Air Conditioner Sizing

[eepstein]

For a PDQ 36 what is the ideal size AC unit? My thought is to have the smallest possible power draw on the genset, but still have enough BTU output to cool the boat on a hot day. As the boat never connects to shore power, the genset will be its sole power source. I have a 2KW genset at the moment, but its a bit small for boat systems an anything but the smallest AC unit. Thanks in advance for any advice.

[Cat Tales]

We recently installed a 16,500 btu unit with 4 discharge vents (closeable), one in each forward stateroom and two in the saloon. The unit is powered by our 2kw portable generator. It pulls 12 amps (13.2 amps at startup). The A/C cools the entire boat to about 79F during the heat of the day in July. At night we set the temp to 77F and the unit cycles on & off approximately every 10-15 minutes, while also charging our batteries at about 30 DC Amps per hour.

[eepstein]

Thanks. Its sounds like 16000 is the right size. May I ask what mfg/model you installed and if you like it? Thanks again.

[Cat Tales]

We installed the FM16R from Flagship Marine - http://www.flagshipmarine.com - 800.316.6426. All the guys are great with any questions you might have, but Ernie was extremely helpful.

Some marine A/C units have variable fan speeds that always stay on, while cycling the compressor on & off. The Flagship Marine unit is similar to your home A/C in that it cycles completely on & off to maintain temp, without variable fan speeds. I prefer this setup for a number of reasons concerning noise and generator fuel consumption on our Honda EU2000.

So far we haven't had any problems, but if we ever did, all parts, including the control box, are user repairable with parts you'd find at any hardware store. Very simple setup.

[maxicrom]

E,
We have a 16,000 BTU Mermaid reverse cycle unit that we had purchased for another boat and never installed, and luckily it was the right size for our PDQ 36. We installed our unit under the STBD settee bench and ran vents to both forward cabins, and four in the salon. The only drawback on our installation is that the evaporator intake fins are on the chart table side of the unit and I added an intake vent inside there as well as another on the other side of the bench in the settee area. It draws OK, I sealed the area around the AC unit so that it draws from both intake vents and we still have storage in the aft section of the bench. We used 3 different vent types running from an air box on the outlet of the AC unit (it has different sized outlets for the hoses and maintains a better flow to the longer runs).

"Knock on wood" it has been working well for the last three years - the Mermaid unit draws about 15A on startup and then tapers off to under 10A in running mode. We shared the head raw water intake with the AC cooling pump and it works fine. I originally went to a lot of work mounting the pump unit under the sink and it was too high to easily prime or have good flow, so I made a foam pad for it and it's wedged inside the vanity door area and has been fine for few years now (plus it is easier to re-prime after winter since it can be easily accessed). We installed a spin off filter inline between the inlet and the pump with a shut off valve on both sides so it can be easily cleaned.

The Mermaid is a pretty good unit and the company is in Florida with a number of models and outlet positions - they usually have good show discounts , we got a very good price at the Annapolis boat show.

If you are going to install the unit yourself it's lot of work with little access. I installed a large PyHi access port on the back wall of the small closet next to the electrical panel for access to run my vent ducting from the AC unit. This is a job you only want to do once. For installing the vents it's worth the extra expense of purchasing the correct size hole saws.

Hope this is helpful,

Mike