Answer Me This, A Goo Question?

[Dave Fleming]

I am as a green pea, well almost, when it comes to using goo's in boat building.
Though I have done a number of laminations over the years.
In another thread re:Arcs/Deck Beam Camber, the point was brought up about Plywood not bending in two directions.
I have observed the 'stitch and goo' method, the' plywood and goo' method and the' veneer and goo' method. I have this view that'plywood and goo' is acceptable for projects that are slim on compound curves and that' veneer and goo' are the preferred choice for more complicated shapes.
I use as an example of this thesis the book A Unit of Time a Unit of Water. Whilst the author has no experience in boat building he does record the methods used at Joel Whites yard on some fairly large vessels. And the articles in WB, on several designs including Whitehawk,seem to bolster that view
They are more conventinal round bilge shapes repleat with all the curves including compound. I saw no mention of plywood as a hull material in any of the those. So is it safe to say that the choice of hull design dictates the 'goo method' to be used?
To my eye t'would be correct but, lets hear it from the 'goo' fans.
:confused:

[Hugh Paterson]

Welllllllll, as a woodhacker and goo specialist, most often its down to the cost of the job, and the preferred construction method.
A lot of the building methods used say 20-30 years ago used pre-epoxy type glues. They in turn took a back seat when GRP/Fiberglass polyester resins came on the market, which in some cases took a nose dive in lieu of the epoxy resins. But whatever you employ from treenails to carbon fibre and pox they all have their ups and downs, you want to see the nick I get into when I have been using epoxy in large quatities for a while :confused: I now have to pop pills to control the blotches, needless to say I tend to avoid it as much a possible now. I am currently experimenting with Polyurathane glues from a caulking gun (Balcotan, Bison etc), good results, waterproof easy to work with, as long as you remember it has a short(ish) shelf life. That and rivets! :D See if you can find a thread or info on "tortured" plywood building methods, I think a couple of the Gartside designs might use it? One of his 15 ft rowboats comes to mind.

Shug

[gary porter]

Dave, there are alot of boats built with plywood hulls but when it comes to alot of curvature it does present some problems. I'm building my second Tolman skiff (21'+) which runs about 10 degrees at the stern and curves up to 30 degrees at the bow. The aft part of the bottom is 1/2" ply which will not make that bend. So, the forward 12' is made up of two layers of 1/4" and this works quite well. The two are scarfed to the 1/2" and laminated together. Plywood doesn't bend well in three dimensions but will bend in one and twist over a long run so it can work for some planking as well like in glued lapstrake situations. For things like frames and such its better to laminate veneer. Gary

[NormMessinger]

Plywood will bend in more than one direction if the plywood is thin enough and the bending required is not to much. The Sweet Dream canoe Lynn and I built over spring vacation is an example.

http://www.imagestation.com/picture/sraid18/p2b6e2373400dd6e7dc89b366c78c2f40/fdce4acf.jpg

See http://www.imagestation.com/album/?id=4291902377 for more of the project.

--Norm

[Hugh Paterson]

Custom skiffs, Thats one hell of a finish you get on those boats, lovely stuff, howzit done out of curiosity, epoxy and long boards? Poly build-up with a spray gun, tell us more? what does a finished boat sell for$$$$

Shuggie

[Hugh Paterson]

Good stuff Custom, bet yer arms hurt with the longboard or do ya have barmaid Biceps?

Shug

[Bob Cleek]

Well, if you are going to cold mold (strip plank as the limeys call it), which may be indicated in some instances, like when you want light weight, (which it isn't... but you might skimp on the framing some) you then have to rip all that stock, incurring considerable waste, and then spile all those strips, one by one, for every layer of lamination. Lotta work when compared to solid wood carvel or lapstrake planking, seems to me. Then there's the expense of the goo... which sure ain't cheap. It always seems to be six of one and half dozen of the other. There's no free lunch!

[Memphis Mike]

Skiffs, I know I am a rookie but I have read a lot and looked at a lot of pichures. I have
never seen that type of hull construction.
So the plywood is cut in thin strips and laid
out perpendicular to the deck to form the hull?

[Keith Wilson]

Back to Dave's original question, there are six ways I know of to build a boat with plywood, as follows:

- Plywood-on-frame, with or without epoxy & fabric sheathing (although these days most hulls are sheathed with glass and goop). "Traditional" plywood construction, the oldest method. Large plywood panels are fastened to wood frames and stringers. Hull shape is pretty much limited to curves in one direction, hard chines. No real limitation on hull size, within reason. The hull shape is defined by the frames, i.e. the plywood is cut to fit the frames.

- Taped-seam (aka stitch-and-glue, tack-and-tape). Large panels of plywood are fastened together at the panel junctions by various methods, and the seams are fastend together with fiberglass tape and epoxy. Hull shape is limited as above. Usually found on small boats, but some quite large hulls (40-50') have been built sucessfully this way. The hull shape is defined by the shape of the plywood panels, and the building form is usually minimal or nonexistent. Beginners often like this method because it doesn't require accurate fits (the sloppy seams are filled with goop) and just about every piece you cut goes into the boat.

- Plywood Lapstrake: Relatively narrow plywood planks are used to plank the boat over a building form. It's much like traditional lapstrake construction except that the laps are glued with epoxy rather than mechanically fastened. Frames can be reduced or eliminated, at least in smaller boats, because of the plywood's cross-grain strength (planks won't split),and the planks are thinner than in equivalent traditional ocnstruction. One variant uses an internal stringer along each lap. No significant limitation on hull shape. Usually used for small boats (can be VERY lightweight) but has also been used for boats in the 25' range at least.

- Tortured plywood: Sometimes sheet plywood CAN be bent into compound curves. This method is used with very thin plywood (1/8" or so) for light kayaks and canoes (see the Sweet Dream above) Seams are usually taped, and the shape of the hull is defined by the shape of the plywood skin. Perhaps it shoud be considered a subset of taped-seam construction?

- Cold-molding: This technique doesn't usually use sheet plywood. Layers of veneer are laid up with epoxy over an elaborate building form to essentially make the whole durn boat out of one single very curvy piece of do-it-yourself plywood. You can make almost any hull shape you can imagine this way, in almost any size. Frames are usually unnecessary. Very high strength-to weight ratio, lots of work, lots of goop. Sometimes a new cold-molded shell is built up over an old plank-on-frame hull.

- "Lapstitch", an unusual variation in which pre-shaped planks are wired together, much like a taped seam hull. However, there is a rabbet cut on the lower inside edge of each plank, so the planks overlap. Once the hull shape is establish, epoxy is dribbled into the lap joints to hold the whole thing together. The result is a glued-lapstrake hull without the need for a building form. This is usually restricted to kit boats where the planks can be cut out on a CNC router.

So there you go. I like ply lapstrake myself.

[Memphis Mike]

I didn't know you built anything that large
Custom. Pretty impressive!

[Bob Cleek]

Skiffs, no question that the developed design you are building is suitable for the construction method illustrated, and probably the best way to go under any circumstances. This is particularly true if the shape lets you get away with some 4' spans aft. Given the adhesives available today, it's a good way to go for that type of boat. My point, however, was that there is no free lunch... it is about the same work and cost either way... for each kind of boat suitable to the different building methods. What you are doing there is clearly cost effective and a good trade off for putting out a quality product into the marketplace. No question. On the other hand, if somebody is going to build a different hull shape, another method is most likely going to be more suitable and most likely that will be the method the designer had in mind when he drew it. Nice job, BTW!

[Donn]

:D

[Dave Fleming]

I'm digestin' I'm digestin'......
Keep the comments comin'.

[Meerkat]

Cleek;
Strip plank and cold molded are not the same, either here or in the UK. Strip plank uses squarish planks, often with a profile in the top and bottom ("bead and cove" or SpeedStrip<tm> a patent of Thompson in the UK). It was historically nailed and glued longitudinally over frames, but these days is primarily epoxy glued. Typically, the frames stay in the boat, but don't have to.

Cold molded on the other hand, uses thin wide veneers of wood that are stapled over a mold and then successive layers are stapled and glued over at different angles to the first layer (3 layers typical) and then the mold is removed.

FWIW, Cold molding has a bad rep in the UK, but they seem to use strip plank more then we do.

I bet you knew all this, but the "limeys" don't call strip plank cold molding! :D