1969 Chris Craft Roamer 46 Refit: Insulation

In the spirit of jumping around from topic to topic, which is pretty much how the project has been going for the last few months, today I’m writing about insulation.

Yup. From a gantry design to laying out the floors in the aft stateroom to insulation, in three sequential posts. Makes sense, doesn’t it? 😉

Believe it or not, there’s actually some reason to the madness.

Anyway, I remember when we sold our Chris Craft Constellation 52, a mahogany hulled boat, for a Commander 42 in FRP. Oh boy…THAT winter was a lesson in thermodynamics. The old woody was so warm. So I tried my hand at insulating the Commander using a variety of materials, which yielded a variety of different ways NOT to effectively stop unwanted heat transfer. It’s all good, though, because lessons learned on my other boats are helping pave the way on our Roamer. And since the Roamer is an aluminum hulled boat, mastering the heat transfer issue will be mission critical.

I am, after all, a happily married man, and I intend to keep it that way.

So, in the category of things I definitely will not do when insulating the Roamer, we have foam board, Liquid Nails, silver tape, or any other materials sold at big box home improvement centers. Shrink wrap tape, while tenacious when used on shrink wrap, doesn’t hold for more than a few months on foam board insulation. Fiberglass batts are great for insulating… houses. On boats, fiberglass holds water and is just miserable when it inevitably fails.

Fortunately, Chris Craft’s original hull coating was in pretty good shape on our Roamer. I think it was called Bitumastic, a semi-hard tar or asphault-like substance, though I’ve heard others call it coal tar. Either way, as you can see in the pic below from when I was removing the old exhaust pipes, Chris Craft gave it a coat of silver paint to pretty it up, and it really does a terrific job of stopping condensation dead.

Good looking silver-painted Bitumatic...so long as there's no oil around

Good looking silver-painted Bitumatic…so long as there’s no oil around

Unfortunately, residue from oil mist of the sort that’s common in engine rooms of all but the most fastidiously kept boats pretty much dissolves this petroleum-based insulation in short order. And, really, Bitumastic (or whatever it was called) stops condensation, but it’s not going to keep the missus warm in the middle of winter. As insulation, adding more of it won’t be of any benefit.

So, here’s what I’m thinking for insulation:

All of the ceiling surfaces, including the new aluminum side decks near the helm station, the bullet proof cabin top, the underside of the side decks, and the V-berth will get an inch or two of closed cell spray foam. The thermal insulating properties of spray foam are great, and word has it nothing is better at filling voids and stopping air infiltration. Most of the two-part urethane foams have to be applied when surface temps are 70* or more to get proper expansion, which is why I’m working on getting bulkheads installed now in the middle of winter: chipping away foam insulation to make room for bulkheads sucks, and by the time the weather warms up I’ll be ready to spray the foam.

For the vertical surfaces, I haven’t decided what to do. There’s no exposed aluminum, so condensation isn’t a concern. I could foam the hull, but that would still leave me with cold air in the hull envelope coming into contact with the back-side of all my cabinets. That could cause condensation problems, plus there would be heat loss through the wooden cabinetry panels. To keep the air conditioned (i.e. warm in winter or cool in summer) interior envelope thermally isolated from the unconditioned hull envelope, I’m thinking of using spray contact cement to attach nonwoven fabric insulation to the backside of all of the wall panels and cabinet back panels that face the hull.

The table below summarizes the information I’ve pulled together on the various insulation options. It also estimates Bang for the Buck, which I define as the ratio of R-value to $/ft^2, with a higher number being better. Sorry the table looks goofy; wordpress is notorious for not being table-friendly.


Width (inch)

W (ft)

L (ft)





Bang for the Buck*


Thinsulate 1″










Thinsulate 2″




















Mist Buffalo Batt









Nonwoven polyester fabric

Spray foam on ebay      







Foam it Green      







Tiger Foam      







Icynene ProSeal      







* Bang for the Buck is the ratio of R-value to $/ft^2, with a higher number being better

3M Thinsulate is easy to handle and install, hydrophobic, and (relatively speaking) very expensive. Weaver Boatworks uses it, and reportedly so do other luxury boat and car manufacturers, though it’s marketed as acoustic insulation rather than thermal. Still, it has a fair R-value. Thinsulate fabric is a mix of polyester and polypropylene, and it’s the very fine polypropylene fibers that make Thinsulate so much thinner and lighter than other nonwoven fabrics with the same R-value. Polyester nonwoven can yield the same R-values, but it’ll be thicker and heavier. And by heavier, I mean a few ounces per square foot, which falls into the “insignificant” category on a 46′ motor yacht.

Thermozite was another product I found online that some camper enthusiasts seem to like. It uses polyester, but it’s a very thin product that’s foil lined. You might see it on the under-side of your hood, for example. It’s less than half the price per foot^2 as Thinsulate, but the R-value is so low that it really drags down the Bang for the Buck.

Which brings us to a surprising entry: Buffalo Batts, which quilters and other crafty sorts use when they need a 1.5″ lofted batt that doesn’t absorb water. It’s a nonwoven polyester fabric, but not faced like Thermozite or Thinsulate. Frankly, I have no idea if a vapor barrier facing is necessary, and the bang for the buck on this stuff is outstanding: the per-inch R-value is less than Thinsulate, but not by a huge amount. And the price is excellent. I’m leaning toward Buffalo Batts as the material I’d use on the backside of all the vertical walls.

But back to the spray foam. Tiger Foam is clearly the best bang for the buck, assuming manufacturer’s coverage data is accurate for all of the products. Tiger Foam’s product info page indicates an initial R-value of 7 and an aged R-value of 6, and the loss of aged R-value has a huge impact on Bang for the Buck. Icynene Proseal, by comparison, claims to be an advanced new formula that’s set the high bar for the industry with an aged R-value of 7, but they don’t sell DIY kits. There’s a potential cost savings of $450 for DIY vs having a pro spray Icynene Proseal. Then again, I know from spray painting that there’s a reason you pay the guy with the magic hand who can lay it on just so. Whether DIY or pro-applied, I’ll be taping and covering the whole boat to protect shiny paint and pretty wood. But, on the other hand, I do like DIY experiences, especially when they work out well.

What a conundrum. If anybody has any thoughts, experience, or suggestions, please feel free to comment.

Next up on our 1969 Chris Craft Roamer 46 Refit: Turning Mahogany Plywood Into Aft Cabin Walls


12 comments on “1969 Chris Craft Roamer 46 Refit: Insulation

  1. humalobutali says:

    Lots of great information and inspiration, both of which we all need!

  2. admin says:

    can’t tell you how much I, for one appreciate all you do!

  3. I did use the Tiger foam this Fall on a project. It is a great product (expensive) and will stick to anything really well. I think the 70 degree temp. to use it in is ideal but can probably work as low as 60 degrees. I have paid to have it done several times and this project was too small for that so I did it. The tips have to be changed every 2 minutes and they send you many but that is all there is to it.

  4. Erik Finni says:

    Hi ihave uesd armaflex and it work vell for me

  5. Conall says:

    I vote for spray foam down to the water line. If you get 1/2″ over all the metal, you now have an excellent vapor barrier which will let you install batt type material. I have some foam detail on my blog. Building Koala used sheet material so check out their blog. Brian building Odyssey also used sheet material on his aluminum build blog and has a lot of detail.


    I also sprayed some insulating paint on some of my port light frames that were not able to get foamed, and would be in direct contact with wood. This stuff worked good as I’ve not seen any sign of condensate on my port light trim. I would not want to depend on this as the insulation system, but it can find a place in terms of the “whole” project. The insulating paint came about from NASA, and has an R value.

    Whatever route you go, cover all the metal that has a chance of seeing drastic temperatures differences on one side vs the other. It’s amazing how much water will drip off of an exposed piece of metal.


  6. William B. Kelleher says:

    Have you checked Armaflex sheets ?

    A designer of aluminum power boats uses it.

    Bill Kelleher

    • 1969roamer46 says:

      Hi Bill.
      Yes, I did look into Armaflex. But it didn’t make the cut for several reasons:
      1) it’s significantly heavier per unit volume than all the rest;
      2) R-value of 4 per inch is fair;
      3) it’s 40% more expensive than even Thinsulate, which has basically the same R-value); and
      4) it’s a lot harder to cut and work with than nonwoven fabrics.
      I was also concerned about getting perfect adhesion. The nonwoven fabrics are very forgiving about filling space and covering entire surfaces even if there’s imperfect glue application. With flat products like Armaflex, less than perfect adhesive would create condensation that would have nowhere to go.

      That was my thinking, anyway.

  7. Marty Molloy says:

    Here’s a little inspiration for you. ;0)

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