The new CLT propeller was fitted to Guardo in June 1990, while she was
drydocked for a series of routine repairs and a full shotblasting of her hull.
On the 18th June, Guardo sailed with her brand new CLT propeller for
some preliminary tests in a seaway not far away from the shoreline, and from the very
beginning several new benefits were appreciated on board: the running of the propeller was
far more smooth and silent; no hull vibrations could be felt at all; the rudder angles
necessary to maintain the ship's course under the automatic pilot command were nearly half
of the angles needed before; and the propeller wake behind the ship was substantially
narrower and straighter.
Later on, it was also seen that the turning circle with full rudder at
one side had a diameter about 80% of the turning circle described before at the same
speed.
Some approximate speed trials were also carried out at opposite courses
with the result that a speed about 0.8 knots higher than before was obtained for the ship
in ballast at constant displacement and constant main engine rev/min.
The crew of Guardo were soon very favourably impressed by the CLT
propeller, although when the propller was being fitted to the ship, their first reaction
was against it, perhaps because of its very odd appearance.
In view of the above good preliminary results, it was decided to carry
out a comparative study on the speed and fuel consumption of the ship along a series of
voyages performed before and after the drydocking where the CLT propeller was fitted, and
also before and after the previous drydocking, which was effected in May 1988.
For the selection of the voyages to be compared, the following
restrictive conditions were imposed:
1). Identical or very similar sea state and relative direction;
2). Identical or very similar wind force and relative direction; and
3). Same maritime area, so that the prevailing marine currents were
similar.
Voyages selected were one in ballast and one at full load, before and
after each of the aforesaid drydockings, which voyages complied well with above
conditions.
Only totalized data for complete voyages have been used, or for
complete days when the concerned voyage extended beyond the selected area, as covered
distance and time needed and FO consumed to cover it.
In all cases, data have been taken from the official reports made by
the Master and the Chief Engineer for each voyage. However, corrections have been made in
FO consumption per hour to take into account the existing slight differences in ship's
displacement and Lower Calorific Value (LCV) of the FO.
