Iveco Marine Diesel Engines, Руководство по установке

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Gliding hulls
The speed of gliding hulls can be obtained through the Equadro formula:
where:
• V : Hull speed
• SHP :Total installed power (HP)
• D : Displacement with hull fully laden (long tons)
• X : Equadro coefficient:
- X : 2,33 - 2,40 Axis lines and astern feet
- X : 2,24 - 2,30 Surface propellers
- X : 2,12 - 2,15 Competition hulls - Deep V
- X : 2,05 - 2,10 Competition catamarans
The formula does not directly consider the boat length, as the fundamental element for the perfor-
mance of the gliding hulls is the weight/power ratio. Anyway, the length is still part of the choice of coef-
ficient X, synthesis of the propulsion efficiency of the hull block (L/B).
Semi-displacing hulls
The factors defining the possible performance of semi-displacing hulls (or semi-gliding) are:
■
Reduced buttlock angles (0°<Ab<7°), i.e. the angle between the longitudinal line of the hull bot-
tom and the line parallel to the waterline, on a vertical plane at 1/4 of the floating width in ft (B.L.A.)
from the longitudinal centre line of the hull.
■
Reduced values of the displacement/length ratio at floating (20<DL<280)
where:
• D : Displacement with the hull fully laden (long tons)
• L.L.A. : Length of the waterline (ft)
Finally, the introduction of the DL ratio in the formula enables the calculation
of the Taylor coefficient and the related speed:
where:
• V : Hull speed (Kts)
With the semi-gliding trim, the power required to reach such a trim can be calculated through the
Barnaby formula:
where:
• SHP :Total installed engine (HP)
• K : Shape coefficient
Summarising table of K value
L.L.A. 20 25 30 35 40 45 50 60 70 75 80
K 2,25 2,4 2,6 2,8 3,03 3,24 3,34 3,73 4,13 4,3 4,45
The above mentioned information regard the boats in perfect maintenance conditions.The bottom and
propeller incrustation can substantially reduce the boat performance.
MARCH 2004 ENGINE/BOAT CHOICE FACTORS
2.32
MARINE ENGINES INSTALLATION