Press Articles

A Modern Lass

The Moonen 84 may look traditional, but she is evolution at its finest

By Dudley Dawson

The newest delivery from Moonen Shipyards is proof that
the theory of evolution is valid, at least in yacht building.
Better yachts don't come from "big bangs," but rather develop
from the designs of successful predecessors. Far from
revolutionary, the 84-foot motoryacht Gogar Lass is a flush
deck cruiser with a round-bilge displacement steel hull,
designed for long-range cruising rather than speed. Yet there
are many clues that she is a step beyond previous launches
from the Dutch yard.

Based on Moonen's 72- and 83-foot motoryachts, Gogar Lass is
the second in the series, following the Moonen 83 Mimi, which
was launched late last year. Moonen is one of the few builders
still producing custom yachts under 100 feet, which allows
improvements on each individual design. With Gogar Lass, Moonen
set out to make a quiet design even quieter, and to improve
turning time with a feature seldom used on yachts.

When I saw Gogar Lass under construction in Hertogenbosch,
Holland, before she launched this year, that feature was one
of the first to catch my eye: a pair of Barke foil rudders.
Working on the same principle as the flap on an airplane's
wing or the articulating trailing edge of a high-performance
wing sail, the after third of a Barke rudder is a separate
piece hinged to the main portion of the rudder.

When holding a steady course, the flap is in line with and
forms a part of the overall foil shape. When the wheel is cranked
over, an internal mechanism forces the flap to a greater angle
than the forward section, yielding the hydrodynamic equivalent
of a cambered foil. This increases lift, or turning force, and
results in faster turns with a reduced turning circle diameter.
It also augments the effectiveness of propeller thrust when
maneuvering. As this provides some of the advantages of a stern
thruster without the added expense and complication, I think it
may make sense for other yacht builders.

Also apparent at the stern was a generous amount of clearance
between the propeller blade tips and the hull. The clearance
was about 30 percent of prop diameter; standard is 15 to 20
percent. The purpose of the extra spacing is noise and vibration
reduction, another of the evolutionary steps Moonen took with
Gogar Lass. The five-blade propellers are swept back with high
skew and include special unloaded blade tips to further reduce
hull vibration.

Carrying the propellers and shafts are oil-bath tubes welded
into single-leg struts. After these are fabricated, Moonen
technicians test them to ensure their natural frequency does
not correspond to the propeller blade or shaft operating
frequency, which could lead to excessive vibration.

Other components in the quest for quiet include insulation of
the engine and accommodation spaces and isolation of all
machinery from the hull structure on resilient mounts. Also
part of the program is operating the Caterpillar main engines
at their 1800 rpm reduced-horsepower B-rating, which will also
result in longer engine life. According to Moonen's sea trials,
sound levels at the 11.2-knot cruising speed are a subdued 59
decibels in the saloon, and less than half that in the
owner's and VIP staterooms.

Visits to Moonen Shipyards are always a pleasure for the
technically oriented. The company's managing director, Emile
Bilterijst, is a naval architect who delights in sharing
details of his yachts. Knowing that Gogar Lass was a
collaboration between outside designer Rene van der Velden
and naval architect Stolk Marimecs, I asked Bilterijst if
he also had a hand in the engineering. With a smile, he
quickly pulled out a binder filled with notes, charts and
graphs of such minutiae as sectional area curves and hull
coefficients.

Although Bilterijst doesn't prepare the drawings himself, it
is his continued attention to the basics of design that makes
yachts such as Gogar Lass possible. Her added propeller
clearance was achieved without excessive draft or hull
pockets by allowing the hull's lines to rise nearly to the
waterline aft. This, in turn, was possible only because of an
early decision to place crew quarters at the stern and locate
the engineroom, and its concentrated weight, closer to amidships.

The resulting hull is a full-bellied form with tapering ends.
This yields a relatively low prismatic coefficient for reduced
resistance at displacement speeds, appropriate to cruising yachts
such as Gogar Lass. As I sighted along the hull's smooth lines,
Bilterijst confirmed what I suspected. This is not a developed
hull form, which consists entirely of two-dimensional curves and
is easy to plate with sheet materials such as steel. Rather,
the hull has significant areas of compound curvature, requiring
more work but allowing a less restrictive shape.

Other Moonen yachts of similar size carry semi-displacement hulls
or planing hulls of aluminum, each appropriate to its speed. This
approach -matching hull form and materials to purpose- has long
been a hallmark of Moonen.

The yard delivered the 120-foot White Heaven III last year, but
most of its production is between 70 and 110 feet LOA. This is in
line with the yard's stated goal, to "create pocket megayachts of
the highest standard, combining traditional elegant styling with
today's requirements in terms of comfort and state-of-the-art
equipment." To fit a cruising yacht into a planing hull, for
example, just to save a bit of work or cost, or to utilize
existing designs or molds, is not part of the Moonen plan.

Even if a yacht is part of a standard series, as is the Moonen 84,
each launch has her own interior design, outfitting and equipment
package. Gogar Lass is similar to Mimi, but sports a clean minimalist
cherry interior, stained dark with a satin finish. Mimi has a closed
galley and a more formal layout on the main deck, while Gogar Lass
carries an open galley with a casual bar at the corner of the saloon
and dining area. Most of the joinery is constructed at the yard, so
special owner requests are no problem.

Gogar Lass carries eight guests in four staterooms belowdecks. The
master stateroom is amidships, shielded from the heat and noise of
the engineroom not only by a heavily insulated bulkhead but by the
master bath and a large hanging locker. A VIP stateroom is forward,
and two twin-berth staterooms occupy the space between.

The wheelhouse is separated from the dining area and saloon by the
galley and day head. As Gogar Lass is expected to spend many nights
under way, this will help keep light intrusion to a minimum. Full side
decks and lockers on the foredeck will allow the crew to handle docking
chores with ease.

Contact: Moonen Shipyards, (011) 31 73 621 0094

SPECS:

LOA 84'6"
LWL 76'0"
BEAM 20'10"
DRAFT 5'11" (half load)
DISPL. 243,000 lb. (full load)
FUEL 4,200 gal.
WATER 800 gal.
HOLDING 130 gal. black; 170 gal. gray
POWER 2x 385 hp Caterpillar 3196s
SPEED 12.3 knots max.

RANGE 2,800 nm @ 10 knots

  Back