Swamp Coolers

[PatrickMcHugh]

We own a 25 foot MacGregor 25 that we frequently sail in the Chesapeake bay. We love the boat and have a great time with it. The only complaint my crew (wife and 2 dogs) have is that it can get pretty hot in the night at the dock when the wind dies down. I'd prefer to anchor out in the open breeze with the hatch open, but sometimes the dock is where we end up.

Has anyone ever had any experience with evaporative "swamp" coolers in this area? I was thinking of building one or buying a small 12v unit.

I'm assuming passing salt through them would not work for long?

Also, would it be possible to simply pump some cool seawater through a small heat exchanger with a fan? Would there be enough cooling?

[Wayne25]

Swamp coolers are made for dryer climates. The act of evaporating water cools the air but also adds humidity by the very nature of the design. They can reduce the temperature going across the coil by as much as 10 degrees in low humidity areas like the SW. However its much less in our rather humid climate.
You could revert to the first air conditioners that used the ice water from melting ice to circulate into a cooling and dehumidification coil. It might last long enough to get you to sleep :-)

[sailingdog]

I don't think a swamp cooler would help much. The 12 VDC fans, like the Hella Turbo or Camframo are the way to go IMHO. Quiet, low voltage draw... the main problem is if the air is static...it tends to get nasty... if you keep the air moving, and these fans will do a good job of that, even really hot, humid are becomes tolerable.

[nimble1]

Do you have power available at the dock? If so, a small 5000 btu window unit will cool your boat down nicely. I adapated one to fit in place of two of my companionway drop boards. I have also seen them adapated to a overhead hatch. They are pretty light and easy to store.

[pdqaltair]

Originally Posted by PatrickMcHugh

We own a 25 foot MacGregor 25 that we frequently sail in the Chesapeake bay. We love the boat and have a great time with it. The only complaint my crew (wife and 2 dogs) have is that it can get pretty hot in the night at the dock when the wind dies down. I'd prefer to anchor out in the open breeze with the hatch open, but sometimes the dock is where we end up.

Has anyone ever had any experience with evaporative "swamp" coolers in this area? I was thinking of building one or buying a small 12v unit.

I'm assuming passing salt through them would not work for long?

Also, would it be possible to simply pump some cool seawater through a small heat exchanger with a fan? Would there be enough cooling?

As a long time Chesapeake sailor I can tell you that on the water the air goes through the dew point every night just after dark, largely because the water gets so warm in the summer. There will be no such thing as evaporation. Towels left hanging on-deck only get more damp. Leaving too many hatches open is even a mixed blessing - more damp. I generally close them down a bit around mid-night, even in the summer.

Sorry.

[PatrickMcHugh]

What do you all think about sending a small weighted tube down near the bottom and pumping that cold water through a heat exchanger with a fan? The water has got to be pretty cold down there albeit clogging the hose with muck would be something i'd have to solve.

[JimMcGee]

I've had good luck with a couple of small fans. I bought two of the cheap O2 fans from West Marine when I bought our boat in July. They can run on 110v or on the built in rechargeable batteries. I was surprised how well they worked and keeping the air moving made a big difference.

That said on those few really hot and humid nights in August AC is the only thing that will keep you really cool.

Jim McGee

[Wayne25]

If you can get cold water into a cooling coil it will work. The BTU depends on the size of the coil the water temperature and the cfm going through the coil.
The formula is BTU = 500 (GPM) (Temperature Difference of the water). The 500 constant assumes some standards. As a ballpark, if you can get 55 degree water or below with a 6 row coil, you may get some dehumidification along with cooling.
Also, the air formula is BTU = cfm (1.08) (temperature difference of the air).
Good luck getting the cold water when you need it.

[PatrickMcHugh]

Originally Posted by Wayne25

If you can get cold water into a cooling coil it will work. The BTU depends on the size of the coil the water temperature and the cfm going through the coil.
The formula is BTU = 500 (GPM) (Temperature Difference of the water). The 500 constant assumes some standards. As a ballpark, if you can get 55 degree water or below with a 6 row coil, you may get some dehumidification along with cooling.
Also, the air formula is BTU = cfm (1.08) (temperature difference of the air).
Good luck getting the cold water when you need it.

I figure this would be an issue, even if we could get a 5-10 degree air temp drop, that would be awesome!

I will be using a 50gph pump sucking in 70 degree water on an 80 degree night, and pushing 60 CFM of air through the heat exchanger with some case fans.

Here's my old college try at algebra.

BTU=500(.83gpm)(10f)
BTU=4,166

4,166=60cfm(1.08)(70-x)
4,166=64.8(70-x)
55.69=70-x
x=-14.31

That doesn't make any sense. I suppose what I need to do is measure some water temperatures at different depths and see if this is even worthwhile. Then i'll need to optimize the system to get the best pump and fans for the job so there is no energy wasted.

[Wayne25]

You mixed the temp difference of air and water. It has to be the temperature difference of the water going in the coil and the temperature of the water coming out of the coil. Same for the air in the air formula.