76 AUGUST–SEPTEMBER 2019 | International Boat Industry ibinews.com
TECHNICAL
SECTOR SPOTLIGHT | STEERING & TRANSMISSION
afterwards, so the boat can still make a safe
port under reduced power. As such, we
sell a lot of units to commercial fishermen.
They often get ropes around their
propellers and these couplings help prevent
damage to the transmission. Many carry a
spare coupling as they are relatively easy to
swap out.”
The coupling itself is made from a time-
proven elastic polymer,
which Frith explains
is more effective than
rubber. “Rubber is
more prone to heat and
solvents, which is why
our material meets all
commercial standards
such as DNV-GL and
Lloyds,” he said.
Another advantage
of the flexible coupling
is the effect on noise
pollution.
“A flexible coupling also helps to reduce
resonance. No two production boats are
the same when it comes to harmonics- there will be different vibrations at
different speeds. Recently, when the
tolerances on shafts and gearboxes became
much more precise, builders began to
dispense with flexible couplings and other
anti-vibration devices. However, they soon
realised that this simply increased noise
within the hull.”CONVENTIONAL SYSTEMS
There are a lot of internal forces acting on
a boat’s engine. The three main vibrations
are described as longitudinal, axial and
torsional, all the result of the rotating
forces within the engine itself. Big ship
engines have to use a
hydraulic ram to push
against the twisting
(torsional) forces as the
engine accelerates. In
addition, there is the
movement of the hull in
a seaway, which has its
own inertia, and finally
the effects of the thrust
of the propeller pushing
or pulling the engine on
its flexible feet.
One solution has been to transfer this
push and pull onto a separate thrust plate,
so the hull takes the power and not the
gearbox. This has been pioneered by the
Aquadrive assembly distributed by Halyard
Marine, where a thrust plate works in
conjunction with a flexible coupling.
A more recent innovation for shaft
drives has been the US- based Seatorque
Propulsion System, which provides anentire drive train including a built-in
bearing housing as a single, easy-to-install
unit. The assembly also removes the need
for dripless seals, stuffing boxes and cutlass
bearings, and in some cases the need for an
intermediate P-bracket. Everything is pre-
packaged and ready to fit.
“We hit the market at about the same
time as the arrival of pod drives,” said Jana
Stolper, Seatorque’s vice president. “We
actually market our product along much
the same lines. The all-in-one system has
opened boatbuilder’s eyes as to what is
available as an alternative to a pod drive
or conventional shafting. A lot of noise in
a standard shaft system comes from the
interconnected parts – different bits of
equipment from various manufacturers
all added to the mix. But our system is
efficient because it is one unit that is fully
encapsulated, eliminating the causes of
driveline noise and vibration rather than
just placating them. We often hear OEMs
tell us how quiet their boats have become.”
Stolper accepts that her encapsulated
system is more expensive than an assembly
of various off-the-shelf products, but soon
pays back in fewer man hours needed for
an installation and the ongoing fuel savings
due to mechanical efficiency.
“The shaft is supported longitudinally in
a non-rotating outer casing and mounted
to the hull using bushings, which are soft
but still fully watertight,” she explained.
“The shaft casing is oil-filled and only needs
a seal and oil change every 5 years or 3,000
hours. For an OEM, a Seatorque assembly
can save up to 2/3rds of the engineering
production time, whilst also eliminating
the alignment issues seen during a standard
shaft system installation. We also offer a full
international warranty and support.”
The Seatorque system is hybrid
compatible and Stolper says the company
has already completed some electric boat
conversions.
“The system is also joystick ready The US Seatorque system is claimed to
save up to two-thirds of installation hours by
providing the whole shaft assembly as one
complete piece of equipment. Note the gold-
coloured housing which minimises noise and
vibration and also helps with fuel economyThe all-in one
system has opened
builders’ eyes as to what is
available as an alternative
to a pod drive or
conventional
shafting