The Gougeon Brothers on Boat Construction - WEST SYSTEM Epoxy

146 Core Boatbuilding Techniques
have to worry so much about close tolerances as you
drill. Increasing the diameter by 1 ⁄4" (6mm), for an
annulus radius of 1 ⁄8" (3mm) makes the job of final
fitting the hull and keel much easier.
To drill the marked keel bolt holes, either use a drilling
jig or ask a few friends to help you do it by eye. In
either case, you need a drill which has a big motor and
in which you can chuck a large bit. <strong>The</strong> drill bit should
have a long shank: in some situations 20" to 30" (500-
750 mm) is an ideal length range. If you can’t purchase
drill bits that are long enough, have a machine shop
weld a shank onto a standard bit.
<strong>The</strong> main goal of the drilling operation is to make all
of the keel bolt holes exactly parallel, matching the bolt
arrangement on the keel. Although it takes some time
to fabricate, a drilling jig produces maximum accuracy.
<strong>The</strong>re are several ways to make jigs. One successful
and simple method is to drill a hole in a large block
of wood, using a drill press to make sure that it is
absolutely square and perpendicular to the bottom of
the block. Another method, shown in Figure 14-22, is
to start with two pieces of stock, saw a line down the
2 pieces of 3" x 6" stock squared and
carved with saw kerf down the center
of each piece
Saw kerf used
as guide for
worm on drill
Figure 14-22 A jig for drilling keel bolt holes.
Pieces
bonded
together
Hole for keel bolt drill completed
and jig set up for drilling
center of each, bond the pieces together, and use the
kerfs as a guide for drilling. You can also rout half-holes
in two pieces of wood and glue them together.
When you have made the jig, set it in the hull. Keep
the bottom of the block in a perfectly flat plane to
guide the drill bit as you move from hole to hole. To
establish a common flat surface for all of the holes,
clamp a thick sheet of plywood over the laminated
floor on which you are working and check it with a
level. Cut oversize holes in the plywood in the area of
the drilling so that you can locate the marks you’ve
made on the keelson or laminated floor. With the drill
bit itself as a guide, drill starter holes at least 1 ⁄2" (12mm)
deep at all locations in order to line the jig up correctly.
It’s a good idea to use a clamp or cleat to hold the jig in
place as you drill.
Although a jig is preferable, you can achieve reasonable
accuracy using a simple sight method to drill the holes.
This method relies on the coordinated efforts of three
individuals: one to do the actual drilling and two “directors”
to sight the position of the drill bit with the use of
levels. This method requires that the drill bit shaft be as
long as possible, permitting maximum visual accuracy
in lining up the drill. <strong>The</strong> two directors must be able
to view the drill, one from the front and one from 90°
to the side, using levels on end to sight and direct the
proper positioning of the drill. <strong>The</strong> driller stands where
he can see the two directors, who point out to him
the direction that the drill motor should be moved to
maintain a true vertical plane while drilling. <strong>The</strong> first
2" to 3" (50 to 75mm) of drilling are the most crucial
because from there on it will be very difficult to change
the direction of the drill. In order for this method to
work, the hull must still be on its lines and the keel
bolts must be oriented perpendicular to the waterline
dimension as they sit in the ballast keel.
<strong>The</strong> lining up of the keel bolt pattern, marking of holes,
and the drilling operation can all take place either on
the inside of a hull or on the outside (prior to turning
the hull upright). If you mark and drill from the outside,
the only added difficulty is that you must mark the
exact centerline of the hull and the fore and aft positions
of the various laminated floor members. You should not
remove the hull from its construction set-up before you
transfer these dimensions with the use of a long level,
both in the athwartship and longitudinal directions.