Steel Hull Insulation Recommendation

Discussion in 'Boat Design' started by Glen Wither, Nov 23, 2021.

  1. M&M Ovenden
    Joined: Jan 2006
    Posts: 365
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    Location: Ottawa

    M&M Ovenden Senior Member

    I'm not sure what you mean by filling gaps frames and corners, do you mean between the frames and the hull? Mine are quite tight against the hull so I woudnt have gaps to fill. We did use in the more wet area of the boat a coating that is very runny with high surface tension so it would coat the steel between the frames and hull. That area of the boat is not insulated though and will be more exposed to moisture.
    I'm not sure if I referred higher in the thread to the page on insulating our boat, I think I answer there to your questions.
    I also mention the lack of dimension stability of armacell (shrinks in cold, swells in heat) an how you need to take that in consideration when you install it.

    Also important is to take in consideration thermal bridges, which i explain how i worked around here The interior shell Basically avoiding any fasteners through the steel that would be exposed to the ambient living environment.

    As for spray vs placed insulation. Main considerations were flammability of the spray options at the time. Armacell having fire ratings is a plus for insurance and would simplify process if we ever needed/wanted some commercial certification. Its also a more simple installation process, with less failure mode. Bad spray job leaves a mess... We were more comfortable not having to worry about the "what ifs" of something going wrong with the spray; its a very subjective argument.
  2. Steelboat
    Joined: Feb 2022
    Posts: 52
    Likes: 9, Points: 8
    Location: Seattle

    Steelboat Junior Member

    Yes I meant the small gaps between the frames and the hull plating, in my case the frames are "floating" with a gap of up to 1/2" (12mm). I will plan to apply a sealant there.

    Your website write-up on insulation is very helpful, thanks. I recommend it to any others who need to insulate.

    I take note of your comment on expansion and contraction, and will try to cut insulation sheets a bit oversize and squeeze them into the spaces. Did you apply glue to the edges of the sheets where they join the frames?

    I agree on the spray foam issues. My boat was sprayed by an experienced contractor in Alberta back in 1991, and most of it remains excellent. The operator did a good job of flowing the foam into corners and gaps. Rare places he did miss eventually caused corrosion, so it matters a lot. Over the years I have had small areas re-sprayed after welding with very mixed results. I believe problems came from metering pump errors, or perhaps feed hose intermittent blockages. Sometimes we got either gooey foam or a brittle product with high porosity. For any smaller jobs sheet foam seems the much better choice.

    I think I will go with about 1-1/2" of foam for the tropics, and see how it performs. I can always add a second layer down the way.

  3. Steelboat
    Joined: Feb 2022
    Posts: 52
    Likes: 9, Points: 8
    Location: Seattle

    Steelboat Junior Member

    I found Armaflex "Class O" sheets. It is much more available than AP grade. Reasonable substitute? Rated quite good for fire resistance.

    For reference- spec sheet attached.

    Attached Files:

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