Topsides colour/inside temperatures in hot climates

[macd]

Some advice, please, from experienced tropics cruisers, regarding the effects of different coloured topsides in reflecting/retaining heat. In theory it's pretty obvious that white topsides will reflect more sun heat; is the obverse true -- that dark topsides will be cooler at night through black body radiation? Or are they just unbearably hot during the day? Any practical observations and experience welcome.

 

[jerryat]

We had International's pale Blue/grey deck paint on our decks when we first went down to the Med. The problem was that we couldn't walk on the decks at all once the sun was up as it burned our feet. Ok, we could wear shoes, but we sail and live in bare feet while aboard, so it was a problem!

Friends of ours had painted their decks with white deck paint having had the same problem, and the effect was magical! So we did ours, painting over the existing paint with just one coat. The change in temperature both on deck and below was astonishing. Far cooler in both respects.

As far as we're concerned, this is the answer, as even our laid teak cockpit gets too hot to walk on during the day.

 

[guernseyman]

Just quickly, because it doesn't relate to the tropics, but it may be relevant that we used to swelter in our white boat till we stuck lightly grey-tinted film on the windows, which are not large. Dramatically now even on the sunniest, hottest day it is cool inside.

 

[Wansworth]

Dont have to be tropical....White Hull and very light green decks with permanent all weather Bimine over cockpit and well made fitted awnings when at anchour,the sun seems to be getting too agressive!

 

[coldandhardy]

There is an opportunity to apply science here. Black no only absorbs all wavelengths of sunlight but it is the most 'emissive' color also. That is to say black objects cool off much more quickly than white objects. I am not totally sure how this can be applied here but I do believe that this curious quirk of physics is under explored in the boating world.

 

[TigaWave]

I've sailed in hot places with teak decks, but mainly white grp. The boat was well insulated with foam core and foam lining.

The main heat problem at anchor as someone else said is through the windows and hatches, best solution is to be able to set up a wide sun awning that will cover the cockpit, hatchway and central hatches as well as side windows. On two boats we had an awning with drop sides that ran from the mast to the backstay, some even rig awnings over fore hatch. They also help in that you can leave hatches open at night in rain squals.

This really makes a huge difference, drop sides are usefull as the sun gets low on one side, we would also have a panel at the rear so that if the sun came down directly aft we could still shade most of the boat.

Hope this helps.

 

[tcm]

i'm in med not tropics.

No, your postulate isn't true: the whiter paint is reflective, the darker paint less relective of sun's heat and thise dramtically affects indoor and underfoot temperature. But the colour of the boat once the sun has gone down seems irrelevant with regards to noticeable heat transfer.

If you paint, it can sometimes be a bit easier on the eyes not to be off-white instead of hi-white

 

[ChrisE]

But with your mega-yot, its geothermal properties could warm the IoW. Have you thought of contacting the National Grid?

 

[Swagman]

I'm also in Med and don't find having a blue hull makes ours any chillier at night than white vessels - but never actually used a thermometer to check!

I'm actually not even sure if with a well insulated foam core, a darker coloured hull makes it appreciably hotter below during daylight hours.

But there is no doubt our blue gel coat outside absorbs more heat than adjacent off white areas. I suspect this will lead to colour fading quicker - and maybe a slow 'baking' of the gel coat over time.

I live with the issues as I like the blue colour - but if you are abvilent about hull colours - lighter simply has to be cooler underfoot when in the sun.

JOHN

JOHN

 

[jerryat]

>> I suspect this will lead to colour fading quicker - and maybe a slow 'baking' of the gel coat over time. <<

That's a very good point Swagman. One of our friends has a black hulled Rival 41 that has been in the Med. or Caribbean for over ten years now. Aside from getting like an oven inside during the day, the real problem is far, far worse. /forums/images/graemlins/frown.gif

The gelcoat is now badly crazed to the extent that, in many areas, it has cracked right through to the under-lying laminate. In short, an extremely nasty and expensive thing to repair. He was quoted £3500-£4000 to re-do the gelcoat about 3 years ago. /forums/images/graemlins/frown.gif

We noticed this crazing (and severe fading) on a few other long-term Med. based boats with dark hulls, though none to extent of our friend's. Ok, his boat is some 20 years old, and no doubt more modern hulls/resins/gelcoats may be better, but it's certainly food for serious thought!

 

[tcm]

i wonder if praps if one feels one simply must have a blue hull then perhaps ensure it is only blue on downward facing parts - it's the upward facing bits that get the worst of the uv - and worse again, these are at the stern so with stern-to mooring the whole thing can look a mess.

 

[jeremyshaw]

Dark modern resins and gelcoats are supposed to be much better at avoiding chalking etc. ; how much better time alone will tell but certainly I know dark boats up to 10 years old looking pretty fine.

 

[macd]

Thanks all. The boat I had in mind has dark blue topsides and very pale grey decks/coachroof. Prevailing opinion seems, logically enough, to be that colour of decks/coachroof far more critical than that of topsides, so maybe I wouldn't bake, after all. Tinted window film will be on the list if bits to order.

 

[Swagman]

[ QUOTE ]
Dark modern resins and gelcoats are supposed to be much better at avoiding chalking etc. ; how much better time alone will tell but certainly I know dark boats up to 10 years old looking pretty fine.

[/ QUOTE ]

Yes I'd agree. Maybe the latest polyesters also handle the hotter temps better now days? Our own epoxy hull / deck is baked in its build process to a far hotter temp than the sun could ever replicate - so I'll keep me fingers crossed!!
Cheers
JOHN

 

[ccscott49]

Dark topsides give a much hotter interior, dark decks are even worse! It shows even when peeps coat there decks with sealers etc, which darken the wood, they find the decks much hotter. Mine are bleached teak, so almost white and I can walk on them all year in bare feet. I love the look of a dark blue hull, especially with varnished upper works etc, but with a timber hull, even splined teak, there is no way I can have mine painted dark. For the tropics and meddy, keep it light. The film I haven't tried, but will!