The Humber Calisto is a 56-ft pilot boat, operating on the Humber estuary on the northeast coast of England. It carries harbor pilots to and from large ocean-going ships. The pilots are local area experts whose job is to help navigate the big ships in and out of port.

The new vessel, which was built by Souter Marine on the Isle of Wight, was equipped with an innovative dehumidification and a/c system to overcome fogged pilothouse windows - a common problem in the cold, damp environment of the North Sea. The Cruisair system was designed and installed by Taylor Made Environmental (Richmond, VA), a manufacturer of marine hvac solutions.

Where's that buoy?

Trevor Goldsmith, managing director of Taylor Made's European operation (Poole, Dorset, England), was responsible for the job. He explained the problem: "In the past, the normal method of defogging the windshield was simply to install heaters and fans to blow hot air across the glass. The problem is that the damp air inside the pilot house instantly condenses on the inside of the glass whenever hit by a blast of cold air or cold water spray."

"For years, the pilots complained about fogged windows," said Goldsmith. "It was an important safety issue when trying to navigate the boat through restricted waters at night. Every time one of the pilots would come in from the outdoors, usually dressed in wet oilskins, the cold air from the open doorway would cause all the windows to fog up. The same thing would happen in rough weather, when cold ocean spray would hit the outside of the windshield, chilling the glass just enough to cause condensation on the inside of the surface."

The solution, according to Goldsmith, was to design a "dry heat" system to remove moisture from the pilothouse. The 24,000-Btu system consists of an a/c evaporator and condenser controlled by a humidistat. The evaporator cools and removes water vapor from the air inside the cabin. The cool, dry air is then pulled through a heating unit, where it is reheated to a comfortable level. The warm, dry air is then ducted to discharge grilles below the windshield. The electric-powered heating unit is supplemented by hot water drawn from the boat's main engines when underway.

Microprocessor-based controls manage the system. The humidistat sends information to the digital control, which turns the compressor on and off as needed to maintain the preselected humidity level.

Steering clear of trouble

The system operates on 240-ac power provided by alternators on the vessel's main engines. It can also be operated off a 7-kW inverter when the engines are not running. Relays provide automatic switchover from ac power to the inverter. As an additional "get home" feature, the circulating pump for the hot engine water and the inline fan run on 24V. Thus, the wheelhouse can still be heated even if the inverter should fail.

Goldsmith said that the Humber pilots are very pleased with the result. "Although we do not have hard statistics, the pilots have told us that the new boat has fewer problems with fogged windows than the older ones. They also expect to reduce maintenance costs for wheelhouse electrical and electronic systems by reducing the moisture content in the cabin." ES