Section 2 Hatchways

201. Hatch coaming

1. The height of hatch coaming above the deck is not to be less than 600 mm in position I and 450 mm in position II . However, it may be of the height given in Table 9.1 where the dredger is less than 30 m in length.

Table 9.1 Height of hatch coaming

2. The thickness of hatch coaming is not to be less than that obtained from the following formula.

However, it is not necessary to exceed 11 mm .

0.05 Ä + 5.0 (mm)

Ch 9

3. The hatch coaming is to be provided with horizontal stiffeners at the proper position and to be strengthened with half round steel bar or proper means on the upper edge of coaming.

4. The hatch coaming is to be supported by rigid brackets extending from horizontal stiffeners to the deck or stays at an interval of about 3 m .

5. For the sliding type hatch covers, the hatch coaming is to be strengthened properly in accordance with the weight of hatch cover.

202. Hatch covers

1. The thickness of hatch cover plating is not to be less than 1 % of stiffener space or 6 mm , whichever is the greater.

2. The steel hatch cover is to be provided with stiffeners at an interval not exceeding 750 mm , and the section modulus of hatch cover is not to be less than that obtained from the following formula.

ÆÅŶË (cmĖ )

Å : spacing of stiffeners (m )

Ŷ : span of stiffeners (m )

Æ : Value obtained from the following formula

0.15 Ä + 12

3. The boundaries of steel hatch cover are to be provided with stiffeners with sufficient stiffness in order to avoid the deflection when handled.

4. The scantling of hatch beams is to comply with the requirements specified in Par 2. However, Å is the space of hatch beams and Ŷ is the length of hatch beam. And, the thickness of wooden covers is not to be less than that obtained from the following formula. However, it is not to be less than 60 mm in any case.

ĖŊÅ (mm )

Å : space of hatch beams (m )

203. Others

1. The depth of hatch beams and breadth of face plates are to have proper scantling in consideration of trimming and deflection.

2. The supporting parts of hatch coaming are to be reinforced properly.

3. The supporting materials to support the hatch beams are to be of steel and the breadth and the thickness of supportings are 75 mm or more and 12.5 mm or more respectively.

4. Each supportings fitted on the side coaming are to have proper devices to prevent falling off the hatch beams.