applications. All other IPS drive parts
in contact with salt water are manufactured from corrosion-resistant stainless
steel. The internal shafts and gears are
machined from forged steel and
remain immersed in an oil bath.
All shafts and gears are manufactured from Swedish steel ingots. These
are forged into rough shapes, which
are then machined into finished parts.
To a large extent, that forging process
determines the strength and fatigue
properties of the final part.
It takes roughly 500 calculations to
set up a gear machine to make the
beveled gears for sterndrive and IPS
applications. In the “old” days, the
calculations alone took three weeks.
With the advent of the first computers
this task dropped to 16 seconds—and
is now nearly instantaneous. The
machining itself is done to very precise
tolerances with a mixture of traditional
machine tools and modern robotics.
Following machining, the parts are
heat treated, a process that determines
the ultimate properties of the load-bearing surfaces of the metal parts.
Briefly put, first the parts are heated to
Hull Design for IPS
At some point in the development
of its IPS technology, Volvo Penta
engineers realized that the boats in
which it was installed would make or
break IPS’s performance and reputation. So Volvo Penta decided to exercise some control over hull design in
order to ensure that performance
lived up to expectations, the idea
being to produce the best-behaving
boats possible. This task is handled
by a department called Sales
Engineering Marine, a team of 10 that
includes four naval architects, and
specialists in propulsion, waterjets,
electronic engine controls, and
documentation.
Volvo Penta requires a considerable amount of design data from
boatbuilders contemplating the IPS.
You can’t just buy an IPS off the shelf
and install it! One important aspect
of the design review is based on a
concept Volvo Penta terms a “true
turn.” This happens when a person
on a boat feels no side forces during
a turn, and is achieved by designing
the hull to make it heel the necessary
amount. In effect, it’s what you do
when you lean a bicycle or motorcycle over to offset the “sense” of side
forces when riding around a corner.
To produce true turns, the Volvo
Penta team has developed guidelines for certain key features of
V-bottomed hull design, notably:
The deadrise (the angle the bottom makes with the horizontal plane)
must be between 10° and 24°—the
greater the deadrise, the more heel in
a turn. Outside the 10°– 24° envelope
there are likely to be excessive steering loads.
The chine flat at the intersection
of the bottom and topsides has a
significant impact on heeling. The
