CAD DRAWINGS BY PAUL SPOONER DESIGN62 CLASSIC BOAT NOVEMBER 2017HOW TO READ LINES PLANS
sketch on a paper napkin in the public bar of a
waterfront pub. Irens, fully equipped with computer-
assisted design software (CAD) and all the rest, insisted
on building a model first so we could really see what she
looked like. How right he proved to be. We made a
second one, then got to work refining bulwarks and
other details, creating a fine-looking vessel that ate the
wind out of most opposition. The CAD came at the end.
Traditionally, once the model was finalised, the vital
shape of the boat was extracted from it. The essence of
this consists of the side-on profile and what are generally
called ‘sections’. These define the curving form of the
boat from deck level down to the keel at regular stations
along her length, taking in slack forward areas, wine-
glass midships sections and long runs to counter,
transom or double-ended sterns. They were deduced
either by sawing the model vertically across at right-
angles to its flat back face so that it was divided into a
number of sections, or by marking where the saw cuts
would have been and lifting the shape of the sections by
a process of accurate measurement called ‘taking off the
lines’. This system worked surprisingly well because, at
model size at least, the hull was known to be ‘fair’. You
could see this with your own eyes. Sometimes, ‘shadow’
sections (full-size mock-ups) were erected before the
final building began. If whippy battens were run around
these, any minor discrepancies induced by problems of
scale or the ‘lifting process’ were revealed. They could
be dealt with by eye before committing expensive,
well-seasoned timber to the saw.
When a vessel is designed on paper, the draft may
start with a sheer line and a general hull profile, but it is
those magic sections which make up the critical forms
that are chalked, full-size, on the loft floor for laying
out the frames. On the lines drawing, the sections are
conventionally shown fanning out from bow to
amidships on the right-hand side of the section plan
(the ‘body plan’) and from amidships to the stern on
the left side. It is theoretically possible to build from
them alone, but to proceed down such a path without
any further checking could be considered reckless.
Paper is a wonderful tool and a skilled draftsman can
perform marvels on it. Dr Harrison Butler, one of the
masters of design, insisted on paper of an extraordinary
quality before he would even begin, lest any movement
in the actual substrate generate the tiniest distortion in
his lines. In the final analysis, however, few can visualise
all the three-dimensional implications of a yacht’s
sections from a two-dimensional body plan. It is,
therefore, also both wise and conventional to fill in
certain details of the vessel in a plan view (from above)Previous spread:
GL Watson’s lines
plans for the
Royal Yacht
Britannia; and a
3D graphic of the
dierent
elements (below)three-dimensional types of yesterday. A profile
drawing is generally all that is offered, because a lines
plan would do little to improve on it.
Before this revolution took place, sailing magazines
rarely hit the news stands without at least one lines plan
of a new boat. Studied with an educated eye, these
revealed a great deal. They were pored over in yacht
club bars, scrutinised on kitchen tables by yachtsmen
home from the office, and generally assessed for the
nature of the vessels about which they spoke so fluently.
Today, the lines plan is largely the domain of the
classic yacht or working boat, yet many users of the
vessels we love have not had the benefit of exposure to
these wonderful documents from childhood, as had
our fathers and grandfathers. Unveiling the enigma in
a few words is not easy, but the apparent complexity
of a lines plan is easier to understand if seen in the
light of its historical predecessor, the half model.
Half models have been around since long before
designers first began drawing yachts. While naval
architects were drafting lines plans back into the 19th
century, half models were used until the Great War as
the primary arbiter of the form of a new vessel to be
built in what one might describe as ‘vernacular’ yards.
The builder and his client, perhaps a pilot or a
fisherman, would discuss the shape each thought best,
the builder would produce a half model and they
would meet again to reopen negotiations. Assuming
the first ‘take’ failed to satisfy, further models would
be produced, or the original modified until both
parties were satisfied.
I can personally testify to the success of this method.
When my small, 40ft pilot cutter Westernman was
designed by Nigel Irens in 1995, she started her life as aWaterlinesButtocksSections“Few can visualise the three-
dimensional implications of a
yacht’s sections from a two-
dimensional body plan”CB353 How to read lines.indd 62 26/09/2017 12:57