Question about hull color

[Musicaltrees]

Are dark colored hulls really that much hotter on the interior? I have often heard that but can anyone who has owned one attest? I'm considering a navy blue Tartan and was wondering.

[zeehag]

i find color overrated. i find the temp of water under the boat more of an issue for heat inside boat than hull color.
funny how that works. i sailed gom in a blue hulled boat., i own white hulled boats. the water in which i currently sit and sail never drops below 78f. is generally 85-100f. that makes for a HOT interior.
if color is an alleged issue, make canvas skirts to keep the sun off the hull. is a practice used here in the tropics for comfort and appearance. it works. it is also pretty. go figger.
btw--when sailing,color has no meaning. colorful hulls sail same as white boring ones.

[John_Trusty]

My concern with dark hulls is keeping them looking good. They're certainly attractive the first few years, but unless religiously waxed after a while the UV degradation of the gelcoat leaves them chalky. The solution is maintaining a good wax coat, and refinishing by compounding and polishing - not fun stuff.

[zeehag]

polishing and waxing is why they made dock workers in marinas.

[Pegu Club]

Well,

It is fact that dark colors absorb more heat energy from the sun than say white, which will reflect more sun energy away.

But, dark blue hulls look sharp. If you live in the north east, say, long island sound, a dark color on the hull likely means very little, but if you live where its hot and sunny all year, then yes it will make a notable difference.

[Scaramanga F25]

They look smart. But in salt water particularly they spot considerably and need to be wiped off, not hosed off.

[S/V Illusion]

Our last two boats were Awlgrip dark green and flag blue respectively. One was kept in Newport, RI, the current one in Florida.
Couldn't ever tell any difference either in terms of either additional heat or difference in climate effect of the dark topsides.

It is largely an academic debate based largely on intuitive thermodynamics.

If it is colored gelcoat, that does require additional maintenance. If paint, it's actually easier to maintain than the ubiquitous vanilla boats.

[Pauls]

Thermodynamics is thermodynamics. In a hot sunny environment a dark surface will be a lot hotter than a white one. Anyone who's walked barefoot in the summer on asphalt and the white painted lines can tell the difference. That is exterior surface temperature.

The other factor is how much insulation exists between the outer surface and the inner surface of the boat. With a lot of insulation the outer surface temp has a relatively small effect. With little insulation it will have a large effect.

So, as regards the OPs question, look at how much insulation there is on the boat you're looking at. Thin glass, little or no insulation, yes the dark hull will be hotter. A thick, cored deck and topsides, not so much.

[skipmac]

Difficult to say when comparing different boats. The hull material, whether or not the hull is cored, whether or not there's insulation on the inside of the hull.

For an apples and apples comparison, I owned a boat with a black hull, painted it white and the difference was dramatic. So my personal experience living on the same boat in the same area, FL and the Caribbean, color made a very big difference.

[S/V Illusion]

Originally Posted by Pauls

Thermodynamics is thermodynamics. In a hot sunny environment a dark surface will be a lot hotter than a white one. Anyone who's walked barefoot in the summer on asphalt and the white painted lines can tell the difference. That is exterior surface temperature.

The other factor is how much insulation exists between the outer surface and the inner surface of the boat. With a lot of insulation the outer surface temp has a relatively small effect. With little insulation it will have a large effect.

So, as regards the OPs question, look at how much insulation there is on the boat you're looking at. Thin glass, little or no insulation, yes the dark hull will be hotter. A thick, cored deck and topsides, not so much.

That is intuitive thermodynamics.

It's easy to equate, incorrectly, that dark absorbs energy more so than light but the effect goes far beyond the simplistic and the effect is the issue here.

Absent any consideration of absorption, heat radiation (transfer)capacity of glass, radiated energy potential, conductivity of glass, etc., making generalities is always a bad idea and particularly with this topic.

Some people think it makes boats hotter inside. Some think they are supposed to think it makes boats hotter (intuition). Some step on black pavement and equate that with ambient temperature in a boat

[AJ_n_Audrey]

No question a dark hull makes the boat hotter inside.

[skipmac]

Originally Posted by S/V Illusion

That is intuitive thermodynamics.

It's easy to equate, incorrectly, that dark absorbs energy more so than light but the effect goes far beyond the simplistic and the effect is the issue here.

Absent any consideration of absorption, heat radiation (transfer)capacity of glass, radiated energy potential, conductivity of glass, etc., making generalities is always a bad idea and particularly with this topic.

Some people think it makes boats hotter inside. Some think they are supposed to think it makes boats hotter (intuition). Some step on black pavement and equate that with ambient temperature in a boat

My example was not intuitive and removed all the variables of different hull designs, insulation, ventilation, location, basically everything except color. I lived on board a black hulled boat. Painted the hull white, boat was much cooler inside.

When I painted the boat white I left a small stripe black for looks. On a sunny day inside the boat I could feel exactly where the black stripe was by the heat radiating from that area of the hull and that radiated heat was not subtle but very noticeable. Also was confirmed by wife and crew so don't think it was all in my head.

To me that experience seems pretty conclusive, all other variables being the same, a dark hull will be hotter inside than a light one.

All things NOT being equal, like a boat with a cored hull or insulation on the inside then the impact of darker hull might not be as significant.

[captain mitch]

Had some friends traveling the Islands with us a few years ago. They had a blue hull Jenneau and complained that they could not keep their freezer cold ( against the hull on the port side) it would run the batteries down running constant.
We made a "diaper" from two layers of white bed sheet, hung it over the side and the problem went away!!
Does that proof the idea, no, but it sure paints the picture.

[KenKo]

One other consideration is that the hull doesn't face the sun to the same extent as the deck and even when the sun is low so that there is more hull exposure, the level of radiation from the sun is less--due to angle, amount of atmosphere the light passes thru, etc. So while the dark hull will be a bit warmer, it might not be as big a deal as it might be. Tolerance of the work needed to keep the beautiful colors clean enough to look good might be a bigger concern!

There is one other possible consideration, which I've not noticed much discussion of. It's the transmission of heat thru the bottom (the surfaces in contact with the water). Color of paint might not be a big determinant here given that it's not radiant heat that's at issue, but rather conductivity. Are there differences in the conductivity or insulating value of different kinds of bottom paint?

[Clipper4730]

We have a Flag Blue 50 ft mono, sailed east coast Bahamas and now in Fl, never uncomfortable so long as there is a breeze. Rarely does the sun hit the side directly, hottest part of the day the sun is directly overhead so I really don't think it matters what color the sides are. A little more work to keep looking good but well worth it! A lite spray with fresh water after a sail then a quick wipe down with a damp towel.....shiny! Ours is painted with Awlgrip and we use Awlcare and Awlwash for cleaning. Don't wax awlgrip it will damage the paint!!!!

Good luck