Boat Insulation – Part 3

This is part three of a three part series. Be sure to check out part one and part two.

Cardboard Stencils

Using cardboard boxes to cut out stencils makes it easy to cut-out material to fit complex shapes in tight spaces.

I finally finished fiberglassing in the hemlock ‘studs’ that will be used as scaffolding to support the upholstery and insulation. The final step was to mount the insulation and upholstery. Unlike a house, almost nothing on a boat is ‘square’ as the concept of ‘level’ doesn’t really exist on a boat. When trying to retrofit anything in tight quarters, construction become even more difficult. My friend Ken taught me a trick a while ago that greatly helps in boat construction: cardboard stencils.

Large cardboard boxes can be salvaged for free from dumpster behind just about any retail store. My favorite local store to get boxes is West Marine. Twice a week they fill up a dumpster with cardboard. Just about any retail store is the same. Once you get your basic measurements, you can cut out a rough shape, then fine tune the cardboard with a knife or scissors until you get a perfectly shaped piece of whatever you’re trying to build. Because it’s easy to bend and fold, you can get it in and out of tight spaces easily. Sometimes it’s necessary to go through two or three versions to get just the right shape. That’s not a big deal since cardboard is free, plentiful, and easy to work with. This technique has served me well whenever I needed to cut out plywood, insulation, or plastic upholstery.

The first step was to get the insulation cut out and mounted. Using this cardboard technique, I cut out stencils for all the insulation needed, then laid them out on a 4′ x 8′ piece of insulation and cut everything out at once. There was a little bit of fine tuning involved, but for the most part the insulation went right in. I ended up using blue Foamular insulation, half-inch thick, with an R-value of 3. I had to special order it, but it only cost about $16 per sheet and I has worked well for other mariners.

Cardboard Mockup

The cardboard mock-up stencils are mounted exactly where the insulation will go.

The process of cutting out the upholstery was almost identical. Once I got all the insulation mounted, I used the exact same cardboard technique to cut out stencils for the upholstery. The only difficulty I had was in drilling out the holes to line up with the T-nut. In hindsight, I should have done this to the cardboard, but instead tried to eyeball it on the final product and ended up with a few extra holes. The upholstery is cheap enough that I could re-do it if I really cared, but I don’t.

I ended up using the Numat plastic sheeting and I was really impressed! It’s virtually mold proof, made from recycled plastic, and cuts easily with a pair of scissors, yet it’s stiff enough to add a significant level of protection to the easily damaged foam insulation. While not sexy in any way, I was really impressed with the utilitarian nature of this material.

Insulation and Upholstery

The insulation is in and the first piece of upholstery is mounted to the studs.

In a year or so, if I decide I need more insulation, all I have to do is remove the upholstery, pop out the t-nuts, fiberglass another hemlock stud on top of the old one, and mount another layer of insulation. Simple upgrade!

In the end, the insulation fit so snugly (thanks to the cardboard stencils) that I didn’t need any sort of glue or adhesive to keep them in place. I opted not glue them to the hull for the sake of easy adjustment later. In a year or so, I’ll probably remove the insulation and upholstery to check for mold and moisture buildup behind the insulation. The only real advantage of using a caulk/glue to adhere the insulation to the hull is to prevent moisture buildup behind the insulation. I don’t know if this is anything I really need to worry about, and I like knowing that I can remove everything easily to get to the hull in case of an emergency.

Insulated V-berth

The V-berth is insulated, upholstered, and much warmer!

The difference in the V-berth since adding the insulation is profound! I’ve eliminated moisture buildup, which was a huge issue before, and it’s much, much warmer to sleep in. Since I used half-inch insulation, I don’t feel like I lost much real-estate in the already snug V-berth.

Related posts:

Adventures in Alaska
Who Needs Radar?!
Winter Cruising Essentials
8 Responses to “Boat Insulation – Part 3”
  1. Nice work Chris! Those snug, warm nights up in the V-berth must be very satisfying. Well done.
    – Katie and Mark

  2. Ryan says:

    Hey, great series as I freeze my butt off in Ballard. Where did you snag the Numat? I cant seem to find anything online.

  3. Earl says:

    Did you go back and check behind the insulation? Did you find any mold or moisture? Thanks for sharing all this info. About to do this to our boat. It makes sense to me to glue the insulation to prevent any moisture problems.

    • Chris says:

      I did go back and check. It’s been about two years since I’ve done the insulation and there is no moisture buildup or mold behind the insulation. There is nothing for mold to grow on, since everything is a composite material.

  4. Anna says:

    Hi There! Awesome post. I am a complete novice to basically all things handy so I’m trying to get as much info as possible before starting on my insulation project. Between your tutorial and the Frugal Mariner’s, I think I have a game plan.

    Can you describe your final beautification step? The white fabric with only the two buttons looks so crisp and clean.

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