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Old 10-03-2020, 13:13   #1
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Overnight Cooling Without Shore Power

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!
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Old 10-03-2020, 13:56   #2
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Re: Overnight Cooling Without Shore Power

Anchor out, open hatches and use fans (if still needed) is the simple answer and typically what we do.
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Old 10-03-2020, 13:57   #3
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Re: Overnight Cooling Without Shore Power

There is a commercial solution, it’s known as a generator, or a windscoop.

Typically when anchored there’s a breeze, so staying cool isn’t a big deal.
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Old 10-03-2020, 14:12   #4
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Re: Overnight Cooling Without Shore Power

Usually it's much cooler on the water than on land, if you can get a shore breeze. So cooling isn't as essential. Which is a good thing because running a generator all night would be loud and annoying.

Basically being hot at anchor is an unusual problem, since the breeze is going to bring the boat down to the water temperature. Which is only a problem when the water is hot, which is usually only a problem in a marina, where there is shore power.

Which is not to say there aren't boaters sitting and suffering in hot anchorages with no AC. There very much are. It's just a minority of the population.

So any solution would have to be exceptionally cheap(low demand), low power(because there isn't much), and powerful enough to overcome sitting in warm water(because that's why it got hot in the first place.).

If there is a solution out there though, go for it.
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Old 10-03-2020, 14:18   #5
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Re: Overnight Cooling Without Shore Power

I agree, sleeping at anchor is usually manageable. If it's overly hot / humid / rainy where I can't keep the boat comfortable at night when we're on a trip, I'll generally try to find a marina with shore power for the night so I can fire up the A/C. Running the generator all night is a last resort in my mind, only if it were so miserable I couldn't sleep and had no other options available.

On a hot day I'll typically turn the A/C on for an hour or so in the evening when I have the generator running for other stuff anyway. Cooling the boat down a bit closer to sunset goes a long way to getting rid of the day's heat soak and making it easier to stay cool overnight.
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Old 10-03-2020, 14:24   #6
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Re: Overnight Cooling Without Shore Power

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Originally Posted by Corvidae View Post
Usually it's much cooler on the water than on land, if you can get a shore breeze. So cooling isn't as essential.
Works for us, no a/c on our vessel

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Which is a good thing because running a generator all night would be loud and annoying.
Only if you don't have a decent genset and sound deadening.
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Old 10-03-2020, 14:26   #7
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Re: Overnight Cooling Without Shore Power

I suppose it depends on your generator installation and your tolerance for heat and humidity. In our case we have a low tolerance and a quiet generator. We run the a/c 24/7 in the summer keeping the salon and staterooms cool and dry, the same with the galley. We air cooled our land home all the time, I see no reason not to cool our water home too.

We do shut the 20kw generator down at night and go to the 12kw unit which works just fine to cool the staterooms. Here in the Bahamas in the winter it’s cool enough to not a/c the boat and just use open hatches. We still cool the staterooms and run the dehumidifiers for an hour or two before bed so we and our guests can sleep in dry bedrooms. That also charges the house and inverter battery banks for the next 12 hours so we can start the night topped up.
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Old 10-03-2020, 14:30   #8
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Re: Overnight Cooling Without Shore Power

Try TrawlerForum.com, sister site to this one with more of a powerboat slant.

I can think of several use cases where very efficient cooling would be beneficial. Buggy areas. Dead breezes. Daytime heat. Cruising under power but not wanting to run a generator. Boats with master stateroom in aft cabin that doesn't get the great breeze at anchor. Marinas that charge a fortune for electricity such as the Bahamas.

Fact is, for many boaters, having a generator aboard is mostly useful for AC. An efficient AC might mean they could bypass a generator and just run off their alternator when underway.

Good luck on your idea

Peter
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Old 10-03-2020, 14:52   #9
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Re: Overnight Cooling Without Shore Power

We have been full time cruisers for 5 years. We have a generator, and AC. Never have we even thought about running the genset to power the AC units while we are at anchor. Not that we have any moral opposition to the idea, is just has never been needed.

Anchored out there is almost always a breeze, and it is far cooler than close to shore.

On the other hand, we would have melted in some marinas without AC.
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Old 10-03-2020, 15:35   #10
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Re: Overnight Cooling Without Shore Power

Bottom line is AC is the only reason many boats have a generator. Cooking can be gas. Water makers are more efficient. And LFP batteries are 5x more efficient and much lighter. Many boats carry fairly large solar arrays that generate 4kwh per day or more. If the OP has a way to air condition a boat (or motor home or tiny home, assuming the secret sauce doesn't use seawater for heat pump) in a manner that fits into the evolving energy budget, she has a very interesting value proposition.
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Old 10-03-2020, 15:39   #11
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Re: Overnight Cooling Without Shore Power

Running AC off of the bank is simply a matter of scaling, some people want to believe there are magic AC’s that can run off of DC direct and pull little power.
Unfortunately that’s not possible, so running AC’s off of a battery bank means a massive, horribly expensive Lithium bank, and even then you have to have a generator to recharge that bank to run the AC’s tonight, and how about the heat of the day?
If your an Engineer it’s not hard to determine the current draw of then most efficient marine 16K AC there is, then of course assume a realistic duty cycle and that’s how much power the bank has to supply over and above the regular house load.

When those costs are added up, it’s most logical to run a well sound insulated generator every night and change its oil every week or so and I guess buy a new one every couple of years, cause it doesn’t get any cooler in the daytime and if you need AC at night when the suns down, your going to need it during the day too, so now you are running a generator what 150 hours a week?
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Old 10-03-2020, 15:42   #12
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Re: Overnight Cooling Without Shore Power

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Originally Posted by mvweebles View Post
Bottom line is AC is the only reason many boats have a generator. Cooking can be gas. Water makers are more efficient. And LFP batteries are 5x more efficient and much lighter. Many boats carry fairly large solar arrays that generate 4kwh per day or more. If the OP has a way to air condition a boat (or motor home or tiny home, assuming the secret sauce doesn't use seawater for heat pump) in a manner that fits into the evolving energy budget, she has a very interesting value proposition.
Explain please how lithium batteries are 5X more efficient, and what do you mean by efficient?
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Old 10-03-2020, 16:07   #13
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Re: Overnight Cooling Without Shore Power

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Originally Posted by SailingKate View Post
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.
You are going to be rich!!!!!!!!

As an engineer what is your answer for the first law of thermodynamics? It has to be be small and reasonably light and affordable.
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Old 10-03-2020, 16:28   #14
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Re: Overnight Cooling Without Shore Power

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Explain please how lithium batteries are 5X more efficient, and what do you mean by efficient?
Actually more than that. Flooded acid cells are rated in the 300-500 cycle range and horribly sensitive to discharge below 50%. LFP are rated at 2500+ cycles with discharge to 80%. 100AH FA is 100 lbs and has 50AH usable. 100 LFP is 25-30 lbs and has 80AH-100AH usable. Initial cost is the only place where LFP under perform.
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Old 10-03-2020, 17:31   #15
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Re: Overnight Cooling Without Shore Power

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Actually more than that. Flooded acid cells are rated in the 300-500 cycle range and horribly sensitive to discharge below 50%. LFP are rated at 2500+ cycles with discharge to 80%. 100AH FA is 100 lbs and has 50AH usable. 100 LFP is 25-30 lbs and has 80AH-100AH usable. Initial cost is the only place where LFP under perform.

None of that is efficiency.
Efficiency is most often considered the amount of power you can get out of a storage source compared with the amount of power you put in.
For example a lead acid battery requires on average to have to have 102% to 106% of the power removed to be put back, if you only return what you took out then over time of course your walking the charge down.

So if an LFP battery is 100% efficient as in you only have to return what you take out, then it’s only between 2% and 6% more efficient than Lead, I have no idea about LFP, but nothing is 100%, nothing.
Most of what you said is simply not true either, like only 300 to 500 cycles or being horribly sensitive to discharge below 50%. The 50% is simply an arbitrary number that was picked back in the day as one that was considered a good trade off of usable capacity and cycle life, and if they only lasted 300 cycles, then that’s less than a year, and most get well more than a year out of their banks.

But I do agree that if you want to run AC’s off of a battery bank overnight, then that really does make more sense with an LFP bank, just I think running AC’s overnight off a battery bank to be a foolish endeavor, cause if nothing else, it’s the heat of the day when AC is needed, not the cool of the night.
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