Foil as radiant barrier

[Capn_Tom]

I am insulating the underside of my cabintop with 3/8" volara foam. Some suggest using a layer of foil as a radiant barrier between the foam and cabintop. I must confess my physics is a bit dated but it seems to me that absent an air space between the foil and foam there would be no benefit from the foil. On the other hand I would hate to glue all the foam in place and then find out a layer of foil would have been beneficial. ??????

[Quetzalsailor]

My Physics is long outdated as well. However, you don't get much radiation reflection at low temperatures. You don't get much radiation below something like 200 degrees, F.

You could, in the early to mid '50s, buy house insulation made of layers of foil-faced paper. When you installed the stuff, which came in a large roll, you pulled it to width to fit the stud space and stapled it to the stud faces. When it was pulled it popped into a three layer hollow arrangement. I think it got most of its insulative value by the air spaces. It was, of course, severely compromised at wiring, odd spaces, etc. (My parents' house was done that way, in the day when most houses had solely Homasote sheathing, or, rarely, as much as 2" of rock wool, for insulation.)

[Robert The Gray]

If my memory of thermal physics from architecture school is correct, Heat is transmitted by infrared rays. these are not in the visible light spectrum. These infrared waves can be transmitted in three ways convection, conduction, and radiation. Convection is heating by the movement of heated air, conduction is movement of heat by direct contact, and radiation is the movement of heat by the movement of the infrared rays themselves. The side deck surface in the sun absorbs the infrared rays through radiation, the heat is transferred through the thickness of the side deck by conduction the inner surface of the side deck then radiates the heat into the interior. If you put your hand near the hot side deck your hand is being heated by radiation, if you were to touch the surface of the side deck you would be heating your hand by conduction. If there were a breeze blowing air across the side deck and your hand was heated by the air then that is convection. Foil only stops the transmission by radiation. The foil glued to the surface of the under deck will stop no heat from the hot surface of the side deck. A foil coating on the top of the side deck would cut way down on the transmission through radiation but you would have a shiny silver boat. The foam and its little gaps of air do not conduct heat well so it inhibits the transfer of heat through conduction. foil on the interior surface of the side deck will only help in keeping the interior warm by limited the amount of heat that is transferred to the hull by radiation. The reason you can use the foil windshield shades from the inside of a car is because glass does not absorb much heat by radiation and therefore the heat can come through the glass and then be reflected out into the atmosphere without anything coming into contact with the infrared rays. Foil over port holes. shade the decks before they get hot. use foil to bounce heat back into the interior when cold outside. hope this helps. I got my BA in Arch In 1979 so I hope I did not make to many mistakes.

r

[Figment]

that didn't make me laugh at all.

Robert, you need a boat.

[Capn_Tom]

Robert,

That was the best explanation I have read even after a thorough Google search on the subject. There is a lot of propaganda by manufaturers of foil faced insulation and plenty of urban legend out there but little hard data. What percentage of boats do you think have foil wrapped ice boxes covered in insulation. I believe the false prophet Casey recommends this procedure.

I skipped the foil, glued in the closed cell foam (and glued my hair together), and reinstalled the headliner. A good day!

[Robert The Gray]

O' great Figment,

If I place the extended thumb of my right hand onto the extreme end of my nose, I can then extend the remaining four fingers, which in actuality are the only four fingers because the fifth is always and forever a thumb, forming a modified cocks comb. The bobbing of the roosters head and the shape of his mullet like appendage have long been considered a classic example of a gesture of flumuxory and stoogeness. I would then accompany this fantastical and historically accurate sign of hoo haa with a forceful exhalation from my mouth with the tongue placed in such a way that there is an oscillating of the upper and lower lips that duplicates the sound of mammal flatulence. As has been stated in his treatise on the origins of civilization, Hector MacGregor's theory of the shame complex holds that it was when we became afraid of human excrement that we ceased to be animals. I also must site the classic corollary by August Carbuncle Dogs Eat P**P. By making both the gesture of the cocks comb and the sound that is produced by the anus of mammals, I have been able to simultaneously show my absolute mastery in the art of ribbing one's contemporary and that I am well versed in the history of the taunting gesture. Of course, what was once a grand and proud visual tradition has been reduced by your humble but smart mouthed author into some kind of run on sentence of a post that may actually clog the toilets in the truck stop of the global super internet highway. Some giant bolus of a thing way past it's prime, swimming under the cheap flickering lights in a sea of antiseptic blue, waiting for the flush of any one with a delete key and half of brain cell devoted to good taste and all that is decent.

I have a ferret in my head and he is hungry.
Must go.

r

[Hulukupu]

Robert, you are rambling.

[Rachel]

No, he's just being Robert The Gray.

He tends to wax poetic, from time to time :^)

[Hulukupu]

P**P is not poetic.

[bcooke]

Robert's 'rambling' has been entertaining and enlightening us on the PCF for many years and his voice will always be welcome here.

[Figment]

Ah, much better.
Glad to see that all is well again.

[bcooke]

and yes, Figment is right. Robert needs a boat. It doesn't have to be a Triton or a 'cruising' sailboat. Just something to get out on the water in.