Insulating a Hull- Does it Work-How to Do?

[David M]

Use spray foam. If you have a gap between insulation the the hull you will still get condensation. Spray foam eliminates this gap. I have spray foam on my aluminum hull.

[biker6977]

David- do you have it on the entire hull or just down to the water line?
If just down to the WL do you get condensation at the WL?
As mentioned before I live in the hot and humid south where the coolness from the water could be used to cool the cabin if I insulate only down to the water line, but I am concerned that the bottom will condensate. I don't want to use AC as I want to be as self sufficient as possible. I will be getting a bimini and will make a tent to go over the deck and make scoops for the hatch and probably also putting in dorados. I do not want condensation- period. But I also don't want to insulate the cool out since it is more often than not hot and humid down here.

I have it on the entire inside of the hull except at the very lowest part of the bilge, so that water does not soak in to the foam.

[Matt sachs]

Originally Posted by David M

Use spray foam. If you have a gap between insulation the the hull you will still get condensation. Spray foam eliminates this gap. I have spray foam on my aluminum hull.

+1.......2- 3 inches of ployurathane is the ticket. thremal, sound and condensation protection.

[jwing]

Originally Posted by biker6977

David- do you have it on the entire hull or just down to the water line?
If just down to the WL do you get condensation at the WL?
As mentioned before I live in the hot and humid south where the coolness from the water could be used to cool the cabin if I insulate only down to the water line, but I am concerned that the bottom will condensate. I don't want to use AC as I want to be as self sufficient as possible. I will be getting a bimini and will make a tent to go over the deck and make scoops for the hatch and probably also putting in dorados. I do not want condensation- period. But I also don't want to insulate the cool out since it is more often than not hot and humid down here.

Go to noaa.gov or your favorite weather data site. Check the history and get an idea of the air dewpoint temperatures.

Assume the air in your boat is the same as the air outdoors.

Measure the water temperature. Assume that the inside of your hull is the same as the water temperature. The hull will provide some insulation, so if you want to be more accurate, measure the temperature of your hull. If the hull temperature is lower than the dewpoint temperature, there will be condensation.

[JPA Cate]

scarlet,

Sapient Sue is away from her computer for a while, so I'm going to answer your question: their boat had no problems in the tropics, but it was going to the colder waters of Canada and Alaska where they had the problems. (SS and I are well known to each other.)

Obviously, the upshot of this is that if there is a way to bring the water-cool into your boat, your intuition was correct, that would be a good deal.

Ann

[UNCIVILIZED]

You can insulate things with flexible closed cell foam, like say, something akin to the foam in wrestling mats. Just cut it to size, to fit around your cabinets, shelves & what not. Then get some 3M Spray Glue, & attach it right to the hull. And once that's done, you can use the same glue again, only this time, to glue automotive carpeting over top of the foam.
Then, if you want it to look fancy, odds are, the place where you snag the carpeting will have edge trim, which you can staple or glue into place. Or you could just get some nice wooden trim, pre-varnish it, & affix it to the hull + over the edges of the carpeting with a simple tube of silicone.

Such is a fairly simple process, & not overly pricey. I did all of the hull sides on a 33'er in a weekend, solo. With only a touch of supervision from a friend who'd done his boat that way.

And honestly, unless you live somewhere where it gets real cold, it's likely that just installing the carpet alone will be sufficient insulation.
That's what I did on my first boat, when I lived in SoCal. Where winter temps never drop below 40 degrees. And I had ZERO condensation, as well as being Amazed at how much installing just simple carpeting warmed up the boat. I noticed the difference right away, like right after I put it on. Even before I fired up my electric space heater.

Ah, FYI, my boats had cored decks. Which is a biggie, in terms of keeping things warm & dry, even when only using a tiny electric heater to stay warm for the winter.
In a pinch, if you wanted to add R-value to your decks, you could get some 3mm plywood, & pre-finish both sides with epoxy. And then add some blue or pink board foam to the plywood. Once you do that, & affix it to the undersides of your decks, I imagine that it'd make a Huge difference in terms of how warm things stay. Especially if done in conjunction with insulating the hull(s)... just with carpeting, or with both carpeting and insulation.

It'd be easy enough to mount some cleat stock to the underside of your deck, to which you could affix the above mentioned insulation style. And if you want things to be Purdy (pretty), platen mold the epoxy finish onto the ply prior to adding the foam & installing your new ceiling.
One can get panels with pretty much a perfect finish by doing things that way. And again, putting in wood trim to class it up even more, with just some adhesive out of a caulking gun's a no brainer.

[charliehows]

The best cure for condensation is ventilation – particularly in hot climates. Sydney gets pretty damn hot over summer but I've never had any problem with damp because i keep the boat well ventilated. You might want to try out combinations of open hatches, covers etc before spending good money on insulation. No matter what you do, close proximity to salt water makes you feel sticky, you just get used to it.

[biker6977]

Thanks Ann for the info. We usually don't get very cold but last winter we did. Since the boat is bare hull right now I want to do what needs done prior to fitting it out. I think I"ll go with the spray foam down to the water line. Should be able to do it for <$1000, which is a lot but like I said I'm not looking to make money but learn what does and doesn't work on a boat down here before getting THE boat. Would it be a good idea to run some PVC midway and top of the sides to allow electrical wires and plumbing to be ran through? I"m going to try and have a layout in my mind prior to doing insulation but I know things might change and I want to be able to make alterations and figure that with it insulated it will be hard to run anything later. What size PVC would be best to use?

[Steadman Uhlich]

Howdy Biker.

I have read your original post and all of the following prior to posting this comment. I offer the following comment in a truly friendly tone of voice, and with the sole intent to help.

Insulating the entire bare hull is something "self-builders" do when making steel boats (at home in the backyard). It is very common for them to insulate the entire interior with spray foam (applied by commercial foam spraying services). This is apparently the
usual way for boats up in PNW area.

So, if you want to know how to do this properly, assuming you will have a bare hull (inside) then I suggest you do your research in areas (websites) devoted to metal boat building. There are many "self built" projects found via blogs. And there is the Metal Boat Society in Seattle area (it has a website with lots of info). In addition, there are videos on Youtube showing how folks finish out their metal boats. And there is a blog that showed how the boat builder got a commercial foam blowing truck to blow in the foam on a 65 foot metal boat. Since you are thinking of spending about $1000 on the foam insulation, consider the cost of getting a commercial truck to blow it in for you.

There are several videos on Youtube related to origami boat building and other metal boats finished with foam insulation. Here is one that is about insulating a narrowboat (England).
Narrowboat Sprayfoam insulation and DIY fitting out - YouTube


In short, I think you will get much more information on "insulating a boat hull" via other sources and much better "see how it is done" via photos on blogs and video clips etc.

Good luck.

[David M]

Originally Posted by biker6977

David- do you have it on the entire hull or just down to the water line?
If just down to the WL do you get condensation at the WL?
As mentioned before I live in the hot and humid south where the coolness from the water could be used to cool the cabin if I insulate only down to the water line, but I am concerned that the bottom will condensate. I don't want to use AC as I want to be as self sufficient as possible. I will be getting a bimini and will make a tent to go over the deck and make scoops for the hatch and probably also putting in dorados. I do not want condensation- period. But I also don't want to insulate the cool out since it is more often than not hot and humid down here.

I have it on the entire inside of the hull except at the very lowest part of the bilge, so that water does not soak in to the foam.

You will get condensation when the water temperature is below the dewpoint of the air.....unless you insulate. You can get condensation in cold, temperate and warm climates. It depends on the two factors that I mentioned.