12 December 2001
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
- 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)