Joe Impellizeri
Sand Dollar

IMPELJR@aol.com

General Info- Sand Dollar is a 1972 33’ SF and like most boats of this size and hull type it didn’t have and installed air conditioner. Last year’s summer heat that hovered between 95 to 98 degrees for over a week made up our minds. We weren’t going to go through that again. Besides, all components for a complete system were less than $1800 and I could install it myself. Sand Dollar has no down steering station and has an L shaped seat in the salon. This is where I decided to install the 16.5K BTU Mermaid Marine Air A/C unit ( http://www.mmair.com/ ). Both the compressor unit and the much smaller electrical component box may at times create a spark, when energized. They contain brushes, relay contacts, and switches, so it is imperative to not have either component mounted in the engine room if you have gas engines. In general, installation was simple. The unit came with very clear and complete installation and troubleshooting instructions. I selected Mermaid Marine Air for a few reasons:

1. I visited the factory in FT. Myers, FL and saw how well constructed these units are. All components that might fail at some time in the future (relays, switches, thermostat, sensors, etc.) are available as off the shelf parts readily available at any A/C repair shop. There are no special printed circuits boards, transistors, or IC chips that are specialized factory components might become obsolete but the factory has a great staff and all necessary parts for this unit and for any unit they ever made since 1983.
2. They have a 5 year all-inclusive warranty; the longest in the industry.
3. The fan unit has a delayed start from the compressor unit. In addition, the very quiet rotary compressor uses a "hard start" capacitor. These two reasons combine to reduce the large amperage surge at startup making the unit easier to run using a generator or if there is reduced pier voltage which increases the A/C units overall longevity.

At the factory I learned that it is necessary to have as much airflow as possible through the unit. Multiple ducts with minimum restrictions are mandatory for a 16.5K BTU unit. To this end I chose to have 3 ducts; a 6 inch duct under the salon seat, a 6 inch duct that runs through the engine room to the galley countertop; and a 4 inch duct that runs through the cabinet in the head into the hanging locker and discharges into the vee berth.

To accomplish this ducting configuration exiting the unit in the confined space I chose, I had to make a plenum. Making a plenum may not be necessary for your situation if you have enough space to use multiple prefabricated ducting at the unit’s discharge.

Making the plenum- I constructed a prototype plenum out of pieces of a cardboard box I cut slightly smaller than the exact size I needed. Using the cardboard prototype I was able to verify all ducting measurements. After a few minor adjustments, I covered the cardboard prototype with clear plastic wrap, then with West system epoxy and woven roving mat. The plastic wrap precluded the epoxy from sticking to the cardboard and of course left a smooth interior surface. The epoxy and mat adds approx. 1/8 inch to all surfaces and is why the dimensions of the prototype were made about ¼ inch smaller all around (to not have it be oversize after construction). This may sound difficult, but careful measurements, a utility knife, duct tape, and a fair bit of patience are all that was needed to ensure a perfect fit before application of epoxy and mat. After the epoxy hardened, I soaked the whole thing in water and the cardboard was easily removed from the inside leaving an epoxy plenum that fit perfectly. See figure 1, Plenum. Note that the plenum has a 6" hole (input to plenum) from the tee connector supplied with the unit, and two discharge holes, a 4" hole on the opposite side that goes through the bulkhead into the cabinet in the head, and a bottom discharge hole that goes through the deck into the engine room and across the boat and up through the galley countertop. The plenum outlet that discharges through the deck for the galley countertop was part of the unit’s construction. The two round holes were cut after the cardboard was removed and I was able to install the new plenum to more precisely locate these holes.

Other installation guidelines – Ductwork is not the only installation requirement. In addition, you must install two hull valves. The first one is for an independent sea water supply to a pump and strainer. I mounted mine in the bilge on a hull stringer to ensure the pump will be self-priming. The second hull valve is mounted above the waterline for the seawater discharge. As a condensate drain, I tee’d into the overboard discharge from the sink in the head. A 20-amp circuit breaker and associated 12 gauge stranded wire supplies the 12-1/2 amp power needed for this size unit. The digital programmable thermostat must be mounted out of the direct flow of air from a duct and as central as possible. Aside from the hull valves, all other components can be installed in a few weekends after the boat is in the water. When installation is complete, get ready for a treat only the larger boats now enjoy…a cool breeze anytime you’d like.