Comfort is an important aspect of the modern yachting industry. In the quest for the most comfortable indoor environment, marine air conditioning consumers are often misguided into purchasing equipment that is larger than required. You may ask, “Well, bigger is better, right?” If you were boating in the Sahara desert I would respond with a wholehearted yes; however, we are entangled in an industry dependent on functionality in multiple environments. This misconception results from our perception of environmental comfort. The uninformed consumer is lead to believe that their source of discomfort is only associated with temperature. In fact, the source of discomfort is more likely a result of high humidity. Your next question is probably, “Won’t a bigger unit remove more moisture from the air?” The very opposite is true. When you turn on the air conditioner in your stateroom, warm moist air from the cabin passes over the cold coil forming dew. The critical temperature at which this begins to occur is appropriately named the dew point. The unit will continue to run until the room temperature is satisfied as governed by the thermostat setting. Subsequently, the unit shuts off and the temperature of the coil quickly rises above the dew point. Intuition tells us that the larger coil, which has more surface area to form dew, would remove more moisture. Intuition in this case is correct; however, as the size of the air conditioning coil increases, the time that it takes to satisfy the requested temperature drops dramatically.

This decreased run time is what leads to the inability of oversized systems to dehumidify. A case study that comes to mind involves a Western Australian built vessel whose oversized air conditioning system was uniquely designed for an arid climate. When this vessel, a 25 m motor yacht, made landfall on the shores of Fort Lauderdale the owner was surprised to discover that his cabins could no longer provide the comfort that he was familiar with. Instead, when boarding the vessel he was greeted to seventy degree air that was as moist as the deepest Amazonian rainforest. A heat load calculation showed an average air conditioning unit size that was fifty percent larger than the required load. In this particular case, the original system was designed with the hot and dry climate in mind. However, it demonstrates the importance of avoiding the operation of oversized air conditioning systems in multiple climates. You’re finally wondering, “What can I do ensure that the air conditioning on my yacht is sized properly?” Make sure that the company representative can explain how they calculated the system size. Every boat is different, so multiplying the square footage by some magic number is not always an acceptable method. Most important, ask lots of questions. Even if you don’t understand that much about the science behind air conditioning, you will feel confident knowing that the specialist is comfortable answering your questions. If he can’t explain why he wants to do something, consider calling someone else.