Overnight Cooling Without Shore Power

[waterman46]

Originally Posted by JBP

If you are thinking of pulling sea water through a radiator with a small pump and a small fan, I think it's brilliant. I've often thought to try it. I have no shore power, no generator, no massive batteries but still would like something more than just a fan.

In tropics, sea water is close to same temperature as the night air.. And in most anchorages since it is not real deep, same temp all the way to the bottom.

Cooler water at useable depth is only available in temperate zones, in general. And in temperate areas, air is usually reasonably cool at night.

[RaymondR]

One of the simplest ways of reducing the temperature in the boat is to shade the decks. Air being drawn across a hot sunny deck is considerably hotter than that from a cool shady deck. I have never tried it but a deck cooled by a fine mist of sea water is probably cooler than that from over a dry deck even if shaded.

I turn my hatch fans down at night and I often have to turn them completely of because it gets too cold with just a sheet on. Lots of fresh, lower humidity air in the boat appears to be the solution. Decked vessels built to keep the sea out appear remarkably efficient at keeping fresh air out unless force ventilated.

[and4ew]

I've often wondered if bringing water up in a hose from 20 or 30 feet down and then watering the deck would work. Moot for us as it rarely gets hot enough in Nova Scotia to be concerned.

[slug]

Originally Posted by SailingKate

I'm new to this community and I'm not a boatowner myself, but I've done some bareboat chartering and my brother is in the process of buying his first boat to do a year of cruising. I'm an engineer, and I have an idea/beginning of an invention for a method of cooling his sleeping cabin overnight while he's not in a marina with access to shore power. I'm still working out the details.

Based on my limited experience, it seems like that would be really useful. But I wanted to ask this community a couple of questions to figure out if it would be a quality-of-life improvement, if it's practical, or or if it's better than other commercially available solutions. Maybe it's not worth pursuing on one or several of those fronts. Or maybe it's something lots of liveaboard sailors would want! So with that purpose in mind, I'd love the opinions of some experienced cruisers:

My understanding is that even if you have a marine AC, you can't run it overnight without shore power. Is that correct? Or is there a commercially available solution I'm not aware of?

How often do you find yourself without shore power overnight? When you do, are you uncomfortable sleeping? Are you in need of cabin cooling?

When you're desperate for overnight cooling, what do you do? Do you just use fans? Improvised swamp coolers (fans blowing over ice)? Is there a DIY solution that you like?

How big of a deal is custom installation? Would you be comfortable running flexible water tubing through from your cabin to the deck, maybe at the cockpit?

How much power are you comfortable pulling continuously from your batteries overnight? I know that running fans is no big deal, but where would you draw the line?

Any insight is appreciated!

I'm new here, so please let me know if this is a violation of the rules about solicitation. I don't have anything to sell right now, but someday I might!

The traditional way to stay civilized ,without modern gizmos , it to use full boat sun awnings

The awnings prevent the boats deck and superstructure from overheating

They also provide very good UV protection , your boat won’t get all burnt up

[LoudMusic]

Heaps of solar. Heaps of batteries. Run the aircon like normal.

[a64pilot]

Originally Posted by wingssail

Sounds doubtful.

"Startup wattage for any new 5000 BTU AC will surge to 1200 watts to 1500 watts momentarily, and will average 900-1000 watts typically whenever its compressor kicks on (www.fiberglassrv.com › forums › 5000-btu-air-conditioner-and-1000-w...)"

That seems high to me, my 8000 unit is rated at 770 watts.

So, lets say 600 watts for a small unit. That is, when the compressor is running, say 50% of the time. Over night, (8 hours), that is 4 hours x 600 =2400 watts. At 12 volts that is 50 amps per hour of operation with compressor, somewhat less with the fan only. Total=250amp hours, per night. Not counting inverter conversion and start-up amps.

Can your batteries take that? What do you use to recharge them each day?

Maybe, but that is high duty cycling.

I would say that small AC and 50% duty cycle don’t go together, small one would have to run continuously, a large one and you get to 50% duty cycle.
So assuming your numbers are correct and I’m no math guy so I accept them, your looking at around 500 AH just for AC.
Then add a house load to that, mine is 150 AH per night. Day use say 200.
So we have 500 + 150 + 200, that takes us to 850 AH in a 24 hr day.

That means your running a generator, nobody has that much Solar, so a large, expensive battery bank, just means you can run the generator during the day.

A small efficient Diesel genset like JClark’s is super quiet, and burns 1 gallon every four hours and doesn’t require $10,000 of battery bank so you can run the AC at night, and costs nothing cause your going to have to have it anyway to recharge that $10,000 LFP bank anyway.

[a64pilot]

Originally Posted by and4ew

I've often wondered if bringing water up in a hose from 20 or 30 feet down and then watering the deck would work. Moot for us as it rarely gets hot enough in Nova Scotia to be concerned.

Depends on where you are, in the Bahama’s with water temp of 80f right now with air temp of 75, no it won’t help.

But up there where you are in Summer when it may get to 80f and the water temp is what 50f? Then yes it should help a lot.

[RaymondR]

Originally Posted by and4ew

I've often wondered if bringing water up in a hose from 20 or 30 feet down and then watering the deck would work. Moot for us as it rarely gets hot enough in Nova Scotia to be concerned.

Never been to Nova Scotia but from where it is situated your proposal could be quiet a good heating scheme for most of the year.

[onestepcsy37]

our boat, a csy 37, was especially built for caribbean cruising without air conditioning. it had one giant overhead hatch and five extra large cabin top hatches. it also had side opening ports, including the all important forward facing port. all were screened, as was the companion way hatch. anchored out in the icw in georgia on a 90 degree night we got so cold from the sea breeze we had to close most of the hatches.



my advice. get a boat with lots of hatches. if it doesn't have them, add them. then anchor out so your boat swings into the wind.

[svMarite]

My wife found a cool trick from cruising women. Close all your hatches except for a 2" gap in the forward hatch. Put an exhausting fan in the companion way. Shade the boat. Creates a vacuum effect drawing in compressed air, if you will, from the hatch, pulls air and heat through boat out the compartment.
We have a fan at the foot of the berth on low. We're quite comfortable.

[chrisr]

we have air con + generator, but simply never need the A/C except on the rare times we're tied up in a marina. being on the water is plenty cool enough for us...maybe a fan sometimes, but that's all

think part of the answer is
- good shade covers during the day
- really good reflective film on the windows (we have a lot of glass)
- plenty of forward facing hatches

if the boat is well designed and set up, you simply don't need A/C - or if you do, you are in the wrong place...i heard of a boat that puts butter on the table...if it goes soft, it's too hot & they head south (southern hemisphere)....too hard and they go north...easy

cheers,

[valhalla360]

Originally Posted by SailingKate

I'm new to this community and I'm not a boatowner myself, but I've done some bareboat chartering and my brother is in the process of buying his first boat to do a year of cruising. I'm an engineer, and I have an idea/beginning of an invention for a method of cooling his sleeping cabin overnight while he's not in a marina with access to shore power. I'm still working out the details.

Based on my limited experience, it seems like that would be really useful. But I wanted to ask this community a couple of questions to figure out if it would be a quality-of-life improvement, if it's practical, or or if it's better than other commercially available solutions. Maybe it's not worth pursuing on one or several of those fronts. Or maybe it's something lots of liveaboard sailors would want! So with that purpose in mind, I'd love the opinions of some experienced cruisers:

My understanding is that even if you have a marine AC, you can't run it overnight without shore power. Is that correct? Or is there a commercially available solution I'm not aware of?

How often do you find yourself without shore power overnight? When you do, are you uncomfortable sleeping? Are you in need of cabin cooling?

When you're desperate for overnight cooling, what do you do? Do you just use fans? Improvised swamp coolers (fans blowing over ice)? Is there a DIY solution that you like?

How big of a deal is custom installation? Would you be comfortable running flexible water tubing through from your cabin to the deck, maybe at the cockpit?

How much power are you comfortable pulling continuously from your batteries overnight? I know that running fans is no big deal, but where would you draw the line?

Any insight is appreciated!

I'm new here, so please let me know if this is a violation of the rules about solicitation. I don't have anything to sell right now, but someday I might!

If it's not too proprietary, can you give us any clue to what your solution is?

As you've seen, the peanut gallery runs off making lots of assumptions that may or may not have anything to do with your idea.

As mentioned the typical solution is to start the generator or claim that you don't need air/con because you are manly enough to survive it.

[Tupaia]

Something like a Caframo 12v fan draws 0.28 A on low setting.



Without resorting to fossil fuel boats relay on solar (does not produce at night) or wind generators. By definition if these were functioning there would be wind.


Any solution needs to be very electrically economical.

[Dockhead]

Originally Posted by wingssail

Sounds doubtful.

"Startup wattage for any new 5000 BTU AC will surge to 1200 watts to 1500 watts momentarily, and will average 900-1000 watts typically whenever its compressor kicks on (www.fiberglassrv.com › forums › 5000-btu-air-conditioner-and-1000-w...)"

That seems high to me, my 8000 unit is rated at 770 watts.

So, lets say 600 watts for a small unit. That is, when the compressor is running, say 50% of the time. Over night, (8 hours), that is 4 hours x 600 =2400 watts. At 12 volts that is 50 amps per hour of operation with compressor, somewhat less with the fan only. Total=250amp hours, per night. Not counting inverter conversion and start-up amps.

Can your batteries take that? What do you use to recharge them each day?

Maybe, but that is high duty cycling.

Your units are all confused here. Let me see if I can sort it out, because this is really the heart of the matter.


600 watts * 50% duty cycle = 300 watt hours per hour or 0.3kWh per hour. So for 8 hours that's 2.4kWh. That's 100AH at 24v o r 200AH at 12v.



My present battery bank (which will be changed this spring) contains about 200AH of usable power at 24v when fully charged. So your scenario would work on my boat today and would work even much better with lithium.



I think actually it could be better than that -- I think you run the AC full blast with the generator on for a couple of hours before going to bed, get everything cooled off well, then let it coast on batteries -- might be much better than 50% duty cycle with no solar gain and assuming you have decent insulation.



Of purely theoretical interest to me since I have never been below 40N in more than 10 years of cruising with this boat and presently at 55N, so I'm heating year round and no AC.


When I was cruising warmer places we did have AC but no generator. As others have commented, at most hot latititudes you can be more or less comfortable at anchor without AC, but AC was a godsend in marinas. Excluding the Sea of Cortez in summer I guess.

[Dockhead]

Originally Posted by a64pilot

Depends on where you are, in the Bahama’s with water temp of 80f right now with air temp of 75, no it won’t help.

But up there where you are in Summer when it may get to 80f and the water temp is what 50f? Then yes it should help a lot.

But what is the water temp 10 meters down? Isn't it a lot cooler than on the surface?


A water to air heat exchanger using cold water from deep down could be really interesting, if there really is cold water there. They air condition data centers and office buildings in Finland using this principle.