I have AC aboard my cat and also run other cats in the charter
fleet with AC. Suggestions based upon my experience:
Installing AC in cats can be a pain. Multiple units makes this much easier, but even more convenient, and cost saving, is to use split units and route
the refrigerant lines to evaporator grills/fans in the cabins rather than trying to route
air duct work. This can save you huge amounts of effort/modifications/dollars/frustration.
The actual AC equipment
for a cat is no different than a monohull
, but the installation
is typically much more involved.
I've run boats with most major brands of AC units and have generally found them all to be quite reliable. They are all of course grossly overprice (just compare cost per BTU to a residential unit), but not much you can do about this unless you have the skills to roll your own.
Also, cats are inherently more difficult to cool. This is because the accommodation areas are more spread out and not contained in a single hull
like a monohull
. You also have much more area above the water
line than you do in a monohull, thus it heats up faster than below the water
line space. This is especially true of the deck
house which functions like a big green house. This is where you will need the most BTUs. Do the calculations for the deck
house area (worksheets available on most manufacturers web site and/or manuals) and then go to the next largest BTU sized unit they have -- at a minimum. External sun awnings and window shades can help dramatically with cooling
the deck house.
Just look around your FP think about where you are going to route air duct work that is a minimum of 6" in diameter? The options are quite limited -- routing refrigerant tubing is way easier.
I also suggest not going overboard
on the number of units. There is one FP in the fleet here (Belize) which has 6 (yes "six") AC units and a large gen set to run them all...it is a maintenance
nightmare -- I have to re-plumb/jury-rig/re-wire something AC related it seems every time I run this boat.
Also, carefully consider the routing of your cooling
water and condensate drain hoses and how they might behave underway in heavy weather
. I have one condensate drain hose that exits under the bridge deck. In heavy conditions, sea water can be forced back up this hose into the condensate tray. This caused corrosion
to form in the tray and nearby components -- had to pull it this year to clean up and repaint (for what they charge for these so-called "marine" units you would think they would be stainless -- nope -- just good old stamped steel
that rusts easily in salt
water). Installing a valve to close it this year, but a better original install idea would be a venturi fitting to draw condensate out the cooling water drain hose.
Also, the ability to direct cooling where you want it is a big help on a cat. In my installation
, I use adjustable vents to do this. For example, during the day when most activity is up in the deck house you may want to focus your BTUs there. In the evening you typically only really care about the cabins. Adjustable fans/vents can help you do this.
My configuration (aboard a Wildcat 35) is one 12K BTU unit which cools the deckhouse and the stb hull
. Plus a 10K BTU unit which cools the two port cabins. This is adequate for my boat, but can't keep up with the deck house (without shade awnings up) on a good hot sunny day.