Title 46

SECTION 172.090

172.090 Intact transverse stability.

§ 172.090 Intact transverse stability.

(a) Except as provided in paragraph (b) of this section, each tank barge must be shown by design calculations to have a righting arm curve with the following characteristics:

(1) If the tank barge is in river service, the area under the righting arm curve must be at least 5 foot-degrees (1.52 meter-degrees) up to the smallest of the following angles:

(i) The angle of maximum righting arm.

(ii) The downflooding angle.

(2) If the tank barge is in lakes, bays and sounds or Great Lakes summer service, the area under the righting arm curve must be at least 10 foot-degrees (3.05 meter-degrees) up to the smallest of the following angles:

(i) The angle of maximum righting arm.

(ii) The downflooding angle.

(3) If the tank barge is in ocean or Great Lakes winter service, the area under the righting arm curve must be at least 15 foot-degrees (4.57 meter-degrees) up to the smallest of the following angles:

(i) The angle of maximum righting arm.

(ii) The downflooding angle.

(b) If the vertical center of gravity of the cargo is below the weather deck at the side of the tank barge amidships, it must be shown by design calculations that the barge has at least the following metacentric height (GM) in feet (meters) in each condition of loading and operation:

where - K = 0.3 for river service. K = 0.4 for lakes, bays and sounds and Great Lakes summer service. K = 0.5 for ocean and Great Lakes winter service. B = beam in feet (meters). fe = effective freeboard in feet (meters).

fe = f + fa ; or fe = d, whichever is less. where - f = the freeboard to the deck edge amidships in feet (meters). fa = (1.25)(a/L)((2b/B)-1)(h); or fa = h, whichever is less. where - a = trunk length in feet (meters). L = LOA in feet (meters) b = breadth of a watertight trunk in feet (meters). B = beam of the barge in feet (meters). h = height of a watertight trunk in feet (meters). d = draft of the barge in feet (meters).

(d) For the purpose of this section, downflooding angle means the static angle from the intersection of the vessel's centerline and waterline in calm water to the first opening that does not close watertight automatically.