Semi-Dugouts; the New New Thing?
First, treat yourself and watch this 7-minute vid. It’s not only beautifully filmed and produced, it’s a miniature boatbuilding and history lesson. The Secret Life of Banka: https://www.youtube.com/watch?v=hZLLLjGu1do
The boat in the vid is a semi-dugout. The bottom of the boat is a solid chunk of wood, perhaps 4-5” thick and 12-14” wide at its maximum. The topsides and bow/stern are simple plywood-on-straight frames with gunwale and seats added last. This build technique is thousands of years old (though the plywood topsides are a bit more recent). The akas and amas are bamboo in this example, but could be anything; this post is mostly about the main hull.
This basic concept has been proposed here before, as a solid foam bottom hull, with plywood above. The “advantages” of the semi-dugout over plywood/foam are extreme low cost (this could be got out of a Home Depot 4X12 with a chain saw); also extreme durability. This boat will rot away to nearly nothing before it loses its structural integrity—will take dragging across beaches, even rocks, in perfect comfort. A mast step is dead easy; chisel out a mortise wherever you like, and just step the mast. The “reinforcing” is an integral part of the boat. Even a ball-and-socket mast step is a doddle.
The boat looks—and is—heavy, but if light weight is desired, the dugout portion could be carved to any thinness desired—even so thin it needs fiberglassing for protection. Semi-dugouts tend to have a rather flat rocker, but again, there are derivations; the dugout bottom can be short and the keelsons/stems long, or the dugout blank can be thick then heavily carved—again a chain saw job—giving more rocker.
Is anybody interested in this type?
like it a lot, also I think it’s easier working with wood then epoxy….
slap it together and go! if boats can be made fast, then they don’t have to
last long,
if they have a winch on the bow and a palm tree on the beach. 1 person can
beech it, then it may even last long…...
finally, in the next clip you could see what i would put on it….....
all the best.
Rael
I’m posting this for Rael because he says my anti-spam robot doesn’t like him anymore. I didn’t even know I HAD anti-spambots.
Thanks daveculp for the link! I really like this fast and cheap way of building a vaka. The “tree” can be foam, pvc/steel/aluminum - pipe or even rebar and concrete. All bent to whatever shape and rocker one wants.
Cheers,
Johannes.
Rael, thanks so much for the link. the transformation of the sculling oar with the line attached was *most* informative. I have spent a lot of time waving oars of various configurations around and essentially going nowhere. Steering was fine (in smaller sizes) but propulsion was a non starter so to speak. I suspect there will be another attempt when Nomad arrives.
Re the dugout, in a sense P52 was of that nature, bottom was 3/4” T&G subflooring ply cross grain w/ 5.2mm underlay ply sides. Never regretted the extra thickness of the bottom and blessed it a couple of times in situations involving oyster shells.
The Banka video was most excellent, thanks.
Cheers,
Skip
Rael, thanks so much for the link. the transformation of the sculling oar with the line attached was *most* informative. I have spent a lot of time waving oars of various configurations around and essentially going nowhere. Steering was fine (in smaller sizes) but propulsion was a non starter so to speak. I suspect there will be another attempt when Nomad arrives.
Though I have never sculled an inch so cannot verify; I was taught decades ago about the rope trick. The rope sets the handle’s height so all the force goes into propelling the boat, not lifting your hand. The biggest aha! for me was that you don’t pull the oar with the rope, but you DO “lead” it with the rope—which sets the angle of attack the right way and the right amount—pull harder on the rope and the AoA increases; lighter touch = less AoA. It’s a guide though, not for the main force, or you will quickly blister your hand. Or so I’ve been told…
Dave
Rael, thanks so much for the link. the transformation of the sculling oar with the line attached was *most* informative. I have spent a lot of time waving oars of various configurations around and essentially going nowhere. Steering was fine (in smaller sizes) but propulsion was a non starter so to speak. I suspect there will be another attempt when Nomad arrives.
Though I have never sculled an inch so cannot verify; I was taught decades ago about the rope trick. The rope sets the handle’s height so all the force goes into propelling the boat, not lifting your hand. The biggest aha! for me was that you don’t pull the oar with the rope, but you DO “lead” it with the rope—which sets the angle of attack the right way and the right amount—pull harder on the rope and the AoA increases; lighter touch = less AoA. It’s a guide though, not for the main force, or you will quickly blister your hand. Or so I’ve been told…
Dave
The Chinese have a much simpler and said to be efficient take on the sculling oar with the yuloh
See
http://www.ayrs.org/Catalyst_N34_Apr_2009.pdf
I use a yuloh on my Siren daysailer. It’s a great way to move out of an anchorage early in the morning without waking anyone. With the centerboard down and the tiller lashed, I can steer with the yuloh while sculling. Realistically, I can move the boat at about 2 knots for an hour before I get tired or blisters form on my hands.
When I finish my proa, I will build another yuloh to suit it. The geometry is very different from the cockpit of a plump little sloop, so I’ll need to think about it first.
like it a lot, also I think it’s easier working with wood then epoxy….
slap it together and go! if boats can be made fast, then they don’t have to
last long. If they have a winch on the bow and a palm tree on the beach. 1 person can
beech it, then it may even last long…...
Thank you, Rael. It occurs to me that with stitch-and-glue technology, all of the frames might be eliminated as well, getting rid of all the tricky mortise and tenon joints. Just cut the rabbet (rebate) into the edge of the dugout portion and glue/nail/stitch the plywood right to the bottom plank. Add gunwales and you’re done—the akas will keep the hull from panting; you’re DONE. Nice boat. 😉
OK, you’ll maybe want a couple of cleats to take the seats, and some reinforcing for the aka mounts (think about just taking lashings down through holes in the dugout plank and back up, then caulk these after lashing)—No bulkheads. Maybe a couple of simple compression members (don’t call ‘em frames!) just glued to the plywood to hold their position.
The real beauty of the dugout form, it has finally occurred to me, is that the big chunk of wood serves as the real “backbone” of the boat, as well as beaching protector, etc. It can take all the structural loads, both “live” and “dead.” So let it do its job.
It also occurred to me that, if even mildly skillfully carved, this chunk of wood might only weigh on the order of 30-35 lbs: Dry Doug fir @ 30 lbs/cu ft)—14” wide at widest, 15’ long for a 19’ finished hull, with a block coefficient of 0.55 and a net finished thickness of 1.5” For visualization’s sake, imagine it as a 15’-long, curved 2 X 12 with pointy ends. Plenty strong, and not particularly heavy. Could get it to 20 lbs if 1” thick, net.
Now add ~ 70 sq ft of 3/8” plywood at ~one pound/sq ft plus maybe 15 lbs of gunwale/aka reinforcement/stem/stern and we have an all-up weight of 105 lbs, not a heavy hull by any means.
FWIW, I found the attached looking at damage from Typhoon Yolanda in the Philippines. In the photo the people are standing on a dozen or more destroyed semi-dugout hulls. These are the complete dugout portions, you can see how thin and light they are. These are from full-size boats, likely between 14’-20’ overall.
Dave
Or how about this. Mold the keel/floor thingie with all of the mechanical features for the mortised ribs and stem, rabbet for the ply, etc. Make the whole thing out of vinylester and glass, just add plywood and lumber. And epoxy for mine, please.
Lots of people have made glass bottomed ply boats (Tom Jones’ Dandy, L7 Trimaran amas, among others) but few have taken full advantage of glass’ inherent capabilities to mold complex features.
Or how about this. Mold the keel/floor thingie with all of the mechanical features for the mortised ribs and stem, rabbet for the ply, etc. Make the whole thing out of vinylester and glass, just add plywood and lumber. And epoxy for mine, please.
Lots of people have made glass bottomed ply boats (Tom Jones’ Dandy, L7 Trimaran amas, among others) but few have taken full advantage of glass’ inherent capabilities to mold complex features.
Ha, I KNEW someone would take it in this direction! “If we just CNC’d the dugout plank…” Why not go a step farther and cast it as a solid block of “plastic wood” (Trex)? Even better, use 10 lb foam.—This is a form of Clark Foam (like for surfboards), but at 10 lb/cu ft density rather than 2-3. It is as hard—and strong—as oak, but at 1/4 the density.
Ignoring the “But that’s not quite a stone-age boat, Dave” argument, there is a potential play for something like this—you could manufacture the dugout planks anywhere in the world by the metric tonne, then send it anywhere else with a set of builder’s plans (how about cast right onto the inside surface of the dugout plank, to be sanded off last, before paint?), showing layouts for the plywood sides, all framing lumber and building tips? A relief movement—as with the Philippines today—could be reduced to a crate full of dugout planks, a couple units of stock standard plywood, another of 1x2’s and we’re all set. A complete neophyte could build a boat in a week, a couple of pros could knock out two-a-day, let the new owner paint it to suit.
Seriously (but the above IS serious!) But seriously, building the dugout plank of fiberglass has an issue; the beauty of the solid wood plank is its strength, rigidity and beaching tolerance, all without much time or money added. (I think I could knock one out in about 2 days’ labor with a skill saw and a single-bevel broadaxe or drawknife.
Cost of materials is very near zero; a hard-to-beat number. Building this of fiberglass brings in absolutely the worst attributes of that material—it’s weak without foam core, fragile with. It’s heavy and expensive if cast solid. It doesn’t take to beaches, let alone rocks very well.
Dave
point taken.
How about concrete with polystyrene filler and polyester fiber.
point taken.
How about concrete with polystyrene filler and polyester fiber.
How about just concrete? High steel content ferro-cement masses about 18-20 lbs/sq ft at 3/4” thick, which can be done (see Jay Benford’s “Practical Ferro-Cement Boatbuilding” He has hulls in there under 20’ long—100% ferro-cement) Be easy enough to build pipe frames for the topsides right into the bottom plank, welding them in place before plastering. Except for rust in these pipes (fill ‘em with concrete so it’s only the outside at risk)
Oops, strike that. Make the mortises round, then use something like this for cutting the tenons: http://goo.gl/NyvpjQ
The ferro cement dugout plank should outlive half a dozen sets of topsides. And before someone asks, it will take about 2.25 cu ft of styrofoam to make the boat unsinkable. 😉
This could be waaay more effective building the larger, ~35’ bankas in the Philippines.
Dave
Hi, I think this thread in another forum is closely related to the discussion here.
http://www.pinoyboats.org/forum/viewtopic.php?f=7&t=3042
Trent