Cooling the Cabin of a Sailboat

[Stillraining]

Cool bit of history ..Thanks!...I would have guessed much older then that.

[nautical62]

Just an observation: The poster appears to have not participated since the OP.

[Stillraining]

But were having fun...

[boatman61]

Originally Posted by nautical62

Just an observation: The poster appears to have not participated since the OP.

Probably to busy in the shed with hammer n saw making dorades while the wifes knocking up windscoops n boat covers....lol
SAVE THE WHALE

[Furface]

Very helpful, thanks s/v jedi and "man" I love that boat.

[avnbuff]

Cooling any boat seems to require a lot of energy. Most of the 'big' boats are satisfied with the $2000 or $4000 units that keep a part of the cabin cool.

This involves pumping lots of water and running a compressor.

The first part of this, the water may hold a secret to getting a cabin cooler. Most of the better refrigeration units pump water around the newly compressed freon to provide a more efficient unit.

The water temperature at depth could be in the 70's even on a really hot Florida day. So, if you are not sailing, what about pulling some up to the cabin area to do a heat exchanger process and cool down the area?

[SabreKai]

From my experience, sleeping in a hot muggy cabin can be made more tolerable by using a dehumidifier. I find that I can tolerate about 6-8 degrees F more in a dry environment than in a humid one. Not to mention that if the AC is on and its still humid, then you feel like you are freezing. So perhaps an efficient dehumidifier might be a better idea? I keep looking at the unit in my apartment. If you could also save the water from the cooling grid, then perhaps this can be used for drinking after filtering. Kill two birds with one stone. But power consumption will have to be as low as possible otherwise it will be useless off the dock and shore power hookup.

As for the boat, open hatches and port, wind scoops, fans, white painted deck and coach roof, an awning over as much deck area as you can fit and insulation. I like the idea of misting water onto the awning. I'll have to try that. Evaporation does do a lot toward cooling the air under the awning.

Sabre

[Wavewacker]

Hi, well, I'm no engineer, but old enought to remember water coolers. Can wate from a few feet down be pumped up and used through a condinser? What about humidity?

[Fishman_Tx]

Works in dry climates ("Swamp Coolers"), but don't work well if at all in humid environments.

[hellosailor]

There's no secret that water makes a better coolant than air. The problem is, water is highly corrosive and expensive to deal with, compared to air. That's why the VW Beetle had an air-cooled engine: cheap, but inefficient.

Once you go to water-cooling your refrigerant system, you can't use cheap aluminum tubing and fins, you need to switch to copper, monel, or other metals that will behave better in salt water. And assemble them more durably. And provide a water pump that won't fail or clog, and filter strainers, and a water drain, and failsafes against something stopping or clogging or overflowing...the complications make it way more expensive than air cooling. (Remember, from manufacturing to retail every $10 in extra costs may become $50 in final price.)

But if you are willing to pay for efficiency, and to keep up with repairs it will need, that's why there are indeed water-cooled systems (AC & refrig) on the market.

[tager]

Swimming is my preferred air conditioning system.

[eyschulman]

Water mist-if you can spray a fine mist of water(dock or ocean) over boat the evaporation and cooler temp of water will cool boat.

[Dockhead]

Originally Posted by avnbuff

Cooling any boat seems to require a lot of energy. Most of the 'big' boats are satisfied with the $2000 or $4000 units that keep a part of the cabin cool.

This involves pumping lots of water and running a compressor.

The first part of this, the water may hold a secret to getting a cabin cooler. Most of the better refrigeration units pump water around the newly compressed freon to provide a more efficient unit.

The water temperature at depth could be in the 70's even on a really hot Florida day. So, if you are not sailing, what about pulling some up to the cabin area to do a heat exchanger process and cool down the area?

That's a really, really interesting question, which no one answered. Made me think. He means that the ocean some depth down is going to be cool, even when it is hot as h*ll and the water at the surface is bathtub warm. Instead of spending tons of energy on a compressor, why not drop a long hose down into the ocean into a cooler layer of water, and pump the water through a simple heat exchanger?

Has anyone thought of or tried such a thing?

He's not talking about a "swamp cooler", which works by evaporation.

[DocBrown]

Some AC systems are getting efficient enough that solar powered AC/heat pump units on a boat are practical. The Mitsubishi Mr. Slim split system line has a 26 SEER 9,000 BTU unit for example and there are 25 SEER 12,000 BTU units. Those numbers equate to approximately 350 and 500 watts peak usage respectively. This is doable with several 200 Watt to 300 Watt solar panels as a power source. It is not as many BTUs as normally recommended for most boats, but at the very least you can keep the aft cabin cool at night for a good nights sleep, and have slightly dryer cooler air during the day. Unless you want a huge battery bank, you will need to budget amp hours carefully anyway.

For boat use some modifications will increase efficiency. The indoor units run on DC, so there is no point converting to AC and then back. You may want (need?) to put the solar panels in series to raise the voltage. In fact I would change the electronics so the entire boat was at higher voltage 24v to 48V, to decrease powers losses in the wiring, but DC to DC converters work too. If you do convert to higher voltage you can still run a small DC to DC converter (such as Vycor) for your 12 volt equipment.

The overall unit gains much of its improved efficiency by using an inverter that supplies power as needed to the compressor by modifying the electric frequency/compressor speed as needed for steady low power operation. That would mean bypassing the rectifier here as well and using a DC to DC converter if necessary to raise the voltage to the necessary input voltage. I wish I had a circuit diagram. The compressor fan is also DC, so it should be run directly too if you stick with air cooling. But who wants that ugly thing on deck.

Here you can look at water cooling. This would mean replacing the condenser with tubing and possibly fins that can tolerate seawater. For best efficiency you would want to passively circulate water if possible rather than waste energy pumping it, but I hate the idea of having it outside the hull. A pump probably uses more energy than the fan you are trying to replace, but you might recover that energy with increased efficiency of a water cooled condenser. If you can draw deeper cooler water even better.

Between water cooling and eliminating the rectification-DC conversion step in the original design it should be possible to get an overall SEER rating better than 26 SEER. I think this would be a good project for an engineering student. As with any non-marine grade electronics a liberal coating of marine grade electronics grease should be applied to all circuit boards and bare connections.

Solar Panels have the added benefit of reflecting light energy including infrared (IR) that makes up nearly half the energy. Some well placed panels can help with cooling, but it is a good idea to have an air insulation layer between them and the boat. Think about reflective window treatments that are designed to reflect IR and it may be ugly but aluminized Mylar is a great light/IR reflector. The less heat you let in in the first place the less AC you need.

[hellosailor]

"This is doable with several 200 Watt to 300 Watt solar panels as a power source. "
Doc, do you think a 9000BTU AC unit will cool a boat that is big enough to carry a 300 Watt solar panel? Given that a single 100W panel is about 2'x3' so a 300W array requires about a 3'x6' space....that's impractical until you hit maybe 36'OAL at a minimum, and even then where do you put it? Cover the bimini?

A 300W panel is going to give you about 1200 watt-hours on the best of days during a full day of production....then you need 2400WH of battery just to soak that up at a 50% cycle rate, with no other loads. And it needs a 210-220VAC power inverter, three goes 10% of your power in the inverter. Power consumption appears to be some 650 Watts, so a full day with 2400WH less overhead and inverter losses means that you may be able to run the AC for three hours before it goes crump.

Feasible, but only for a small cabin on a BIG BOAT with an even bigger excess battery capacity. Or back to the trawler-genset scenario.

Too much money, too much equipment, too much real estate for the majority of sailboats and sailors.