Yesterday I had an opportunity to sea trial a new 45-foot Tiara, (nice
boat, as always). The boat was simply part of the "supporting cast" and
the star of the day was Volvo's new IPS drive system.

The IPS system "reinvents the wheel", if we use the term "wheel" in its
nautical sense and refer to the (4) propellers that drive the boat.

Ever since some time in the 1800's, when paddle-wheel technology was
swept aside in favor of propellers, 99% of all motorized boats have
been powered with props that face aft at or near the transom.
The Volvo IPS system uses a pair of duo-prop drives, mounted well aft,
with the props facing forward and "pulling", rather than "pushing" the
boat through the water. The section of the drive
that follows the props functions as a rudder, (as well as an underwater
exhaust outlet), offering additonal stability in addition to
maneuverability beyond that provided by the props pushing the stern to
port or starboard, (the entire unit rotates during a turn). IPS is only
offered for twin engine configurations.

The drive units do not turn 360-degrees, so the drive concept. isn't
really the same as is now used on some of the largest tugs and
fireboats. It isn't possible to set the props at 90-dgree angles from
the keel, and reverse is accomplished by shifting gears rather than by
spinning the props around to face aft. There will be no running
25-knots, transom first, in the new Tiara. :-)

The IPS system makes a dramatic change in the handling characteristics
of a vessel, especially when comparing the same size vessel with
standard inboard propulsion. A secondary benefit of the technology is
that the engines are moved well aft to create
additional interior space in the boat. The Volvo engines are coupled to
the drive units with a very short shaft, perhaps 12-18" in length. As
Tiara never built a boat where the shaft angle exceeded 11-degrees,
previous models all had fairly long shafts.
The new Tiara is touted as the "first midcabin Tiara express cruiser",
as there in a new stateroom with a pair of single bunks
(athwartship) aft of what was formerly the forward bulkhead for the
engine room.

The two propulsion packages the Volvo offers with the IPS system are
the IPS 400 with the 310 HP engine, and the IPS 500 with the 370 horse
diesel. Our Tiara was equipped with the IPS 500.
We pulled away from the dock and motored down a breezy fairway at
Elliott Bay Marina in Seattle. The fairways there are notoriously
skimpy, and a good cross wind was blowing, butI decided our controlled
exit from a tight slip was due more to the judicious use of the bow
thruster than any special magic with the drive system. Kevin Piper,
sales manager for the local Tiara dealer (Crow's Nest Compass Point
Marine Group) was at the helm- (my customary preference in a brand new,
unfamiliar boat belonging to somebody else in tight quarters)- and he
was moving up the learning curve by offering demonstrations to the
marine press and a list of interested sales prospects.

The first indication of the surprising capability of the IPS drive
sytem was the super sharp but fully controlled 90-degree turn we
executed at the end of the fairway. Kevin put the port engine in
neutral while leaving the starboard engine engaged, forward, at idle,
and the boat came around instantly. This large express cruiser responds
as nimbly as an I/O vesel about half its size.

We got up to plane quickly and smoothly. Tiara offers trim tabs on the
boat, but apparently more in response to popular demand than
any actual need. We didn't use tabs and there was very little bow rise.
Once the typical cruising family puts 1000 pounds of gear into the
forward compartments, the bow rise could be so little that it would be
difficult to detect.

"Quiet, please! I'm trying to hear the engines!" The system isn't
really that quiet, but placing the engines closer to the transom and
the use of the underwater exhaust reduces engine noise substantially.
On this epxress cruiser design, with no aft cabin bulkhead between the
helm and the transom (and without any canvas rigged) we could hear the
sound of the water churning in our stern wake above the noise of the
engines. Even at the highest speeds. Very nice.

One aspect of the ISP that will take a bit of time for some experienced
boaters to enjoy and appreciate is the computer controlled steering.
There is no mechanical or hydraulic resistance at the wheel. It turns
freely, and a computer interprets the wheel position and instructs the
IPS drives accordingly. Kevin Piper calls this "fly by wire". One of
the benefits of the computerized steering is that the wheel is
automatically centered (as the drives return to center) each time the
boat is restarted. There is no need to count rotations from lock or
consult a rudder angle indicator before departing a dock.

We did some sharp high speed turns, slow speed pivots, and generally
put the boat through a group of maneuvers out in the bay.
Compared to the response one would expect from an inboard boat in this
category, the ISP drive system makes a very, very agile boat.

While we were able to experience the improved maneuverability, we
didn't have any way to test some of Volvo's additional claims for the
system. Volvo has published test results that show the IPS system
operates more efficiently than standard inboards. Top speed is said to
improve by about 20%, acceleration by about 15%, and fuel economy (and
therefore range) by as much as 30%. Much of this reported increase in
efficiency is thought to be the result of no struts and shafts
interrupting the flow of water to the prop, and the increased
efficiency of directing the prop wash in the direction desired to move
the stern rather than "bouncing" it off an angled rudder.

Factors in favor of the system seem to be: 1, improved manuverability,
2, more cabin space in many hulls, 3, quieter operation, and 4,the
reported improvements in mechanical efficiency.

Most people who consider IPS system for the first time react with the
alarmed observaton, "What if I strike a log? There are no shafts or
struts protecting the props!" The bad news is that if a boater strikes
a log with the IPS system, there is a potential for tens of thousands
of dollars damage, just as there has always been
for boats with traditional inboards. The good news? You may be less
likely to sink as the result of a log strike with the IPS system. Boats
are lost every year when shaft struts are pushed through the hull or
torn away to leave an enormous hole in the bottom. The drive unit on
the IPS is designed to break free in the event of a catastrophic
collision, and leave the hull intact.

The IPS system may not be ideal for every boater, but it will certainly
be appreciated by those for whom the specific benefits
of the system are priorities. To its credit, Volvo hasn't simply
trotted out another goofy marketing gimmick but rather has introduced a
dynamic change that may someday be viewed as the moment boaters
"reinvented the wheel."