170.170—Calculations required.
(a)
Each vessel must be shown by design calculations to have a metacentric height (GM) that is equal to or greater than the following in each condition of loading and operation:
Where—
P=.005 (L/14,200)2 tons/ft2 . . . for ocean service, Great Lakes winter service, or service on exposed waters.
P=.055 (L/1309)2 metric tons/m2 . . . for ocean service, Great Lakes winter service, or service on exposed waters.
P=.0033 (L/14,200)2 tons/ft2 . . . for Great Lakes summer service or service on partially protected waters.
P=.036 (L/1309)2 metric tons/m2 . . . for Great lakes summer service or service on partially protected waters.
P=.0025 (L/14,200)2 tons/ft2 . . . for service on protected waters.
P=.028 (L/1309)2 metric tons/m2 . . . for service on protected waters.
L=LBP in feet (meters).
A=projected lateral area in square feet (square meters) of the portion of the vessel and deck cargo above the waterline.
H=the vertical distance in feet (meters) from the center of A to the center of the underwater lateral area or approximately to the one-half draft point.
W=displacement in long (metric) tons.
T=either:
(1) the lesser of either 14 degrees heel or the angle of heel in degrees at which one-half the freeboard to the deck edge is immersed; or
(2) for a sailing vessel, T = the lesser of either 14 degrees or the angle of heel in degrees to the deck edge.
The deck edge is to be taken as the intersection of the sideshell and the uppermost continuous deck below which the sideshell is weathertight.
(b)
If approved by the Coast Guard Marine Safety Center or the ABS, a larger value of T may be used for a vessel with a discontinuous weather deck or abnormal sheer.
(c)
When doing the calculations required by paragraph (a) of this section for a sailing vessel or auxiliary sailing vessel, the vessel must be assumed—
(d)
The criterion specified in this section is generally limited in application to flush deck, mechanically powered vessels of ordinary proportions and form that carry cargo below the main deck. On other types of vessels, the Coast Guard Marine Safety Center or the ABS requires calculations in addition to those in paragraph (a) of this section. On a mechanically powered vessel under 328 feet (100 meters) in length, other than a tugboat or a towboat, the requirements in § 170.173 are applied.
[CGD 79-023, 48 FR 51010, Nov. 4, 1983; 49 FR 37384, Sept. 24, 1984, as amended by CGD 88-070, 53 FR 34537, Sept. 7, 1988; CGD 85-080, 61 FR 944, Jan. 10, 1996; 61 FR 20556, May 7, 1996; CGD 95-028, 62 FR 51217, Sept. 30, 1997]
(a)
If required by the Coast Guard Marine Safety Center or the ABS, each mechanically powered vessel less than 328 feet (100 meters) LLL, other than a tugboat or towboat, must be shown by design calculations to comply with—
(1)
Paragraph (b) or (c) of this section if the maximum righting arm occurs at an angle of heel less than or equal to 30 degrees; or
(2)
Paragraph (b) of this section if the maximum righting arm occurs at an angle of heel greater than 30 degrees.
(2)
A righting arm (GZ) of at least 0.66 feet (0.20 meters) at an angle of heel equal to or greater than 30 degrees;
(4)
An area under each righting arm curve of at least 10.3 foot-degrees (3.15 meter-degrees) up to an angle of heel of 30 degrees;
(5)
An area under each righting arm curve of at least 16.9 foot-degrees (5.15 meter-degrees) up to an angle of heel of 40 degrees or the downflooding angle, whichever is less; and
(6)
An area under each righting arm curve between the angles of 30 degrees and 40 degrees, or between 30 degrees and the downflooding angle if this angle is less than 40 degrees, of not less than 5.6 foot-degrees (1.72 meter-degrees).
(3)
An area under each righting arm curve of at least 16.9 foot-degrees (5.15 meter-degrees) up to an angle of heel of 40 degrees or the downflooding angle, whichever is less;
(4)
An area under each righting arm curve between the angles of 30 degrees and 40 degrees, or between 30 degrees and the downflooding angle if this angle is less than 40 degrees, of not less than 5.6 foot-degrees (1.72 meter-degrees); and
(5)
An area under each righting arm curve up to the angle of maximum righting arm of not less than the area determined by the following equation:
A=10.3 0.187 (30−Y) foot-degrees
A=3.15 0.057 (30−Y) meter-degrees
where—
A=area in foot-degrees (meter-degrees).
Y=angle of maximum righting arm, degrees.
(d)
For the purpose of demonstrating compliance with paragraphs (b) and (c) of this section, at each angle of heel a vessel's righting arm is calculated after the vessel is permitted to trim free until the trimming moment is zero.
(e)
For the purpose of demonstrating acceptable stability on the vessels described in § 170.170(d) as having unusual proportion and form, compliance with paragraphs (a) through (d) of this section or the following criteria is required:
[CGD 79-023, 48 FR 51010, Nov. 4, 1983, as amended by CGD 85-080, 61 FR 944, Jan. 10, 1996; CGD 95-028, 62 FR 51218, Sept. 30, 1997; 62 FR 51353, Sept. 30, 1997]
This subpart applies to each vessel for which the lightweight displacement and centers of gravity must be determined in order to do the calculations required in this subchapter.
(a)
Except as provided in paragraphs (c) and (d) of this section and in § 170.200, the owner of a vessel must conduct a stability test of the vessel and calculate its vertical and longitudinal centers of gravity and its lightweight displacement.
(b)
An authorized Coast Guard or ABS representative must be present at each stability test conducted under this section.
(c)
The stability test may be dispensed with, or a deadweight survey may be substituted for the stability test, if the Coast Guard or the ABS has a record of, or is provided with, the approved results of a stability test of a sister vessel.
(d)
The stability test of a vessel may be dispensed with if the Coast Guard or the ABS determines that an accurate estimate of the vessel's lightweight characteristics can be made and that locating the precise position of the vessel's vertical center of gravity is not necessary to ensure that the vessel has adequate stability in all probable loading conditions.
[CGD 79-023, 48 FR 51010, Nov. 4, 1983, as amended by CGD 95-028, 62 FR 51218, Sept. 30, 1997; USCG-1998-4442, 63 FR 52192, Sept. 30, 1998]