CLASSIC BOAT APRIL 2016 45HISTORY OF HOLLOW SPARS
timber spirally around a central spine or mandrel.
Although McGruer had only built model spars before
1911, with comments from the experienced and
interested Reiach, McGruer and his son (also Ewing)
continued to develop the idea.
Eventually opting for removable metal tube mandrels
over which the plies were glued, the results were very
promising. In 1915 they registered the first of their
patents and established the McGruer Bentwood Hollow
Spar Company in Lambeth (and later Gosport). Cutting
the plies of clear spruce, with the grain at 45 degrees, the
round, oval and streamlined (pear-shaped) spars and
struts they produced were lighter, stronger and more
stable than anything else available.
In about 1916, via the Airship Department of the
Admiralty, they were introduced to a key factor in
perfecting their method: a ‘cold setting’ glue invented by
O. Messmer of Basle in Switzerland called Kaltleim (later
sold as Certus), which made production easier and the
spars more reliable. Casein was, in particular, more
moisture resistant than many of the earlier glues.
McGruer spars were used in aircraft (wing struts on
the Vickers Vimy bomber), as well as radio masts,
billiard cues, stretcher poles, organ pipes, walking stick/
tent poles, and shovel handles for the 1924 Everest
expedition (on which Irvine and Mallory were lost).
The largest spar made by the method was a boom for
the King’s yacht, Britannia, in the winter of 1920-21.
Britannia had had a steel boom when re-rigged for
cruising in 1901, which subsequently kinked and finally
broke when racing at Deal in 1920. McGruer wrote that
the replacement was 85ft long and 17in diameter;
having made one for Lulworth (Terpsichore) at 16in,
and priced Britannia’s accordingly, he was persuaded by
the sailmaker Tom Ratsey to add an inch “for the King
you know, my boy, better be safe”.
BERMUDAN RIG
McGruer’s bentwood spars probably represent the
pinnacle of wooden strut and spar development. They
had some disadvantages; they were always expensive to
produce, locally heavier wall thickness for fittings and so
on was very hard to achieve, and only simple tapers could
be accommodated. McGruer wrote that it was really only
economical to build spars on this method if there were
several made on the same mandrel, and developed what
he termed his “four piece” method for one-off spars,
which was a refinement of the hollowed out method.
Rare examples of his bentwood spars still survive and are
testament to the methods he developed, and the skill of
his workforce, many of whom were women. Demand for
the more lucrative repeat orders such as wireless masts
evidently tapered off, and the company eventually went
Two crew tying
in a reef on
Britannia’s
McGruer-built
boom in 1921.
This was the
the largest spar
made by the
cold-set methodinto receivership in 1933, the yacht spar business being
insufficient to keep it going. By that time, the bermudan
rig was well on the way to near universal adoption, a
process facilitated by the growing reliability of hollow
masts that encouraged rigs to get taller.
Ironically, given that it was an American who brought
the hollowed-out method to perfection, Nathanael
Herreshoff tended to prefer the barrel-stave system for
his spars. His son, L Francis, claimed the method was
invented by his father c1906, which cannot be correct if
the descriptions of Steven’s spars for Maria in c1845-50
and others are accurate, but he did refine the method.
There seems little evidence that the progress made in
America gave him a head-start though; his 1895
America’s Cup candidate Defender had only a hollow
gaff, whereas GL Watson specified a hollow boom, gaff,
spinnaker pole and topsail spars for Valkyrie III.
The gelatine glues that L Francis says were used by his
father were still primitive, but the spars produced were
generally fairly reliable. L Francis himself developed a
‘four piece’ method (different to McGruer’s), making
spars out of rectangular boards with various treatments
at the corners. Among the tallest wooden masts ever
made was one for the 1929 J-Class Whirlwind that L
Francis designed. Of box form, and approximately 170ft
overall from heel to tip, the maximum section was
25½in x 16½in with a 2½in wall thickness.
Uffa Fox, writing in 1935 about Whirlwind’s mast,
noted: “Such a spar is possible only because of our
modern strong and waterproof casein glue, so strong
that the wood fibres tear apart before the glue parts.”
Still better glues were emerging; the various modified
formaldehydes were mostly developed between 1910 and
1940, including the well-known resorcinol types.
The International Rule, which was introduced for the
1907 season, had a generally negative influence on spar
building in Europe. The First Rule prohibited hollow
masts for classes above 10-M, but that only covered the
lower mast. Topmasts, booms and other spars could be