Steel hull isolation: alternatives to foam?

[MikeJohns]

Nothing fuzzy. And it has been mentioned:

Originally Posted by MikeJohns

If you have moist living space air circulating and coming into contact with the bare steel behind the insulation , then it will condense ..........
……..if the insulation is a good fit around the periphery of the cavity it acts as a vapour barrier ( providing it's closed cell foam)

To reiterate:
Providing there is a either a vapor barrier or a closed cell foam is used, and these are a good fit in the cavity then very minimal condensation will occur.
Even if there is a considerable amount of 'free' air present such as in the fibre glass insulation sheets. It tends to dry out after a few cycles and relplacement humid air doesn't diffuse well through small gaps to replace the dry air within.
For example the fibre-glass stay surprisingly dry providing there is a vapour barrier and that they are not in a zone where they can get wet.

A small amount of condensation really isn't an issue anyway even on a steel boat providing it's properly painted and water cannot pool.

Nothing differentiates building from marine products, it's the material properties that determine whether it's OK in a marine application. We use polystyrene in ships freezers too and that was not fire retardant either!

[ImaginaryNumber]

If you are boating primarily in warm weather during the summer months then having tight-fitting closed-cell foam panels may be adequate. One recent poster mentioned being a year-around liveaboard through subfreezing weather. In that case it is well worth the extra effort to either adhere the foam to the hull, or meticulously seal the edges of the foam panels.

Many folks complain how portholes or hatches condense and drip. Even a single bolt extending from the outside into the interior, if not insulated, can drip annoyingly. These types of problem areas can be a challenge to insulate and still retain the functionality of the passageway.

It's best not to assume that wet insulation will dry out. The small amount of air that seeps through cracks, which you are hoping will dry out your insulation, may just as easily be bringing in more water vapor to condense. One poster mentioned how a small break in the seal of a double pane window resulted in liquid water buildup inside the window, not a drying out of the window.

Not surprisingly, it's much easier to plan for and insulate a boat while it's being built, rather than during a retrofit.

[Frosty]

Originally Posted by ImaginaryNumber

Not surprisingly, it's much easier to plan for and insulate a boat while it's being built, rather than during a retrofit.

Errr yeah,-- you dont say. sorry--- but yeah you don't say

[MikeJohns]

Originally Posted by ImaginaryNumber

If you are boating primarily in warm weather during the summer months then having tight-fitting closed-cell foam panels may be adequate.

You are over theorizing this to the extent of being paranoid about even a little condensation. Importantly you don't consider the internal lining and it's effectiveness as a vapor barrier in cold weather the moisture doesn't come from the outside air it comes from the inside living space. There are several things you can do (as in a building ) to reduce the humidity inside, like opening a window !

There are two issues, one is to insulated to reduce heat transfer to keep the boat both cooler and warmer. The other issue is water vapor from the living space in winter contacting cold surfaces. You don't need to make the insulation the vapor barrier but it's more convenient if it does act as such, if you want you can use a separate vapor barrier designed just for the task such as building foil paper.

Originally Posted by ImaginaryNumber

One recent poster mentioned being a year-around liveaboard through subfreezing weather. In that case it is well worth the extra effort to either adhere the foam to the hull, or meticulously seal the edges of the foam panels.

Water will condense on the surface if it's below the dew point as was pointed out well enough. The amount of moisture is dependent on the moisture level of the air inside not the outside temp.

Not just boats but Aircraft, even Cars are a good extreme case in cold altitudes/weather. In larger vessels the hull is bare inside and the cabin walls are away from the hull and insulated, I'd be looking for that sort of system for extreme cold, you'd also want to insulate the cabin soles.

Originally Posted by ImaginaryNumber

..............It's best not to assume that wet insulation will dry out. ................. One poster mentioned how a small break in the seal of a double pane window resulted in liquid water buildup inside the window, not a drying out of the window.

That sort of observation is completely misleading.
The double glazed cavity pressure cycles and this exchanges the air in the cavity. Moist air is drawn in and condenses, the moisture cannot escape it's a very effective moisture trap since it will vent dry air and suck in moist air. Consider now how it would work if you drilled a big hole in the base of the window cavity through into the wall cavity. Then you might see how it can dry out.

[MikeJohns]

I received a few emails in reply from queries to suppliers of so called Insulating-Paints and got some very confused replies. Particularly there is a lot of confusion between Reflection, Emissivity and conduction. There’s a lot to this that appears intuitive but is easily misunderstood.

People who haven’t studied thermodynamics can get quite confused by heat transfer. There is considerable complexity to the subject and I will try and keep this simple.

Heat energy can be radiated even through a vacuum, a vacuum stops conduction very effectively, but not radiation. Something apparent to anyone standing in sunlight. A thermal mass heated in the sun re-radiates that heat and can be uncomfortable to stand close too, like a city street on a hot day. Long after the sun sets the road is not only be warm to touch but you can feel the heat radiating. The surfaces ability to radiate energy is call Emissivity. You can coat the surface with a material that doesn’t radiate heat very well ( low Emissivity) and it will be more comfortable to be close to when its hot like a whitewashed wall.

The paints that claim to be insulation paints are either reflective or have a low Emissivity or both. They reflect the energy before it heats the surface from the outside but for most applications not significantly better a simple white paint. But paint can reduce the radiant heat from the surface as well and that can be significant inside. Although it is still not proper low thermally conductive insulation and again any low Emissivity coating will do quite well in comparison (read white paint ).

A matt black surface will radiate the most energy and a polished white or shiny surface the least. Even a wrap of Aluminium foil in close thermal contact around a hot exhaust pipe will make it appear cooler to a hand hovering over the surface because it reduces the radiant energy. The same holds for a highly polished stainless steel surface, for example a wood stove flue, the surface is always hotter than a person can judge from feeling the radiated energy on the palm of the hand. But touching the flue leads to a severe burn.

Similarly the handy IR based temp measuring devices ( laser pointer spot metering) measure radiant heat not true surface temperature. Like your hand they must be calibrated to the Emissivity of the surface.

It’s important to understand that despite the Emissivity being low the surface temperature is still the same, in fact in can be even hotter because of the reduction in radiated energy. Convection heating occurs from air contact with the hot surface and only conduction not Emissivity makes any difference to this, so eventually interior spaces will warm up to ambient temperatures through convection which is just conduction and circulation.

True insulation has a low thermal conductivity and the some of the misleading tests on supposed insulation paint deliberately confuse reflection radiation and conduction and often the paint vendors themselves don’t appear to know the difference. It would be similar to claiming that the foil backed insulation only needs the foil to work.

Interestingly the foil on foil backed insulation will only work to reflect heat into a cavity or air space if it’s in contact it will simply conduct energy from the contact surface. Foil reflects heat and energy back into a space but it doesn’t reflect ‘cold’ any more than a mirror reflects darkness.

Heat energy can travel from radiant to conduction to radiant and so on, a hard vacuum conducts radiated energy better than air does. Air is a better insulator to radiant energy than a vacuum is.

To insulate you need a real insulation and to a purchaser of insulation only the inverse of Thermal Conductivity (called the R value) really matters. The higher the R value the better the insulation.
Paint is not an effective insulation nor can it ever be, it’s just too thin, it cannot have a sensible insulating R value much above zero. You really need R values of around 1 or more. But less insulation is needed in a boat than in a house, small spaces are easy to heat and wall areas are considerably less.

So in conclusion and relative to fraudulent claims of insulating paint ask the following What is the Emmissivty of the paint surface (it will lie between zero and one), then compare that to any white paint (some of the so called insulating paints are actually more emissive than cheap white paint or even no paint). What’s it’s reflection coefficient compared with white paint? and finally what’s the R value. That defines the material properties sufficiently to stop you being duped. There are more material properties that the savy person will be aware of but I very much doubt any paint manufacturer will be able to give you any detailed figures for data such as velocity factors.

The replies to my own queries showed the paint vendors and manufacturers are very keen to mix the values and obfuscate the real facts while making very fraudulent claims. The trouble is that they sound very convincing if you are not well versed in heat transfer and it has convinced most of the paint vendors enough for them to regurgitate the fraudulent claims.

[Northman]

Mike,
that was a very illustrative summary! I tried to add some reputation points, but apparently have to "spread some around" before being able to add to yours again.
Anyway, much appreciated!
Walter

[pdwiley]

What Mike's post boils down to is, it seems nobody gets taught basic physics in schools any more.

Waay back I was taught that there were 3 modes of heat transfer - convection, conduction and radiation. It was obvious to me that insulating paints couldn't be working as claimed.

So thanks for that, the inside of my hull is a nice bright white, there's a lot of paint there and I'll regard its insulating value as zero, just as I thought.

The foil backed polystyrene should help with radiation & conduction and - if well fitted (hah) - pretty well eliminate convection cells.

PDW

[rwatson]

With no first hand experience, if you have gaps behind the foam, I was told that you will save a lot of grief if you use something like paint-able bituminous compound to fill in the stringers that touch the hull, so that condensation can run straight in to the bilges, and not pool against the hull.

Even with a good paint system, pooled water starts problems pretty quickly.

[pdwiley]

Originally Posted by rwatson

With no first hand experience, if you have gaps behind the foam, I was told that you will save a lot of grief if you use something like paint-able bituminous compound to fill in the stringers that touch the hull, so that condensation can run straight in to the bilges, and not pool against the hull.

Even with a good paint system, pooled water starts problems pretty quickly.

Yes, I've been told that as well. Of course you're supposed to have drain holes in the stringers to let water run down but I'm willing to bet that these get blocked real fast as they can't be huge in a small boat.

A question exercising my mind is, should I insulate in the forepeak & lazarette areas where 'stuff' gets stowed but it's not living space? I can see some arguments both ways but I've at least a couple months to decide how I'm going to decide.

PDW

[pha7env]

Enjoying this post, except for a few additudinal flareups! What i'm getting, is there is no one answer that fits all. Thus is life. But can i surmise from all the posts, and yes i read them all, that if it even relatively flammable or at all water absorbant, it is a no no. Otherwise, keep the condensation from the metal with paint and foam(or not), and keep air from moving from the hull outward and inward by any closed cell layer that fits the , your fire and absorption guidelines. What am i missing?

[pha7env]

Oh, and unless you are Steve Dashew, insulating the bilge may cause problems! (New i missed something) Have a great day!

[MikeJohns]

Originally Posted by rwatson

With no first hand experience, if you have gaps behind the foam, I was told that you will save a lot of grief if you use something like paint-able bituminous compound to fill in the stringers that touch the hull, so that condensation can run straight in to the bilges, and not pool against the hull.

Even with a good paint system, pooled water starts problems pretty quickly.

Ray
After painting apply a small bead of polyurethane sealant filleted with a finger to seal the small gaps and there should be drain holes, if not then yes, use enough sealant to prevent a water trap, use a small bead and completely fill the last bit of the low end .

Inside maintenance is as important as outside. A lot of steel boats get a bad name from steel European production boats will a seamless glued in fitout that has to be destroyed to access the inside of the hull for inspection or repainting. Enough of the linings should be able to be removed to inspect and access most parts.
A lot of problems can be stopped if hatch and port coamings extend just past the interior lining, then any leaks are easily evaporated and there's no sea water dripping behind insulation. That really kills the inside.

To put interior corrosion in perspective it's always the water traps that cause problems. I've seen large areas of deck head on a 54 foot Jongert that were unpainted and only had small amounts of flash rust after 25 years but they were behind glass wool insulation and a ply ceiling. The same boat had rusted through the lower hull in places despite no longitudinal framing (just transverse) from bilge water slopping around (and inadequate bilges).

[MikeJohns]

Originally Posted by pha7env

Enjoying this post, except for a few additudinal flareups! What i'm getting, is there is no one answer that fits all. Thus is life. But can i surmise from all the posts, and yes i read them all, that if it even relatively flammable or at all water absorbant, it is a no no. Otherwise, keep the condensation from the metal with paint and foam(or not), and keep air from moving from the hull outward and inward by any closed cell layer that fits the , your fire and absorption guidelines. What am i missing?

Do a good job of the paint eliminate water traps or at least seal where the paint film tends to crack in water traps. Use any suitable insulation (and that includes glass wool). Don't get hung up about sealing everything from water vapour in the air.

Reduce interior humidity in cold weather with good ventilation, keep your bilges well ventilated too. And you can heat and ventilate they are not mutually exclusive as some people think.

Never insulate a potentially wet bilge (on a sailboat that can extend quite a long way up the side with shallow bilges).

[pha7env]

sounds reasonable! thanks

[harshjaiswal]

I am also building a steel boat and after reading this discussion, I decided to find out prices for armaflex. I found an equivalent grade from a different manufacturer for around 10 USD per sq mt. I dont think its that expensive considering we are building a yacht. Anyways thanks for the help.