My father and grandfather were engaged In prospecting, logging, trapping, guiding
and similar occupations in the bush on the rocky Canadian Shield where small boats were used. Before
leaving the workforce I was employed in scientific computer systems. I enjoy dabbling in small homebuilt craft of minimal
cost and their associated numbers.
The design Is for a solo river and marsh boat. It is intended to be very manoeuvrable and to be light enough for
cartopping, portaging, and dragging over beaver dams in the many small rivers, creeks, and marshes which cover the northern
precambrian landscape. Propulsion is by way of oars used for rowing, poling, and paddling.
LOA |
13' 9.5" |
LWL |
8' 6.5" |
Beam |
2' 9" |
Height |
12" |
Weight |
62 lb |
Displacement |
300 lb |
Capacity |
238 lb |
Draft |
4.5" |
Freeboard |
7.5" |
Wetted surface |
20.75 sq ft |
|
|
Approx weight: |
40 lb - |
2 sheets plywood |
17.5 lb - |
0.635 cu. ft. spruce framing |
1.5 lb - |
screws |
1 lb - |
glue & edge sealer |
1 lb - |
paint |
61 lb total |
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Fastenings wood screws and glue, screws spaced 3" apart
-
112 1.75" #8 screws for gunwales
-
274 0.75" #6 screws for everything else
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metal oar locks as desired (3 shown in drawing)
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Scantlings:
framing cut from a 10' 1x12 board with .0076 cu ft sawn to waste.
-
gunwales 2 each 14' double thick .875"xl.5"
-
chine logs 2 each l4.25'x.875"x.75" beveled 26.39 deg
-
deck stringers 4 each l'x.875"xl.5" beveled 26.39 deg
-
deck spreaders 4 each 2.75'x.875"xl"
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hull spreaders 2 each 2.75"x.875"x2" ends beveled
26.39 deg
-
hull spreader ends supported on 3"x.875"x2" beveled
blocks
This boat has the same outside dimensions as a canoe but Is
the antithesis in shape. It was designed mathematically using a computer program to arrive at an optimal two sheet model for the
competition. A copy of the open source computers program can be taken from
file InverseLoonie.bas on https://www.ncf.ca/~ag384
. I hope you will derive enjoyment from using the computer program to
design boats of various sizes with this shape. As Barend Michelson points out, hull shapes can be truncated for different
uses. Hulls of this shape can be nested.
notes:
mathematics - the hull is cut from sheet goods using arcs of two
circles. It is analyzable mathematically using geometry and trigonometry to calculate angles, lengths, areas, and volumes.
The computer program displays construction measurements. It displays points on the arcs for drawing with a batten.
model - the enclosed taped seam paper model shows the shape of
the hull in three dimensions. It needs to be removed from its plastic wrapper and to have the edges pulled together as the tape
is folded over them. The edges may have to be pinched to take their shape.
construction - It may be obvious to note that the two sheets of
plywood can be clamped and cut together. And that one Side can be cut off and used as a template for the other. The boat is good
for either stitch and glue or beveled chine log construction. For completeness the design shows the latter. The bevel
is constant. Interior and exterior chine logs are equally facile to attach as there are no interior corners at bow or stern. Also
obvious, the chine logs are attached to the side panels first. The bottom panel is bent onto the sides. Quarter inch plywood
will bend to the bottom radius which is displayed by the computer program. The flat sides are lacking any extra strength from
bending so spreaders have been added 1/4 of the way in from each end. One foot is sliced off each end of the 16x4 butted plywood
to put on the ends as bow and stern decks. I'd suggest they be attached down between the sides at the level of the bottom on
beveled stringers. The bottom is slightly shorter than the sides due to the differing lengths of the arcs. The ends of the sides
can be rounded off to match the bottom. The computer program estimates the amount to be trimmed off but It is best to wait
until the bottom and sides have been joined. I like to drill holes in the decks or framing of small boats for painters and tie
downs instead of buying and screwing on deck hardware. The extent of temporary construction molds, if any, is left to the builder's
discretion.
propulsion - oars for rowing, poling, and paddling. I prefer to
buy inexpensive oars from a discount sporting goods store and reinforce the tips with fibreglass and resin. I prefer less
expensive marine polyester resin available from the same discount sporting goods stores, drilling small holes in the wood to help
he resin adhere. The oar tips will have to be built up at the start of each season. There are so many configurations and
preferences for fastening oars to hulls that I hesitate to specify one for the design. Metal oar locks are purchased with
the oars. They can be screwed right into the sheer as the sides are high enough to provide the required seven inches of
clearance. The oars will be used sitting and kneeling on the bottom. Eye elevation is helpful for viewing ahead in these
waters. A lightweight floating cushion/kneepad can be made from blue foam. For those who prefer a chest high oars they can be
fastened to sticks poking up above the gunwales. Such sticks can be pivoted on bolts through the gunwales to fold out of the way.
An oar can be hung outboard of the gunwales to be used for steering by mounting an oar lock on an extension of a spreader as
shown in the drawing. An interesting device is a U-shaped frame across the gunwales with a back rest in the base of the U and the
oar locks at the ends. This sort of device can slide along the gunwales for fore-and-aft trim, and it better braces the gunwales
at the right spot for rowing than do spreaders. It can serve as a carrying yolk when portaging.
Addenda;
a) drawing showing top, side, and end views
b) drawing showing material cutting patterns
c) sketch of boat
d) listing of computer program
e) taped seam paper model of hull shape |