Inside your boat....hotter or cooler than outdoor temps?

[S/V Illusion]

Originally Posted by LakeSuperior

Illusion, you are unaware and do not understand basic physics/engineering principles of heat transfer that are well known. For example, contrary to your statement the primary mechanism that shuttle tiles use to shed heat on re-entry is radiation.

Unless there is a special type of coating on the topsides the dark topsides get hotter than a white one. This difference can be significant. If the hull is cored then the temperature of the inside of the hull will not get as hot.

I am quite familiar with basic thermodynamics as we are debating here.

To state the obvious:
Materials including shuttle tiles and colored fiberglass give up their heat energy from radiation, albeit at different rates. Neither are good conductors and therefore the amount of heat generated is indeterminate and likely trivial. What you are using is intuitive science - not supportable principles.

The question remains - how much heat is added to a boat interior by incidental radiation from a vertical surface?

Absent any data, you are just guessing and perpetuating a myth.

[thomm225]

Originally Posted by S/V Illusion

It's 91 degrees right now where we live in Florida. The breeze is also 91 degrees. I can turn on the fan and it's still 91 degrees. No amount of ventilation is going to change anything.

Sure it will!

If it's 91 degrees and there is a breeze or you have a fan on you, it's much better than 91 degrees and no breeze.

My experience with this is after hurricanes in Florida in July when the power was out for a few days.

During the day, we'd have the prevailing sea breeze and it wasn't too bad in the shade but sometimes at night nothing and you'd sweat like crazy

[LakeSuperior]

Originally Posted by S/V Illusion

I am quite familiar with basic thermodynamics as we are debating here.

To state the obvious:
Materials including shuttle tiles and colored fiberglass give up their heat energy from radiation, albeit at different rates. Neither are good conductors and therefore the amount of heat generated is indeterminate and likely trivial. What you are using is intuitive science - not supportable principles.

The question remains - how much heat is added to a boat interior by incidental radiation from a vertical surface?

Absent any data, you are just guessing and perpetuating a myth.

This statement reinforces my earlier comment. I cannot take the time to fix your misunderstandings of heat transfer. You are muddying the waters for folks trying to solve a problem.

[Pete7]

Originally Posted by LakeSuperior

This statement reinforces my earlier comment. I cannot take the time to fix your misunderstandings of heat transfer. You are muddying the waters for folks trying to solve a problem.

Hmm, is there a reason for all those pretty little houses on the Mediterranean shorelines being painted white

[hsi88]

Sorry I'm late to the party, but I was on vacation.

Black transfers heat better. That is why motorcycle engines in particular are painted black. The engine is hotter than the outside air. Black makes sense. But better transferring of heat also means it absorbs heat better if the underlying material has that characteristic. Here is a test of paint colors on cars. Not scientific, but I think it makes the point.

Paint Color Temp (F)
Light Gray 110.6
White 92.6
Black 146.3
Dark Red 132.7
Pearl White 87.6
Black 143.4
Dark Gray 131.7

And I might point out that black clothes in the summer for cooling becomes pretty moot when sitting in bright hot sunshine. White in the open sun is your friend. Ideally, the interior material would be black (the part against your skin) and the outer cover would be white.

[LakeSuperior]

Originally Posted by hsi88

Sorry I'm late to the party, but I was on vacation.

Black transfers heat better. That is why motorcycle engines in particular are painted black. The engine is hotter than the outside air. Black makes sense. But better transferring of heat also means it absorbs heat better if the underlying material has that characteristic. Here is a test of paint colors on cars. Not scientific, but I think it makes the point.

Paint Color Temp (F)
Light Gray 110.6
White 92.6
Black 146.3
Dark Red 132.7
Pearl White 87.6
Black 143.4
Dark Gray 131.7

And I might point out that black clothes in the summer for cooling becomes pretty moot when sitting in bright hot sunshine. White in the open sun is your friend. Ideally, the interior material would be black (the part against your skin) and the outer cover would be white.

Most of the suns energy is in the visible band (why nature evolved our vision in these wavelengths). What this shows is that the darker paints absorb more of the solar energy and therefore the surfaces get warmer.

In the infrared where the motorcycle engine radiates heat, much like a light bulb filament, the colors all transfer heat exactly the same. Convection actually does most of the cooling for an operating motorcycle engine. A motorcycle engine is painted black because it looks good and not for heat transfer reasons. For most paints color doesn't matter if there is no sun.

[Sandero]

in summer cooler... in winter depends on sunlight/cloud cover and outside temps

[SecondBase]

Originally Posted by bailsout

Awnings.

Awnings. Awnings, fans and windscoops. I'm thinking about tint as well.

[Bill O]

Originally Posted by Copacabana

I live in the tropics. The summers are HOT! I have no AC on my boat and have never felt the need for it. However, I have a scheme to keep the boat cool in the summer. I use big awnings to keep the sun off the deck. These awnings are suspended over the deck, allowing the breeze to flow under it and through the hatches. I can keep all the hatches open in the rain (very important!). I also have lots of hatches that can be opened in either direction. My boat is white. My deck is off-white. Even the slightly beige colour of the deck will heat up if exposed to the sun at noon. I never stay in marinas, so I have the advantage of anchoring in the breeze. I have fans in all sleeping areas and galley, but seldom use them. My deck is Divinicell cored and has an insulated headliner, which also helps. I find the boat remains cool during the day. By the end of the day (sundown) the boat will normally feel warmer inside than outside air, but that's because the air temperature drops in the evening and the boat retains the heat for a while. By bedtime it has already cooled down again. There is no question that without the awnings, hatches, white paint/decks etc. the boat would be unbearable in the summer.

Will have to agree with everything Copacabana does to keep the boat cool. We do not have AC and with our boat closed up it can be cooler inside than outside. In fact some come on board and think we have AC running it's so cool!
Our decks are white and you can walk on them any time of day barefoot. If they are too hot to walk on (the barefoot test), then you are heating the interior of the boat. Another reason we would never consider to have teak decks for a boat in the tropics.
We have also insulated under the deck for the whole boat with 1" blue foam. Similarly, the use of a mylar faced insulation sounds like a good suggestion. (previously mentioned).
One of the factors somewhat skipped over is the water temperature. If the water temp. is over 85F, it will be very hard to cool down the boat. Even if the air temp drops in the evening, it will take a boat much longer to cool down.

Bill O.

[zeehag]

funny i repetitively mention water temp. as ours gets 100f easily and every year, it is imperative to shade topsides for optimal cooling.
funny also the number of marine air cond units that cease functioning in this area.. keel cooling..hahahahaha might dream up a better way as these do fail in this hot water just when needed most. even the dock water can cook eggs.
my neighbors use partial covers for their shading.. they complain their air conditioner is failing to keep up. when they covered the open area they had much better results from their air conditioner window unit. they also use a 5000 btu window unit, as do i, with excellent results when boat is covered successfully. they have a hunter 29.5 to my formosa 41.
hot water under my boat makes my cabin sole warm, same as radiant heating warms a lubber's winter floors. with my bilges and wood sole, i am comfy. fiberglass boats with shallow bilges are much warmer inside with hot water below em. in marinas i place scatter rugs on my wood soles..keeps interior a little cooler.

[zboss]

I hate to admit it but one of the reasons we want to get a desalination unit is so we can use fresh water to wet the deck down on a regular basis during the summer. We have used saltwater for this a few times and that’s just a bad idea.

[zeehag]

Originally Posted by zboss

I hate to admit it but one of the reasons we want to get a desalination unit is so we can use fresh water to wet the deck down on a regular basis during the summer. We have used saltwater for this a few times and that’s just a bad idea.

if you gonna wash wood decks with fresh you will learn that is a worse idea. make covers for your decks and douche em with salt water n have coolness with shaded decks.
shade also works with fg decks. fg gets hotter than wood. burns. i use sea water from under my boat to cool and wash. hay oi got a formosa it is allergic to fresh water.

[kriskret]

Originally Posted by softdown

Just got my boat in the springtime. Will be working on the bottom for awhile, still drying out some osmotic blisters.

I see plenty of talk about air conditioning etc. Which leaves me wondering about typical cabin temperatures in more tropical regions. Lets say that we are using a white fiberglass boat. For this debate, lets say we are in the Caribbean.

It is interesting that ~80F indoors feels about as "comfortable/uncomfortable" as ~90F outdoors.

5*C -( around 10*F difference) makes a difference between in and outside temperature. AC should be put that the difference won't be to big. You coming in and out , and in again and for example : you put your AC on 68 *F and outside temperature is 98*F , so , sooner or later you will catch sour throut or worse and consider thermal shock also.

[Olddan1943]

I have an American Tug, generator, 2 reverse cycle a/c, a built in electric heater in salon and stateroom, white topsides, British racing green hull and a red bottom. The British racing green hull came with the boat.... I changed from black to red bottom. My excuse? Easier to spot if the boat turns turtle. LOL
Interestingly, in the summer, I use very little hot water in the shower..... the water temp in the basin keeps the fresh water comfortably warm. Winter time, now that's a different story.
Hot or cold outside, the key is (in my mind) to reduce the humidity inside the boat for my comfort.
What we need is a hull and topsides that will change color depending upon the outside temp.
Of course that will mess with the USCG documentations and search and rescue operations. LOL