Iveco Marine Diesel Engines, Installation Handbook

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The block coefficients are included in the following table:
Type of boat Coefficient C
b
Speedboat hulls with V bottom, gliding 0,30
Hulls for sports fishing with length up to 12 m (40 ft),V bottom 0,35
Pilot boats with length below a 12 m (40 ft) 0,35
Semi-gliding hulls (patrol and cruise boats) 0,40
Displacing hulls for cruise, yachts with sail and auxiliary engine 0,45 - 0,55
Fishing boats 0,50 - 0,55
Heavy duty boats 0,55 - 0,65
Tug-boats 0,60 - 0,75
Powered flatboats 0,70 - 0,95
Relative speed (Taylor ratio)
It is the ratio between the boat speed, expressed in knots, and the square root of the floating
length, expressed in feet.
This coefficient is a parameter which makes it possible to compare similar bottoms with the action of
waves and therefore their resistance to the hull motion: equal relative speeds correspond to compara-
ble waves.
Experiments and tests carried out on different types of boats pointed out that there is a limit value to
the speed beyond which any further increase requires excessive and expensive power growth.
For displacing hulls, the speed limit is for value ratios around an average of 1.34.
At this speed , the hull generates a wave as long as its floating hull length. Any attempts
to go beyond this speed, by increasing the engine power, make the hull stem lift thus creating expen-
sive and very often dangerous sailing conditions.
Actually, it rarely happens for bigger merchant ship hulls to exceed value 1 of this ratio
, while
in smaller hulls it is possible to reach values up to 1.2-1.3.
On semi-displacing hulls, it is possible to gradually obtain growing ratios as the hull
characteristics become more and more similar to the gliding type: 1.7 for fast displacing hulls, from 2.5
to 3 for semi-displacing hulls.
MARCH 2004 INTRODUCTION
1.20
MARINE ENGINES INSTALLATION