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Old 26-01-2010, 09:46   #1
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Cooling the Cabin of a Sailboat

Hi everyone!

I am a mechanical engineering student at Georgia Tech and am currently working on a project that involves providing a better cooling for a sailboat cabin. First off, is there even an issue with the current systems that are implemented in cabin cooling? Such as, does it use too much electricity or gas or is not very effective? I am basically trying to see if there would even be a demand for such a project before I get too involved in it.

I would appreciate any comments about cabin cooling.

Thanks,
Sara
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Old 26-01-2010, 10:17   #2
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Not to sound like an ass, but as one engineer to a student I have to say that if you are trying to solve a problem you must first understand the problem. Asking questions is fine, but spending a summer in a sailboat is better. You learn so much more by being there.

I hope you get some good info here but it will never replace getting out there, remember that as a engineer, get out of the office and on the shop floor, use what you are trying to design and always ask more questions. And understand the problem fully before even starting to try to solve it.

Good Luck
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Old 26-01-2010, 10:20   #3
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Sara,

Most sailboats use 1 of three methods to cool the cabin. Listed in order of increasing complexity the are:
1 - Open hatches / ports to allow breeze in
2 - Run 12v fans to provide breeze (while small and don't move air like a household ceiling fan, they are efficient that even the smallest of on board batteries can run them all night long without issue.
3 - Run heat pump colling system. This is a water to air heat exchanger that works like your AC in your house except it uses water to provide cooling vs the outside air. Check out the systems from Marine air. I have a 20K BTU system on my 35' boat. This system works great and will provide house like temperatures inside the boat in even the hottest of weather, however it requires either the generator or shore power to operate.
There could be a market for a system someplace between 2 & 3 above that would draw lets say less than 5 amps per hour to operate at 12volts DC that could provide cooling to the cabin air like an AC system does.
Good Luck.
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Old 26-01-2010, 11:10   #4
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We're using an AC system off my old Chevy S10. Engine bracketing is a pain in the butt, but everything else is gravy. And Before ya'll start; YES it only works when the engine is running, but doesn't take 15-20 minutes (less!) to cool the boat off for night and that's all we need (I caught hell in my original thread).
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Old 26-01-2010, 11:19   #5
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For anyone who doesn't like to run a gen set or anchor in highwind anchorages where a windmill will work, airconditioning is too high a price to pay. A simple thing like a full boat awning will lower the temperature significantly making the boat livable even in the tropics. Also, anchoring out where the boat will fare into the wind and keep a breeze flowing through the boat is a big help. Solar panels might be able to keep up with the draw of an A/C unit but you better have a lot deck to mount them on.

Sitting at a dock is usually sweltering because of lack of airflow. Of course, then you have access to all those coal fired electrons to power an A/C unit.
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Old 26-01-2010, 11:43   #6
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Sara,

Cooling a cabin of a sailboat that is kept in a marina/on a trailer and is occasionally sailed for a few hours at a time (this is how a vast majority of sailboats are used) is not a problem. At the dock you can use a shore power to supply either a built-in or a portable AC unit, and you don’t really need an AC in a day sailor while sailing, for you spend almost all time in the cockpit where it won’t be effective at all. With a long range cruiser of modest size, air conditioning presents three major problems: power consumption, interior volume it occupies, and reliability. Price is also a significant consideration. With larger yachts these problems diminish: they usually have generators running constantly or almost constantly, interior volume is abundant, there is a mechanic on board to address reliability issues, and a price is relatively less important (for someone who owns a million dollar yacht).

So ideal cooling solution for an average sailboat would be something that runs exclusively on solar power (solar thermal electric, for example); does not occupy too much space (less than a couple of cubic feet or so); does not require maintenance, or needs a very basic one only occasionally; and is relatively inexpensive. Cooling capacity should be somewhere between 10 and 20 thousand BTU/hour, in case you can get that far. If you can come up with such a solution, it may be commercially viable product, although the market size is extremely small. You can estimate that only 1% of population owns sailboats, and only 1% of those sailboats are active cruisers in need for an AC; these are rough estimates, but you can appreciate an order of magnitude for the market in comparison with residential or automotive cooling, for example. (So I don’t think that your Technology Transfer Office will get too excited about it.)
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Old 26-01-2010, 12:08   #7
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The ideal system would be some sort of convection system using seawater. It's like a heat exchanger without a pump, although a backup pump would probably be needed.
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Old 26-01-2010, 12:21   #8
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boats in general don't have insulation from the sun. i have seen temps of 100 degrees or more in my boat in florida. how you gonna cool this unless you use a standard air conditioner when the outside air temps are 90 degrees or more? then there is the humidity problem to be solved as well.
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Old 26-01-2010, 13:00   #9
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Sara,

I write from the perspective of a degreed naval architect and marine engineer as well as a long-time liveaboard.

There are number of a/c systems available for recreational boats. They have the advantage (over conventional land-based systems) of using water for cooling (talk to your therm prof). The issues with recreational marine a/c are marine growth in the cooling circuit, extreme heat-loading in a poorly insulated space, low sales volume, and generally poor installation practices.

Good luck with your project.

sail fast and eat well, dave
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Old 26-01-2010, 13:02   #10
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Yes Sara, there would be a demand for a a/c unit that could cool a small/med size sailboat
that is extremely power efficient, reasonably compact and dependable for a attractive price
as stated in post #6 ...if it would be economically viable to develope is the question.
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Old 26-01-2010, 13:06   #11
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Originally Posted by Fishman_Tx View Post
We're using an AC system off my old Chevy S10. Engine bracketing is a pain in the butt, but everything else is gravy. And Before ya'll start; YES it only works when the engine is running, but doesn't take 15-20 minutes (less!) to cool the boat off for night and that's all we need (I caught hell in my original thread).

I still say it can't be done.
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Old 26-01-2010, 13:56   #12
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When I'm at anchor, everything is about amps. Between my solar panels and wind generator I can expend around 80-100 amp hours per day. My refrigeration system eats up around 60 ah daily. That only gives me 20-40 ah to play with. The 12v. fan installed over my berth works within that limit. To sell me an air conditioning system you'd need to find one that's not going to exceed my energy budget. Running a generator to power an air conditioner is not an option.
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Old 26-01-2010, 14:11   #13
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Dang, Frank, why didn't ya tell me that before...

Condenser in engine compartment..
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Old 26-01-2010, 15:00   #14
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As an engineering student you must have already noticed that the greatest potential is the moderating temperature of the water that the boat is sitting in compared to the ambient air temperature. Exploiting this potential should allow heating in winter as well as cooling in summer. 'take the advantage of surface area, Aythya crew
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Old 26-01-2010, 15:45   #15
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Exploiting this potential should allow heating in winter as well as cooling in summer. 'take the advantage of surface area, Aythya crew
and what you have around you - yachts have masts - which is a chimney - which heat would rise up naturally - perhaps with a little fan help - or use a sail material tube hoisted up the mast from a hatch - screw thread on the outside to create lift in surounding air - now source the cool air to enter the boat - cooled by water

Oh and who and where is your market? US and European yachties perhaps, enough money to buy yachts and can afford to go off sailing away from existing marina infrastructure.

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