Building the Tunnel King - Part 3
by Matthew Green
Continued
The tunnel bottom (or top, depending on your point of view!) is installed.
The scarf joint can be glued before or after panel installation. Note: The screws are staggered to prevent splitting the tunnel
side cleats and bottom battens.
Link to additional photos at the bottom of this
page. |
Bottom Battens
The main longitudinals are four 1x2" bottom
battens. They run from motor board to bow piece and are attached to the solid
wood transverse members. At the transom, the batten ends need to be angled 10
degrees and left short of the main transom member to accommodate the tongue of
the motor board. Later, when the hull is turned over, angled gusset blocks are
fastened at the junction of each batten and frame member.
Tunnel Planking
The tunnel top (or bottom depending on your point
of view) is planked next; either 1/4 or 3/8" plywood may be used. The
tunnel planking should be a snug fit in the tunnel, so some trimming with a
plane may be necessary. Fasten as specified, being sure to stagger your screws
to avoid splitting the tunnel side cleats and bottom battens.
From now on, when you install plywood pieces on the
boat, make sure you wipe up the epoxy that squeezes out of the solid
wood/plywood joint. Simply taking a gloved finger and wiping it along the
joint, making a small fillet, works great. This is a quality touch and helps
keep dirt and water from being trapped in crevices, et cetera. Chipping away
dried epoxy blobs is not my idea of a good time!
The "hull" is now flipped over to allow
installation of the chine log and sheer clamp. Three or four people can easily
flip the boat over. At some point during this stage of construction, limber
holes should be drilled at the lowest point of the plywood frame gussets to
allow bilge water to drain aft. Forstner or brad-point drills should be used to
prevent splintering the thin plywood frame gusset.
Bow piece
The bow piece is made from two identical halves.
They are provided with the frame kit; otherwise they are made from a full-size
template provided. The bow piece is located by the bottom battens and notches
in the tunnel side panels.
Sheer Clamp
The sheer clamps are quite challenging to install.
They fit into notches in each of the frames and another notch at the bow piece.
The problem arises when you try to make the sheer clamp mate with the bow
piece. While they are at basically the same plane (the sheerline on the Tunnel
King is not curved), they are at diverging angles, and the bow piece, being
3/4" plywood, will not bend very much to mate with the sheer clamp. This
will be compounded if your sheer clamp stock is too stiff to bend easily (as
was the case on my boat).
Glen-L does not detail a procedure to ease this
problem. They suggest using a cross-brace between the bow piece ends the ease
their bending, but I didn't find this helpful. I ended up steaming the
sheer clamps into place, modifying the bow piece notches, and adding additional
blocking below the joint. As long as your joint is adequately fitted, fastened,
and blocked, I wouldn't worry if it isn't made in exactly the same
fashion or location specified. This joint must simply be strong and result in a
fair sheerline.
Chine Log
To further complicate the joint described above,
the chine log terminates at this point as well. The chine is notched over the
existing bow piece/sheer clamp joint. Like the sheer clamp, the chine is
notched into the frame members. I strongly suggest steaming the chine into
place. With my grandfather helping me, we steamed the chines, temporarily
screwing them into their notches, and clamping the forward end approximately in
place. After letting them "cure" overnight, we undid the clamps; the
spring-back was minor and overcome with hand pressure. As one person held the
chine, the other used square, bevel, and dividers to transfer the required
notch shape onto the chine. We then cut the notch with chisel and rasp. The
chines were then glued and screwed in place and blocking fitted behind them. It
should be noted that the hull is not particularly stiff at this point, so when
members are bent into place, they should ideally be done simultaneously to
avoid twisting the structure.
Fairing
Now that the "skeleton" of the lower hull
is complete, the chine log and sheer clamp must be faired and bevelled before
they can be planked. This is best done by filing (or "rasping")
notches in the chine and sheer at each frame at mating angles to the frame. You
them plane in between the notches, producing fair curves. A long-board will
help in this procedure as well.
Side Planking
The 1/4" side planking is installed next,
again scarfed as required. This piece need not be closely fitted; simply make a
somewhat oversize panel, glue and screw it in place, and then trim off the
excess. It was at this point in construction I switched to #6x1" screws
rather than 3/4-1" 12-14 gauge boat nails: I found I could more easily
bend the panel in place with one hand and operate the drill with the other.
Also, when doing final side panel trimming with a plane, I could easily remove
and replace the odd screw that was too near an edge; removing ring-shank boat
nails is extremely difficult.
Runner Bottom Planking
The 3/8" runner bottom planking (the bottom of
the sponsons) is installed next. You will find considerable fairing is
necessary on the bow piece and runner stems to make the plywood lay flat.
Glen-L details a tricky transition joint for the junction of the side planking
and runner bottom planking, but this is only necessary if the hull is NOT
fibreglassed. I assume you are building an epoxy boat, so don't concern
yourself with this step; concentrate on doing an accurate fairing job and
properly fastening the runner panels. You may find the panel pulls tight around
the runner keels and chine, but bows outward slightly between them, where there
are no fasteners. Weights and temporary blocks installed inside the sponsons
can be used to pull the planking tight to the frame gussets. This is important
to ensure the riding surfaces of the boat are flat. As before, I left the
panels slightly oversize and trimmed them after the epoxy had cured.
Bottom Finishing and Glassing
Congratulations, you have now fully planked the
hull of your Tunnel King! Your work has only just begun, however. Those
hundreds of screws holes and other divots must be filled, the plywood, if not
already epoxy coated, needs a prime coat, and everything will require LOTS of
sanding. I have some advice regarding screw hole filling on this boat: use the
hardest epoxy filler you can bear to sand because it will be subjected to high
compressive loads as the boat cuts through chop. I used an "easy-sanding
fairing mix", which was child's-play to sand, but after two seasons of
use, the filler (under a layer of 4 oz. cloth and epoxy), had compressed
1/16" or more, leaving these neat dotted lines of screw holes the length
of the bottom. I spent weeks under the boat grinding the depressions away and
refilling and glassing them properly. This is simply one of those learning
experiences and I hope future builders will avoid my mistake: just because the
product literature says a certain goop is suitable for a purpose in general,
does not mean it is suitable for YOUR project.
It's a good idea to go over the entire hull
with a long-board as part of your final sanding on the bottom filler. Keep in
mind the edges at the runner keels, chines, and transom MUST BE KEPT SHARP; you
may need to build them up if your sanding was excessive. Don't
underestimate the amount of time you will spend on filling and preparing the
bottom; I spent two weeks preparing for glass, and it was time well spent.
Now the hull bottom is ready for glass. Heavy cloth
or roving is entirely unnecessary and will only add lots of weight. I used 4
oz. "boat cloth", which only required about three coats of epoxy to
fill the weave. There are lots of other reinforcing fabrics available, but
since the cloth on the Tunnel King is not really needed for strength, many of
the fancy fabrics are unnecessary; feel free to use whatever you wish. I
strongly urge first time 'glassers to read up on this subject beforehand.
WoodenBoat and Glen-L are both good sources of material on wood-epoxy
fibreglassing. You will find covering the hull with glass much easier if you
break it into smaller parts. I did mine in four pieces: two from the centre of
the tunnel up to the inner sponson edges, and two more covering the sponson and
side planking. After glassing the bottom, the spray rails should be attached to
the hull sides.
Bottom Painting
Painting over epoxy is a much-debated topic, and I
won't get into it here. Sufficed to say, surface preparation is the key,
and make sure you select a paint that will cure over epoxy. I brushed and
rolled Petit Easypoxy over a fair, well sanded, and well washed surface, and
four seasons later, I'm still very happy with the results.
More photos
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