PATENT STEEL HATCH COVERS

Patent steel hatch covers having direct securing arrangements, e.g. MacGregor Steel Hatches are a great improvement on the portable type previously described and are universally fitted for weather decks. They consist of plated covers stiffened by webs or stiffeners, watertightness being obtained by gaskets and clamping devices.

Securing cleats and cross joint wedges, together with suitable jointing material are to be fitted, the cleats are to be spaced to ensure weathertightness with a minimum of two per panel at the sides and with one arranged adjacent to each corner at the hatch ends. The cross joint wedges are spaced about 1.5 m apart.

The portable sections of folding covers are connected to one another and can easily and quickly be rolled into or out of position, leaving clear hatchways and decks. The normal practice is for the lengthwise opening of patent hatches but sideways opening hatches are found on some particular types of ships, e.g. OBO carriers, see pages 85 and 125. Patent steel hatch covers may be operated manually or hydraulically. The illustration shows a folding patent steel hatch cover.

The wheels at the sides of the hatch sections, eccentric rollers, are used for raising the hatch section clear of the coaming and for rolling it along the coaming trackway. As shown the axles of these wheels are so adjusted that when the hatch is in the closed position the weight is no longer borne by them. The jointing fits tightly on the coaming and the hatch is made completely weathertight by fitting and securing the cleats.

The roller is used when the hatch cover is pulled into its stowage position. It engages on the plate edge at the ends of the hatchway and the hatch section is turned into the vertical. Wires, chains or bars attached to the stub axles of these rollers at the centre of the wheel enable all the hatch sections to be drawn back and forth together.

The cross joints are made weathertight as shown with cross joint wedges.

HATCH COAMING

Hatch coaming is a steel structure welded on the weather deck, along the perimeter of the opening on the deck. On top of the coaming plate a bulb end flat bar is welded termed as the table top of the coaming.

The table top is mounted with a compression bar on Port and starboard side coaming, and bulb angle bar at the forward and aft end for providing surface of compression enable achieve weather

tightness of the hatch covers; a track way is mounted for providing a surface for movement of the pontoon eccentric wheels, and flat bar for housing of quick acting cleats.

The hatch coaming plates are adequately strengthened by stays welded at intervals of not exceeding two meters, on all the four sides of the coaming, in addition longitudinal stiffeners may be welded.

The weather deck is fitted with doubler I insert plates at each corner of the hatch opening.

The deck opening corners are rounded off to avoid point of stress concentration; the radius of the corner rounding within the region of 0.3 length from fore and aft end, must be not less than 305 mm, else where not less than 150 mm.

To achieve weather tight joint between the pontoon end and table top of the coaming, each pontoon houses rubber packing along its perimeter; the rubber packing is compressed against the

compression bar on the table top under the pressure of its own weight, additional pressure is exerted by the quick acting cleats and cross wedges; minimum Two quick acting cleats must be provided on each pontoon, the quick acting cleat must nit be more than 30 Cms, away from each corner.

As per load line rules, hatch coaming in position 1 must not be less than 600 mm, else where not less than 450 mm; however, to comply with factory act requirements the height of the coaming is usually not less than 760 mm.

The purpose of hatch coaming is to prevent any water from deck entering the cargo compartment or through the pontoon overlap end, hatch coaming also forms a barrier to prevent accidental fall of

personnel while working on deck.

Hatchways

Hatchways in the majority of dry cargo ships extend across the deck for approximately one-third of the beam. In special types of ship, e.g. container ships, colliers etc., much wider hatchways are fitted as will be seen from the separate cross-sections of these types.

Special arrangements must be made to compensate for the structural discontinuities caused by these large openings; insert plates of increased thickness may be required at the hatch corners as shown. The arrangement of hatch coaming and adjacent structure with rounded hatch corners is illustrated. Note that the hatch coaming should be extended beyond the corner to form a bracket. The deck opening corners should be well-rounded to a reasonable radius, or eliptical or parabolic in shape, to avoid a concentration of stress at these points.

The deck plating forms an important structural member, especially at the strength deck, in resisting longitudinal stress, but only the plating clear of the hatches can be considered in this respect. If hatchways are made unduly wide, the effective width of this plating is reduced and the thickness has to be increased in order that the cross—sectional area of the steel is maintained.

In addition to the plating, beams will also be cut at hatchways and the ends of the half beams will be connected to the hatch coamings and supported by deck girders. The deck girders are usually integral with the hatch coamings as illustrated. At the ends of the hatchways, in the case of transverse framing and at the sides in the case of longitudinal framing deep hatch end beams will be fitted to support the coamings. A pillar will often be placed near the hatch corners at the intersection of the deck girder and a strong beam.