Open-Type Channels. A change from one direction of the channel into

another can be accomplished for an open-type channel without the

introduction of a curved bend, provided the vessels encountering the bend

are highly maneuverable and the change in direction is not too large.

Such a bend is called a straight-line bend and is shown with alternative

methods of widening the channel in Figure 5-19.

Restricted-Type Channels. If the bend occurs in a restricted-type

channel, the change of direction is large, or the maneuvering

characteristics of the vessels frequently using the channel are poor,

introduction of a curve in the channel becomes necessary. In designing a

channel curve, the critical factor is determination of the radius of the

curve. The criteria upon which the radius, R, is based are the length, lv, of

the ship entering the channel and the angle of deflection, α, of the

channel bend. The general rules governing determination of the radius

are as follows:

- Minimum R = 914.4 m (3,000 ft) for a ship under its own power.

- R = 365.8 to 609.6 m (1,200 to 2,000 ft) for tug assistance.

- If the angle of deflection is greater than 10 degrees, the curve

should be widened at the inside curve.

- The tangent length between consecutive curves where there

are no obstructions should be 304.8 m (1,000 ft) or 2 lv (where lv

= length of the largest ship using the channel), whichever is

larger.

- Reverse curves should not be used except in special situations.

Rules governing the radius, based on angle of deflection, are:

R = 3 lv minimum for α < 25 deg.

R = 5 lv minimum for 25 deg. < α < 35 deg.

R = 10 lv minimum for α > 35 deg.

Rules governing the radius, based on vessel length, are:

R = 1219.2 m (4,000-ft) minimum for lv < 152.4 m (500 ft)

R = 2133.6 m (7,000-ft) minimum for lv = 152.4 m (500 ft)

R = 2133.6 to 3048 m (7,000 to 10,000 ft) for (152.4 m (500 ft)

< lv < 213.4 m (700 ft)

5-49