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Keeping A Sailboat Cool Without Shore Power

May 29, 2018
294
Canel 25 foot Shiogama, japan
I cruised SE Asia for 3 years.
There is nothing you an do about humidity.
A fan will move air across your body, but if your sweat can't evaporate you stay hot and clammy.

There are a few things that you can do to cool down the cabin little.
The first , as suggested is a reflective tarp cover.
This will stop the direct suns rays from heating up as much of the horizontal surfaces as possible.
No matter how well the deck is insulated it will adsorb heat and even as the evening cools down, emit that heat into the cabin.

You can use a small positive displacement pump to supply a hose system the dribbles water over the cabin top and decksides ( and even the tarp).
Even in high humidity this will evaporate away, taking some of the stored heat from the cabintop an give you a cooler evening.

Lastly, cool showers. Called a "mandi" in Indonesia.
All you need is a bucket in the cockpit and a ladle.

Traditional boats laird hessian bags all over the decks and kept them wet. Not sure how well that worked though. It still felt stifling below.

gary
 
May 24, 2004
6,768
CC 30 South Florida
The problem with boats is that the sun will heat the deck which has poor insulation and the interior of the cabin can heat up to 30F over the interior temperature of the cabin. The best measure that can be taken is to tent the deck with canvas as it will hold the sun and the space of air between the canvas and the deck will serve as insulation keeping the interior close to the ambient temperature. Spraying the deck surface with water will induce evaporation which causes cooling of the surface. If you have a hose at the marina you can spray the deck once every hour. This will not give much, but every little bit helps. Here in Florida with our high humidity we use a Honda 2000 portable gas generator to run the air conditioner when away from shorepower. In older and smaller boats we used to carry a portable window unit air conditioner which we would install in the companionway at night. We would connect the generator output to the boat's shorepower inlet and plug the A/C to a regular receptacle. On cooler nights we had a sock that would direct air into the bow hatch. As air flow is an important factor of cooling we make ample use of fans.
 
Jan 25, 2011
2,219
S2 11.0A Anacortes, WA
Back in the mid nineties, we had a ‘80 Gulfstar 44 cc ketch that we lived on for 10 yrs. The headliner throughout was cloth with a lot of little holes and was pretty dirty when we bought it. I ripped it down and glued double sided bubble wrap to the cabin top. The double sided was bubble wrap with aluminum on both sides. Reinstalled new cloth. The difference was remarkable (summer and winter)and I know newer boats don’t use cloth headliners. But???
 

TomY

Alden Forum Moderator
Jun 22, 2004
2,648
Alden 38' Challenger yawl Rockport Harbor
Our boats awning gets increasing use every season. Even on the coast of Maine, many mid-days would be intolerable on deck. During the high sun hours, the awning shades the cockpit, the companionway area and much of our side decks in the saloon.

With the dodger front panel raised, a cool breeze moves below the awning and through the cockpit.

We attach various sun blocks to the edge as the afternoon sun goes low. Or we just collect on the side deck that is shaded.

We couldn't sail without it.


Christmas Perry Creek 2021.jpg
 
Mar 20, 2015
2,223
C&C 30 Mk1 Silver Harbour, Lake Winnipeg
Outland hatch covers are good.
They look great. Easy to store. No button snaps like cloth types. Likely last longer than cloth.

Depends on the fan and the battery bank. At dock, of course, it does not matter.
In this case.. as the thread title says...shore power is not available.. (nor do I really want an annoying noisy generator or the inboard running at the dock)

Box fans do make a lot of sense if you have the power to run them though. :)

You can use a small positive displacement pump to supply a hose system the dribbles water over the cabin top and decksides ( and even the tarp).
Even in high humidity this will evaporate away, taking some of the stored heat from the cabintop an give you a cooler evening.
The best measure that can be taken is to tent the deck with canvas as it will hold the sun and the space of air between the canvas and the deck will serve as insulation keeping the interior close to the ambient temperature. Spraying the deck surface with water will induce evaporation which causes cooling of the surface. If you have a hose at the marina you can spray the deck once every hour.
Our boats awning gets increasing use every season.
The awning, possibly combined with a misting system, seems like the best option when at the dock or even anchored.

If works well in SE Asia then it works anywhere IMO.

The port covers would be great when we aren't aboard or don't need a lot of light below.

I kinda hate drapes inside a boat and in houses. I'd rather have tinted ports with a reflective outer coating for privacy and heat reduction.
I noticed that Sam Holmes has some type of shutters on his ports.
For our needs the plastic external covers should be the cheaper and universal alternative.

Passive solar design in housing is a bunch of little things that quickly add up to a large result.

Between a deck awning, port covers etc. it should be more than enough for these two northerners who make an effort to acclimatize. (We haven't used the central air in our house for decades)

Thanks for the great replies all !

As usual this forum, with all that personal experience, is a great help. Not to mention...this thread will be a good resource for others in the future.
 

Blitz

.
Jul 10, 2007
609
Seidelmann 34 Atlantic Highlands, NJ
I have had good success with sunbrella hatch covers, that were purchased on this site over ten years ago. but it doesn't seem like they carry them anymore, maybe a phone call.