Article by Capt. Steve Katz
Keeping Cool
It has been a hot few weeks here in Ocean City and staying cool while enjoying boating is not always easy. While cruising across the bay and ocean waters usually provide a cool breeze, remaining stationary while fishing or at the dock can turn too hot in a hurry.
It is not just for large boats, many small boats come equipped with air conditioning or have been re-fitted with an air conditioning system. There are even marine air conditioners that can be powered by ships batteries, eliminating the need for shore power or a generator.
A marine air conditioner is similar in operation to a residential air conditioner. A household air conditioner has refrigerant that is pumped through the system by a compressor to remove heat from inside the house by the evaporator (indoor unit) and discharge the heat to the outside air at the condenser (outdoor unit). In a marine air conditioner, a compressor circulates refrigerant to the evaporator in the cabin and discharges the heat into the seawater using a water-cooled condenser.
The most popular marine air conditioner is a self-contained unit, meaning the compressor, condenser, fan, and evaporator are all in one compact package. The package just needs electricity and seawater brought to its location. Often a limited amount of ductwork is needed to direct the cool air to the proper location.
Larger boats or unique situations may use a split air conditioning system, where the compressor and condensers are installed remotely, usually in the engine or mechanical room and just the evaporator and fan are installed in the cabin area. This system is more expensive than an all-in-one unit and more complex to install due to the refrigeration and power lines that need to run between the two components. The advantage is that the compressor and sea water systems are kept out of the way, located with other machinery. The evaporator and fan in the cabin are quiet and take up less space than an all-in-one unit.
Large sportfishing boats and yachts use a completely different system, called a chiller system. This is a system with most components installed in the machinery room. A chiller cools a closed loop fresh water supply, maintaining the fresh water at 55 degrees or so. This chilly water is circulated through the boat using insulated pipes in a loop through the boat. A specialized air handler, similar in theory to a car radiator, is installed in the areas that need cooling. The cold-water flows through the air handler and a fan forces cabin air through the cold-water evaporator, producing chilly air inside the boat. These systems are the most expensive to purchase and install though they can be more efficient with less maintenance than operating numerous smaller units.
A marine air conditioning system needs regular maintenance, the primary areas of concern is seawater flow and air flow. A problem with one or both areas will often cause the system to activate a self-protection mode and shut down until the problem is fixed, usually resulting in a HPF or high-pressure fault error shown at the thermostat. If this occurs, it’s best to check and clean the air filter(s) at or near the cabin fan and clean the seawater strainer and or the associated seawater plumbing lines. The rule of thumb is that a marine air conditioner needs to have 3gpm of water 12,000 Btu/hr at the unit, if you have multiple air conditioners you need to check the water flow at each unit individually. If more than one system shares a common pump, you will also need an electrical pump relay and water supply manifold.
There are also specialized refrigeration systems, like air conditioners that chill a cooler or fish box, like a custom refrigerator. These systems are laid out similar to the comfort cooling systems above, though the evaporator is built into the drink box or fish box. While these boxes are usually incorporated during the boat building process, a custom drink box or fish box can be designed and retrofitted into a existing boat.
Owning and maintaining a marine air-conditioning system requires slightly more maintenance than a residential unit. Besides checking and cleaning air filters, which are often in inaccessible locations, maintaining the sea water cooling system is the most difficult. It’s amazing how fast mud, silt and marine growth can accumulate in the plumbing, especially in the summer months, restricting the water flow and causing the air conditioning to shut down due to high refrigerant pressure. If you store your boat in the winter months, be sure the air conditioning seawater system is winterized and prepared for freezing weather. §
