#### § 171.065 Subdivision requirements— Type I.

(a) Except as provided in [paragraphs (c)](/on/2024-09-23/title-46/section-171.065#p-171.065(c)) and [(f)](/on/2024-09-23/title-46/section-171.065#p-171.065(f)) of this section, the separation between main transverse watertight bulkheads on a vessel, other than one described in [paragraph (b)](/on/2024-09-23/title-46/section-171.065#p-171.065(b)) of this section, must not exceed—

(floodable length) × (factor of subdivision)

where—

the factor of subdivision is listed under FS in Table [171.065(a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)).

(b) The factor of subdivision used to determine compliance with [paragraph (a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)) of this section must be the smaller of 0.5 or the value determined from Table [171.065(a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)) if—

(1) The vessel is 430 feet (131 meters) or more in LBP; and

(2) The greater of the values of Y as determined by the following equations equals or exceeds the value of X in Table [171.065(b)](/on/2024-09-23/title-46/section-171.065#p-171.065(b)):

[![](https://img.federalregister.gov/EC01MR91.018/EC01MR91.018_large.png)](https://img.federalregister.gov/EC01MR91.018/EC01MR91.018_original_size.png)

or

Y = (M + 2P1)/(V + P1−P)

where—

M, V, and P have the same value as listed in Table [171.065(a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)); and

P1 = the smaller of the following:

(i) 0.6LN (0.056LN) where—

N = the total number of passengers; and

L = LBP in feet (meters).

(ii) The greater of the following:

(A) 0.4LN (0.037LN).

(B) The sum of P and the total volume of passenger spaces above the margin line.

(c) The distance A in Figure [171.065](/on/2024-09-23/title-46/section-171.065) between main transverse watertight bulkheads may exceed the maximum allowed by [paragraphs (a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)) or [(b)](/on/2024-09-23/title-46/section-171.065#p-171.065(b)) of this section if each of the distances B and C between adjacent main transverse watertight bulkheads in Figure [171.065](/on/2024-09-23/title-46/section-171.065) does not exceed the smaller of the following:

(1) The floodable length.

(2) Twice the separation allowed by [paragraphs (a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)) or [(b)](/on/2024-09-23/title-46/section-171.065#p-171.065(b)) of this section.

(d) In each vessel 330 feet (100 meters) or more in LBP, one of the main transverse watertight bulkheads aft of the collision bulkhead must be located at a distance from the forward perpendicular that is not greater than the maximum separation allowed by [paragraph (a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)) or [(b)](/on/2024-09-23/title-46/section-171.065#p-171.065(b)) of this section.

(e) The minimum separation between two adjacent main transverse watertight bulkheads must be at least 10 feet (3.05 meters) plus 3 percent of the LBP of the vessel, or 35 feet (10.7 meters), whichever is less.

(f) The maximum separation of bulkheads allowed by [paragraphs (a)](/on/2024-09-23/title-46/section-171.065#p-171.065(a)) or [(b)](/on/2024-09-23/title-46/section-171.065#p-171.065(b)) of this section may be increased by the amount allowed in [paragraph (g)](/on/2024-09-23/title-46/section-171.065#p-171.065(g)) of this section if—

(1) The space between two adjacent main transverse watertight bulkheads contains internal watertight volume; and

(2) After the assumed side damage specified in [paragraph (h)](/on/2024-09-23/title-46/section-171.065#p-171.065(h)) of this section is applied, the internal watertight volume will not be flooded.

(g) For the purpose of [paragraph (f)](/on/2024-09-23/title-46/section-171.065#p-171.065(f)) of this section, the allowable increase in separation is as follows:

[![](https://img.federalregister.gov/EC01MR91.020/EC01MR91.020_large.png)](https://img.federalregister.gov/EC01MR91.020/EC01MR91.020_original_size.png)

where—

“total volume of allowed local subdivision” is determined by calculating the unflooded volume on each side of the centerline and multiplying the smaller volume by two.

(h) The assumed extents of side damage are as follows:

(1) *The longitudinal extent of damage* must be assumed to extend over a length equal to the minimum spacing of bulkheads specified in [paragraph (e)](/on/2024-09-23/title-46/section-171.065#p-171.065(e)) of this section.

(2) *The transverse extent of damage* must be assumed to penetrate a distance from the shell plating equal to one-fifth the maximum beam of the vessel and at right angles to the centerline at the level of the deepest subdivision load line.

(3) *The vertical extent of damage* must be assumed to extend vertically from the baseline to the margin line.

(i) The maximum separation between the following bulkheads must not exceed the maximum separation between main transverse watertight bulkheads:

(1) The collision bulkhead and the first main transverse watertight bulkhead aft of the collision bulkhead; and

(2) The last main transverse watertight bulkhead and the aftermost point on the bulkhead deck.

(j) The minimum separation between the following bulkheads must not be less than the minimum separation between main transverse watertight bulkheads:

(1) The collision bulkhead and the first main transverse watertight bulkhead aft of the collision bulkhead; and

(2) The last main transverse watertight bulkhead and the aftermost point on the bulkhead deck.

[![](https://img.federalregister.gov/EC01MR91.021/EC01MR91.021_large.png)](https://img.federalregister.gov/EC01MR91.021/EC01MR91.021_original_size.png)

Table [171.065](/on/2024-09-23/title-46/section-171.065)(a) (English units)

| Vessel length (LBP) | Criterion numeral (CN) | FS |
| --- | --- | --- |
| | CN less than or equal to 23 | A |
| Vessel length greater than 392 feet | CN greater than 23 and less than 123 | F1 |
| | CN greater than or equal to 123 | B |
| | CN less than or equal to S | 1 |
| Vessel length greater than or equal to 200 feet and less than or equal to 392 feet | CN greater than S and less than 123 | F2 |
| | CN greater than or equal to 123 | B |
| Vessel length less than 200 feet | | 1 |
| | | |
| --- | --- | --- |
| Where— | | |
| FS = the factor of subdivision. | | |
| CN = 60((M + 2P)/V) + 30000(N/L2) | | |
| A = (190/(L−160)) + 0.18 | | |
| B = (94/(L−85)) + 0.18 | | |
| F1 = A−((A−B)(CN−23)/100) | | |
| S = (10904−25L)/48 | | |
| F2 = 1−((1−B)(CN−S)/(123−S)) | | |
| L = the length of the vessel (LBP) in feet. | | |
| M = the sum of the volume of the machinery space and the volumes of any fuel tanks which are located above the inner bottom forward or aft of the machinery space in cubic feet. | | |
| P = the volume of passenger spaces below the margin line. | | |
| V = the volume of the vessel below the margin line. | | |
| N = the number of passengers that the vessel is to be certificated to carry. | | |

Table [171.065](/on/2024-09-23/title-46/section-171.065)(a) (Metric Units)

| Vessel length (LBP) | Criterion numeral (CN) | FS |
| --- | --- | --- |
| | CN lesthan or equal to 23 | A |
| Vessel length greater than 120 meters | CN greater than 23 and less than 123 | F1 |
| | CN greater than or equal to 123 | B |
| | CN less than or equal to S | 1 |
| Vessel length greater than or equal to 61 meters and less than or equal to 120 meters | CN greater than S and less than 123 | F2 |
| | CN greater than or equal to 123 | B |
| Vessel length less than 61 meters | | 1 |
| | | |
| --- | --- | --- |
| Where— | | |
| FS = the factor of subdivision. | | |
| CN = 60((M + 2P)/V) + 2787(N/L2) | | |
| A = (58/(L-49)) + 0.18 | | |
| B = (29/(L-26)) + 0.18 | | |
| F1 = A−((A−B)(CN−23)/100) | | |
| S = (3323.5−25L)/14.6 | | |
| F2 = 1−((1−B)(CN−S)/(123−S)) | | |
| L = the length of the vessel (LBP) in meters. | | |
| M = the sum of the volume of the machinery space and the volumes of any fuel tanks which are located above the inner bottom forward or aft of the machinery space in cubic meters. | | |
| P = the volume of passenger spaces below the margin line. | | |
| V = the volume of the vessel below the margin line. | | |
| N = the number of passengers that the vessel is to be certificated to carry. | | |

Table [171.065](/on/2024-09-23/title-46/section-171.065)(b)—Table of X

| Vessel LBP in feet (meters) | X1 |
| --- | --- |
| 430 (131) | 1.336 |
| 440 (134) | 1.285 |
| 450 (137) | 1.230 |
| 460 (140) | 1.174 |
| 470 (143) | 1.117 |
| 480 (146) | 1.060 |
| 490 (149) | 1.002 |
| 500 (152) | 0.944 |
| 510 (155) | 0.885 |
| 520 (158) | 0.826 |
| 530 (162) | 0.766 |
| 540 (165) | 0.706 |
| 550 (168) | 0.645 |
| 554 (169) and up | 0.625 |
| | |
| --- | --- |
| 1 Interpolate for intermediate values. | |

[CGD 79-023, [48 FR 51017](https://www.federalregister.gov/citation/48-FR-51017), Nov. 4, 1983, as amended by USCG-2007-0030, [75 FR 78085](https://www.federalregister.gov/citation/75-FR-78085), Dec. 14, 2010]