Black hull ok?

[JeremyFowler]

I'm busy repainting this old 39ft Cavalier. I want to paint the hull black but someone mentioned that there could be potential issues with differential expansion/delamination? The hull is GRP with 2 skins of 6mm GRP and about 19mm of end-grain balsa(?) in between.
Based in New Zealand, temperatures are never extreme here, although a trip to the tropics is possible. The superstructure is a light yellow.
I don't need comment on the aesthetics, only on the practicalities/engineering aspects, pretty please...:-)
Cheers!

[Jim Cate]

One practical issue is when you paint any dark color over white every scratch stands out starkly. This may or may not matter to you.

Jim

[akopac]

In the tropics your going to have a lot of heat buildup. Our deck was powder blue and we couldn’t walk on it in Mexico. I painted it white and the problem went away. You might consider AC, a genset, and good refrigeration?

[Chenega]

“There are only two colors to paint a boat, black and white, and only a fool would paint a boat black.”
N G Herreshoff
I painted my H28 (L Francis) Hull Black and it was beautiful with contrasting bright work.

My favorite boat to sail… flying a cruising spinnaker, main, mizzen staysail, and mizzen. She flew!

[Montanan]

There be a very good purpose that most hulls are painted white and really no good purpose to paint it black.

The black paint will adsorb a great deal more thermal energy even in moderate climates and more so in the tropics where the insulation is greater. Expect it to be very hot to the touch and inside when the sun is on it. And it will make refrigeration and freezer work especially hard and very inadequately due to the radiant heating from the hull.

Here is a site that tests the temps of cars painted different colours.

https://www.meguiarsonline.com/forum...ar-s-paint-get

White car 110 degrees F
Black car 168 F

58 degrees F the difference!

Also, black is very difficult to see hence a distinct navigational hazard.



Snipets copied from a related topic posting on Sailnet:

https://www.sailnet.com/threads/hull...%20the%20touch.

"Also, for those that like the aesthetics of a coloured hull please remember that the only people who can see your pretty hull are not you. When you're on your boat you can't see it. When you're on shore you can only see a bobbing blob; and when you're in your dinghy leaving your boat you're looking forward; and when you are coming to your boat you're more worried about scratching the paint than the colour of it."


. . .

“White or the wrong color”
1. Heat
2. Fades rather quickly in the tropics and doesn’t restore to original color with common cleaning agents.
3. Any scratches or imperfections very obvious.
4. Repair requires large area or entire hull to color match as fade with aging will be different in new v old areas. This is true with white as well but much less obvious.
5. Dark v light areas will thermal expand/contract as different rates stressing underlying structures. More of an issue will metals but true to lesser extent in grp.
6. Additional expense. Even professionally done jobs may last no more than 5 years.

. . . Thermal camera results:

"I just shot the black stripe on our boat outside. It is pretty cloudy today and there is no direct sun on it. The air temp is 86F.

Outside on the hull:

The white hull is 96F.

The black stripe is 138F.

Inside the boat, that black stripe is outside a 1/2" foam core (and corresponding fiberglass skins), a 1/4" air gap, and 1/4" foam backed vinyl trim on 1/8" plywood.

Below the stripe is 78F.

The stripe area is 96F.

I know this is worse in direct sun."

[clockwork orange]

Not a good idea. While it is not likely to cause structural issues you may need to paint it again in a year or so. The surface temperature difference between a white boat and a black is considerable and it is going to see temperatures it has never seen before and the post curing coupled with the shiny new paint job may lead to a pretty ugly surface appearance. The woven roving in the laminate will likely stand right out. The good news is that if you do another round of high build and painting after a year or so it will usually look good from there on out. Lot of extra work though. Better to keep it a light color imho.

[Montanan]

Might this be the vessel?

Yellow topside, white hull.

https://www.yachtworld.com/yacht/197...r-975-8075299/

[clockwork orange]

Wow, three very good posts while i was composing mine, I'm a slow writer i guess. Great points about the refrigeration, etc. My son and his girlfriend bought a cat in Florida with the non skid picked out in a kind of sand color and you could not stand on it barefoot while the smooths were fine, and that was not even a dark color.

[Spot]

"Black Cars look Better in the Shade"-Gino Vanelli circa 1984 pop music

Montanan already covered it but here is the picture I am always trying to find online:

[Montanan]

Originally Posted by Spot

"Black Cars look Better in the Shade"-Gino Vanelli circa 1984 pop music

Montanan already covered it but here is the picture I am always trying to find online:

Spot On, pun intended.

The graphic highlights the issue of needing to have an epoxy system that is high heat compatible being yet another issue as to avoiding painting a white hull black.

The graphic clearly indicates the huge temperature differential.

Pretty sure one could bake bread in the cabinets along the sunny side and melt most everything else.

Color matters, [and that is not a political remark ]

[Oeanda]

We’ve always liked our black hull and never had any issues whatsoever, but around here any extra heat is generally welcome. In hot locales there’s no doubt it would be hell.

[boatman61]

I looked at it this way.. the sun is only going to hit the hull directly while heat is still building or easing and even then one side at a time or fore and aft..
You want what pleases you, or what white boat owners (90%) say..

[Montanan]

Originally Posted by Oeanda

We’ve always liked our black hull and never had any issues whatsoever, but around here any extra heat is generally welcome. In hot locales there’s no doubt it would be hell.

Attachment 255439

That be true sailing in beautiful Brrrrr Coldlumbia.

[boatpoker]

Originally Posted by boatman61

I looked at it this way.. the sun is only going to hit the hull directly while heat is still building or easing and even then one side at a time or fore and aft..
You want what pleases you, or what white boat owners (90%) say..

Depends how you use the boat.
Weekenders vs. Full time cruisers are likely to see this differently.

[Montanan]

Other forum references:

https://forums.ybw.com/index.php?thr...in-med.217501/

https://forums.sailboatowners.com/th...advice.143666/

Appearance is a major drawback as the black will show each and every scratch and rub and will show dirt and evaporated solid deposits from any water source.

"Painted my transom black. It's impossible to keep looking good. Salt water dries white, diluted salt water after cleaning smears white, rain water running down it leaves white streaks, any tiny amount of wax after a polishing leaves white dust.".

Yet, black hulls look and work well on ice boats, as the color contrasts well with the snow and ice and solar heat gain is not too much of an issue.