Air-conditioner
on a boat

I ONLY anchor out when cruising. It is quiet, bug-free, breezy, and peaceful. You don't need AC. But, while living and working onboard [in a marina], having AC would be a plus since you cannot "swing into" the wind as you would at anchor, and I KNOW your cabin space, clothing, and expensive computer equipment would benefit from the cool, dry air.

Among things that we specifically avoided based upon 1st year experience:
A/C: we cruise in an area where there are steady trade winds and we are always at anchor getting a breeze.

The Texas coast is as hot and muggy as any place on the water outside of some tropical rivers. Yet we manage to sleep pretty well without A/C. There are three key ingredients to comfort in the heat.

VENTILATION. This lets out the hot air out, and lets in the cooler air off the water. We have ten opening ports, two large opening hatches, two dorades, and two exhaust vents. And there are STILL some places I wish we had more ventilation. Summer nights, I tie a piece of canvas over the forward hatch to funnel the air down it. This helps a lot. But so do the two opening ports.

INSULATION. The heat in your cabin comes from your boat deck getting hot, and to a lesser extent, your topsides. The more insulation built into your deck, and between the deckhead and the deck, the better.

LIGHT HULL COLOR. As Herreshoff said, there are only two colors to paint a boat -- white or black -- and only a damn fool chooses black. If you're buying a boat, buy a white one. If you're repainting, stay with white.

Ok - the AC thread got me going here. I have a few practical hints for living aboard in HOT weather. These are my own take on it. I will mention products because we've tried a variety and decided we like certain ones best.

SUN SHADE: Scotty Ann came to us with full covers that go from the Bimini over the cockpit all the way to the forestay. The shade over the boat makes a HUGE difference in the internal boat temperature. The shade over the cockpit is almost always there and prohibits using the mizzen sometimes. Design around this if you can. The rest of the shades require we either motor or be stationary. I can't figure out how to have them up and sail too.

VENTILATION: At the dock that AC sounds great, but we use a BIG shorepower fan in or near the forehatch (if it isn't blowing right on us.)

VENTILATION: WM sells a product called a "Windscoop". We are on our second one. The first died in the UV after a few years. These work very well. I would make some modifications to the design, but they are related to our boat setup.

VENTILATION: There are fans mounted directly above each of our bunks so that they blow directly on us from close range. Another fan is on a big clip and can be moved around to suit whoever is sweating most just then. The best we have found so far is a toss up between the Hella killer 12 volt fan and the Calframo 747 killer 12 volt fan. We are using the Calframos (WM again). The Calframo's seem to get a noisy bearing after about a year of constant use but they put out SERIOUS air.

VENTILATION (KINDA): Know those straw beach mats they sell? They are some kind of straw or reed or something and are sewn along the edges with fabric. If you cut these to the size of your bunk and edge them with duck tape or something to keep them from coming apart they will help keep you comfortable in your bunk. Put them between the sheet and the bunk. This helps cure the stickiness where you come in contact with the bunk. The let some air flow between you and the mattress. Don't underestimate how much this will add to your comfort and they cost very little.

BOAT COLOR: The suggestion for white topsides is good. But, there is a downside to white decks, cabinsides etc. You are going to blind yourself in the tropics. The white is too reflective and it becomes uncomfortable to be aboard without sunglasses. We use a color similar to the color of light beach sand. The reflectivity index is somewhere around 70%. It is actually concrete patio paint from ACE hardware or the equivalent. The darker color doesn't heat the deck so much that you can't walk barefoot and doesn't fry your eyes either. None of this tip helps you with tupperware, but for our woodie it works well.

SUNSHADE: When you design your cockpit sunshade (absolute necessity) think about side shades that can be moved to follow the sun. Moe decided on the shade cloth they use for gardens. The mesh filters out 70% of the UV if the specs are right. This allows some air to get through the mesh at the same time. There is velcro on the sun shade sides and the side shade is moved as needed to provide a shaded area when in the cockpit.

Downside of AC when living aboard:

I lived aboard in South Carolina for three years in the late 70's early 80's without AC. I had no AC in the car, and was working outside as a poolside bartender so no chilled cubicle either. I found as spring departed I got used to the temperature and humidity slowly; such that it felt *normal*. Going to grocery shop I'd be shivering my cojones off in August!

My last year there, "company" moved aboard and she insisted upon AC. That year was the worst as I got used to a lower temperature and felt like I was roasting outside all the time at work or play ... Thanks to that AC messing with my system, we hardly ever sailed that summer, and worse, I'm convinced the temperature differential is what caused condensation (sweating) to develop where the bulkheads joined the hull - starting considerable rot.

For now I am working and staying in a cheap (relatively) marina. One can afford to do this while working, and it uncomplicates matters substantially regarding work. Plus, Florida in the summer is kin to a sauna bath - 100 degree days with 100% humidity. Air conditioning is no luxury. It's a requirement. And that's really the only reason for the marina. Otherwise, I think I might just anchor out and put the money into the cruising fund. ...

> I've heard that AC is mandatory in a marina, but when anchored out ?

Florida in the summer is typically hot, humid and still. Much of the time there is no wind, marina or not. My need for an air conditioner is partially determined by my personal type. I have a low threshold of sweating and heat exhaustion. I generally have a low tolerance for heat. I know other people that stay on the hook all year, though, and don't seem to have the problem with it that I do. They'll be cool as a cucumber and I'll be soaked with sweat. Different strokes for different folks.

You can deduct 2 to 4 degrees F from the published daily temps because it is usually cooler on the water. A good bimini top, big awnings, and wind scoops at the hatches help tremendously. Frequently, just about when we think it is just too hot, a nice little breeze will cool us a bit. A twelve-volt fan or two, placed correctly will do wonders for making those muggy nights quite pleasant. The summer thunderstorms also cool it down some. Most people do just fine if they do the right things.

If you want to run an air-conditioner from batteries:

• Air-condition the smallest possible area (just the cabin where you sleep).
• Air-condition it only at night, and only after the boat has cooled as much as possible naturally. Much less power required, partly because much of the heat and humidity to remove comes from the humans.
• Use a very small air-conditioner that will run more continuously than a big unit. This will keep the humidity at a steady, low level.
• There are some expensive DC-powered air-conditioning systems available, usually as part of a refrigeration system. Other than those, you need an inverter to drive the air-conditioner from batteries.

... The smallest marine or domestic window air conditioners (5000 BTUs) draw about 5 amps at 120 volts. That requires about 50 amps at 12 volts ... try to determine if the blower motor uses a capacitor. A capacitor fan motor is far more efficient than other cheaper motors. ... At night, when efficiency is most important, the fan can be a bigger energy user than the compressor, because the compressor runs only a small fraction of the time. ...

... Generally speaking, it takes at least a 1000-watt inverter for a 5000 BTU air conditioner. It will be called upon to provide 600 watts to run the air conditioner and about 3000 watts for a fraction of a second for starting. ...

[Run engine in daytime and early evening, with alternator charging batteries and driving inverter, which drives air-conditioner. Then shut off engine and have batteries drive inverter and air conditioner at night to maintain cool compartment.] ...

... I have found that the total power consumed overnight is about 200 amp-hours. ... you need 500 amp-hours more battery than you would have needed without the air-conditioning. That's at least four more golf cart batteries ...

... You are demanding a lot out of each component [alternator, batteries, inverter] so you have to treat them right. One of the biggest problems with DC systems is inadequate wire size. ...

There's a reasonable live-aboard community here in Hong Kong, and although those without shore power and on a swinging mooring do without aircon, most people tied to the dock find it a necessity in the summer - I certainly do.

There are three types of aircon in general use, each with its pros and cons. The specialist marine units (which I have) work well underway or at dock, until a plastic bag or jelly fish gets sucked into the intake in the middle of the night! The domestic 'window type' units are cheap, but noisy, and difficult to seal in the marine environment, so not recommended if you go out on your boat a lot. But, the most popular round here for live-aboard use is a domestic 'split' type system. The compressor unit is in a separate enclosure and can be mounted on the roof or someplace else out of the way, whilst the heat exchanger and fan unit is mounted inside. The two are connected by a power cord and copper pipes carrying the refrigerant. This way the bulky and noisy bit is outside. I can't comment on whether these type of units are widely available in the US, but they are very common in Asia both in their domestic variety, and larger heavy duty version for shops and offices.

One word of caution. The outside units, although built to take whatever the weather can throw at them for many years, are not specifically built for the marine environment - i.e. regular dousing in salt water, so not many true cruising boats would use this system. My local aircon engineer also worries about the fixed runs of copper pipe carrying refrigerant gas fracturing under stress in a cruising boat. Having said that, one of the two local Nordhavns uses this type of system! My personal view is that it is the best system if you spend most of your time at dock, but if you go out regularly, I'd stick to the marine units. These are also now available in split versions, with the compressor units tucked out of the way in the or lazarette, and just the fan units in the living accommodation. Much quieter, and don't take up so much locker space. Same concerns with long runs of refrigerant carrying pipe, although there are chilled water versions available if you see this as a problem. This type of split marine unit only becomes viable on larger boats though - in the 50 foot and up category. This is what I'll go for on my next boat.

[Re: using non-marine air conditioners:]

RV air conditioning units are cheap and can be readily adapted to sit over a hatch. They cool using air only, so there's no thru-hulls to install or water pumps to sink your boat or strainers to clog. The trade-off is lower efficiency (i.e., more input power to move x calories of heat), but that doesn't matter much when running off a generator.

What's more, RV units are designed to sit outside in the elements, and endure the constant vibration of driving down a road. The only thing they're not specifically engineered to tolerate is salt, but if you shop around for one made mostly of plastic and aluminum, I'm sure it would last many years.

Another advantage of using an RV system on a hatch, is that you can easily remove it for the fall, winter, and spring where you won't need it anyway. You wouldn't need or want to even wire it in; just run it off an extension cord.

[Re: best place to buy a 10000 BTU air conditioner:]

Any local RV dealer that sells motorhomes and travel trailers. Coleman makes a great rooftop unit that bolts right onto that leaky cabin hatch, requires no salt water pump, filters, cleaning, nuisance, priming, etc. It also has the hot fan motor and the really hot compressor/condensor OUTSIDE the boat so you get to use ALL the cold air inside the boat, not just part of it. Roofair units are quieter because the noisy compressor and fan are OUTSIDE the boat, not sucking up cabin space with the unit, all that hose-in-the-storage-locker, etc.

The other nice feature you can get on an RV unit is a "Easy Start Kit" that slowly starts the compressor with electronics that eliminates that huge SURGE of current on your genset every time it comes on. A lot smaller genset will power a lot more AC with this "kit" installed. I've never seen one on the water-cooled units ...

I know, I know, it's NOT "marine" or "nautical", it's COLD! That's why every tugboat uses them, not those noisy damn things stuffed in a cabinet. Did I mention you can even get them with HEAT PUMPS FOR WINTER or just strip heaters to heat the cabin SAFELY without some space heater to trip over and burn it to the waterline??

PS - the thermostat, power switches, etc., that produce sparks are also OUTSIDE the boat! No gas fumes on top of the cabin roof!

MarineAir is a great unit. I have a 9000 and a 12000 BTU on my 44' Beneteau with a single large March pump, when both units are on you can "hang meat" in the boat. Have only had to replace a starting relay once.

I agree with Cool Change. We have a Marine Airrrrrrrr on our Hunter 380. It has been one of the most reliable systems on our boat (which is a lot considering the Texas heat in August).

I've got the MarineAir 9000 and 6000 on The Lost Soul (56' Formosa) and it works bitchin!

Mounting a household window air-conditioner on a boat:

• Hard to find a good vertical surface to mount the AC on.
• Mounting via plastic and duct tape isn't very durable, and leaks rainwater.
• Maybe use a large plastic storage container, inverted over a hatch. Make a divider inside to keep supply and return air flows separate.
• Best: use construction foam board with aluminum foil on both sides. Open hatch, set AC in opening, then cut and caulk pieces of board to cover the triangular openings and separate the air flows. Then construct a box that covers the whole thing, except for air vents, and keeps out water and sun.

Look for an a/c unit that has the cold air discharge on the front side rather than across the top. This makes it easier to put a deflector between the cold air discharge and the room air intake. This is not so important in a window, but in an overhead installation in a hatch it lets a lot more cold air come down w/o being sucked right back up in the intake.

With 4 reverse cycle A/C units on our boat, at any one time I'm lucky if 2 work. The main problem is the reversing valve itself. I have been able to revive them sometimes by rapidly reversing them under pressure to shake the piston loose. You do this by removing the electrical operating coil and using a strong magnet - I use a magnet recovered from an old RADAR magnetron. You place it where the electrical coil was and when it is in the right place, you will hear the pilot valve click audibly - either with the A/C on or off. The pilot directs the compressed gas from the compressor to a larger piston that is supposed to slide in the tube and reverse the flow. By cycling it many times by hand this way I have been able to shake it loose and get it running again. Physical thumping may help but be very very careful about how you thump it since the slightest dent in that soft copper will certainly stop it working.

I've found that there are three main things that cause the valve to stick. First is dirt in the freon - especially if the system has been opened. Second is overheating, especially if it is a replacement and the installer did not keep it cool enough during installation. Third is the age of the compressor. The available high pressure from it gets less with age until there is no longer enough to operate the valve. The valves seem to benefit from regular cycling rather than leave them in the cooling position all summer. I strongly recommend cycling it once every time you turn the A/C on just to keep it free and to stop it settling against the end and sticking. Your thermostat probably will not go high enough in summer to get it to go to heating so you may have to do it after the room has cooled to the normal thermostat setting.

I had one valve replaced some years ago. I had to remove the unit from the boat since most A/C companies will not come on a boat to work on it. It cost about $400 and worked until we left that port and has never worked since - stuck on cooling again. I would have been much better off putting that $400 towards purchasing a new unit.

Re: Sizing marine air-conditioner and inverter:

I had a 35' sailboat in Galveston Bay with a 16,000 BTU A/C. This unit would barely keep up on a hot summer's day, but would be loafing in the evening. A lot depends on shading and headliner insulation. You can probably get by with 12,000 BTU on your 28' boat.

Boat air conditioners roughly draw 1 amp at 115 v for each thousand BTU/hr of capacity. Whether you can run your a/c from an inverter depends on how long and when. To try to run a 12,000 btu/hr a/c for 24 hours on a hot Florida summer day on a battery/inverter system is practically infeasible. To run it for 8-10 hours overnight might be possible.

Here are some numbers for the latter situation: 10 hrs x 12 amps x 115 v x 0.5 service factor (the time the unit cycles on and off) = 6900 watt hours AC. 6900 watt hours would equal 6900 div 12 volts div 0.9 efficiency = 640 amp hours DC. To supply 640 amp-hours DC, you are going to need a battery bank of at least 1280 amphours so you don't discharge it below 50% for decent life. This is about a dozen group 27 12v batteries at about 40 lbs each or about 500 lbs of batteries. A 2000 watt inverter would handle this load adequately.

To recharge 640 amp hours would require more than 4 hours of charging with a high output, large case alternator charging at 150+ amps.

So, it may be feasible, but it doesn't seem too practical. If all you want to do is cool the forward cabin at night, you might install a separate 6,000 BTU/hr A/C for only that cabin. The foregoing numbers should drop in half. That might be getting into the realm of practicality.

One of the major problems with this setup is the startup current required by the compressor. I tried this once with a 2600 (1800 continuous) Heart inverter and a 6000 BTU reverse air. It would not start the unit but would run the unit. I started it with generator power and ran it off the inverter. Next problem was after it satisfied the demand it would shut down and would not restart.

Not a real practical method of cooling. Try a small box fan and a quick shower. Works wonders.

... Get professional help when you size an air conditioner, as one of the keys to comfortable humidity control is correct sizing. Pick a unit that is too large, and a cold, clammy environment that short-cycles will not provide the comfort you were expecting. The cooling and heating capacity is measured in BTUs (British thermal units), and a typical small unit for an aft cabin may be 9,000 BTUs.

The unit most often on smaller vessels is self-contained on its tray and requires a separate pump for the condenser water. Larger yachts can have tubing that carries refrigerant vapor/liquid to and from the engine-room-mounted compressor to a cabin-mounted evaporator or "air handler," or it may send chilled water to a fan unit. Any style of unit can produce substantial amounts of condensation, and these tray drains must be maintained. In a wooden vessel, the condensate must be captured in a sump and then pumped overboard. A fiberglass vessel can have condensate drain into the bilge.

Poorly maintained condensate drains can smell and make a mess of a cabin. We recently refitted a boat that lost a complete bulkhead due to freshwater rot from a badly designed condensate drain.

The air side of the evaporator or chiller is a reverse radiator and has fins that help with heat transfer. These must be cleaned and straightened if damaged, so system efficiency is maintained. The unit can ice up if airflow is compromised either at the unit or if ductwork is crushed or an outlet is blocked.

The pump most often picked for condenser cooling is a centrifugal pump, which has definite pros and cons. It will not self-prime and has to be below the waterline. After a launching, it must be bled out, as it cannot clear trapped bubbles of air. On the pro side, it has a very long duty cycle, is quiet and does not require a lot of power. Make sure all plumbing rises gently from seacock to strainer to pump. This is one of the few places for a forward-facing scoop on the through hull. Always check waterflow as you put the air conditioner online.

Most problems are air related, and ductwork cannot be squeezed in, and thermostats have to be in a location away from a direct blast of cooler air from the outlet. Remember to exercise the reverse-heat cycle occasionally to help unstick the reversing valve, although it is not very effective heat in the spring, as the water is so cold. In fact, I have seen it make a slushie leaving the condenser outlet early in the season.

Several things can cause "frosting over". For example, if the unit is not getting enough cooling water due to some type of blockage, OR if it is not getting a sufficient amount of return air (filter blocked) ...

I have a Marine Air unit, and it froze up one time when I sucked a plastic bag into my water strainer and it partially blocked the cooling water flow ...

Something I'm going to try: I will buy a couple of old car radiators at a junkyard, then solder a tube from one to the other and connect flexible tubing to two 12-volt blowers. One inside the boat blowing out and the other inside the boat blowing in. After I drop the radiators into the S.F. Bay I expect to get about 60-degree air coming into the boat.

In other climates one would need to find the depth at which the water was cool enough to make this work and sink the radiators to that depth.

[Having the heat-exchanger in the water and pumping air, should be more efficient than systems that pump water and have the heat-exchanger in the boat.]

> Would there be a humidity problem ?

I intend to make the twin radiator unit sit underwater at an angle so the condensed water will collect at the lowest point. I will use a bilge pump to remove the water from the cooling system.

The "DC" air conditioners I have seen all were simply 120 vac units with an inverter included. They draw huge amounts of power.

In the past I have used the portable units that expel the heat through a pipe to a window or such, and found them to be much less effective at cooling and also at removing the moisture from the air, which is an important part of cooling. It was a 6000 btu unit on a 28 foot boat in Jacksonville.

Then I used a 7500 btu window unit on the same boat that would freeze you out. ...

Consumer Reports also found portables less effective. I have not seen one up close, but with 1 hose, they must be expelling inside air to dump the heat. This air will then be replaced with humid outside air. Air conditioners do not work well until they have dehumidified the area. ... A large part of the cooling energy is used up dehumidifying, therefore it is important not to introduce extra humidity. Humidity control is important for mold control also.

Good window A/C units have an EER of 10, that is, they transfer 10 BTU per watt of power used. This is probably as good as you will get, roughly speaking. So, a 5000 BTU A/C will draw 500 Watts, approx. At 12V, even with a pure sine wave inverter you will draw 40-50 amps. Non-sine-wave inverters, add 20% power usage and subtract a lot of A/C compressor life. Essentially, there is no free lunch, and, it is doubtful that you would be happy with less than 5000 BTU. Easiest way out: Your choice of A/C be it window, RV or Marine and a Honda 2000 generator. You could run an A/C off a large house battery bank, but how would you replace all that energy? Don't buy a 1000 Watt generator, they are only about 700W continuous and will not run your battery charger (depending on size), water heater or microwave.

Practical Sailor did a test of fans recently.

The Caframo came out on top. Attributes:

1. Moves the most air at the lowest noise level
2. Has a on-off-on switch (two speeds)
3. Large variety of mounting options including permanent, suction cup, and large clip-on.
4. Comes with DC cigarette-lighter style "plug" that can be cut off for permanent installation, but if you want to use it as a "roamer" you don't have to buy a plug.
5. $20 Less expensive than Hella Turbo (which don't have switches!)
6. And in my opinion, they look nicer and are much less obtrusive.

I have a Hella and a Guest. The Hellas are quiet, draw very little amps but don't rotate. The Guest does rotate, draws a little more, not quite as quiet, cost is about half of Hellas.

We have used both Guest and Hella, and finally bought a couple of Panasonics. Right, a 110 volt house fan, runs off the inverter, very quiet, 1/2 the cost of a 12 volt "marine" fan, and twice the output. Had figured on throwing them away in a few years, so far have lasted over five and still going strong.

When Hella fans start to squeal, prevent total failure by lubricating the shaft bearings under the blades and under the switch with 90W oil.

I have fans at the foot of the berth. Cheap ones I get at auto parts stores, K-Mart, etc., for about $12-$15. Metal guards come off by removing fasteners, plastic ones are molded to the case so I cut them off with small diagonal cutters. ... with the guards off they produce more air flow quieter, and are easier to clean. I hook them up with two center off switches so they can be turned on across the 12 volt line for power, or in series together then across the line for quiet operation.