Underway Air Conditioning


We purchased the Shearwater IV with a standard 16,000 BTU/Hr marine air conditioner that used flowing sea water to dispose of the heat produced when the unit cooled he boat. It was replaced in 2016 when the original unit failed. The new unit is much quieter but still is fairly noisy at night.


We went looking for a better (for us) way.  In the meantime, I purchased an inexpensive GE AHV05LWQ1 5,050 BTU/Hr window air conditioner and mounted it on the roof, blowing in one of the hatches. I suspected from previous boats this unit would cool nearly as well with much less power consumption. Turned out to be true. This is a discontinued GE window unit with mechanical controls. Mechanical Controls are superior to electronic controls in this environment because they retain their settings when the power is momentarily interrupted as you switch from Shore Power to internal Inverter or Generator power.

On the very hottest days we have seen so far (mid 80’s) the unit cycles and keeps the boat fairly comfortable after we install the front sun reflecting curtain similar to the one used in a car. The unit easily keeps the boat comfortable at night.

The lower power consumption of the approximately 5000 BTU/Hr unit (under 4 Amps running) made it possible to run the unit on an inverter that converts the 12 Volts produced by the main engine alternator to the 110 Volts required by the Air Conditioner. This means we can have a cool boat in Florida summers without running the very noise Mace generator.

Our plan is to purchase a 6,000 Btu/hr RV rooftop air conditioner to replace this inexpensive test unit. So far, the lowest power rooftop unit we can find is to large for our power restrictions since we want to run the air conditioning on the power produced by the main engine alternator underway.

This led to some unique mounting challenges – we didn’t want to drill any holes or damage the structure of our boat.

Lots of duct tape, some foil wrap, and a trucker’s strap – good to go with no rain leaks.

We continue to use the factory supplied air conditioner (replaced in 2017) on very hot days or when first entering the Shearwater” after she was powered down for an extended period. I find the air distribution on the factor air produces an uncomfortable draft at the helm seat while leaving the forward cabin relatively un-cooled.

So, I had a small diffuser made out of sailcloth that we stuck to the top and bottom of the air diffuser with Velcro. The diffuser easily allows us to adjust the amount of cool air being sent to the forward cabin or the dining and cooking area while eliminating the drafts on me when I was driving. We don’t often use it any longer, since we don’t use the factor air much.