Keeping the Cabin Cool

[FecklessDolphin]

I have read here that teak decks can make the cabin too warm in tropical climates. Is a dark hull just as bad? Which do you think would be cooler, teak decks with a white hull or fiberglass decks with a dark hull?

[Mike Vogdes]

White fiberglass hull and decks with Reflectix insulation under the headliner.

[s/v Jedi]

Balsa cored hull and decks with white coating.

[FecklessDolphin]

Thank you for your suggestions, but my question is which contributes more to cabin heat, a teak deck or dark topsides. I am suspecting a boat with a fiberglass deck and dark topsides would be cooler than one with a teak deck and a white hull, but I wanted to ask people who may have actually experienced each.

[TacomaSailor]

I never found any difference in the temperature inside a boat due to color - it was all due to the quality of their awnings and their ventilation patterns.

We spent three summers in the Sea of Cortez where the daytime air temp did not drop below 90 F for 100 days in a row and WATER temps were seldom below 88 for months at a time and was frequently above 93 F (the thermal cutoff for my water cooled refrigerator compressor - PITA) for days at a time.

We were thrilled when night time air temps dropped below 85 F.

The color of the hull and color/material of the deck made no difference as far as I could tell. Six boats spent most of those summers together. Some had teak decks, some had white decks, some had white hulls, creame hulls, light blue, and black hulls.

They were all incredibly hot inside at times! Sitting in 90 degree water for weeks at a time ensures that everything in the boat is at least 90 degrees no matter what the sun does.

There were many nights where the down slope adiabatic winds would blow at 25 knots and 100 degrees F for hours at a time. The color of the deck or hull made no difference. One evening the "elephante" wind started to blow at 40 knots and the temperature of the cotton sheets on my bed went from 94 degrees to 106 degrees in three hours.

What makes the biggest difference is the full boat awning that is installed and used every time you anchor. Especially important was the ability to tilt the awning to keep the rising and lowering sun from heating the cabin sides.

Many days when the air temp was 97 and the sun directly overhead the headliner in our white deck/cream hull would reach 110 degrees without the awning. With the awning in place the headliner would be ambient temperature.

The other big issue was ventilation - our boat has 14 opening portlights and three opening overhead hatches and a solar powered exhaust fan. We also used two big wind scoops. We could pull the slightest breeze into the boat.

Other boats I spent time on had far fewer port lights and had little internal airflow - they seemed much warmer inside.

Here is a link to my blog entry about our first May in the Sea of Cortez with no awning and pictures of the resultant awning: Sun Awning

[daddle]

Hmmm. Here in the sunny Philippines I can stand on the white parts of the deck. But burn my feet on the light grey nonskid parts. Dark blue would be ten times worse. Only a fool would bring a dark blue boat to the tropics .... And they do. There are two moored here. Crazy.

[TacomaSailor]

Anytime from mid-May to late September in the Sea of Cortez ( 24 N to 29 N) I could not walk in bare feet on our white decks during mid-day - I literally blistered them several times.

I guess I have tender feet?

[rebel heart]

No real huge difference in my opinion. We're down here in Mexico right now and the sub tropical sun is definitely a roaster. The awnings make a big difference, but in some places the wind kicks up so high you can't really keep them up full time.

The biggest thing is airflow and fans at night. Every berth should have one of the nice three speed campfrano fans or whatever the name is. Windscoop too for when at anchor.

As someone else mentioned when the boat is sitting in 85 degree water, the interior is going to be about the same. Doesn't matter what color it is.

[s/v Jedi]

It's unbelievable! Now, the question of a darker color meaning a higher temp inside the boat has become a matter of opinion!

Also, it seems that somebody once found that this might have to do with rays from the sun. It's rumored that these are not active during the night. Logic, (I know, here I am with that nasty logic again) dictates, that may be the color makes no heat difference at night but does so during the day!

[zeehag]

i found lovely tarps to be the answer in tropix..lol...air moves under them and sun doesnt hit the decking. awesome !! shade rocks.....even a bucket of water on the deck is an improvement over nothing.

[ReMetau]

We have teak decks and use a Shadetree to help minimize the sun. One nice thing about teak is that you can wet it down to help cool the inside of the boat.

[TacomaSailor]

"It's unbelievable! Now, the question of a darker color meaning a higher temp inside the boat has become a matter of opinion!"

"As someone else mentioned when the boat is sitting in 85 degree water, the interior is going to be about the same. Doesn't matter what color it is."

No logic necessary - just some thermal dynamics. Check out the links at the bottom of this message for actual experiments that confirm what I propose here. There are hundreds of such experiments posted on the web - not to mention many similar experiments I conducted in my physics classes.

I think if you conducted a simple experiment you would find the logic in the 2nd statement above in the specified situation: Very hot sunshine and very warm water where the thermal mass of the water far exceeds the thermal mass of the boats.

Let two similar sized boxes with thermocouples inside float, semi-submerged in 88 degree water in the Mexican sun for a week or so. One box is colored white and the other black. Start the test after the boxes have been afloat for several days and have reached thermal equilibrium with their marine environment. The volume of the water would have to be many magnitudes greater than the volume of the boxes.

Each morning, as the sun rises and heats the boxes exteriors, the temperature rise in the white box would be less steep but later in the day both boxes will have an internal temperature that stabilizes at about the same temperature.

The lower internal temperature due to less energy absorption would be short term and not significant. Additionally, as the black hull heats it also radiates infrared energy more efficiently and since only the exterior is black it radiates that energy outward - back into the air.

Then, when the sun goes down the black box will radiate away the absorbed energy at a faster rate and thus it's internal temperature will drop more quickly after sunset. Eventually the internal temperatures of the two boxes will stabilize at approximately an equal temperature.

So - when you really want cooler internal temperatures, evenings and at bed-time, the black hull might be better.

Sure - a light colored deck and/or hull reflects sunlight or absorbs LESS infrared energy from the sun BUT in real life when both boats are soaking in very warm water the hull color makes little difference.


OR - maybe my empirical observations on dozens of boats over three summers in one of the hottest marine environments in the world were in error.

Here is a link to an real life test - black and white automobile sitting side by side in 96 F sunshine - after 30 minutes of simultaneous testing the digital thermometer in each read the same.

http://www.bimmerfest.com/forums/showthread.php?t=71317

Here is another link - a science fair project that duplicated my proposed experiment:
https://docs.google.com/presentation...s#slide=id.p26

External color made no difference to internal temperature!

[sageofsalem]

Exposed to sunlight a darker color deck makes for a hotter interior. I just repainted the coach house and deck with white replacing much light grey non-skid and the boat is noticibly cooler. I can't speak to the teak part of the question as I never had a teak deck (and never will).

[daddle]

TacomaSailor - Nice try but your test and references are completely irrelevant to the situation in a boat. It is common knowledge that dark surfaces have absorb more heat in the sun. It is common experience that dark automobiles are hotter inside than light ones. All else being equal, a dark hull or deck will cause a higher temperature inside. Here is actual science on the subject if autos:

http://m.phys.org/news/2011-10-silve...rs-cooler.html

In this boat, here in the PI, I don't think water temperature has much to do with the interior temperature. Airflow certainly does.

[somedayy]

There is also something called a convection current(look it up, if you don't know what it is). It is a pretty important factor here.

Why do you think all the Arabs where black-for looks?