insulation - only polyethylene?

[stantale]

Hi All,

I know this has been re and re and revisited a few times on the board, but here goes for a very basic approach:

Seems like the cheapest insulation is to get rolls of 1/4" closed cell polyethylene and then glue a few panels together to make 1/2" to 1" thick mats. I may add a layer of thermal foil to for reflective insulation on the inside. Cost is about $80 for 90 feet of the stuff by 50" so its cheap. I'm not going to use panel insulation like celotex because of the fitting issues.

Two questions:

1) Anything wrong with going that route? A few people (as an example the site that has a precise walk through of insulating the v-berth) seem to use polyethylene, bubble-wrap, then PE again, then silver lining. Just wondering whether that is necessary, or even functional in terms of insulation.

2) In cold climes, would you insulate below the water line (i.e. where the water is close to freezing most of the time). I don't quite understand why you wouldn't want insulation below water line except in the Caribbean and other toasty places where it might actually help cool your boat.

Thanks,

-stantale

[mitiempo]

I use 1/2" Ethafoam, usually by itself against the hull. Where it is not visible by itself and where visible either thin ply panels over or varnished slats screwed to epoxied vertical pieces the thickness of the Ethafoam. In the V-berth there were glassed beams 1" deep so I used Reflectix against the hull, a layer of 1/2" Ethafoam and then another layer of Reflectix to make up the thickness. The V-berth is the only place where I would sleep so close to the hull so the extra helps here.

Yes, in cold climes I would insulate below the waterline in lockers and such. That along with ventilation in the lockers will all but eliminate condensation.

[ottos]

Originally Posted by stantale

1) Anything wrong with going that route? A few people (as an example the site that has a precise walk through of insulating the v-berth) seem to use polyethylene, bubble-wrap, then PE again, then silver lining...

-stantale

I'm not sure if this is the site you were referring to, but if not the Frugal Mariner did a writeup. They do follow Sailnet, so perhaps they'll chime in.

.

[stantale]

yes, thank you, that is the site.

The specifics of why layers were chosen as they were is not fully discussed, so I was just wondering what the benefits were. For example it seems that reflectix works best with a layer of air in front of it, which the base layer on frugal mariner doesn't have. So why not just two layers of polyethylene (which has a gas in it with better insulation properties than the bubble wrap)

Maybe I'm overthinking this, but what else do I have to do with my time ;-)

[mitiempo]

Different types of insulation work to eliminate or reduce different kinds of heat transfer. A layer of air has no benefit in front of Reflectix as far as I can see.

From the Frugal Mariner:

[stantale]

Not sure that is correct. Below is from the Reflectix site. I've seen recommendations of 1" of air in front of the aluminum layer for it to work at all.


What if There is No Air Space Present on Either Side of the Product?

No Air Space = No Reflective Insulation Benefit
(An R-1.1 is provided from the product itself for the Reflective/Double Bubble material.)

If You Install 2 Layers of a Reflective Insulation, Does the R-value Double?

With multiple layers of product and airspaces between each layer, enhanced performance will be gained. If the product is simply “doubled” (with no air space between the layers), a very minimal benefit is obtained (R-1.1 (per layer) for the Reflective/Double Bubble product).

[mitiempo]

If you install 2 layers of Reflectix you will double the R value because it comes from the bubble wrap and not the foil. There is air space because of the bubble wrap - built-in in other words. The foil reflects radiant heat but does nothing for R value by itself.

[stantale]

agreed, the only issue is that the non-reflective insulation from the bubble wrap for reflectix is quite bad (1.1 per their site) and that's all you've got if you don't add air in front of the aluminum foil. That means the unscientific "claimed" R-values of 6+, which are already highly disputed, are completely void (pardon the pun.)

The thing that keeps coming up is the "built in" air layer works with the foil - according to reflectix site, that just doesn't work. Their 1.1 value is for the whole layer of product, reflective material plus the bubble layer. You have to put spacers in, in fact they have all kinds of advice on how to make spacers:

Reflectix Inc. | All About Reflectix® | Frequently Asked Questions...

"An R-1.1 is provided from the product itself for the Reflective/Double Bubble material."

I really just care about whether it needs an air layer separate from the product itself to work better than straight polyethylene, and according to their site I would conclude yes. And that's not feasible on a boat.

Straight polyethylene has a much higher R value - due to smaller bubbles, and gas filled rather than air - so it seems it would be more efficient to install 3/4 of polyethylene than 3/4 of reflectix if there is no air gap between product layers.

Again, absolutely not an expert, and just trying to get to what I should go with. Correct me if I'm wrong - it's damn confusing parsing the literature!

[mitiempo]

Straight closed cell foam of any type will have a higher R value than the Reflectix. The bubble wrap the Reflectix has does very little for R value and the foil is not there for R value either, but to reduce heat loss through radiative means.

My first choice would be a closed cell foam like the Ethafoam I mentioned earlier. I am using the Reflectix to build up thickness and gain a bit on radiative heat loss. A possible bonus is a larger radar return which has been said of the Reflectix.

I have insulated several boats with the 1/2" Ethafoam by itself in the last 20 + years and it works very well. I have lived on several boats for a total of about 15 years and a friend has lived aboard for almost as long. His boat is insulated with Ethafoam against the hull in all areas including below seat lockers and his boat is very warm and comfortable all winter. My current boat is partially insulated and it will be finished soon.

[stantale]

radar reflection is a great reason - thanks for reminding me, I saw that thread too.

Any ideas where to source Ethafoam (I assume you use flexible rolls rather than planks?)

Good luck finishing up your boat - I'm way behind you...