PVC stringers?

[Stephen]

Hi all,

I have been using marine grade plywood for stringers in the v berth to house Reflectix insulation and wonder about using PVC tubing of some sort when I get to the cabin are.

I read about its use and wonder what you think? It would offer the flexibility needed since the plywood was not such an easy method.

Stephen
Albin Vega 27
Vancouver, BC

[Ceasar Choppy]

What are you proposing to use the stringers for?

Stringers are structural so they shouldn't be flexible. But using PVC to support the fiberglass you would use to make stringers is perfectly acceptable since it is the fiberglass that gives the strength to the stringer and not the underlying material.

[Quetzalsailor]

Are you writing about stringers which are structural reinforcements or are you writing about 'nailers' for affixing an interior finish? Stringers could be anything (wood, foam, cardboard, half a piece of pipe, etc.) and, when overlaid by enough fiberglass, it's the glass doing the work. Such a stringer makes a dandy place to screw into for interior finishes. Nailers can be done similarly, or if made of a screw-holding material, can be bonded by epoxy to the hull. Look at my post in 'Questions and Answers', 'LeComte Ports' and you'll see plywood strips bonded with polyester and cork-filled polyester. Elsewhere in the boat, these strips are screwed into the inner lamina of a foam cored deck; elsewhere still, interior bits are screwed into foam cored stringers on the hull.

I see no advantage in using PVC pipe for either stringers or nailers; brittle, not all that strong or screw-worthy, heavy.

[Stephen]

Thanks,
Sorry I wasn't very clear - this is all new to me. The guy currently insulating the forward cabin (V Berth) is using 2 1/2" marine ply glued to one another to create the 1" space for 1/2" Reflectix insulation allowing for 1/2" gap for ventilation. He is finishing with Arborite over 1/8" plywood.

I was thinking that using PVC offer more flexibility for gluing to the hull when the time comes to insulate the main cabin. The guy I hired does not do glass work, and hasn't much experience with boats which is why we didn't do this I'm assuming that using glue is ok?

Any help is much appreciated.

Stephen
Albin Vega 27

[Rachel]

Hi Stephen, and welcome to the forum!

Okay, so it sounds like you are installing what I might call "cleat stock," vertically, then placing insulation between the cleats, and then ceiling over it (horizontal strips of wood).

I'm not sure I'd be comfortable with glued on plastic, but that would be something to check: the compatibility of the glue and the plastic, as in, would it really hold. I have seen people glue (with thickened epoxy) wooden cleats to the hull for this purpose.

Are you then screwing the ceiling strips into the cleats (I assume?). If so then screw holding power is something to also think about.

If you are fiberglassing over the cleats, then that is a bit different.

I'm thinking out loud here about the ventilation, and how that would work. Okay, so you have a continuous 1/2" gap inboard of the insulation. Next you have to get air to that gap so that it is moving air. If you leave gaps in between ceiling strips that would work, but then would you leave gaps with the insulation there to show through? (Maybe you are painting it white, or something?).

On the other hand, you could leave a horizontal gap at the bottom and at the top (running the ceiling without gaps), and get a nice chimney effect. But, if the strips go all the way down to the berth/settee flats, wouldn't the cushions block the lower gap and mess up the ventilation?

I'm interested in how you are doing this, as I could see myself attempting a similar project someday.

Rachel

PS: I have seen people do the whole insulation project with *no* air space, going on the theory that if no air can get in, you don't need ventilation. CharlieJ (a formerly active member here) did that on his boat. He used 1/2" plywood cleats, kerfed on the back so they would take a curve. He filled the kerfs and glued the cleats to the prepped, bare hull with thickened epoxy, then friction fit 1/2" isocyanurate insulation board. Over that went closely spaced varnished ash ceiling boards. The screws were not bunged, so although they don't plan to take it down, they can. They live in Texas and did the project a few years ago - no complaints (and they are out cruising now).

[Zach]

I've pondered ripping cellular pvc decking board (Azek is the trade name... the white stuff thats real flexible) into square cleats and glassing it in place. It takes epoxy, and is heat formable with a heat gun so no stiff legs or screws into the hull while the epoxy sets... and won't ever rot.

I have made some stringers out of PVC pipe. It sucks to work with when you go to glass it in. You have a round radius, on a hull that is warping in a convex curve. You need a huge fillet on each side to make the glass lay in nicely. A smear of cabosil on the first layer across the top of the tube doesn't hurt. I'll be grinding out what I did last fall and scrapping the idea...

I wouldn't use PVC pipe, as its screw holding power sucks unless its schedule 80 stuff... then its heavy and doesn't flex to the hull. I was using 4 inch tube... If you choose to use it anyway I found it easiest to rip on a bandsaw. Just build two fences that follow the angle the saw sets... push a straight stick through with a line drawn on it, follow the line, mark the side and use that angle rather than 90 degrees to the face. Now clamp two boards, one on each side equal widths apart.

Scribe a line across the inked words on the tubing if they are straight... just lay a long straight edge across them. The other way is to drill 3 holes equally spaced in a stick for pencils... Cock the rig sideways and let the middle one ride the top... that'll scribe your center line. The other easy way is to clamp a straight board to a bench, clamp the tube in the corner, then cut a piece of wood with a square cut out of it... L shaped, with a notch for your pencil at the apex... then ride it along the length. Pencils suck on PVC, but follow it with a sharpie.

The fences take a little tweaking to get right, the back side has to open up a bit to keep the tube from wanting to pinch down on the blade. When you get it right you could rip miles of perfectly straight, evenly cut stuff...

I guess you could use a full round piece, and pull a cabosil fillet the whole way around, but you'd burn a lot of resin in the process unless its a very small diameter.

I used a hot glue gun to stick them in place... If you are dealing with a real rank curve, 5 minute epoxy and cabosil would be a better bet. Let it set in the pot till it gets warm, add cabosil (acts like an insulator and makes it kick off faster...) then plop it in place. I found with the hot glue I didn't have enough hands to make it happen.

Cheers,

Zach

[Stephen]

I've got some photos of the insulation project in progress, this should make it easier, especially since I don't know many of the terms people are using. The one important term I've just learned is Kerfing. This really answers my issue with the stringers ability to conform to the hull.

http://picasaweb.google.com/VancouverVega


Stephen

[Rachel]

Hi Stephen,

Looking at the photos, a couple of thoughts come to mind:

1) Depending on what you plan to ceil with (ceiling being hull liner; material that will go over the cleats/insulation, such as horizontal slats of wood), the cleats look a bit far apart to me. Now, I'm not there, and I don't know your ceiling plans, so it may be just fine. I'm just bringing it up as a consideration.



2) I'm still not sure I see how the 1/2" gap between the insulation and the ceiling will work out, but again, I don't know the details of the rest of the installation and my doubts may be completely unfounded.

Maybe you wouldn't mind telling us about the ceiling details?

Rachel

...especially since I don't know many of the terms people are using.

PS: Speaking of ceiling (hull liner, on what would be the walls in a house): The surface above your head is the "overhead", the part you stand on is the "sole," and the "floors" are actually structural members beneath the sole (or were, traditionally - you may not really have them in a fiberglass boat; or at least not in the traditional sense, such as were in place on wooden boats). Whee! :D

[mitiempo]

Hi Stephen
I wouldn't use pvc for the reasons mentioned - excess weight and not good at holding fastenings. Kerfed wood is best, held on with thickened epoxy. The glue being used may not be a good long term idea. Even though kerfed the strips will still try to straighten so an adhesive that never gives up is best. And I know on none better than epoxy for this desired permanence. The other thought is that the gap isn't necessary. A gap between a hull and ceiling strips is necessary if there is no insulation, with adequate ventilation as Rachel posted. With insulation this gap isn't needed, so I'd put the inner liner right against the insulation. As suggested many use ceiling strips for the inner liner. It looks good and isn't as plain as arborite. Here's an example:

ps How did you end up doing with your electrical?

[Stephen]

Thanks for all the feedback.

As for finishing, we have left a 1/2" gap then 1/8 white laminate on 1/8 marine plywood.
That's the first I've heard of not needing a gap for circulating air.

When I insulate the main cabin next I'll "kerf" the plywood.

Stephen

ps will add more photos later.

[Rachel]

Hi Stephen,

I may not have been clear before in my musings on air circulation. I didn't mean that one does not need a gap for moving air, but rather that, if it were me, I would either want a way for air to circulate, or else I would probably go for no air at all.

From your description, I couldn't see how there would be any "chimney effect," or any way for air to circulate. For example, if there were a 1" gap at the bottom and a 1" gap at the top (running the length, fore and aft), then as air heated up in the "chimney" it would rise and suck cool air in from beneath, and you would have moving air. In my experience, moving air discourages mold and mildew, and carries away moisture.

However just having an air space, without circulation, seems to allow - or maybe even promote - mold, mildew and etc.

For me, if there were not going to be moving air, I think I would rather have no air at all, and eliminate gaps as much as possible.

I'm not an expert in this area, so I'm completely open to correction; but here you have my thoughts on it anyway.

Rachel

[mitiempo]

I agree with Rachel. If insulation is not used an air space is left between the hull and the ceiling strips or whatever is used to line the visible side. Ceiling strips will usually allow air flow between the strips and spaces can be left at the top for warmer air to escape. The air gap is the separation between the cooler hull and the warmer interior. But with insulation all examples I've seen don't have a gap between the insulation and the inner lining. Houses don't either.