HEATING AND VENTING

Mr Meme says: You have to warm up your boat and continuously draw the less humid air from outside to remove the dampness from within. It works best if you force-draft and heat the air up on its way in.

Heating and Ventilation:

"Air-changes" which is the number of times all the air in all compartments on the boat is changed for fresh air per hour, is the most important aspect of keeping your boat warm, dry and healthy.

There is a set minimum rate on ships and housing accommodation.

We compared the humidity of the air inside the boat with the air outside and found on all occasions, even when it was raining that inside was far more humid than outside. As an example, outside on the foredeck humidity would be 68% and inside would be 82%.

At a humidity of 100% the temperature that was read at that point would be DEW POINT.

It makes it easier then, to understand that DEW POINT would form on a cold surface in contact with moisture laden air.

To prevent this from happening the inside air must be displaced by warmed up outside air which has less water content than the air inside.

This will allow the moisture to be gathered up by the warm dry air and with hot air rising it will be discharged to outside at a high point at the main hatch or companionway of your boat.

We fitted a Webasto Airtop diesel fired heater in each engine compartments of our catamaran.

Each unit has three air delivery points and are arranged as follows:

One for each after cabin, one on each side of the common Saloon one in the Heads port side and one for the main cabin on the starboard side.

On each heater unit air was drawn from a grid on the stern.

Depending on outside air temperature the whole inside of the yacht may be warmed up to  21 degrees centigrade and the humidity is seen to drop considerably as soon as the heaters are switched on.

Ideally if the heaters could be run continuously day and night, all compartments would remain warm and dry. This however was not possible for us as we are reluctant to leave the boat with any thing switched on at all, even our computers must be unplugged and shore power switched off.

It is important that the hot air ducting be fitted correctly. We wrapped the ducting from the heater outlet to the hot ait delivery control vents with a full layer of Glass Wool bonded with duct tape.

The thermostat sensors that controls the air temperature is placed on either side of the saloon. The saloon temperature governed the temperature of the rest of the boat. Each cabin is adjusted by opening or closing the individual flap on the delivery.

When the desired temperature is reached the heater output is reduced to maintain it by slowing the fan down and reducing the amount of fuel consumed. The burner also cuts out and cold air is delivered to a point where it fires up again.

The heater may be noisy if it is mounted in an open compartment or if there is no sound insulation in the compartment and the ducting is not insulated.

To reduce humidity the air must always be taken from the outside unless it can be split to take 1/3 re-circulated from inside and 2/3 from outside.

To us our heaters are quiet whispering warmth that would keep the boat warm and dry in all compartments including the bilges, if they were allowed to run 24 hours a day and 7 days a week.


Venting the Galley

Galley Extraction Fan

Boiling tea pots and cooking on the stove is a main source of water generation which increases the humidity on board substantially.

The fire detector on our boat was a big nuisance during steak or lamb chop fries until we fitted an extractor fan above the galley range.

Mouth watering aroma emanating from the galley was often interrupted by the smoke alarms screeching but a simple extractor unit was fitted above the stove which draws the air above the stove top directly out of the boat into the cock-pit.

For 75p we bought a small plastic bucket from the DIY paint section of our favorite store TRAGO MILLS and modified it to be a base for the wall extractor fan and fashioned an insert out of plywood which was fitted in way of the partially opened sliding window.

 It works like a charm. Having two speeds we are able to clear the air of moisture and smoke and as a bonus , when the central heating is switched off, fresh air from outside is drawn in through the heating system to all compartments.

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