Since its invention thousands of years ago, the wheel has helped civilization advance to far greater heights. It didn't matter that the first wheels were made out of stone; mankind finally found a way to transport goods much easier. Unfortunately, the wheel means just half the job done. With a hollow core, how can it be put to use for carts and other vehicles?
The answer lies in the other half of the machine: the axle. By designing a fixed platform where the wheel can freely turn, early civilizations came up with the first modes of transportation like the chariot. The need to continuously lay down rollers, like what the ancient Egyptians did when they were building the Pyramids, was eliminated.
The key in keeping the wheel and axle tandem working lies somewhere in the middle: the wheel hub. Early wheel-and-axle machines incorporated the wheel hub as part of the wheel, but today's wheel hubs are separate, allowing easy tire and axle replacements. Even the individual parts of the wheel hub can also be replaced: lug nuts, washers, bearings, you name it.
As long as the wheel hub is there, the wheel and axle will continue working together, hauling your boat or taking you where you need to go.