PREVIOUS |  TABLE OF CONTENTS |  NEXT

6. Bottom area

6.1 Subject to paragraphs 6.2 to 6.6 and section 8 the bottom area is that area of the bottom of a ship inboard of the flat of bottom line (FOB.)

6.2 On ships with ramp type sterns the bottom area may be continued aft up the ramp if

• the sections do not make an angle to the horizontal greater than 15 degrees, and
• it does not extend further aft than a section that is 3 times the diameter of the foremost propeller forward of that propeller.

6.3 On ships fitted with an effective knuckle or a reamer the bottom area may be extended forward of the FOB line, provided the requirements of section 8 are complied with.

6.4 On CAC4 ships the bottom area need not extend more than 80 metres aft of the aft end of the bow area.

6.5 Ships fitted with an ice skeg must use an area factor of 0.2 for the forward two-thirds of the bottom area, and an area factor of 0.1 for the remaining portion of the bottom area.

6.6 Ships not fitted with an ice skeg

• and that are CAC 4 vessels must use an area factor of 0.3 in the forward 55 metres of the bottom area, an area factor of 0.15 in the next 25 metres, and an area factor of 0 may be used in any remaining portion of the bottom area;
• and are either CAC1, CAC2 or CAC3 vessels must use an area factor of 0.3 for the forward 80 metres, an area factor of 0.15 in the next 40 metres, and an area factor of 0 may be used in any remaining portion of the bottom area.

Table 2 ^
Factors for hull areas

7. Mid body / stern area ^

7.1 Subject to section 8 the mid body/stern area is all the hull area below the ice freeboard line (IFL) which is not a bow area, iceskeg area, bottom area or a transition area adjoining one of these areas.

8. Transition areas ^

8.1 Subject to section 3.1, between and above the bow area, iceskeg area, bottom area and midbody/stern area there must be transition areas.

8.2 The transition areas must be arranged in the area with the lower area factor (AF) set out in Table 2.

8.3 The transition areas must be arranged such that the graduation of area factors (AF) complies with that set out in Table 3 and additional transition areas must be arranged as necessary to ensure compliance, except that where the area factor of 0.15 is used in the bottom area, no additional transition area is required to the area using the factor of 0.15 .

Table 3 ^
Graduation of hull area factors

8.4 The extent of transition areas must not be less than that set out in Table 4.

9. Class factors ^

9.1 The class factors are obtained from Table 5 for the given category of ship.

10. Design pressure ^

10.1 The design pressure in megapascals is obtained from table 6, for the appropriate design parameter.

Table 4 ^
Minimum extent of transition areas between the main hull area

Table 5 ^
Table of Class factors

Table 6 ^
Design Pressure

11. Shell design pressure ^

11.1 The shell design pressure is dependent on location and frame spacing. It is not constant in any area, as the frame spacing used in determining the pressure is measured along the chord of the spacing at the shell, and is not a nominal spacing at the middle plane .

11.2 Subject to the minimum's in paragraph 11.3 the design pressure (pDE) for the shell plating must be obtained from the formula:-

where
"AF" is the area factor for the area of the hull shell in question obtained from Table 2;

"CF" is the class factor for the Category obtained from Table 5;

"OF" is an framing orientation factor equal to

1.0

where the angle is equal to or greater than 70 degrees (a transverse frame),

where is between 20 and 70 degrees (an oblique frame), and

where is equal to or less than 20 degrees (a longitudinal frame);

"" is the displacement in thousands of tonnes;

"P" is the shaft power in megawatts;

"S" is the frame spacing of the first level of support measured in metres normal to the moulded lines of the frames on the chord of the moulded surface of the shell;

"U" equals:

0.8 in the Bow and Iceskeg areas and their transitions,

0.4 in the Mid Body/Stern area and its transitions, and

0 (zero) in the Bottom area;

"" is the acute angle in degrees between the chord of the water-line and the line of the first level of framing supporting the shell. Where the first level of support is the stiffening with the lower scantlings and the closer spacing (See Figure 7.).

11.3 Notwithstanding paragraph 11.2 the design pressure (pDE) for the shell plating must not be less than

MPa

in the bow area and mid body/stern area for vessels of category CAC1, CAC2 and CAC3,

MPa

in the bow area and mid body/stern area for vessels of category CAC4,

MPa

in the bottom area for vessels of category CAC1, CAC2 and CAC3, and

MPa

in the bottom area for vessels of category CAC4;

where
"OF" is a framing orientation factor equal to
1.0 where the angle W is equal to or greater than 70 degrees,

where W is between 20 and 70 degrees, and

where W is equal to or less than 20 degrees;

"S" is the frame spacing of the first level of support measured in metres normal to the moulded lines of the frames on the chord of the moulded surface of the shell;

"U" equals:

• 0.8 in the Bow & Iceskeg areas and their transitions,
• 0.5 in the Mid Body/Stern area and their transitions, and
• 0 (zero) in the Bottom area;

"" is the acute angle in degrees between the chord of the water-line and the line of the first level of framing supporting the shell.

12. Shell plate thickness ^

12.1 The thickness of the shell plating must be obtained from the following formula:

millimetres

Figure 6 ^
Illustration of stiffener spacing and span

ENLARGE IMAGE

where
"S" is the frame spacing of the first level of support measured in metres normal to the moulded lines of the frames on the chord of the moulded surface of the shell;

"pDE" is the design pressure determined in accordance with section 11.1;

"fv" is the nominal yield strength of the steel in megapascals; and

"CA" is a correction equal to 0 if a high impact resistant coating is applied to the exterior of the hull, and 2.0 if no such coating is applied. In all cases an internal coating protecting against corrosion should be applied.

PREVIOUS |  TABLE OF CONTENTS |  NEXT