NEWSWAVE - HSVA

Fig. 1 Brash ice test
These power requirements can
be calculated with the formulae
given in the regulations or as an
alternative they can be obtained in ice
model tests, i.e. the performance of the
ship is demonstrated in model tests in
brash ice channels. Figure 1 illustrates a
typical brash ice model test setup
The guidelines for the verification of
the ship’s performance for ice classes
through model tests have changed in
December 2005.
The main changes are:
➢ Increase of the thickness of the
brash ice channel
➢ Increase of the friction coefficient
between model surface and ice from
µ = 0.05 to 0.10.
8 NEWSWAVE 2006/2
BRASH ICE MODEL TESTS –
CONSEQUENCES OF THE
CHANGES IN THE GUIDELINES
FROM DECEMBER 2005
The Finnish – Swedish Ice Classes 1C to 1AS were developed
in order to provide power requirements
which ensure a certain ship’s performance in brash ice channels.
As compared to the old guidelines
for brash ice model tests, these changes
result in a higher power requirement.
Figure 2 illustrates the increase in delivered
power due to the change in the
guidelines for ice class 1B and 1A for a
PANMAX tanker. But also with the new
guidelines it can be stated that the performance
of model tests leads to lower
power requirements compared to that
required by the given formulae. In some
cases a reduction of up to 30% of the
required power can be achieved.
If the vessel is equipped with a controllable
pitch propeller the engine
which has been chosen for good open
water performance will be able to deliver
the required power in brash ice channels.
by Karl-Heinz Rupp
In the case of a fixed pitch propeller
the motor limit curve restricts the available
power in brash ice as the propeller
loading is significantly higher. Figure 3
illustrates that in these cases HSVA can
assist you to find a solution where the
vessel is able to fulfil the new power
requirement guidelines without any
change in the ship design for ice class 1A.
However, in other cases changes may
be necessary. But of course especially
in these cases, HSVA can offer you
assistance in finding cost efficient
solutions.
Fig. 2
Comparison
of old and new
guidelines,
delivered power
vs. brash ice
thickness