Yacht surveyor and designer Andrew Simpson
cruises in his own-design 11.9m (39ft) yacht Shindig.
Read his blog at http://www.offshore-sailor.com
Monthly musingsMonthly musingsAndrew Simpson
The trouble with
tris... and cats
Why windage, width and sailing ability matter
T
he impact of catamarans and
trimarans onto the
recreational sailing scene
gathered momentum in the
1960s and 1970s. Names like
Arthur Piver, Jim Brown, Derek Kelsall,
and to a lesser extent this humble pen
pusher achieved various degrees of
prominence in those decades and the
future looked rosy for cruising multihulls.
The photograph that heads this page
was taken in Lowestoft. The occasion was
the 1970 two-handed Round Britain and
Ireland race when shades of black or
white were the principal photographic
options in common use. Mike Ellison and I
had just arrived in Lowestoft in a trimaran
named Three Fingered Jack. I had
designed the boat specifi cally for offshore
use and had stolen the 3FJ name from the
tug that brought Cleopatra’s Needle to
London in 1819. It embarrasses me to
reveal that portly fi gure on the foredeck
was me, luxuriously padded against the
hostile weather. After an obligatory
48-hour stopover, this was to be the start
of the fi nal leg to Plymouth where we were
to fi nish tenth amongst 20 fi nishers. At 26ft
5in we were by far the lightest boat in thefl eet. By comparison, fi rst over the line
was Ocean Spirit at 71ft overall while the
smallest boat with Mike McMullen and
Martin Read on board weighed in at 25ft
6in. We fi nished 16th, passing through the
breakwater into Plymouth Sound in the
early hours of the morning.
But, enough of nostalgia. There’s no
doubt about it that trimarans with their
relatively low profi les can deliver
performance and can sail offshore with
safety. But their beam makes them
awkward inhabitants of
crowded anchorages
and, perhaps more
signifi cantly, downright
unwelcome in marinas- some of which may
not have the space to admit them at all.
Recognising this problem, various
attempts have been made to produce
designs where the fl oats (some prefer to
call them amas) could be drawn in to
reduce the overall beam. A notable and
early example was the John Westell
designed Ocean Bird, the fl oats of which
were mounted on hinged structures
resembling a pair of steel gates.
Now, such contrivances worked
relatively easily with smaller craft, but
when size increases the problems ramp
up dramatically. The increased leverage
caused by extending the beam creates
huge loads that must structurally be borne- easy enough on smaller craft but
increasingly challenging as size increases.
In the current multihull world catamarans
and trimarans emerged pretty much
together but cats now outstrip tris by a
large margin. And it’s easy to see why. In
the days when swinging moorings were
the general choice, the area swept by the
moored boat was the same – length being
the determining factor. But the increasing
spread of marinas tipped the scales very
much in favour of narrower overall beam
in which non-foldable trimarans didn’t
score well.
Which is a pity. Having designed built
and sailed both tris and cats, it’s my
opinion that tris have an easier motion
when at sea. This is because a
catamaran’s buoyancy is located at
maximum beam causing the boat to
respond more abruptly to wave action. In
some ways a trimaran has more similarity
to a monohull, though of course the angle
of heel is much less. Also, since the main
accommodation is usually arranged
around the centreline there is less
slamming that might be subjected to the
underside of a catamaran’s bridge deck.
My recent sojourn aboard Shindig in the
Caribbean brought me starkly face to face
with a modern trend in catamaran design - some of which bear more resemblance
to larger powerboats than they do their
twin-hulled forebears. The tendency
seems to be upwards in terms of deck
layout – what might be described as fl ying
bridges having sprouted atop the more
conventional cabin-tops. Typically, they
have awnings even above that. This of
course means lifting the boom to an
appropriate clearance height – in some
cases somewhere
around a third of the
way up the mast. From
such a vantage point the
helming crew gets a
wonderful view of what’s
going around them but the extra windage
and invaded sail area can’t possibly
enhance their boat’s sailing ability,
particularly when beating to windward.
But no doubt this kind of design fusion
between sailing and motoring will gain
popularity – but not if you prefer
performance to luxury. In short I believe
that apart from the driving force the wind
provides, excessive windage is a curse
to multihulls.
Andrew Simpson
‘The tendency seems
to be upwards in
terms of deck layout’
Three Fingered Jack, an Andrew
Simpson design offshore trimaran