Floatin' Foam

Late Summer 2019 - Boats are heavy, but they float. Barges and floating docks can hold equipment even heavier than a boat, but they still float. This may seem like it defies logic, but it obviously works. If you are interested in potential opportunities using flotation foam in marine applications, understanding how and why these applications work can help you, so let’s dig into some of the details.

A few thousand years ago, Archimedes discovered that when an object is submerged in a liquid, the volume of the liquid that it displaces is equal to the volume of the object. Closely related to this idea of volume displacement, is the principle of buoyancy which focuses on forces, instead of volume.

Buoyancy is an upward force, exerted by a fluid, that opposes an object’s downward gravitational force, the weight of the immersed object. The magnitude of the buoyant force is equivalent to the weight of the displaced fluid, or the weight of the fluid that would otherwise occupy the volume of the object. Flotation occurs when the upward buoyancy force is greater than the weight of the object, so the object must displace enough volume of liquid that the weight of the displaced liquid is greater than the weight of the object.

Let’s look at a real-world example. Take two jet skis and put them in the water, they float even though they weigh 800 pounds. For this to happen, they have to displace more than 800 pounds of water and still float high enough that they don’t take on water, adding to their weight.

Assuming a basic U-shaped hull design, like below, we can determine how much of the hull will be below the water line to displace enough water to make our jet ski float.

To float an 800-pound jet ski, the hull has to displace 800 pounds of water, and at approximately 62.4 pounds per cubic foot, that means the water line will occur at the point that the hull displaces 12.82 cubic feet of water. I’ve done the boring math, and with our 11-foot ski, about 7.25 inches of the hull will be underwater when the ski floats by itself. When I jump on, adding an additional 230 pounds, approximately 8.5 inches of the hull will be underwater. Because water is fairly dense, at 62.4 pounds per cubic foot, the shape of the hull can easily displace enough volume to float the ski and a rider or two.

If the hull of my ski springs a leak and starts to take on water, the weight of the ski increases as more and more water enters the bottom of the ski, and at some point the weight of the ski, and the added water, will be greater than the weight of the water that the ski can displace, which means it will sink.

These concepts work the same way with big boats and barges.

There is mostly air at the bottom of big boats, barges and pontoons, and when they leak, the density change is massive. The low-density air at the bottom is replaced with much higher density water rushing in through the leak. The speed of the leak determines how much time the vessel has before it is in danger of sinking.

Repairs become necessary with old vessels that have a history or high risk of leaks which results in, pulling them out of the water and taking them out of commission. This means the owners and managers of these vessels may be interested in solutions and repairs that minimize risk—and flotation foam can offer this solution.

Using flotation foam will add a little weight to the vessel, by replacing low-density air with approximately 2 pounds per cubic foot foam. When flotation foam is used in the lower levels of marine vessels, when they leak, the water does not come in as fast because the water absorption rate of closed-cell flotation foam is extremely low. This results in massive benefits for the vessels, mainly more time in the water when they begin to leak and less risk of a total loss.

Flotation foam can offer a great solution to various flotation issues. They can be processed through the same equipment you already use, and with a little learning curve on how to use these materials, the processing methods and application techniques, could easily offer additional revenue for your business.  

*Spray Foam Magazine does not take editorial positions on particular issues; individual contributions to the magazine express the opinions of discrete authors unless explicitly labeled or otherwise stated. The inclusion of a particular piece in the magazine does not mean that individual staff members or editors concur with the editorial positions represented therein.