Tom Cat- Carvel Built?

[TomFF]

I've been waiting to hear some scuttlebut on the article on Tom Cat in WB 176.

The 12'6" cat boat is billed as a "traditional carvel-planked boat over steam-built or laminated frames."

But in lieu of cotton pressed in the caulking seams they used thickened epoxy and the entire hull was coated with epoxy and glass cloth.

I've searched the forum archives for references to this procedure but found nothing on it. Have you guys heard much about this being done? What about those doing restoration? Anyone out there glass the boat instead of recaulking? How well does it work?

[WFK]

I have to be honest,....I've been waiting for this topic to come up. How could any one question some one with the background of Mr. Garden, but on this issue,.....I'll step out and do it. With all thats been written as well as shown about this method, I can't believe he'd do this. I suppose that you could look at it like it's a way to solve various issues that you'd have with a conventionally planked boat, plus coupled with the fact that I'm sure this will be a "dry sail" boat, meaning it'll be pulled after each sail, it could very well be around for many years. I personally think that under normal use, long term, this boat won't be around. Other than that,...she's a beaut!

Bill

[Fooler]

I think the key here is the Western Red Cedar for the planking. Being so soft, it will shrink/swell without putting large loads on the glass skin or the frames- its much more likely to crush its grain structure than snap a frame or start to shed the cloth. It would be a different game with harder/stronger planking.

Steaming/clamping the planks sounds like a chore- I'd strip it. ;)

[ 12-30-2003, 12:53 AM: Message edited by: True Grit ]

[rbgarr]

I think it will be great whether drysailed or not. I'd love to have this boat!

I had a Beetle cat years ago and the thin carvel planking lead to constant leaking, although of a minimal amount. I could have done without it, and this method seems fine to me.

[Aramas]

There were a number of boats built that way in Britain fairly recently, and they seemed to do rather well - until people started taking them to the Med. There are several threads on the aftermath on the YBW forums - suffice to say, several gaping cracks running the length of the topsides over an inch wide are not an attractive feature in a cruising boat. "Like the plague" is the phrase that comes to mind when I consider whether I would avoid a boat built that way.

I don't recall if the British boats were glass sheathed though - that may be enough to relieve the inherent tendencies, but then again, perhaps not.

Stip planking works well because the planks are narrow and consequently the strain (movement) is much less in any given plank.

[Todd Bradshaw]

I think True Grit may have nailed it on the head. My Star was western red cedar planks with glued seams (with some sort of a tongue & groove or shiplap-type joints). The WRC checked constantly. You couldn't sand and paint the thing fast enough to keep up with them. I finally diagonally veneered the topsides and dropped a layer of glass on the arched bottom which stopped it. In the five more years that I owned the boat it was dry-sailed and stored outside under a cover with no more problems.

[MAGIC's Craig]

This article was unable to detail many of the fine little touches Bill built into his cat. Up close, she is truly a gem , with a deep subtlety to her shape derived from Bill's far-ranging years of experience.

He gave a lot of thought to the planking and skin and I understand had the help of some of the Jespersen crew (who are not new to red cedar and epoxy construction) to handle the fairing/epoxy/ BID sheathing.

Vicky and I have, on occasion, come across Bill ghosting along in this wee craft, and it is inspiring to imagine being able to manage the same when (or if) I get to his age.

A lovely catboat smile.gif

[Fooler]

These days everyone thinks of quality wood as being CVG, while in the past it was more common to use flat sawn boards for planking. This would make for significantly less expansion/contraction in the planking, but would produce the checking mentioned above. Being an older fellow, ;) , Bill may have considered this in his scheme of it all. smile.gif

[Garrett Lowell]

What I'm interested in is the clamping method Mr. Garden employed after steaming the planks and clamping them to the frames to avoid having to do any backing out.

[siberianswampdonkey]

What's the point? Why not just build it strip with fiberglass sheathed over?

[Keith Wilson]

Around here, despite the conventional wisdom, glassing over carvel or batten-seam planking on small boats is pretty common, and generally sucessful. I think there are a couple of reasons for this:

- Thin planking, so that the strength of the wood-epoxy bond is larger relative to the expansion forces. I certainly wouldn't try this on a big boat.

- The boats are kept on trailers and the moisture content of the planking doesn't change much. Keeping them in the water all the time would probably be OK too, but that's not an option in Minnesota. The New England practice of hauling out for the winter would seem to be produce the largest changes in moisture content.

Soft planking wood doesn't seem to be an essential requirement. A lot of the boats done this way are old production powerboats planked in some sort of mahogany; much harder than red cedar. Perhaps the greater force from expansion is balanced by higher tensile strength of the wood; the failure mode of glass sheathing is often that the wood ruptures just below the surface, rather than the epoxy failing.

And one thing has always bugged me - why does the conventional wisdom say that a strip-planked hull expands and contracts less than an equivalent hull planked with wider boards? Assume three identical small boat hulls, one strip planked with sheathing both sides, one strip planked in the old way with frames and no sheathing, and one carvel planked. Assume that the planking wood is identical, and that the grain is oriented the same way in all three. For a given increase in moisture content, the change in girth of the hull will be the same for all three.

An old-style strip-planked hull is only restrained on the inside and usually has light stem-bent frames, so expansion may cause the hull to change shape slightly, increasing the curve to accomodate the expansion. As the planks dry, each seam opens less because there are more of them.

A sheathed strip-planked hull changes moisture content less in the same condiditons, a good thing because it is restrained on both surfaces.

Perhaps someone who knows more about the behavior of wood and caulking could enlighten us?

Maybe the reason they planked Garden's catboat carvel is that they had the wood and the skill, and it was easier and more fun. Strip planking tends to substitute drudgery for skill; a very good tradeoff in some cases. I don't see any reason it couldn't be strip planked.

[ 01-02-2004, 10:27 AM: Message edited by: Keith Wilson ]

[Aramas]

And one thing has always bugged me - why does the conventional wisdom say that a strip-planked hull expands and contracts less than an equivalent hull planked with wider boards? Assume three identical small boat hulls, one strip planked with sheathing both sides, one strip planked in the old way with frames and no sheathing, and one carvel planked. Assume that the planking wood is identical, and that the grain is oriented the same way in all three. For a given increase in moisture content, the change in girth of the hull will be the same for all three.
True, but the stress and strain is distributed over many more glue lines. As you pointed out, the hull fractures at the glue lines. If you ignore the planking in between and think of it as a chain of wood/glue interfaces that rupture at a specific strain (ie elongation) then the more links you have in the chain then the more strain can be accommodated before reaching failure mode.

It's not so much that the glue is stronger than the wood or vice versa - it's just a case of discontinuities causing stress concentrations at that point.

[ 01-02-2004, 10:07 PM: Message edited by: Aramas ]