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|
 I
grew up in
Northern Illinois, where lakes are plentiful
and many families own at least one boat. My father was an avid
fisherman, and he tried to pass that passion on to my brother and me.
He was successful with bro, less so with me. I was more interested
in reading a good book, and later in
speed (no, not the drug). Many of my friends had boats, and I owned a
14-foot runabout.
Most of our free time in the summer was spent either on water skis or
towing someone on water skis. I've always had an affinity for boats and
water, though I left it lie dormant for many years. The urge to follow
in dad's footsteps and build a boat has grown over the past several
years to the point where I can no longer ignore it. I don't have a lot
of room, and even if I did I'd be reluctant to take on a project so big
it would take years to complete. I decided on a plans for a KC 10, a
10-foot pram from designer Ken
Swan in Oregon. It's
large enough for a couple of people, relatively simple "stitch &
glue" construction, and it can be rowed or sailed.
Oddly enough, though I grew up with a need for aquatic speed, today I'm
not all that interested in a smelly, noisy, expensive, and
maintenance-intensive outboard motor. I like the idea of free energy
(wind in the sail) and exercise - in moderation, of course - with oars.
A 10-footer is small enough to
lug around in my pickup - no need for a trailer. As with all my
projects, I work on the boat when I feel like it, and then only when
other aspects of life don't get in the way. If you're at all interested
in this project, you won't have to worry about missing anything if you
don't drop in for a couple of weeks.
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Imported marine plywood can be had
in 5-foot by 10-foot sheets. No
local supplier in this part of the Great American Desert carries 5 x 10
sheets. ("Desert" implies a lack of water, hence a lack of demand for
boats, eh?) I looked into ordering
from suppliers on the East Coast and in Houston, but the shipping costs
more than doubled the price. Two sheets of 6mm (1/4") shipped to my
door would have been over $400, way more than I wanted to spend.
If I was going to build this boat I'd need to make my own 10-foot
sheets from locally obtained 4 x 8 footers.
The method of making long sheets from short ones is called scarfing.
The ends of both pieces are planed or sanded at a steep angle and then
epoxied together. Epoxying unscarfed ends of plywood would result in a
very weak joint, one that would probably break on lifting the piece off
the bench. Scarfing provides a much wider area for the epoxy to grab.
Scarfs are generally made in a 1:8 to 1:12 ratio. For 1/4" plywood, the
scarf extends for a minimum of 2" (1/4" times 8). I needed to scarf
four pieces to get two 4 x 10 sheets, so I ganged the sheets and
sandwiched them between two sacrificial sheets. When done right,
the ply lines should be parallel. This picture shows I'm almost
there, with just some fine tuning left. |
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A completed scarfing of two sheets
(one 8-foot and one 2 1/2-foot).
The joint would be strong
enough as is, but my instinct to over-engineer leads to a
belt-and-suspenders approach. Also visible is a 4-inch wide strip of
4.25-oz fiberglass cloth. The joint will have a strip epoxied to both
sides. It ain't coming apart. |
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A composite of two
photographs. I did a "pre-assembly" to make sure everything fit before
I start mixing epoxy. The bow transom is missing because I still had to
cut it out when this was taken. The 'glassed scarf joint is
visible about two feet forward of the stern. |
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The completed pre-assembly,
with a temporary spreader to better get a feel for the lines.
Everything fits, so now it gets disassembled, cleaned off, and
reassembled for the stitch & glue part. I was going to build the
boat in the garage, but with the onset of winter the temperature there
would frequently be below that recommended for curing epoxy. I'll be
doing the inside stitch & glue in the basement. By the time I
finish that, spring will be here and I can move the boat upstairs for
the exterior work. I just hope I don't have to cut the thing in half to
get it out of the basement. (Yes I've checked, and I think it will work.)
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Starting the final assembly now. I
had to use zip ties in a couple of spots to pull things together.
Plywood is not very cooperative sometimes. Note the two spreaders
instead of one in the previous photo. |
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This is the junction of
the bottom, aft transom, and port side. Bare wire in other than
18-gauge is hard to find. If I had 16- or 14-gauge I might not have had
to use the zip ties. On the other hand, my puncture wounds would have
been more severe. I actually like the zip ties better, but they
require bigger holes. I guess if you're drilling a lot holes in the
bottom of a boat it doesn't matter much if they're 3/16" or 1/4".
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Prior to filleting the inside seams
I masked the outside of each seam to avoid any gruesome problems with
potential squeeze-out. The bottom seams are more apt to cause trouble
if epoxy squeezes through, quite possibly epoxying the boat to the
bench (which would make it even harder to get the boat out of the
basement), but I was having so much fun I continued, taping up the
sides of the transoms. Limiting the squeeze-out also makes
it easier to shape the outside of the seams later for
taping. |
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The aft transom filleted and taped
with 4" x 10 ounce fiberglass tape. Working alone makes this a hectic
process. The first step is to lay on an unthickened coat of epoxy on
both sides of the seam. This acts as a primer, prewetting the wood so
it doesn't suck all the epoxy out of the tape, and allows a stronger
bond with the fillet. After the primer coat, thickened epoxy is laid
across the seam and smoothed with a round rubber spatula. Last,
fiberglass tape is saturated with epoxy and then laid over the fillet.
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Forward transom filleted and taped.
No turning back now, it either makes the bend out of the basement or it
becomes firewood. Just kidding - it's not a good idea to burn plastic. I had figured one hour, max, for all
the seams. Believe it or not, it
took almost
two hours to get the two transoms to this point, and I still have the
side seams to do. |
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Side
seams are taped. I let the
epoxy cure for several days. It takes more than 24 hours for it to
reach full strength, and I've read horror stories of people
stressing a joint too soon and having it fail. I turned the boat
over, removed the wire ties, and radiused the outside edges.
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