Help support the WCHA Forums by making a tax-deductible donation!

Good intro book?

Discussion in 'Strippers, Stitch-n-Glue, and Other Wood Composite' started by ddewees, Oct 23, 2007.

  1. ddewees

    ddewees Woodworker

    I have a job this winter building a replica of a double-ended skiff of late 1800's vintage. It was strip-built originally, though put together with nails rather than glue. The owner envisions bead-and-cove strip construction, with fg cloth set in epoxy on the outside, and everything painted inside and out. Lofting and molds are already done. I have done some boat building, including a good deal of work on w/c canoes, but have never done much with strip construction. Can anyone recommend a good reference on basic building techniques?
    Don in Vermont
     
  2. Dan Miller

    Dan Miller cranky canoeist Staff Member

    Hi Don,

    Ted Moores "Canoecraft" is pretty much the bible on the subject. If you are planning to put ribs in it, then also latch onto a copy of John Michne's book about build Adirondack Guideboats. If you are not planning to rib it, then I don't think you can get away with omitting glass on the interior... Apart from some hard to find videos about Walter Walker, there is not a helluvalot about traditional strip building techniques.
     
  3. OP
    OP
    ddewees

    ddewees Woodworker

    Thanks for the information, Dan. The "bible" should be good enough, at least in this case! I am in the fortunate position of having the original boat available for study, so there will be some reverse engineering when questions arise. It is a 16' pike skiff, built by a local Vermont builder and used on Lake Champlain. The boat will have ribs (as does the original, of course), but pretty much for show. The tentative plan is to encapsulate the hull inside and out with epoxy - probably with glass inside, too - then glue in the ribs and coat them, then paint the whole thing to match the old boat. Lots of goo for a wooden boat replica, but it should be dry and low maintenance for a long time.

    I'll look for the books you suggested. Thanks again.
    Don
     
  4. Todd Bradshaw

    Todd Bradshaw Sailmaker

    Cedarstrip construction without the interior fiberglass is extremely weak, so the ribs better be plentiful and far more than just cosmetic or your boat will split lengthwise along any weak spot in the grain. Epoxy coating alone will seal the wood, but without the cloth it adds virtually no strength.

    The original edge-nailed (or sometimes doweled) cedar strip constructions generally used strips that were much thicker than the typical modern B&C canoe type.
     
  5. OP
    OP
    ddewees

    ddewees Woodworker

    Todd,
    Thanks for making the point about balancing forces on inner and outer surfaces of the hull - I'm seeing the same advice about glassing both sides in several sources. Assuming I do this, do you see a down side (aside from creating headaches for future refinishers) to gluing in ribs over the fiberglass to simulate the appearance of the original? As I mentioned, all surfaces are to be painted.
    Don
     
  6. Todd Bradshaw

    Todd Bradshaw Sailmaker

    I suppose that there are several options. I don't know anything about the design, but if you are using typical 1/4" canoe-type strips, keep in mind that if the hull is much wider than a canoe you may need to add something just to keep the bottom from bouncing. This kind of up-and-down flexing is really hard on the bottom and eventually leads to long, lengthwise splits down the bottom of the hull. The outside fiberglass is in the wrong place to help prevent it (in compression) so it's up to the inside layers and any other interior reinforcement to keep the bottom together (in many ways, the interior glass on a stripper is far more important and under more stress, in tension, than the outside fiberglass is).

    The lightest option on the inside is fiberglass with the resin neatly squeegeed on the surface to remove excess. It has the highest fiber-to-resin and strength-to-weight ratios. It also provides a non-skid cloth texture. Drawbacks are that the texture looks like fiberglass and can pick up dirt easier, down in the weave.

    Option #2 would be to add filler coats of plain resin on top of option #1 to hide the weave and then sand it to a smooth surface before painting. It would add some weight and you lose the non-skid, but you also lose the obvious fiberglass look. The sanding job isn't much fun, but without it it's hard to get a neat-looking fill job.

    As long as you're sure that you can get them down tight to the hull without water-trapping voids under them, ribs could be glued-in on top of the fiberglass layers (the filled, option #2 surface would probably make a nicer looking base for them). Depending on the boat's beam and bottom shape, ribs could also be a contributing structural member to help stiffen the hull in general and resist bounce. This, however, is where you tend to fall out of the known world and off into uncharted territory. Ribs and/or half-ribs have been added to over-sized strippers as stiffening aids since the early '70's, but I don't think anybody has ever sat down and figured out a foumula for how big they need to be or how many need to be installed to gain a particular amount of strength and stiffness.

    "Cosmetic" ribs, as thin as 1/8" would probably have big enough shadow lines to give the visual effect that the boat is ribbed, but the inside fiberglass layer(s) would need to be heavy enough to do the bulk of the structural work. Thicker ribs (like W/C canoe ribs) are big enough to be structural, whether you add a few to beef-up the glass, or space them like a canoe and eliminate the fiberglass. Deep, narrow ribs (like guideboat ribs) are certainly structural. Spaced a few inches apart, you could likely eliminate the interior fiberglass.

    I'd love to be able to tell you exactly how many layers of what weight of fiberglass and what size and spacing of ribs might be needed to build the various options, but as far as I know, that information hasn't been figured out yet for stripbuilding and different bottom beam measurements and differing amounts of roundness or flatness in the bottom shape will also effect the potential answers. I'm sure that the job is do-able but you may be inventing the technology for that particular boat as you go.
     
  7. garypete

    garypete LOVES Wooden Canoes

    Epoxied-in ribs

    I built one strip canoe that had FG cloth and epoxy on both sides of the hull, then had cedar ribs epoxied into the interior.

    I found it necessary to steam bend the 1/4" x 2" white cedar ribs using the epoxied hull as a female mold. After a couple days to allow the ribs to dry in the hull, I marked precisely where each rib was bent into the hull. That told me exactly where I should place each rib when I epoxied the ribs back into the hull.

    I used thickened epoxy on the outside curvature of each rib, forcing the sanded, ready-to-varnish ribs back into their original position in the hull and securing them near the sheerline with clamps. The fit was pretty good on each pre-formed rib except at the very bottom of the hull at the centerline. As I pushed down harder to get each rib into intimate contact with the hull, the rib would sometimes buckle up away from the hull at the centerline. Applying pressure to each rib near the centerline where it wanted to not lie flat required some creative and jerry-rigged push sticks attached to "temporary" thwarts. Sueezed-out epoxy was wiped up neatly, giving a finished appearance.

    The final result looked OK but the process was really labor intensive. I found that even though I could get by with only 4 oz cloth on the inside, there was no weight savings as I had to roll on several filling coats of epoxy resin so the weave didn't show, as Todd alluded to above.

    I sold the canoe, so don't know how the ribs fared as far as staying in contact with the hull. I suspect that the varnished ribs might swell with water exposure while the epoxied-encapsulated hull would not, possibly creating big sheer forces that might break the hull/rib epoxy bond.

    Good luck.

    Gary
     
  8. OP
    OP
    ddewees

    ddewees Woodworker

    Further thinking on ribs

    Gary and Todd,
    Thanks much for your thoughtful responses, and sorry I was not paying attention to this forum for a few days. I'll start by admitting that its early enough in this project that I haven't yet focused on details, such as the dimensions of ribs in the original boat. Most of these double-ended rowing boats - similar to the livery boats seen throughout the NE in the late 1800's - had hardwood ribs with a half-round profile, pretty closely-spaced. The Rushton pulling boats had ribs like this, and so does the one I'm copying. The guy who is paying for this will want it to look like the original, so I expect to duplicate the rib detail (except for fastenings, I suppose.) So, back to where this started: maybe it should be ribbed out for real after the hull is fiberglassed on the outside but only faired on the inside (no cloth, but clear-coated with epoxy). If the ribs were good enough to hold the loose basket of strips together in the old boat, wouldn't they do the job of balancing out the forces exerted by the fg on the outside? The only difference would be that they would be glued in (albeit with considerable labor, as Gary notes). Any thoughts?
    Don
     
  9. garypete

    garypete LOVES Wooden Canoes

    Glued Ribs

    Anytime a small open boat or canoe hull gets epoxy on the outside and only varnish on the inside, there's a potential problem if the inside gets wet in a rainstorm or a capsize. Contrary to what you might think, varnish is not a perfect water repellent and will allow some water through to the wood beneath. Wet wood swells, and can break its bond with fiberglass and epoxy. In fact, I've separated a cedar/ canvas canoe that had been fiberglassed using this expansion principle. I sank the entire canoe in a lake for a few days to let the wood expand and the fiberglass/polyester peeled off in one large sheet.

    The problem with differential expansion caused by epoxy encapsulating just one side of the hull might be solved by also epoxy encapsulating the inside planking and ribs. Experiment first with brushing your spar varnish over an epoxy coated piece of scrap wood. Some epoxies get an amine blush that might interfere with varnish adhesion to the epoxied planks and ribs.

    If your customer promises to keep the boat stored in such a way that rainwater will not stand in the hull for several days, I'd build the boat in the traditional way, put several coats of just good spar varnish on the inside, and use FG cloth, epoxy, and spar varnish on the outside.

    Gary
     
  10. OP
    OP
    ddewees

    ddewees Woodworker

    Encapsulation

    Gary,
    You'll note that I did propose to coat the inside with epoxy, though w/o the fiberglass cloth. Perhaps I should just go ahead and glass it inside and out, but there comes a point when the extra weight and the work involved may not be worth it if adequate strength and stability can be achieved by providing structure to support the hull (ribs) while sealing it against moisture (epoxy). I do expect that this boat will be well cared for, but intend to provide a decent product in any case.

    Thanks for the suggestions,
    Don in Vermont
     

Share This Page