Section 7 Freeboard

701. General

1. The requirements of the 1988 LL Protocol, including those relating to certification, should apply to all units and certificates should be issued as appropriate. The minimum freeboard of units which cannot be computed by the normal methods laid down by that Protocol should be determined on the basis of meeting the applicable intact stability, damage stability and structural requirements for

transit conditions and drilling operations while afloat. The freeboard should computed from the Protocol where applicable.

2. The requirements of the 1988 LL Protocol with respect to weathertightness decks, superstructures, deckhouses, doors, hatchway covers, other openings,

not be less than that

and watertightness of ventilators, air pipes,

scuppers, inlets and discharges, etc., should be taken as a basis for all units in the afloat condition.

3. In general, heights of hatch and ventilator coamings, air pipes, door sills, etc., in exposed positions and their means of closing should be determined by consideration of the provisions regarding both intact and damage stability.

4. All downflooding openings which may become submerged before the angle

of inclination at which

the required area under the intact righting arm curve is achieved should be fitted with weathertight closing appliances.

5. With regard to damage stability, the provisions of 402. 1 (2), 402. 2 and 602. 2 should apply.

6. The Society should give special consideration to the position of openings which cannot be closed in emergencies, such as air intakes for emergency generators, having regard to the intact righting arm curves and the final waterline after assumed damage.

702. Surface units

1. Load lines should be assigned to surface units as calculated under the terms of the 1988 LL Protocol and should be subject to all the conditions of assignment of that Protocol.

2. Where it is necessary to assign a greater than minimum freeboard to meet the provisions regarding intact or damage stability or on account of any other restriction imposed by the Society, regulation

6(6) of the 1988 LL Protocol should apply. When such a freeboard is assigned, seasonal above the centre of the ring should not be marked and any seasonal marks below the centre

marks of the

ring should be marked. If a unit is assigned a greater than minimum freeboard at the the owner, regulation 6(6) need not apply.

3. Where moonpools are arranged within the hull in open communication with the sea, the the moonpool should not be included in the calculation of any hydrostatic properties. If

request of

volume of the moon-

pool has a larger cross-sectional area above the waterline at 85% of the depth for freeboard than

below, an addition should be made to the geometric freeboard corresponding to the lost buoyancy. This addition for the excess portion above the waterline at 85% of the depth for freeboard should be made as prescribed below for wells or recesses. If an enclosed superstructure contains part of the moonpool, deduction should be made for the effective length of the superstructure. Where open wells or recesses are arranged in the freeboard deck, a correction equal to the volume of the well or recess to the freeboard deck divided by the waterplane area at 85% of the depth for freeboard should be made to the freeboard obtained after all other corrections, except bow height correction, have been made. Free surface effects of the flooded well or recess should be taken into account in stability calculations.

4. The procedure described in Par 3 should also apply in cases of small notches or relatively narrow cut- outs at the stern of the unit.

5. Narrow

wing extensions at the stern of the unit should be considered as appendages and excluded

for the determination of length (L) and for the calculation of freeboards. The Society should de-

termine

the effect of such wing extensions with regard to the provisions relating to the strength of

unit based upon length (L).

703. Self-elevating units

1. Load lines should be assigned to self-elevating units as calculated under the terms of the 1988 LL Protocol. When floating, or when in transit from one operational area to another, units should be subject to all the conditions of assignment of that Protocol unless specifically excepted. However, these units should not be subject to the terms of that Protocol while they are supported by the sea- bed or are in the process of lowering or raising their legs.

2. The minimum freeboard of units which due to their configuration cannot be computed by the nor- mal methods laid down by the 1988 LL Protocol should be determined on the basis of meeting ap- plicable provisions regarding intact stability, damage stability and structure in the afloat condition.

3. Where it is necessary to assign a greater than minimum freeboard to meet intact or damage stabil- ity provisions or on account of any other restriction imposed by the Society, regulation 6(6) of the 1988 LL Protocol should apply. When such a freeboard is assigned, seasonal marks above the cen- tre of the ring should not be marked and any seasonal marks below the centre of the ring should be marked. If a unit is assigned a greater than minimum freeboard at the request of the owner, regulation 6(6) need not apply.

4. Where moonpools are arranged within the hull in open communication with the sea, the volume of the moonpool should not be included in the calculation of any hydrostatic properties. If the moon- pool has a larger cross-sectional area above the waterline at 85% of the depth for freeboard than below, an addition should be made to the geometric freeboard corresponding to the lost buoyancy. This addition for the excess portion above the waterline at 85% of the depth for freeboard should be made as prescribed below for wells or recesses. If an enclosed superstructure contains part of the moonpool, deduction should be made for the effective length of the superstructure. Where open wells or recesses are arranged in the freeboard deck, a correction equal to the volume of the well or recess to the freeboard deck divided by the waterplane area at 85% of the depth for freeboard should be made to the freeboard obtained after all other corrections, except bow height correction, have been made. Free surface effects of the flooded well or recess should be taken into account in stability calculations.

5. The procedure described in Par 4 should apply in cases of small notches or relatively narrow cut- outs at the stern of the unit.

6. Narrow

wing extensions at the stern of the unit should be considered as appendages and excluded

for the determination of length (L) and for the calculation of freeboards. The Society should de-

termine

the effect of such wing extensions with regard to the requirements of the 1988 LL

Protocol for the strength of unit based upon length (L).

7. Self-elevating units may be manned when under tow. In such cases a unit would be subject to the bow height and reserve buoyancy requirements which may not always be possible to achieve. In such circumstances, the Society should consider the extent of application of regulations 39(1), 39(2) and 39(5) of the 1988 LL Protocol, as amended, and give special consideration to such units, hav- ing regard to the occasional nature of such voyages on predetermined routes and to prevailing weather conditions.

8. Some self-elevating units utilize a large mat or similar supporting structure which contributes to the buoyancy when the unit is floating. In such cases the mat or similar supporting structure should be ignored in the calculation of freeboard. The mat or similar supporting structure should, however, al- ways be taken into account in the evaluation of the stability of the unit when floating since its vertical position relative to the upper hull may be critical.

704. Column-stabilized units

1. The hull form of this type of unit makes the calculation of geometric freeboard in accordance with the provisions of chapter III of the 1988 LL Protocol impracticable. Therefore the minimum free- board of each column-stabilized unit should be determined by meeting the applicable provisions for:

(1) the strength of the unit’s structure;

(2) the minimum clearance between passing wave crests and deck structure (see Ch 3, 707.); and (3)intact and damage stability.

2. The minimum freeboard should be marked in appropriate locations on the structure.

3. The enclosed deck structure of each column-stabilized unit should be made weathertight.

4. Windows, sidescuttles and portlights, including those of the non-opening type, or other similar openings should not be located below the deck structure of column-stabilized units.

5. The Society should give special consideration to the position of openings which cannot be closed in emergencies, such as air intakes for emergency generators, having regard to the intact righting arm curves and the final waterline after assumed damage.