is no measurable benefit of an air-bubbler system
Canmar Kigoriak during icebreaking with a bare
hull and also with an epoxy-coated hull.
on ships with unconventional bows. Captains of
On the Canadian icebreaking supply vessel Rob-
Bay-class Great Lakes icebreakers report that air
ert Lemeur, this system has been effective in reduc-
bubblers are very useful for docking or leaving the
docks under ice conditions.
range (Dick and Laframboise 1989). On the Swed-
To assess the effectiveness of hull lubrication by
ish icebreaker Oden, the water-deluge system has
an air-bubbler system, the ratio of shaft power
been upgraded to act as a bow thruster by direct-
saved at a given speed in level ice to the power re-
ing the flow to one side of the ship. With a control
quired to operate the system is computed. If this
system and a modified nozzle design, it is possible
ratio is more than one, there is a net power saving
to obtain a side force of 0.1 MN at the forward tip
in operating the system. According to the data com-
of the ship.
piled by Keinonen et al. (1991), this ratio for the
air-bubbler system of hull lubrication is generally
less than, or in some cases barely greater than, one.
The reason for such low efficiency is that lu-
POWER AND PERFORMANCE
brication is not provided around the bow water-
line, where it would be most effective.
As expected, installed power increases with ship
size as represented by ship beam. The power-ver-
Air-bubblerwater injection system
sus-beam plot of the data on existing polar ships
This system, installed on the German icebreaker
(Fig. 20) shows a trend of increasing power as a
Polarstern, injects air into the water being pumped
function of beam. Except for a few data points,
to nozzles at the sides of the ship below the ice.
there appears to be a well-defined relationship
Airwater jets have also been installed below the
between power and beam.
water on the Canadian icebreaker Ikaluk and the
Using information on the performance of ex-
newly converted Russian icebreaker Mudyug. The
isting polar ships in ice, Dick and Laframboise
ratio of power saved to the power expended is
(1989) plotted the bollard pull/beam vs. the ice
about one (Keinonen et al. 1991).
thickness an icebreaker is capable of breaking at a
speed of about 1 m/s or 2 knots (Fig. 21). For com-
parison, the data are normalized on performance
Recent developments, such as the water-deluge
for a speed of 2 knots. There appears to be a well-
system and low-friction epoxy paint, have allowed
defined minimum performance. For a particular
the use of unconventional bows on sea-going ves-
bollard pull/beam, the range of ice thickness above
sels (Johansson et al. 1994). A water-deluge sys-
a minimum performance value represents an im-
tem throws several tons of water every second on
provement in icebreaking capability of the hull
top of the ice ahead of the bow. This not only re-
shape. Figure 21 shows that the most recent ships
duces friction between the ice and the hull but also
have more efficient hull forms.
submerges the broken ice pieces to help them move
down under the hull. This was first installed on
the Canadian icebreaker Canmar Kigoriak, which
was fitted with a blunt spoon-shaped bow, to solve
the ice pushing problem experienced with uncon-
ventional bows in the late nineteenth century. One
time, when the water-deluge system was frozen
solid, the Kigoriak could not make good progress
through a broken ice cover because of the ice-push-
ing problem. With the water-deluge system operat-
ing perfectly a few days later, she was able to make
good progress in this same broken ice field
(Johansson et al. 1994).
According to the data compiled by Keinonen et
al. (1991), the power saved as a result of operating
Figure 20. Power vs. beam for icebreakers (after Dick
a water-deluge system is much greater than the
and Laframboise 1989).
power expended. These data were collected for the