Boatbuilder’s Notes
CRAFTSMANSHIP
Riven timber
Robertson screws
About 100 years ago the Canadian Peter Robertson invented
the square-drive screw, with a tapered socket in place of a
slot. Robertson’s contemporary slogan of ‘Drives like lightning’
was no hollow boast – it’s still a superb screw. Whereas
slotted screws are prone to burring under torque (see
right), the square-tipped Robertson driver finds its deep
socket instantly and holds firm to the last grunt. The screws
pictured above were salvaged from 70-year-old cabinetry
and are fit for re-use. Robertson screws are popular with
American boatbuilders but near-impossible to find in
Britain. A silicon-bronze type is available from the
US-based Jamestown Distributors. Robin GatesTEXT AND PHOTOGRAPH ROBIN GATESIn a less machine-driven age the small boatbuilder
converted locally grown logs into timber using a froe and
maul. The froe works by riving, that is splitting a log
along the natural planes of weakness where medullary
ray radiates through it like spokes in a wheel. The
L-shaped froe, with blunt knife edge, is started by resting
it across the diameter at a spot where it can get stuck
into rays on both sides of the pith and is then struck hard
with the maul – a heavy rough-hewn mallet.
A short log will soon split in two but a longer one will
require the froe to be repeatedly twisted by its handle to
open and ease the split forward. This yields halves which
are further split into quarters, eighths and sixteenths
according to the diameter of the log and size of timber
needed. The timber is then stacked between sticks of
the same species to air dry.
Riven timber has straight grain along its full length
which makes it stronger than sawn timber; where grain runs
out to the sides in sawn timber it is prone to break. Riven
timber also seasons with less shrinkage and distortion. For
applications subject to tension and compression, such as
the bent timbers of a planked wooden hull, riven timber is
the best. These small pieces of riven ash are ideal material
for spreaders and jumper struts under compression from
their shrouds and stays, for which ash has the particular
advantage of high shock resistance.(^1)
Driving the froe
into an ash log
(^2)
The log split into
quarters
(^3)
The froe splits
the log into
eighths and then
sixteenths
(^4)
Ash air drying
between sticks
(^5)
Straight-grained
riven ash planed
flat and square
Ring of fire
These days many screws are made on the moon. This is no giant leap of the
imagination but simply one small step of assumption. When a new screw head
disintegrates under tightening one assumes it is made of cheese, therefore a
lunar import. The screw is stuck halfway, like the Grand Old Duke of York, neither
up nor down. Having immediately taken steps to control the rising fury within,
find a sharp drill bit wider than the screw shank and narrower than the screw
head. Drill out the screw head without excessive pressure as you don’t want to go
through the head into the timber. When drilled out, the head will be a little ring
of hot metal around the drill bit end; remove it with a pair of pliers so as not to
burn yourself. Wind out any other good screws holding the timber down and
remove the piece of timber from the job.
Remove the offending screw shank with a pair of pliers. Or if someone has
been watching the whole mishap and you need to regain a morsel of credibility,
tighten your drill chuck on to the screw end and reverse it out. Will Stirling
ROBIN GATES
WILL STIRLING
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