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protected from logs and lines. This work is still in the initial
stages of development and shows great promise. A 10%
increase in thrust has been achieved in most cases so far.
Midship Blisters:
One of the most recent advancements comes through the
use of significant appendage fairings. Having reduced the
bow wave with a fine entrance angle and the use of a bow
bulb, attention was turned to reducing the midship hollow.
It was reasoned that this would help reduce drag by reduc-
ing the overall wave train and increase stability underway by
reducing the midship hollow. Essentially, the goal was to
duplicate the success of the bow bulb with a midship bulb or
bilge blister. By adding a large fairing at the root of the sta-
bilizer fin a midship wave would be created cancelling out
the hollow (Fig. 4). Although this technology is still very new
a maximum reduction of 6% in resistance has been
achieved over a range of speed from 8-16 knots with no r
sistance penalty all the way up to 20 knots (Fig. 5).
A separate program at the University of British Columbia
seen reductions of up to 10%. In this program they have
experimented with midship bulbs. The rationale is the sa
but the execution appears to produce better results. A joi
research program is planned to explore this in greater de
Comparison to a typical trawler:
On comparing powering estimates to other existing vesse
without this technology it is found that the author’s teste
designs proved to be 30% more efficient and can operat
over a wider range of speed (Fig 6). This has been ocean-
proven in full size vessels on long offshore passages. Lo
fuel consumption means less fuel to carry to achieve lon
range. Less fuel means less weight to carry. Less weight
means a smaller engine required and less structural wei
to carry it. Which means less overall weight that requires
less power to move and lower fuel consumption, etc. The
Continued next
Fig. 4 Midship Blisters
Fig. 5 Bi-foil Skeg
To determine shaft horsepower (SHP), divide EHP by the
appropriate overall propulsive coefficient (OPC). For open
propellers, a conservative value would be 0.55.
Fig. 6 Typical Trawler vs Fox 86