Today, you can find an abundant number of kayak types easily available for purchase - so why build a boat yourself? I feel that following the generation of a boat from a bundle of wooden strips to a usable kayak is satisfaction per se, especially when it is based on the beautiful designs of historical kayaks developed by the Eskimos in arctic regions, and when the project culminates in the view of a completed frame, as you can see in the figure above. In addition, I was especially stimulated by the idea of introducing a special feature, forgotten today but evidently used in ancient kayaks, a deliberately generated flexibility of the boat's hull. The first part of my contribution (chapters Nr. 1-5) focusses especially on the latter aspect from a more theoretical point of view, including the considerations of how to construct the movable parts of the boat. In chapter Nr. 6, I describe the procedure I actually applied finally - perhaps a stimulation to those who enjoy imparting their own "spirit" on objects of their personal use.
When nowadays you ask a sailor, a kayaker or a surfer whether
a flexible hull might be advantageous, they all will agree that
a flexible boat is more sluggish and has a lower maximum speed
than a corresponding rigid one. A racing boat which has become
flexible, or "soft" is considered a spoilt one.
Given this point of view, it is amazing to note that hull flexibility
is being increasingly regarded as a potentially desirable quality
by those who study native boats from the coasts around the Aleut
Islands and South Alaska, considered to be among the most dangerous
areas in the world. In these areas the native Eskimos developed
a special type of kayak which, by general agreement, is considered
to be extremely well adapted to their difficult local conditions.
Specialists in these baidarkas (so named by the Aleut) noticed
a particular feature which led them to conclude that flexibility
had been incorporated deliberately into these boats (J. Lubischer,
ref. 6). Special bony joints, incorporated between the wooden
elements of Aleut baidarkas, allow small, smooth movements at
these junctions to occur. Different explanations have been proposed
in order to explain the significance of this stuctural feature.
The simplest explanation is the assumption that they had been
introduced in order to reduce creaking noises during exposure
of the boat to external stress (J. Heath cited by G.Dyson, ref.
5, page 23). There are, however, some arguments in favor of additional
specific functional benefits that such ivory joints might have
had.
As pointed out by G.Dyson (ref. 5, page 22ff.), one functional
benefit may have been an improved ability to cope with dynamic
stress caused by oncoming seawaves or waves coming from behind.
When the boat was hit by a sudden, strong wave, flexibility in
the construction induced by incorporation of the bony joints may
have helped to minimize the impact. In addition, when the hull
was exposed to extreme tension due to passing the trough, a construction
as light as that of the native Aleuts, could have withstood such
forces only by reducing the hull's stiffness.
As a third advantage to hull flexibility, early ethnologists and
recently J. Lubischer (ref. 6) proposed that speed may have been
the most important factor. "The waves represent more water
that has to be accelerated out of the way, at the expense of the
kayak's own momentum" (G. Dyson, ref. 5), an effect which
is expected to be greater in a rigid boat as compared to a kayak
which is able to bend over the waves. The effect of absorbing
frictional energy due to bending of the hull was thought to have
dampened the boat's speed, which then could have been minimized
by incorporating the friction-reducing ivory bearings in the baidarka
skeleton.
Quite a different (fourth) aspect of hull flexibility concerns
resonant behaviour, as extensively discussed and analysed by G.
Dyson (ref. 5). When the waves attain a certain frequency they
may cause resonant swinging of a flexibly built hull. This effect
is generally considered to be disadvantageous since it imposes
extrem bending forces to the hull. The effect of this mechanism
might have been lessened by using joints which allow the different
pieces to move with only modest frictional resistance.
With respect to hull flexibility there appears to be a fifth,
quite different role not adequately considered in the cited reports.
Flexibility might play a great role in laterally stabilizing the
boat. In contrast to a rigid one, when a flexible boat is running
perpendicular into a wave or when it is exposed to waves coming
from behind, its hull may not only withstand the bending forces
much better as pointed out above, it will also gain improved lateral
stability as explained in the following section.
In the classical calculation of a ship's uprighting forces, the
torque is determined by the interaction between the center of
gravity and the center of bouyancy (as determined by the geometrical
center of the immersed part of the boat). As a simplified rule,
the torque is determined from the cross section of the boat amidships.
In reality, however, it is the bouyancy of each section of the
hull that contributes to uprighting during tilting. The narrow
parts of the boat near stem and stern, however, have no uprighting
effects due to their more or less round shapes. The shape of stem
and stern gains importance, however, when the boat is running
into a wave or is taken up by a wave coming from aft. In a rigid
boat, immersion near the ends increases while that of the center
part decreases correspondingly. In this way the influence of the
broad, stabilizing mid part, and thus its overall lateral stability
is reduced.
In contrast, the stability of a flexible boat is not disturbed
when it may bend into the trough of the wave. Stem and stern bend
upwards and prevent the mid part from becoming lifted upwards.
This maintains its stabilizing efficiency. In addition, bending
causes the center of gravity to shift downwards in relation to
the boat's axis of rotation, which also improves its static stability
- similar to laying in a hammock.
When the boat passes the crest of the wave, it bends in the inverse
direction. The mechanism which stabilizes a boat in this situation
applies to both flexible and rigid ones. When on the crest of
the wave, stem and stern are lifted partially out of the water
and correspondingly, the midpart is immersed deaper. This increases
the role of the broad centerpart in regaining stability.
All these considerations led me to the idea of building a kayak
with hull flexibility. Since this feature was evidently incorporated
into those native Eskimo boats used under the difficult maritime
conditions of Alaska's coasts, it was logical to use a traditonal
model from this area as an example. The following description
refers to a two-hole kayak found near Kodiak Island which was
analyzed by John Heath in 1962; the plan is published as a drawing
in the article "Arctic skin boats" by H. I. Chapelle
(ref. 2) and available on an enlarged scale from the Washington
State Historical Society and Museum (plan BC-69, Fig 179, page
197; address: Ship Plans, Division of Transportation, Room 5010
NMAH, Mrc 628, Smithonian Institution, Washington, D.C. 20560,
USA).
The final result was a semi-replica rather than an exact copy
of the traditional boat with respect to shape and material. First,
I was forced to introduce changes into the cockpits since they
were not large enough when using the original dimensions. Second,
it soon became obvious that it would be impossible to get original
materials like leather as a covering or baleen for lashings. Therefore
I looked for alternative, appropriate modern materials of the
boat's skin and interconnections between the wooden pieces which
should maintain the beauty of the native Eskimo kayak while attaining
a predictable flexibility and strength which whould enable practical
use of the final product.
Before describing the construction actually applied, I want
to reflect on some general problems inherent in flexible constructions.
In building a non-flexible hull, the intention is to join together
all elements of the boat as fast as possible. In a flexible construction,
however, it has to be considered that the external bending forces
will induce movements in virtually all parts of the boat and,
in addition, these movements occur to quite a different degree
within the boat's skeleton. This point is of special significance
since it implies that the elastic property of each element, the
joints and the wooden pieces themselves, has to be adapted to
this specific demand. The aim is to construct the boat in such
a way that on bending of the entire hull, each element is subjected
to approximately the same percentage of its maximum bending tolerance.
When this is not considered and the single pieces are simply connected
somewhat loosely together, the following effects will result.
When the bending tolerances of the individual elements differ
dramatically, bending of the entire body affects that element
first which is weakest and - the general problem of flexible constructions
- this particular part of the body is subjected to indeed the
entire, undampened strength of the external force. Its maximum
bending tolerance is soon surpassed and it will break. The same
effect then applies to the next weakest piece, and so on.
Inadequately distributed elastic tolerances give rise to an additional
effect, which complicates matters further. When the external force
has caused the weakest element to break, the construction gives
way somewhat due to a partial loss of stability. When this occurs,
the external force's kinetic energy affects the next element in
addition to the static bending energy.
A simple experiment shall illustrate this mechanism. Take two wooden rods of equal size, structure and quality. Coat one of them with fiberglass/epoxy resin. Tie cords at the ends of the rods and fix the ends of the cords at firm points like a swing. Now load the rods at their midpoints with gradually increasing weights (take a bucket and fill it slowly with sand or water). Determine the weight needed to break the rods.
In my experiment the uncoated rod withstood a weight of 48 kg; that of the coated one only 34 kg! Why did the coating reduce the bending tolerance? The effect may be explained by the differing elastic properties of both rods which allow kinetic energy to develop to quite a different degree. When the weight begins to load the coated rod, the entire weight acts exclusively on the fiberglass coating. Due to its much greater stiffness, the wood does not support any of the weight in this phase. At a certain load the fiberglass coating tears, now allowing the weight to drop by a certain degree. In this state two factors gain importance. The wooden rod is forced to bend especially in that small section where the coating has torn (and where the bending tolerance is soon surpassed) while the remaining parts don't bend due to their still intact coating. Another cause of the observed difference results from the fact that the weight gains kinetic energy during the falling movement which adds to the static load of the weight itself. Both effects are expected to have caused the greater resistance to a load in the uncoated rod as compared to the fiberglass coated one.
The earlier considerations and the result of the latter experiment
reinforce the necessity of building a flexible construction such
that each element contributes to the support of an external force
with about the same percentage of its specific bending tolerance
during different amounts of force applied.
I intended to construct the hull in such a way that its stem and stern would be able to bend by about 10 cm up and down, respectively. Gunwales, deckbeams, stem, and stern should be joined firmly together since they are the basic constructional elements of the kajak and behave more or less as a freely swinging body. However, the deck line has to be able to shorten and the keelson line to lengthen during bending upwards and vice versa. In order to maintain this effect in the completed frame, the following connections had to be introduced (Fig. 1):
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| Fig.1. Distribution of joints introduced
into the baidarka skeleton. All numbered interconnections were
built from the elastomer Sikaflex 260® joints Nr. 2, 3, 8,
and 9 are made lamellar, Nr. 1 and 10 as sliding interconnections.
Arrows indicate direction of movements when stem and stern bend
upwards (the opposite direction on bending downwards).   |
During the sliding movements between deckstringers and deckbeams
(point 2), the bending energy should transfer from the stem and
the stern via the deckstringer to the cockpit coamings. In this
way the cockpits should act as circular springs which absorb oncoming
impulses. This principle required the lateral supports of the
coamings to be movable, too.
The question arose as to whether joints should also be introduced
into the keelson. All surveyers of historical baidarkas have stressed
the point that natives always built the keelson in three separate
pieces, in contrast to the gunwales each of which was evidently
made of one plank always. There appears to be general agreement
that this division contributed to flexibility. However, I don't
believe that the ability of the boat to bend up and down was the
fundamental purpose behind the split construction. As pointed
out above, the keelson line has to be able to shorten and to lengthen
during overall bending. The bending forces to which the keelson
is exposed during this process are rather small and a one-piece
keelson should withstand such forces without any problem. The
configuration of the keelson joints demonstrated by Lubischer
(Fig. 3 and 4 in ref. 6), might at best have served to absorb
any sudden impulses hitting the boat from underneath, but it appears
rather unlikely that they were constructed in order to allow lengthening
and shortening. When the keelson is bent upwards, the rectangular
parts of the joint touch each other and impede further flexing
upwards. Instead, I believe the keelson's split construction is
linked with the problem of maintaining lateral symmetry in a wooden
frame. A great problem of unsealed wood is its tendency to warp
with age and with changes in environmental humidity. When the
pair of gunwales is cut from one piece of wood with the grain
arranged symmetrically, as described by W. Brink (ref. 1), the
negative effects of warping are overcome. In the completed kayak,
warping of such gunwales will cause some flexion of the boat up
or down but no asymmetrical deviation will occur. This principle
of reciprocal compensation cannot be applied to the keelson, however.
It appears to be nearly impossible to get a piece of wood that
stays in line over time along a distance of 5 to 7 m. However,
this aim is presumably much easier to attain when the latter element
is divided into three separate pieces. Changes in the linearity
of any one piece will at least in part be compensated by its neighbouring
piece.
For this reason I decided to use wood which had been glued together
in two layers. This greatly reduces warping, and I did not introduce
joints into the keelson. Though I initially prepared three separate
pieces, I ultimately glued them firmly together.
The classical procedure for attaining a movable, yet extremely
firm connection between wooden pieces is to tie them together.
A certain disadvantage of this method is the possibility that
the joint's position may slightly dislocate and that creaking
noises may occur during later bending of the boat. My experiences
with silicone rubber led me to the idea of testing whether such
material might also allow the construction of a mobile connection.
To test the adhesive strength, I placed two pieces of wood parallel to each other at a distance of about 2 mm and bridged the cleft with different elastomeres. While one piece was kept firmly fixed, the other one was gradually weighted down (by fixing a bucket at the lower piece and gradually filling it with water); in this way, the interconnection was exposed to sheer stress of increasing intensity. The weight pulling down the lower piece was determined and expressed as weight per connected area. Most of the boat's interconnections could be expected to experience forces of similar magnitude during use. The different elastomers tested enabled interconnections of greatly differing strengths. I obtained the best results with the polyurethane glue Sikaflex 260® (Sika GmbH, Hamburg, FRG). With this material I determined a maximal tolerable load of 25kg/cm2.
Next the question arose as to how to apply the glue between the
wooden pieces in such a way that it did not restrict the previously
described principle of hull flexibility.
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| Fig. 2. Connection between hull stringer
and rib.   |
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| Fig. 3. Procedure for building the lamellar
joints (No. 2, 3, 4, 8, and 9 in Fig. 1). 1.: Front view of the
packed glass plates; 1a. and 1b.: side view showing laterally
the spacers and medially the elastomer which is pressed into
the medial clefts, then covered with a plastic foil. 2. and 3.:
After polymerization the glass plates are removed, the length
of the lamellae trimmed to 6 mm, a thin layer of the elastomer
applied to the surface of the wooden pieces which are to be joined,
and the pieces gently pressed together.   |
|
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| Fig. 4. Construction of the sliding joints
(No. 1 and 10 in Fig. 1). Cross sectional view during polymerisation
of the elastomer (left) and in the finished state (right); for
lateral view of the final joint see Fig. 5 and 6.   |
|
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| Fig. 5. Stem of the baidarka skeleton (upside down) showing the joint between stem and keelson. | Fig. 6. Stern of the baidarka (upside down) showing the joint between stern and keelson. | |
Before describing the process I followed in building the baidarka,
I want to share some considerations regarding selection of an
adequate covering. I reflected at length on this point. The skin
had to be sufficiently firm; I didn't want to be constantly afraid
of a stone or anything else that might cause a hole in the covering
during use of the boat. It also had to be applicable in such a
way that folds could be avoided, a precondition which soon led
to the exclusion of finished materials. Finally, it had to correspond
with the historical appearance of the entire construction. Although
attractive, I soon rejected the idea of using leather since no
adequate material was available and even if it had been, its durability
is inadequate. Only the use of textiles proved to be realistic,
which had to be impregnated after the sewing process.
Textiles I had available were 1.) a canvas-like, firmly woven
cotton (450 g/m2), 2.) a linen fabric (315 g/m2),
3.) a polyester fabric (230 g/m2), and 4.) a nylon
textile offered by G. Dyson (510 g/m2). The cotton
and linen textiles had the best aesthetic appearances, the others
looked somewhat "artificial" and synthetic.
The most important characteristic, however, appeared to be the
material's mechanical strength. In order to evaluate this feature,
I tested its resistance to tearing. If a sharp object such as
a rough stone or a shell comes into contact with the boat's skin
and penetrates the surface, the object will continue to tear at
the fibers and extend the initial hole into a tear. This effect
appears to correspond best with the forces to which the fibers
are exposed when the fabric as a whole is torn apart. Therefore,
I prepared samples of about 20 cm 10 cm and made a longitudinal
incision of about 5 cm in each. One corner was fixed with a tie
at a firm point; a second string was fixed at the other corner.
Then I stood on a pair of scales which I had placed exactly below
the fixing point and, while looking at the scale, I pulled at
the free string until the fabric began to tear. The final value
was calculated by subtracting my body weight from the weight indicated
on the scale at that point.
The following data (refering to uncoated fabric) were obtained:
1.) the canvas-like cotton: 9 kg, 2.) the linen fabric: 16.5 kg,
3.) the polyethylene material: 6 kg, and 4.) the nylon fabric:
more than 80 kg.
Before definitively selecting a material, I had to choose an appropriate
impregnation. G. Dyson experienced the most success with a neoprene
coating. However, it was impractical to have his material sent
because of the flammable solvent. Therefore, I had to run my own
experiments. I tested the following agents: 1.) linseed oil, 2.)
linseed oil primer, 3.) Latex primer, 4.) Acrylic primer, 5.)
Coelan ``Bootsbeschichtung®, 6.) and 7.) two ``GummilösungenÔÔ,
neoprene-based: Patex®, Henkel, and the polychloroprene kautschuk,
GXGQ 8802, Conti-Tech, Breslauerstr.14, D-37154 Northeim, Germany.
The first finding I made was that these liquids penetrated the
fabrics to significantly varying degrees. The low-viscosity solutions
1, 2, and 4 penetrated completely, agents 3 and 5 to a lesser
degree and 6 and 7 to the lowest degree. The latter compounds
formed a layer in direct contact with the material, however, they
could not diffuse into the closely packed bundles of fibers.
On first sight, the latter effect appeared to be disadvantageous
but testing the tensile strength of the impregnated tissues revealed
an unexpected result: The strength of the materials treated with
the completely penetrating liquids declined greatly. For example,
the canvas' resistance to tearing was reduced from 9 to 4 kg,
that of the nylon fabric from over 80 kg to 40 kg after impregnation
with Coelan. On the other hand, application of the neoprene coating
to the nylon yielded a result no less than 80 kg.
The most plausible explanation is the following: In the untreated
fabric, the tearing force applied causes a shifting in the arrangement
of the fibers at the point of incision such that tearing can only
occur when a greater number of fibers are torn at a point in time.
In contrast, when the fabric is impregnated, such a shift in the
weaving cannot occur. At a point in time the external force affects
only a few fibers, which tear under much less effort, one after
the other.
A different characteristic of a boat's skin is its resistance
to abrasion. In principle, this feature depends on the elastic
properties of the material: An elastic material yields when it
comes in contact with abrasive particles and the latter elements
lose their energy. In contrast, firm material is affected by the
undamped energy of the abrasive object. The effect is most evident
when sanding a piece of rubber and a piece of varnished wood -
the differences in the amount of material sloughed off are exteme.
Regrettably, I did not find a method for quantifying this factor
simply. On a qualitative basis resistance to abrasion was expected
to be best in the elastic materials, the Neoprene-based elastomeres
(Patex and GXGQ). Linseed oil and linseed-oil based varnish are
much less elastic. When exposed to greater deforming forces, they
become plastic, retract no more and soon tear. This characteristic
applies to Latex primer as well and is even worse in this respect.
Based on these findings and the observation that the material
doesn't undergo a reduction in resistance to tearing, I decided
to use one of the neoprene-based glues. Since only the compound
GXGQ formed a smooth surface when dry, I finally used the latter
material.
After describing some general physical principles and methods
to solve the specific problems that arise when a construction
needs to be flexible and firm at the same time, the following
section will deal with the procedure I actually performed. As
outlined above, my model was the two-hole baidarka, drawn and
described by J. Heath (ref. 2). In principle, the method of construction
should be applicable to other types of baidarkas as well.
In the event that somebody wants to build a boat using the description
given here, it should be noted that some details applied and described
on the following pages were not essential, but yet proved to be
quite helpful. (E.g., I used a helling and moulds as primary supports
of the frame). Also different materials may be substituted for
those used here, according to local availability. However, the
designer should consider the strength, weight and aesthetic appearance
of the materials. The reader is especially referred to the descriptions
of e.g. Ch. Cunningham (ref. 3) and W. Brink (ref. 1) who describe
the building of a one-hole Greenland-style kayak and an Aleut
baidarka, respectively. They give excellent instructions in great
detail in the handling and preparation of wood and coverings.
They apply the traditional method of tied junctions for connecting
the wooden pieces. In contrast to the present approach, however,
they do not focus on hull flexibility as is done here.
The first procedure I did was to transfer the plan I had obtained from the Washington State Historical Society and Museum to an exact 1:10 scale by photocopy, which greatly facilitated all of the following procedures (Fig. 7).
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| Fig. 7. Plan of the Kodiak baidarka as drawn
by J. Heath with the present modifications included (see text).
Arrows indicate positions of the deckbeams and cockpit supports,
respectively. Reproduction of the basic plan by courtesy of the
Smithsonian Institution, NMAH / Transportation.   |
Next I selected five cross sections (section Nos. 3, 6, 10, 14,
and 17) to prepare moulds. The diameter of the hullstringers (1.0
cm) and that of the keelson (3.0 cm) had to be subtracted from
the outlines of the cross sections (Fig. 8).
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| Fig. 8. Plan of cross sections (see Fig.7)
and of the moulds. Numbers correspond with No. of section planes
in the original drawing of J. Heath. They had the following distances
from top of stem: 91 cm (No. 3); 205 cm (No. 6); 317 cm (No.
10); 437 cm (No. 14); 544 cm (No. 17).   |
As mentioned above, I used a helling to facilitate the construction.
In principle, it consisted of four planks screwed together in
such a way that they formed a firm block of 15 cm 15 cm 400 cm.
Before mounting the moulds, I placed all plates on top of each
other and drilled small holes (4 mm diameter) through all moulds
at corresponding points (Fig. 8). I drilled 6 holes, two in the
plane of symmetry, and two pairs, 1.5 cm distant to this line
at the lower and upper margin of the moulds, respectively. After
having mounted the plates to the helling by the use of rods, their
correct position could be controlled by shining a light through
the respective holes. This test could be repeated whenever the
question of a shift in the plane of symmetry arose. This was of
special importance after the upper part of the boat was completed
and the frame turned around in order to enable a better mounting
of ribs, hull stringers and keelson.
I had straight-grained pine wood of 3.0 cm 1.2 cm and 220 cm
length available, which I could connect to each other by scarfing
and gluing with epoxy-resin. Two pairs of these planks of about
600 cm length were prepared for each side. Next, the position
of the ribs was taken from the plan, indicated on the gunwales,
and incisions of 22 mm (width) 10 mm (hight) 6 mm (depth) cut
into the outer side of the inner plank in order to enable the
attachement of the ribs to these holes later. The inner planks
were tied to the moulds at the respective incisions. No problem
arose with respect to bending the divided gunwales into the predetermined
shape.
I prepared the deckbeams from solid pieces of fir, according
to the dimensions given in the original drawing of J. Heath (2.85
cm 4.1 cm in the mid part, 1.25 cm 5.1 cm at the ends). I placed
the deckbeams at the following positions (see also Fig. 7). The
following data refer to the distance (cm) from the top of the
boat. 1.): 102, 2.): 154, 4.): 261, 5.): 336, 7.): 463, 8.): 513.
Deckbeams 3 and 6 were changed to cockpit supports (see below)
and were placed at 204 cm and 404 cm. After fitting their free
ends exactly to the inner surface of the gunwales, they were fixed
with epoxi resin, a median copper screw and two wooden dowels
of 4 mm diameter.
The medial parts of stem and stern were made of waterproof
plywood, 10 mm thickness. Next, using epoxy I glued solid pieces
of lightweight wood onto both sides of these plates. At the stem,
the maximum thickness was 8 cm, in order to enable cutting of
the specific shape of the stem. Recesses had to be created for
the connection with the proximal ends of the gunwales. The shape
of the stern was much easier to form. Planks of 10 mm thickness
were glued onto both sides of the medial plate and the margins
were rounded.
The connection of stem and stern to the gunwales proved to be
rather difficult. First I tried to trim the distal ends of the
planks such that they fit exactly to the surface of stem and stern.
After applying epoxy resin onto the interface, I tightened the
connections with screws. Since my sawing technique (by hand) was
not correct enough to attain exactly symmetrical oblique sections
of the gunwales, I did not succeed in arranging stem and stern
accurately in the plane of symmetry. Therefore I changed my procedure
as follows: I filled the (just unequal) space with epoxy-resin
thickened with microballoons to a creamy consistency. Then I adjusted
and attached stem and stern so that they were exactly in the plane
of symmetry. This task was made easier by use of the holes in
the bulkheads (see above). All pieces were then kept in place
until the resin had hardened. I applied the screws at the end
of this procedure.
I made the deck stringer from straight grained pine wood, (2.2
cm 3.2 cm), the same material used for the keelson. The proximal
section of the front part was formed by a separate strip such
that the result was a deepening between stem and proximal section
of the deck stringer (Fig. 7 and 11). The stringer was connected
firmly to the stem and stern with epoxy; to deckbeams 1, 2, 6
and 7 with lamellar connections as described above; and to the
cockpit coamings with the elastomer in solid form. All connections
between the deck stringer's mid-section and the deckbeams and
cockpits were also made with of solid elastomer (see also Fig.
1).
I sewed strips of ash-veneer, 2.5 mm 50 mm so that they formed a length two times the circumference of the coaming. After flattening both ends, I attached one end with clamps to long nails which had been positioned in a plate in the desired oval shape. The second layer was glued with epoxy resin and attached with clamps. The same procedure was applied to glue 4 layers of strips, 20 mm in width around the upper margin of the coaming. (In order to accelerate the latter procedure, I glued all layers in one session - a non-advisable approach!
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| Fig. 9. Cockpit of the baidarka showing
the modified supports which proved to be necessary for an easy
entrance and exit.   |
For hull stringers, I used pine wood which I could buy in strips
of 200 cm length, already cut to a half cylinder. They had to
be scarfed and glued together with epoxy resin and their edges
slightly smoothed by the use of a plane. With respect to the keelson,
I used straight grained pine wood, composed of two layers as described
above. Three sections were scarfed and glued with epoxy resign.
A plane was used to attain the specific cross-sectional shape
of the keelson. The finished hull stringers and keelson were tied
with cords to the points indicated on the moulds (Fig. 8).
After finishing the latter steps, I connected the keelson to the
stem and the stern. This procedure has also already been described
above.
Since my goal was to restrict the inner space of the boat as
little as possible, I wanted to build the ribs rather flat. Therefore,
I had to use a relatively firm wood. Again, I used ash, a hard,
yet elastic wood (veneer of 2.5 mm thickness). For each rib I
prepared two pieces of 20 mm width each which could easily be
bent without hot steam. Only the mostly curved ribs (1-5 and 37-39)
had to be bent with this method. Even these pieces were easy to
prepare, since simply immersing them in water of about 60C for
a few minutes was enough to enable proper bending. During drying,
the strips were held to their shape with tape.
Mounting was performed as follows (Fig. 2): In the first step
the elastomer was applied to the marked area on the hull stringer.
A small piece of cardboard (5 mm 5 mm 1 mm), placed just into
the elastomer, served as a spacer which prevented direct contact
of the wooden pieces that might occur during mounting due to clamping.
To prevent the glue from touching the wood outside of the joint,
I used tape. The outer layer of the rib was glued first and held
in place with small clamps. After polymerization of the elastomer,
the overflow glue had to be removed - despite the tape, an ennervating
task. It's possible that incomplete filling of the cleft, such
that no overflow could occur, would have sufficed also. The inner
surface of the outer stripe was sanded, the inner stip attached
with epoxy resin and its surface smoothed by sanding. The end
result is demonstrated in Fig. 10.
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| Fig. 10. Inside view of the baidarka towards
the stem.   |
Having completed these steps, the outer plank of the gunwales
could be mounted. In order to not interfere with the elastic attachment
of the ribs' ends in the gunwales, I used the elastomer for connecting
the outer plank of the gunwale with the inner one.
The last step in finishing the skeleton was to make the wood waterproof.
For this purpose I applied a thin layer of the epoxy-resin; only
one application was necessary. However, this material proved to
be less well suited than I had thought - the entire skeleton became
less elastic due to the spreading of the resin over the surface
of the elastomer joints. Strongly bending the entire boat greatly
restored the flexibility and taught me that a varnish which remains
soft, e.g. linseed oil, would have been much better. The finished
skeleton is shown in Fig. 11.
 |
| Fig. 11. The finished skeleton of the baidarka.
  |
The nylon fabric I ended up using is available in a width sufficient
for a complete enclosure of the boat. The sewing method I applied
was recommended by G. Dyson (ref. 4): a cross-stitch with two
threads. For a needle I used a strong, straight darning needle.
I sealed the border of the cut fabric with the GXGQ-glue. A few
minutes after its application onto the cut margin of the material,
the outer 2 cm of the fabric were folded. The fold stayed in place
due to the gluing efficiency of GXGQ - an advantage over the method
of cutting the fabric with heat (solding iron). - Adaptation of
the material to the boat's shape was excellent; therefore the
lengths of the sutures were relatively short and special darts
only had to be applied behind the back cockpit.
The application of GXGQ proved to be quite difficult. A prerequisite
is that no solvent (toluol) has evaporated before use, otherwise
an even coating isn't possible. During the application process,
gloves and an adequate gas mask have to be worn. The application
has to be repeated several times, as soon as the preceding coat
has lost its fluid consistency. Additional applications after
several weeks necessitate an intense sanding of the surface. -
When the layers are too thick, bubbles develop which have to be
carefully removed before the solvent has completely evaporated.
Primarily, the color of GXGQ is rather ugly: a mixture of gray
and green. However, upon exposure to light, it slowly changes
to a light brownish tone which gives the boat quite a natural
appearance. Each subsequent coating, however, attains a different
level of color; in other words, when it is applied only to circumscribed
areas, its extensions remain permanently visible thereafter.
After having finished the coating, I fastened a strip of nylon
material around the cockpit coaming. For this purpose, I prepared
strips of rubbered nylon, 1.5 cm wide. In the still uncoated material
I pulled out some fibers at a distance of 1.5 cm, applied the
glue GXGQ and, after it had dried, cut the fabric along the indicated
lines. These strips were glued around the cockpit coaming in three
steps, each separated by a phase of drying: 1.) attachement of
one end in the deepening of the coaming; 2.) gluing the remaining
strip while applying constant tension during the hardening process;
3.) gluing the end and the entire external surface of the coaming.
For seats I used waterproof plywood, of 2.0 mm thickness, which
I placed into the boat's interior. In order to prevent the plates
from shifting, I glued small pieces of wood (2 cm 1 cm 1.5 cm),
onto the underside in such a way that they exactly enclosed the
keelson, one pair per free space between the ribs. Each plate
was held in place by a screw and a nut. The scew with its head
fixed downward on the keelson (by use of a separate piece of wood)
was placed into a slot, that was sawed into the plywood along
its median line. In order to improve handling of the nut, I enclosed
it in a wooden knob. A cushion on the bottom plate and at the
cockpit coaming made the seat quite comfortable. I did not prepare
spray shirts by myself but had them individually manufactured
by a firm offering paddling equipment (Helmi-Sport, Neustadt a.Rbge,
Germany). -
The baidarka was ready to launch (Fig. 12)!
 |
| Fig. 12. The finished baidarka - on return
from launching.   |
When paddling the boat, it was pleasant to note that no blowing
noises arose when it passed a wave and its stem reentered the
water. It was a nice feeling to realize that the hull's flexing
movements in the feet which was due to the fact that on bending
up and down, the distance between seat and feet decreases and
increases. During these movements no creaking noises became discernible.
Although I have not yet used the boat under extreme conditions,
when paddling on a lake in smaller waves, it soon became evident
that the boat does not destabilize when its stem or stern is taken
up by the waves. The built model of a Kodiak baidarka is relatively
broad and one might argue that this feature caused the latter
effect. What I believe, however, and what I have confirmed in
these first experiences is that it is not so much the width of
the boat that has caused the described effect but rather the flexibility-induced
prevention of steady \emph{changes} in lateral stability, that
occur in a rigid kayak when passing through the waves.
These practically observed and theoretically postulated advantages
of a hull's ability to bend when exposed to external stress raises
the question why no greater interest exists in the attainment
of flexibility for boats other than baidarkas. With respect to
improved lateral stability, this effect is supposedly much less
important in other boats since it is attained by other means:
in sailing keelboats the center of gravity is placed beyond the
center of displacement and dinghys and surf boards are stabilized
by their relative shortness and extreme flatness. Therefore, I
suppose that flexibility as a stabilizing factor remains of special
interest primarily in those sea kayaks in which the center of
gravity lies above the waterline and which are rather long and
narrow. When boats like these light baidarkas are exposed to the
especially difficult maritime conditions as those of Alaska's
coasts stability appears to be a quality of greatest significance.
I would like to thank my son Thomas for installing the computer text program and for introducing me to its usage. I am indepted to Marie for reviewing the English style and to Anja for scanning the figures and arranging them in the text.
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