Summer arrived this year well and truly with a bang and the long hot days are here where the average boatie heads straight to the marina and jumps on board to head out to the cooling airs and delights of the open waters. However, on arrival at the boat, the doors and hatches are often flung open to a huge gust of hot fetid air that had builds up unbearably inside the cabin over the long, hot days.

Sometimes, the heat build-up cannot be dissipated by the outside breeze and cabin temperatures can stay in the high 30's or even more. Fans are next to useless and tend to flatten already depleted batteries. The long awaited weekend away can turn into a sweltering disappointment made worse by the frustration of indecisions of whether or not to risk opening windows for a breath of air or being eaten alive by midges and mozzies.

Luckily for us, we live in an age of technical wizardry and help is at hand. The once undreamed of luxury of air-conditioning in small craft is now a reality due to huge advances in boat electrics, silent generators and efficient marine air-conditioning units that are a marvel of compact engineering.

HOW IS 'COLD' GENERATED?
In order to cool cabins that are too hot caused by direct solar radiation onto cabin decks, sides and roofs, real relief can only be provided by an efficient air-conditioning unit. These units literally take away the heat from the area or body you wish to cool. A good example of how this happens is when a highly volatile liquid, i.e. meths or alcohol spirit is poured over your hand, you will experience an acute sensation of cold. This is because the liquid spirit or meths is evaporating into the atmosphere. The liquid is using the energy to evaporate from your hand to enable it to vaporise. Your hand provides the heat necessary to do this. If it were possible to create a closed circuit in which the evaporating liquid was 're-captured' and sent round again to repeat the process, permanent cold would result.

This is exactly the principle used in refrigeration and air-conditioning. Generally speaking, it is preferable to use a closed-circuit system where the air in the cabin is continuously recycled. Why a closed circuit system? Closed circuits use the already cooled air that has partially had the heat removed already so it makes sense to 're-cycle' it instead of introducing fresh hot air which needs heaps of 'energy transference' to get it down to a comfortable temperature.

THE POWER SOURCE
Like everything in life you don't get something for nothing and in order to power air-conditioning systems, a substantial power supply is required. Ironically, in hot weather, the poor old fridge is already first in the queue for battery power and there's never much left over for the ever hungry air-conditioner. However, as mentioned, it is possible to box clever and with a little bit of applied science, some 12 volt evaporator systems that pull a fridge down to -10 degrees centigrade can be robbed of cool air via a blower (or sucker!) back out in to the cabin for cooling.

Some small 12 volt compressors (The Danfoss) used by newcomer WAECO PACIFIC Refrigeration have truly amazing output for their size and electrical consumption. Energy is efficiently used for true refrigeration and minimal power use in these systems and now even 20 footers can enjoy the luxury of a small energy efficient air-conditioning and refrigeration supplemented by new age amorphous silicon solar panels to provide oomph into the latest high tech batteries. Captain Cook would roll over in his grave if he knew what was happening today!

THE BLACK ART OF CHOOSING
With modern boats it is quite difficult to ascertain specific size requirements for system outputs. There are many deciding factors. What size boat? What window area? Is the glass tinted? Are there any curtains or blinds? Even such factors as interior furnishings can affect the outcome. Mahogany heats up to 70 degrees cent, lightwood can be only 45 to 50 degrees cent.

Do doors and hatches close tightly? There are even more questions to answer but generally a good rule is to try and keep as much heat as possible outside the boat. Heat that never gets in doesn't require cooling. Remember, professional advice is worth its weight in gold. Don't guess yourself, you will invariably get it wrong.

MAINTENANCE
Generally, electrical outputs are high with air con systems and your electrical system must be able to cope. This means all cables and connections must never remain hidden and neglected for years. Corrosion, loose wires, dodgy in-line fuses, can all undermine the electrical efficiency of your system supply and help to keep the volts working efficiently.

Vigilance is required and fridge/air-conditioner pipes must be insulated and kept corrosion free. At the first sign of diminished performance, call in the refrigeration mechanic as gas may be leaking causing low pressures and damage to valves, bearings and internals. Batteries too must be checked for A1 electrical storage capability and solar panels should be monitored for output performance and component age breakdown. Nothing lasts forever!

Internal heat build-up can be prevented by fitting solar vents so there is a free, fresh air flow and the air inside the cabins has a fighting chance when the unit is initially turned on. The same rules apply, if the heat doesn't get in you don't have to waste energy cooling it down. If the cabin temperature is 5 degrees cent more when the blinds are open, shut 'em!

Remember, with that big initial handful of electricity an air-conditioner requires when it first starts up, ensure all wiring, fuses, contact breakers and generators can cope and keep spares handy wherever possible. Regular oil changes keep gennies sweet, oil is cheap, but generators are really expensive!

CONCLUSION
From the aforementioned, it is clear to see each boat has its own specifications for air-conditioner requirements but oddly enough these systems are linked closely to the crew's needs. A happy medium is necessary to make sure all runs well. To ensure both human and boat systems run smoothly together, good planning is required where air-conditioning is concerned, perhaps more so than any other on board!....stay cool!