I’m looking for a (scientific) study that deals with the subject that white ships get less warm than dark colored ships. Unfortunately I haven’t been able to find any good articles or studies on this topic (I find one on car colors). I hope someone can help me further and maybe know of a study on this topic.
A little extra background: Why are some types of ships (like cruise ships and yachts) commonly painted white?
The answer could lie in some basic physics (and of course a little tweak of aesthetics).
These types of ships often sail in areas with a lot of sunshine, such as the Mediterranean and the Caribbean Sea.
Being the best reflector and worst absorber in the colour spectrum, white colored exteriors are logically save the ship from getting heated up, reducing the burden on air conditioning systems.
Does anyone know if this indeed the reason and is there some research to back-up this claim?
I have no research. Just anecdotes and a little observation.
The boats we operate are essentially reefer boats. On the run between Alaska and Seattle the increased energy load on the reefer plant is marked on hot summer days once the vessel leaves the cloudy GOA and approaches Seattle, even though water temps did not change much Not a problem now with modern reefer plants, but noticeable.
Back in the 1980s / 1990s operating other boats with less efficient reefer plants it would be a problem in the hottest days of summer. The worst part of the problem was right under the cargo hatches, where there were no reefer coils to remove heat from the space. The plating would absorb heat energy via insolation , then radiate it into the hold, even though the underside had 12" of foam insulation.
In the distant past (mid-20th century), reefer ships were often painted white to reduce insolation, easing the work of the reefer plant in removing heat from the cargo holds.
Knowing this, the way we eased the problem 30 years ago was to paint the cargo hatches (16’ X16’) white. The sensors in the cargo hold noted reduced temps, and the chief engineers noticed the loads on the reefer system were eased, even with such small areas involved.
But we could never convince, for complex reasons, the Powers-That-Be to paint the entire weather deck white. If we had, I have no doubt it would have greatly reduced insolation to the deck plating, and kept the cargo holds cooler with less energy from the reefer plant.
Thank you for your response. I have similar experience boating in the Caribbean. There, the roof of the bridge was always painted white by the ship’s crew, but this was also a change that was not allowed to be made as permanent.
I’d imagine there are some kind of “scientific” studies out there. I believe some kind of super white paint has been developed for buildings to keep them cool, the issue was they’re also blinding reflecting the light if I remember correctly. I could be misremembering. I do know for a fact that it makes a difference on ships as I’ve observed the different paint colors radiating different amounts of heat. Don’t have a good answer for why as much as possible isn’t painted white to reduce heat load, the couple times I brought it up everyone shrugged it off.
Reefer ships are still painted white, to this day, for this reason. One exception is I’ve seen some Dole ships that were painted an off-white/buff type color.
You probably won’t find an academic scientific study on ships specifically. You could find studies in other areas of engineering that are generally applicable, or specific characteristics of paint. The general knowledge is that dark colors absorb more energy from the sun , whereas white reflects the sun. It’s the same whether you’re talking ships, cars, office buildings, or houses.
I remember reading an article some time ago about a tanker company painting the deck of one of their ships white instead of the common red color and that it had an effect on the temperature inside the tanks. I don’t remember any other details but you might be able to pin it down with some research.
Painting the deck white absolutely works. On one of my ships, the staterooms below the bridge deck had red decks overhead from the shipyard. Painting those decks white significantly lowered the temperature in the staterooms they were directly below.
I know you’re not looking for antidotal evidence, but I was told that Green was actually settled on because it was the best compromise between reflecting heat, and blinding the crew on the bridge with a glare on a sunny day. I’d argue that the white car articles apply to ships as well, it’s not like physics change once you get past the sea buoy.
USS La Salle (AGF 3) was painted white while she was flagship of the Middle East Forces. Maybe there’s something buried in the preservation NSTM for painting/coating that gave a justification for it.
Our fleet in the GOM was painted white with grey or red decks. The Northern fleet was painted green. Go figure. Cold up north, hot down south. Agree with the concept.
The Hospital Ships, Annesley Bay
Source: The British Medical Journal, Vol. 1, No. 369 (Jan. 25, 1868), p. 76
Published by: BMJ
Stable URL: https://www.jstor.org/stable/25213623
“There were experiments made, at the suggestion of Captain Tryon, chief transport officer of the expedition, as to the relative attractive and retentive properties of different pigments for painting the ships with. He found that, when a ship was painted with white-wash, the sides were 18 degrees Fahr. Cooler than when painted black, 7 degrees cooler than the slate-colour of the Liverpool transports, and 3 degrees cooler than white paint. We are to whitewash as soon as we get the necessary ingredients form the store-ship.”
When calculating HVAC system and cooling load, the solar heat gain calculation includes colour . For a light surface an excess temp of 12K is used, while for a dark surface 29k is used. For 1 m2 assuming the same insulation on both bulkheads the white surface gains 7,2w, while the dark surface gains 17,4w. This can be quite alot on a large ship.
A simple way to see this in action is to see the difference in a black and white car on a sunny day. The black car is quickly like a sauna and hot to touch while the white car will stay cooler for longer.
It is VERY obvious if you walk around barefoot that even a light grey deck is much hotter than a white deck underfoot. Some fiberglass airplanes suffer degraded strength when too hot, they are almost all painted white.
My own boat was repainted from light blue to dark blue, next repaint will be back to a light color. The increase in heat below is noticeable
The question is not are darker colors hotter, the question is how does this translate to the inside of the vessel. For a solid fiberglass hull or an uninsulated steel hull, the outside temp and the inside temp are about the same. For a vessel with significant coring and/or insulation, it might not make all that much difference.
