Once the electronics and plumbing were complete, the installation became a woodworking project, since I had decided to built my own ducting out of 1/2-inch plywood. This offered a much smoother flow than convoluted tubing and enabled me to direct the air in straight runs exactly where needed. The main duct was 8 inches wide by 4 inches high with ducts branching off into the two cabins. I also channeled some air overhead across to the starboard side bathroom and main corridor. A further advantage of plywood was it didn’t need insulating like the thin flexible pipe normally used for ducting.
I bought the more expensive teak adjustable vents, since they offer better air flow distribution and can be closed off completely if required. They also look nicer than plastic vents. I was advised to use 3-inch square vents for cooling the two front cabins and heads. This didn’t seem large enough to me but proved exactly right in practice. I used 7-inch by 3-inch vents for the saloon and aft cabin. I actually combined three vents to deflect air more evenly in different directions into the saloon.
It was all quite straightforward and I completed installation of the forward unit in a week. It was marvelous to finally press the “on” button and feel the machine blow a blast of cool air into the cabins and saloon. Mike arrived with flow and pressure gauges and declared this was the most efficient system he had seen on a small sailboat.
I cleared a space for the aft unit by moving a couple of drawers in the aft cabin. Installing this unit was easier because I was now “experienced” and the seawater pump was already fitted. I again built the ducting as a straight-through plywood box in the aft cabin with branches supplying the aft head and rear area of the saloon. As part of the system, the dedicated vent blowing into the galley pleased my wife. The condensate was connected into one of the cockpit drain pipes.
Both units work independently, except for the common seawater pump that feeds one unit, even if the other is switched off. This provides great flexibility. When there are just the two of us on the boat, we sometimes switch the forward unit off or close the vents into the two forward cabins. This has the benefit of blowing more cool air into the other areas.
The electrical draw from both units is too high for a single shorepower cable, so I ran a second shore cable into a new AC breaker panel. I needed this anyway to handle our electric kettle, toaster, microwave, and washer/dryer. I also had to modify the wiring from the 6.5kv generator to feed both panels when running the air conditioners on generator power.
In the summer, Florida gets to 95/105F with oppressive humidity. These two machines now keep the inside of the entire boat at a nice, dry 75F. Cool dry air or heat spreads evenly throughout the interior and no area is warmer or cooler than any other.
The aft unit ducting passes just under the cockpit floor. As the cockpit has a fully enclosed Bimini, I now have an idea that I could deflect some cool air into the cockpit, using a waterproof vent. This would make it very pleasant for sundowners on hot sticky evenings.
The total cost for both units was around $4,600, including pipes, plywood, wire, and vents. This, of course, did not include my labor, but on a boat that’s supposed to be fun!
Even though we tend to take our air conditioning for granted now, it is still one of the best investments we have made on our boat