[Code of Federal Regulations]
[Title 46, Volume 7]
[Revised as of October 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 46CFR173.095]

[Page 167-168]
 
                           TITLE 46--SHIPPING
 
   CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY (CONTINUED)
 
PART 173--SPECIAL RULES PERTAINING TO VESSEL USE--Table of Contents
 
                            Subpart E--Towing
 
Sec. 173.095  Towline pull criterion.

    (a) In each towing condition, each vessel must be shown by design 
calculations to meet the requirements of either paragraph (b) or (c) of 
this section.
    (b) The vessel's metacentric height (GM) must be equal to or greater 
than the following:
[GRAPHIC] [TIFF OMITTED] TC01MR91.032

where--

N=number of propellers.
P=shaft power per shaft in horsepower (kilowatts).
D=propeller diameter in feet (meters).
s=that fraction of the propeller circle cylinder which would be 
intercepted by the rudder if turned to 45 degrees from the vessel's 
centerline.
h=vertical distance from propeller shaft centerline at rudder to towing 
bitts in feet (meters).
[Delta]=displacement in long tons (metric tons).
f=minimum freeboard along the length of the vessel in feet (meters).
B=molded beam in feet (meters).

[[Page 168]]

K=38 in English units.
K=13.93 in metric units.

    (c) When a heeling arm curve, calculated in accordance with 
paragraph (d) of this section, is plotted against the vessel's righting 
arm curve--
    (1) Equilibrium must be reached before the downflooding angle; and
    (2) The residual righting energy must be at least 2 foot-degrees 
(.61 meter-degrees) up to the smallest of the following angles:
    (i) The angle of maximum righting arm.
    (ii) The downflooding angle.
    (iii) 40 degrees.
    (d) The heeling arm curve specified in paragraph (c) of this section 
must be calculated by the following equation:
[GRAPHIC] [TIFF OMITTED] TC01MR91.033

where--

HA=heeling arm.
[thetas]=angle of heel.
N, P, D, K, s, h, and [Delta] are as defined in paragraph (b) of this 
section.

    (e) 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.
    (f) For the purpose of this section, at each angle of heel, a 
vessel's righting arm may be calculated considering either--
    (1) The vessel is permitted to trim free until the trimming moment 
is zero; or
    (2) The vessel does not trim as it heels.7