of water, equal to its own weight. There is a real great explanation of this involving "concrete canoes" and the engineering competitions that happen around the world - just click here to read the wikipedia article. 

Even the Titanic can sink

What you learned is that as long as the boat doesn't have water inside, it will float and displaces a volume of water equal to its own weight. Now what happens if one puts a hole in it? Yes, even the mighty Titanic sinks if it has water inside. At that point it becomes a big hunk of steel and plunges to the ocean floor.

With that refresher under your belt, lets return to what you heard in the pool store, this time armed with a little science fact on your side. "Yes, I don't carry those fiberglass pools. You know, they'll pop out of the ground, " you may hear. Next time consider asking what is special about a fiberglass pool that causes it to spontaneously "pop out of the ground" even when full of water? It will be great fun to actually listen to the answer. The answer should be, just like the Titanic, if it is full of water, it simply can't float. So what is the truth? All three pool shells: concrete, vinyl liner, and fiberglass may heave due to the buoyancy of water, when they are 1) empty and there is 2) a high ground water table. The weight of the shell has nothing to do with the problem.

The truth is in the details

One interesting side note, of the three pools, only the vinyl liner can truly "float" when full of water. We have to look at the structure to understand this concept. The liner is actually held in place, by the downward force of the water. This is the only thing that holds the liner in place. Unlike a fiberglass or concrete shell that has a complete pool structure to hold the shape, the liner is completely dependent on the water to maintain the shape. As a result, when ground water gets under a liner pool, then the liner can actually deform (bulge up at the bottom) and "float" the liner. Now don't get the wrong idea, we would never suggest that you don't buy a liner pool because of this. It is a minor issue and should not be a primary consideration when deciding what pool type is correct for you. Each pool type has its own advantages and disadvantages to consider.

At the same time, we think you should question anyone that tries to use this as a "feature" or sales technique to drive you from one pool type to another. If someone resorts to such inaccurate messages in order to drive you to a specific pool type, what else might they mislead you about?

So we now understand that it is the upward buoyant force, or the weight, of the displaced water, that causes a 90,000 ton aircraft carrier to float. We also have learned that this same force can be created in your pool when two conditions exist: the pool has ground water under it and the pool is empty. Trilogy Pool Builders actually address this situation in two ways. In areas where soil conditions allow, our pools are installed on a bed of gravel. As well, the builder will typical backfill the over excavation (i.e. around the pool) with the same gravel. This results in an effective "French Drain" around your entire pool shell. If you are concerned about a high ground water table in your yard, then simply install a length of perforated PVC pipe, in gravel, at the deepest point of the pool hole. Should you ever need to drain the pool, then be sure to remove all water from this "well point" before draining the water from the pool. In this way, you will protect your investment for years to come.

So the next time you hear, "those fiberglass pools, will pop out of the ground" we invite you to ask this person (with a smile) exactly how this will happen. Sit back and enjoy the entertaining answer. With some of the stories we have heard, it's a wonder we don't open an airline and simply float pools from point to point. In all sincerity if they can't answer the question, do you really want them digging in your backyard?