Construction - I
The construction technique for the NIS 18 is similar to other
plywood designs. The shape of the hull is defined by the
bulkheads. The Tiki 21 and Bobcat were a "stitch and glue"
type of boats, where copper wire was used to hold the bulkheads
to the hull sections. The joints were then glued in with epoxy
and fiberglass tape. This technique is pretty simple and doesn't
require a building frame like more traditional wooden boat
building. The NIS 18 requires a building frame, so this
experience will be a bit different for me. The frame holds the
bulkheads while the hull pieces are glued on. Each joint is held
together by a cleat -- a piece of trim glued to both surfaces.
Since the boat is 18 feet long, it requires a technique to
attach several sheets of plywood together. Even some of the
bulkheads are too big to fit within a 4' by 8' section. I've read
a lot about scarfing and will use that method to construct the
chine logs and rails. But scarfing plywood at the recommended 8:1
angle requires a special tool and procedure that I'm unwilling to
undergo. Having used the butt-block method before, I am using it
here. It is simple, strong, and very quick to accomplish.
I have decided to make a number of slight deviations from the
original construction plan. Usually it's because I think it will
make my life a little easier.
The first is to glue the cleats for the hull on the bulkheads
before putting them on the strongback (the building frame). It's
just easier to do and it actually helps eliminate some of the
slight warping that is inevitable after each bulkhead is cut. I
was careful to make sure that the cleats didn't interfere with
the strongback components.
The construction plans call for 300 lbs. of lead as part of
the keelson, being thin strips glued and bolted to the hull. This
strikes me as being a true pain in the rearmost section, so I am
opting to distribute that part of the ballast internally. How
this is distributed will be covered later, most likely after I
observe the boat in the water.
There a couple of minor design changes I will make. First,
make the beam an extra 2 feet...no, just kidding. I am raising
the floor of the port head to the same level as the bunk. I don't
plan on putting a head onboard; I'd rather have the storage space/seat
on that side.
Taking a clue from the longitudinal bulkhead under the
cockpit, I'll be putting a similar bulkhead under the bunk. It
will serve to strengthen the both the bunk and the hull
underneath where it will probably be receiving the most
punishment. It also serves to provide more watertight spaces for
floatation. The extra weight overall will probably be around 20
Progress Report - Start to Apr. 1999
The first stage has been
mainly focused on 2 major steps: building the bulkheads
and the centerboard trunk. Including the transom there
are 8 bulkheads, labeled A through G (the transom doesn't
get a letter, it must have flunked high school athletics).
Bulkhead B merely functions as the forward cabin end and
doesn't extend much below the deck.
These images at right show
the bulkheads in order from the bow (at top) to the
transom. Bulkheads C, D, and E were too big to fit on a
single sheet of plywood, so I had to form them from 2
sections. I chose to match the sections together at the
reference waterline which is clear of any structural
A note here on waterlines. There are two: the
displacement waterline, where the designer expects the
boat to rest in the water when properly loaded, and a
reference waterline. Kirby has drawn the reference
waterline exactly 1 foot above the displacement one to
aid in measuring all of the different components and also
to lay out the boat correctly on the strongback. This
line, along with the centerline, is drawn on each
bulkhead on both sides, making further alignments easy.
The slot cut into bulkheads
D and E betrays the location of the centerboard trunk. It
is located 1 foot to starboard of the centerline. If it
was on the centerline, it would not only severely hamper
the area in the cabin, but it would also cut into the
cockpit. I remember seeing a beautifully kept catboat
many years ago at a wooden boat show in Port Townsend. It
looked especially sleek with low freeboard and
inconspicuous cabin. Unfortunately the large centerboard trunk come up
almost to the cabin top! I am thin, but it would take
someone even thinner to utilize what little space there
was below. Kirby has done a good job here to remedy this
problem without much detriment to performance. I don't
expect the centerboard to show above the waterline unless
the boat is pressed over 35° or more to port.
The funny notch in Bulkhead F is also centerboard related,
allowing the block and tackle that raises the board
to run back to Bulkhead G. Both F and G show the shape of
the cockpit and coaming. The cockpit seat is level, but
the floor slopes down to the transom.
Also quite evident from these bulkhead photos is the distinctive
sharpie hull shape known for ease of construction.
Here is a closeup of the
transom, looking at the inboard side. The glued section
is reinforcing for the gudgeons. The 2 holes are cockpit
drains. Just visible are the lines drawn for where the
cockpit will meet the transom.
This shows both sides of
Bulkhead E, the topmost being the forward side. Notice
the butt blocks for joining the top half of the bulkhead
to the bottom half. It is 6" wide so it overlaps
both sides by 3". The vertical buttblock is for
reinforcing. I plan to put a big U-bolt on the aft side
to use for safety harnesses. I figured that having some
extra wood there wouldn't hurt. The butt blocks at the
cabintop curve is common to all of the cabin bearing
Looking at the aft side of the bulkhead
shows the cleats glued for taking the hull sections. They
do not go to the corners because those will be cut out for the chine logs and
centerboard trunk bedlogs.
Again, the slot for the
centerboard is clearly seen. The other larger hole is to
provide access to an otherwise inaccessible space under
the cockpit. All the other spaces will be accessible from
hatches in the cockpit seats.
This is a picture of
Bulkhead D looking at the aft side. This shows the space
of the cabin interior. An additional cleat has been glued
on the port side to indicate the position of the seat.
This is the aforementioned floor that I decided to raise
for additional storage space.
I have not cut out the trunk
slot completely in this picture so the bulkhead would
retain some stiffness. Once the slot is cut the bulkhead
is pretty floppy. After it is glued to the trunk, though,
the stiffness will return.
These 2 pictures show the centerboard
trunk apart and together. The black interior is not
paint, but epoxy mixed with graphite powder to give it
some sense of lubrication. The interior width is 3/4"
and the board will be 1/2" so it won't be that tight
The extra height on the port side sheet is a
small change I made to the building procedure. Since the
port side of the trunk coincides with the cockpit, I
extended that section to the top of the cockpit seat to
give it some continuity and strength.
The hole you see in the aft middle section
is where the centerboard control line exits the trunk, and
that is also where Bulkhead E is located.
The curve of the hull was measured on one side, and the other
side was cut to match. The bedlog at the base of the trunk was
not bent, but glued on oversized and then cut to match also.
I had to do all of the glueing of the trunk on my kitchen
floor because it was too cold in my garage for the #2 Hardener to
The final part of this construction phase is to prepare
everything for being assembled on the strongback. Once I glued
together the centerboard trunk, I took the liberty of fitting the
4 bulkheads (C, D, E, F) on the trunk. Everything seemed to match
up correctly. I didn't see any glaring errors, which is good. I
made the cuts for the chine logs in the bulkheads and a few other
The next step is mostly a mental one. To say goodbye to all my
garage space before assembling the strongback. I won't see that
space again until I roll out a completed boat maybe a year down