Adding Core to a Finished Hull

Triton 185 · Post by **Triton 185** » Wed Jun 04, 2008 11:23 pm

Hello,

I have a 45 boat that was laid-up in 1974. The hull is solid glass. I am considering adding core on the entire hull above the water line for added strength and insulation. As well, because the boat is a shell with no sole and only 3 sets of bulkheads I am thinking of running the glass laminate over the core and then continuing down into the bilge for added strength below the water line.

What type of glass and resin would you suggest? Should the bulkheads be removed to do the core and glass work or should they be left in place? How do you feel about adding core above the waterline? All thoughts appreciated.

Thanks,

Stephen

Post by **Tim** » Thu Jun 05, 2008 6:00 am

That's a lot of potential work. Is there a specific and perceived construction deficiency with the original hull that leads you to believe the additional strength is needed?

Jason K · Post by **Jason K** » Thu Jun 05, 2008 9:36 am

If you really feel additional stiffness is necessary, wouldn't longitudinal stringers accomplish the same goal?

bcooke · Post by **bcooke** » Thu Jun 05, 2008 9:46 am

Buying a different boat that meets your structural requirements would be a lot easier and cheaper.

What type of glass and resin would you suggest?

Epoxy resin is the only choice to consider for repair and bonding to previously cured material.

I am just full of opinions today...

Triton 185 · Post by **Triton 185** » Thu Jun 05, 2008 11:27 am

That's a lot of potential work. Is there a specific and perceived construction deficiency with the original hull that leads you to believe the additional strength is needed?

Hi Tim...no there is not any structural issue with the hull. The goal is to provide some insulation on the hull and I have looked at a variety of alternatives. I am sensitive to mould and think encapsulating some core could be a good way to insulate without some of the other drawbacks of other materials. If I am to do this, I would see the added strength as a bonus.

Any comments on materials would be appreciated.

Jason K · Post by **Jason K** » Thu Jun 05, 2008 11:32 am

If the sole purpose is insulation, then I would strongly suggest abandoning the idea of adding core material, which I think is a lot of cost and work for very limited benefit, and using materials specifically designed for the purpose. I believe Britton insulated his Triton and I know others have as well. I'll leave more specific advice to them.

Triton 185 · Post by **Triton 185** » Thu Jun 05, 2008 11:46 am

Epoxy resin is the only choice to consider for repair and bonding to previously cured material.

What about vinylester resin, does that work on cured fiberglass?

Triton 185 · Post by **Triton 185** » Thu Jun 05, 2008 11:58 am

Hi Jason,

Thanks for the reply. It would be interesting to know what Britton has used

CharlieJ · Post by **CharlieJ** » Thu Jun 05, 2008 1:06 pm

we used foam insulation from the home use market. It's foil both sides urethane foam, 3/4 inch thick. We staved the hull sides, fit the foam between the staves and then overlaid that with ceilings. We used varnished ash. Somewhere on here is some pictures of Tehani showing the ceilings.

feetup · Post by **feetup** » Thu Jun 05, 2008 1:19 pm

There were two areas on my hull that were always cold to touch, and that weren't enclosed by settees or lockers. Under the dinette and in the head. I glued narrow planks of western red cedar with thickened epoxy to the hull like ceilings in these points. They are about 3/8 inch thick and I stained them slightly to match the teak sole. The cedar is very light in weight, and flexes well to the curvature of the hull. Cedar is very rot and mildew resistant and smells good too. I only needed to apply pressure in about 4 spots to bring them tight to the hull. They offer a surprising amount of insulation, and once varnished they look like carvel planking. Much nicer to the bare feet. The cedar is soft and easily damaged but the only thing that touches it is feet under the dinette and almost nothing in the head.
I saw pictures of a job done that way in the vee birth of one boat in mahogany, and I have seen ceilings screwed to small "ribletts" epoxied to the hull leaving an air space behind.

Feetup

bcooke · Post by **bcooke** » Thu Jun 05, 2008 3:19 pm

It would be interesting to know what Britton has used

Britton used Armacell AP, a closed cell foam material used in commercial shipping and US Navy boats. Expensive, but pretty good stuff.

http://www.armacell.com/www/armacell/ar ... enDocument

I got talked into the 1" thick stuff but that is probably overkill. Hey, what's an extra half inch or so in the big scheme of things?...

The closed cell foam has some anti-microbial action to it; its fire resistant and meets commercial shipping fire/toxicity regulations. Despite being 'closed cell' if you force into a bucket for a week it will absorb water. It dries out again pretty quickly with no apparent ill effects though.

The foam sheets are glued to the hull with contact cement, also expensive and quite smelly. Use lots of ventilation or you will be arrested for using an illegal substance after a few minutes of exposure. Gluing the foam to the inside surface of the hull eliminates any water condensation that can occur where the cold hull meets moist air.

Just for good measure and because I have a bunch lying around, I also have the foil lined air bubble stuff (readily available at Home Depot) that I stuck behind the panels (unglued, just lying in there) on the hull areas above the waterline. The foil helps with radiant heat and boosts my radar image and it is cheap.

A warning though; I read Ferenc Mate's chapter on insulating his boat and he made it sound like a weekend project. It isn't unless you are willing to have exposed foam everywhere. Otherwise you are going to build an interior liner for the entire hull in the process. This makes the interior project much more complicated and time consuming. In the photo you can see little blocks epoxied onto the hull. These blocks are what are supporting the interior panels. Naturally, some panels are featherlight and need next to nothing to support them. Other features like hand pumps need real supporting structure.

My insulation project might be more time consuming than others simply because the entire hull from sole to deck is insulated. Under the settees, under the sole iteself, Under the V-berth and V-berth water/waste tanks, everywhere. The saloon is still apart but no inch will be missed there either. Due to global warming, the north pole is expected to be ice free in the next 20 years or so and I want to be ready :-)

You don't have to go as far as I did. It was a learning experience for me and some people say I have a slight tendency to go a bit too far (go figure). Some people use some rigid foam from Home Depot on the back of their cabinets and call it good. I don't know enough to make a proper comparison. In the boatyard the insulation system I have seems to work pretty good...

bcooke · Post by **bcooke** » Thu Jun 05, 2008 3:23 pm

What about vinylester resin, does that work on cured fiberglass?

Not as good as epoxy.

Post by **Tim** » Fri Jun 06, 2008 6:24 am

Triton 185 wrote:
That's a lot of potential work. Is there a specific and perceived construction deficiency with the original hull that leads you to believe the additional strength is needed?
Hi Tim...no there is not any structural issue with the hull. The goal is to provide some insulation on the hull and I have looked at a variety of alternatives. I am sensitive to mould and think encapsulating some core could be a good way to insulate without some of the other drawbacks of other materials. If I am to do this, I would see the added strength as a bonus.

Any comments on materials would be appreciated.

If you want insulation, you'd be better served, as others have suggested, to install dedicated insulation and/or air spaces. Rather than spend your time and resources on a large and messy "structural" application (i.e. the core installation and encapsulation) that's wholly unneeded, instead spend the time and money on actual insulation and its attractive and effective installation.

This approach will get you further down the project road in a more efficient and effective way, as the end result will not only work better in the long run, but, when properly planned, will also serve in part as your finished interior and/or locker interiors.

For insulation, you can use nearly any closed-cell foam product, as long as it resists nuisance water and as long as you can conform it to the hull as needed. The cat's meow would be semi-rigid foam installed in such a way as to leave a small air space between it and the hull laminate. You don't need huge thicknesses of foam to have the insulation and condensation-reducing effect you're probably going for.

bcooke · Post by **bcooke** » Fri Jun 06, 2008 7:04 am

The cat's meow would be semi-rigid foam installed in such a way as to leave a small air space between it and the hull laminate.

Ummm... with an airspace between the hull and semi-rigid insulation wouldn't you get some condensation in the airspace? A tight bond with the hull is a key component of the installation of the Armacell product I am using.

Air is a good insulator though and an airspace will definitely add to the 'R' value of the insulation being used. Its the trapped moisture over time that would bother me.

Post by **Tim** » Fri Jun 06, 2008 8:44 am

Given the unlikely ability to truly eliminate all air spaces between any insulation and the hull, it seems like moisture, if it exists, would be more likely to be trapped if the insulation is bonded to the hull, whereas with a small air space there's circulation and ability for said moisture to harmlessly dissipate. The idea isn't to create a closed, stagnant air space, but instead to create a space in which air can actually circulate behind the insulation and other coverings.

Air circulation and cleanliness is the key to avoiding disgusting moisture problems on any boat. One wants to take steps to avoid anything that traps moisture, should it exist.

Maybe I'm all wet in the theory crowd, but my boat is dry. I'll bank on that.

Quetzalsailor · Post by **Quetzalsailor** » Fri Jun 06, 2008 9:14 am

If there's no structural problem, don't add structure. Uffa Fox's comment comes to mind, "Weight is for steam rollers."

You really do have to think about where the moisture collects in an insulation system and there's lots more opportunity for excess moisture in a marine environment. Encapsulation of closed cell material is a great solution, but also the most difficult. Adding a wood ceiling is a great solution with the particular advantage of maintaining ventilation behind it, good looks, and doing the whole job of insulation and finish in one swell foop. Any sort of spaced-away ceiling would do the same thing.

A friend who used to work building small 'glass sailboats reports that they experienced blistering where there was a moisture-proof cover used during storage. Maybe there were other issues there, but I've always been chary of trapping moisture against (or in) fiberglass. (Not yet chary enough to pull my refrigerator/icebox apart and get the after-market urethane foam away from the hull, but soon!)

bcooke · Post by **bcooke** » Fri Jun 06, 2008 9:35 am

Maybe I'm all wet in the theory crowd, but my boat is dry. I'll bank on that.

If it works, it works.

Triton 185 · Post by **Triton 185** » Sun Jun 15, 2008 12:04 pm

We staved the hull sides, fit the foam between the staves and then overlaid that with ceilings.

Charlie, did you leave space between the ash strips for air circulation?

Triton 185 · Post by **Triton 185** » Sun Jun 15, 2008 12:15 pm

Britton used Armacell AP, a closed cell foam material used in commercial shipping and US Navy boats. Expensive, but pretty good stuff.

Hey Britton, I have done some reading on this insulation. I like it’s resistance to mould and its fire rating etc. As well, I see they have some with peel and stick adhesive. The big question is the cost. What is it a square foot (for the 1” material) and roughly how much did you use on your Triton?

Triton 185 · Post by **Triton 185** » Sun Jun 15, 2008 12:35 pm

Thanks for all of the input. I have decided to add staves to the hull interior with some insulation and a wood ceiling.

I just need to settle on the type of insulation and whether the ceiling slats should be spaced, tight or perhaps a combination.

Rachel · Post by **Rachel** » Sun Jun 15, 2008 12:46 pm

185,

Charlie and Laura have been off sailing the Texas 200, but I know their boat (lovely!), and they don't have space between the ceiling boards.

Their staves are 1/2" plywood, kerfed on the back and then epoxy-glued to the hull sides. Then foil faced insulation (not sure but it may be polyisocyanurate) is friction fit between the staves (so no air there - they also didn't want them to squeak when the boat moved). The ceiling boards are then attached to the staves.

So, even if the ceiling were to have gaps, there would be no-place for air to circulate to. And also, foil would show through.

The ceiling is varnished ash and is quite nice (and light-colored).

This is me talking now, and not Charlie, but when I was researching-then-building a dwelling, I found that when it comes to enclosed, insulated cavities, you either need to have good air circulation (probably best, when practical), or no air circulation at all (or as close to that as possible).

Rachel

bcooke · Post by **bcooke** » Sun Jun 15, 2008 4:52 pm

You have to go to a sales rep for a price but I think I spent about $700 for two rolls of the stuff (4 foot wide and I don't remember how long). It also comes in 3x3 sheets. The ArmacellI used is not adhesive backed but uses a proprietory contact cement to stick the insulation firmly to the hull. It looks like regular contact cement and it works really well. There is certainly no air gaps between the hull and insulation and it is tough to pull off.

As for how much I used I really can't remember. A lot depends on how crazy you are going to go about it. I think the cabin area is about 20 feet long (x2) and freeboard is roughly 3-4 feet? So 160 square feet? I also went down below the waterline, under the cabin sole, and plan on adding it behind the galley and between the V-berth and anchor locker so I probably used more than most people would.