Steel Hull Insulation Recommendation

Discussion in 'Boat Design' started by Glen Wither, Nov 23, 2021 at 8:12 PM.

  1. Glen Wither
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    Glen Wither Junior Member

    Hello folks, late to this party but here is my thought on insulation a steel hull. Comments welcome.

    Insulation is being used to keep the interior either cool or warm, depending on where the sailing/mooring is located. The interior will be moist if you live aboard in a winter season, and will be dryer if air conditioned in a tropical climate. In terms of the physics, the steel hull is acting as an air barrier and a vapour barrier. Moisture will condense on the inside surface in a cool climate. This condensation will make its way into the bilge, while vapour-laden air will be present in the cabin. The goal is to avoid trapping moisture between insulation and the steel to avoid rusting or mildew forming on finishes. Paint also serves to protect the hull. The best insulation in my view is an iron slag-based 'wool' like Roxul, rigid, and designed to allow water to move vertically within the mat via gravity. Roxul makes marine insulation, but it is expensive and used for industrial or defence marine applications. It does not burn or off-gas, which is a huge advantage over foams. They make a cheaper board used in the residential industry called DrainBoard. It is 1" thick, placed on the outside of foundation walls; it insulates and allows ground water to migrate to the foundation drains. Water does not degrade the insulation as it dries out continuously. A double layer of this boat results in about an R9 thermal resistance. Most steel boats have a 2" space. The boards can be removed for hull inspection, as they are loose-laid, if you allow the interior finishes to be easily removable. My boat has teak slats that are screwed to the verts on the hull flanges. While a pain to remove, you can inspect random locations to gauge the degree of rusting, if any.
     
  2. M&M Ovenden
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    M&M Ovenden Senior Member

    Hi Glen,
    I think the best insulation is a closed cell neoprene (Armacell) . It's insulation and a vapour barrier.
    Cheers,
    Mark
     
  3. Glen Wither
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    Glen Wither Junior Member

    Thanks for the reply. Armacell has those qualities, yes. The methodology is key, not necessarily the material. Arnacell, and its competitors, is also flammable and develops smoke. Slag is fireproof. As far as a vapour barrier is concerned, it is efficient when it is continuous. We cannot create a continues barrier or retarder in a ship. (FB and steel are also vapour barriers, and are continuous, just on the wrong side of the insulation. ) Neoprene also lasts between 8 and 35 years depending on exposure. Slag is forever. Glues used to hold neoprene in place should be epoxy, if the epoxy doesn't melt the foam. Armacell has never been tested with glues as far as I can determine. Other glues will degrade and result on gaps between the hull and the barrier, leaving it open to causing corrosion or mold. My personal preference is to let condensate flow through to the bilge. The cheap insulation has the same insulating level R as the foam. Let the hull dry naturally as opposed to trying to seal the entire boat interior I say. Paint does a wonderful job of sealing steel.
     
  4. fallguy
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    fallguy Senior Member

    The way this is done in home construction is a plastic vapor barrier is laid upon the concrete.

    For steel, it would require a barrier. And moisture staying behind must not be allowed to migrate through the barrier.

    An air gap in home construction of 1/2" is typical between the wood walls and the concrete. In a home; the plastic is to prevent mildew from entering by sealing all around.

    I don't see why polystyrene would not work in a boat. Fireproof, no.
     
  5. Mr Efficiency
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    Mr Efficiency Senior Member

    well painted steel, some sheets of polyethylene foam held on with spots of blu-tack here and there, what could go wrong ?
     
  6. gonzo
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    gonzo Senior Member

    I don't think "most boats have a 2" space". It depends on the design. Some have more and others less. Further, if the framing has longitudinal stringers, the insulation would have to be installed as separate small panels. Further, I don't understand how loose laid boards will stay in place when installed on a boat. Ceiling panels need to be fastened or otherwise secured, or they will fall off. Also, the interior of a dwelling or boat will be very dry in winter if heated. That is the reason to install humidifiers to furnaces. There are several insulation materials that are easy to install and have higher R values. For example: Dow Thermax Sheathing, 2 inch, 4 x 8 foot, Polyisocyanurate Foam Insulation (pallet/22) https://www.bestmaterials.com/detail.aspx?ID=24889&gclid=EAIaIQobChMIw8HFkuiz9AIVQpJbCh0_8g2AEAQYAyABEgLjOfD_BwE
     
  7. Glen Wither
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    Glen Wither Junior Member

    Gonzo. Polyiso is terrific as an insulation and is fire resistive, almost no off gassing too. Price wise though…..beaucoup. Loose laid rigid insulation is a tight fitted application, between stringers and verticals, and can be installed as the interior finish is placed. It is the interior finish that “sandwiches” the board. Live abords here in southern Ontario run de-humidifiers constantly in Winter. I think the rock wool is still the better choice, and I expect it won’t squeak like a poly board underway. Thoughts?
     
  8. Barry
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    Barry Senior Member

    Glen
    Unless the hull steel has been rolled or heat formed, the surfaces are developable but can have curves, obviously
    It can be a bit of a chore to fit rigid insulation or even foam insulation into spaces that may have 4 sides that are are orientated in different directions.
    So the trick is to cut a bunch of scrap wood strips, say about 3/32 of an inch thick by 1 1/2 inches wide. The thickness to make the strip slightly rigid but able to be cut with tin snips
    Lets say that you are trying to get the shape of a non square 4 sides insert whose dimension are 32 inches x 30 x 28 x 26 ( not sure if this would even be a real set but is fine for the discussion) and you are trying to get a panel to fit say between two frames and two stringers.

    Assume the wood strips are 36 inches long.

    Take a 36 inch strip and lay it against the hull and the adjacent stringer, ie so the strip follows the stringer and is against the hull. Cut the wood strips maybe a 1/2 inch shorter than the measurement where they are going to be installed.
    With a hot glue gun handy, place the first strip in place, give it a shot of glue at the end of the strip, (obviously not against the hull) , place the next wood strip into place against the glue, the glue sets almost instantaneously, then put a bit of glue
    on the second strip and move around until you have made the 4 sided "profile.
    Then all you have to do is pull out the "perimeter form" and lay it on your rigid foam, mark the foam and cut it and the foam will fit back into the area that you need it to fit

    We did this when we were installing marine acoustic foam/insulation in some of our aluminum hulls. To cut the semi rigid foam, we used an electric jig saw. This was extremely fast and accurate.
     
  9. M&M Ovenden
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    M&M Ovenden Senior Member

    valery gaulin and fallguy like this.
  10. Glen Wither
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    Glen Wither Junior Member

    Yup did so. No joy. Anyone here know what the H-17 1974 Thermal and Acoustical Insulation, Sheathing Materials and Fire Retardant Coatings rule is from ABYA?
     
  11. Glen Wither
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    Glen Wither Junior Member

    The Bruce Roberts 36 I am looking at now is a hard chine hull with 2.5” stiffeners. The previous owner bolted wood strips to the stiffeners and installed teak or mahogany slats on the cabin ceiling and sides.
     

  12. M&M Ovenden
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    M&M Ovenden Senior Member

    Hi Glen,
    I'm not sure to understand what you are asking, you seem to have made your mind about what you want. I'm also confused about some of your comments...

    Armacell's fire rating make it an insulation of choice for strict marine standards of passenger and commercial vessels. Out of curiosity, I tried to burn armacell, without success. It does not want to burn and I did not get any smoke from my attempts to burn it (an experiment i actually dared doing in my house)

    I dont understand your comment about glue in regards to armacell. They sell the glue for the application. No, it's not epoxy that is not what is recommended to stick armacell. Contact cement is the appropriate manufacturer recommended adhesive and it sticks like flies to ****, you will tear the material before you can undo the bond. They even have a low VOC contact cement which is much nicer to work with. I very much doubt Armacell neglected testing adhesives, its a pretty big industry used world wide in most demanding conditions. Armacell can also be purchased with sticky back and t also sticks like flies to ****.

    You are right, methodology is important. The trick, with any insulation, is to leave no thermal bridges (exposed cold steel to interior warm air) to limit condensation on the steel (or dripping in the boat, that's not fun either). Armacell does have properties which facilitate that, it's flexible, can be glued to the surface it covers and to itself (edges can be glued end to end to form seamless coverage) and comes in several thicknesses (you can overlapped several thickness with staggered, no matching seams). Being closed cell and not porous, it creates a pretty damn good vapor barrier.
    Anyhow, you don't have to like or want to use Armacell but your comments made me wonder if your opinion on the material was based on flawed understanding of the material. One big draw back, it's pricey.

    I am also a little confused by your idea of "letting condensation flow to the bilge" ...through the insulation? Surface tension will maintain moisture between your hull and insulation; and within the insulation if it is porous. Lack of air circulation will not favor drying, and insulation does just that, it limits air circulation. Also, if letting condensation flow, what's the plan under the deck?

    We lived aboard our previous steel sailboat frozen into the Ottawa river for two winters and the insulation lesson from it was "perfect vapor barrier is key" and "any thermal bridge will drip". Our current boat is not in the water at the moment but I have been working inside, heating with a woodstove over a few Canadian winters. It is warm and bone dry. Crazier is how cool it stays in the summer, even with the black hull.
    It's insulated with multiple staggered layers of glued armacell, with special attention to having all the steel covered and absolutely no fasteners creating thermal bridges to the frames.

    Cheers,
    Murielle
     
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