where *D *= turning diameter (m)

brackish = 0.85 and fresh = 0.75)

length (%).

bare steel = 1.33 and old bare steel = 2)

For rounded vessels with fully effective rud-

ders, and in level ice of thickness equal to 60%

of the icebreaking capability at 1m/s

plus half the snow depth (m)

where *PMB *is the percentage of waterline length

σf = flexural strength of ice (kPa)

representing a parallel midbody (%).

ψ = average flare angle in bow region ()

For rounded vessels with partially effective rud-

ϕ = average buttock angle in bow region

ders, and in level ice of thickness equal to 60% of

().

the icebreaking capability at 1 m/s

For rounded-shoulder ships, an expression (us-

ing the same symbols) for the ice resistance at a

speed of 1 m/s is given as

For chined vessels, open water resistance is ex-

pressed in terms of Froude number

{1 0.0083 (*t *+ 30)} {0.63 + 0.00074 σf}

ψ)1.6}

{1 + 0.003 (ϕ

5)1.5}.

{1 + 0.0018 (90

where *R *= open water resistance (kN)

Based on the full-scale data, an expression for

the energy to penetrate an unconsolidated ridge is

given as

For vessels of rounded shapes, open water re-

sistance is expressed in terms of Froude number

{1 + 0.012 (90 ψ)}

where *E*R = energy for ridge penetration (MJ)

Propulsive performance is defined as the ratio

(m2)

of net thrust to the shaft power (or specific net

thrust). Keinonen et al. (1991) compared the pro-

(rubble only) (m2)

pulsive performance of different icebreakers at full

power. The data are shown in Figure 24a for dif-

brackish = 0.85 and fresh = 0.75)

ferent speeds for ships having ducted propellers,

whereas similar data for ships with open propel-

bare steel = 1.33 and old bare steel = 2)

lers are shown in Figure 24b. A comparison of the

data for the single-screw, ducted, controllable-pitch

ψ = average flare angle in bow region ().

system of *Kigoriak *and *Arctic *with that of twin-

screw, open, controllable-pitch system of *Terry Fox*

shows that the net propulsive performance of the

For vertical-sided chined vessels, and in level

ducted systems has an advantage of 27% over the

ice of thickness equal to 60% of the icebreaking

open system at low speeds. However, this advan-

capability at 1 m/s

tage decreases at higher speed until both systems

have the same specific net thrusts.

27

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