18" x 24" Multi-Bolt Semi-Flush Manhole with Center Lifting Handle (Model #MB504-1824A) - Painted Steel

This semi-flush manhole serves as a primary access closure for high-traffic deck areas where a standard raised coaming would disrupt operations. The central, recessed drop-handle allows shipboard personnel to securely lift and maneuver the cover plate once the 24 perimeter high-tensile fasteners are unbolted. By recessing the sealing flange slightly below the deck line, the assembly mechanically compresses the commercial-grade Buna-N gasket to maintain watertight integrity under severe deck wetness and hydrostatic head pressures.

Intended Use Cases:

• Access to large fuel oil, ballast, and freshwater storage tanks located in high-traffic cargo spaces.
• Inspection hatches for deep dry voids and cofferdams underneath vehicle or cargo working decks.
• Removable equipment clearance openings where a low deck profile is mandatory for operations.
• Structural retrofits on heavy-duty workboats and deck barges requiring an accessible, low-clearance hatch solution.

Primary Industries & Vessel Types:

• Flat-deck cargo barges, hopper barges, and ro-ro vessels.
• Ocean-going push boats, harbor tugs, and offshore supply vessels (OSVs).
• Commercial fishing vessels, crabbing boats, and processing platforms.
• Marine infrastructure equipment, floating cranes, and spud barges.

• Low-Profile Semi-Flush Deck Profile: Sits nearly level with the deck plate to minimize cargo snagging and vehicle obstruction while keeping the sealing perimeter protected.
• Integrated Center Lifting Handle: Recessed flush within the cover plate to ensure a smooth deck line while offering immediate mechanical leverage for manual removal of the heavy-duty plate.
• High-Density 24-Bolt Securement: Distributes clamping force evenly across the larger 18" x 24" span to prevent cover deflection, eliminate stress concentrations, and guarantee zero-leakage performance.
• Resilient Buna-N Gasket Composition: Delivers superior resistance to marine oils, fuel, and saltwater, ensuring a long-lasting, watertight seal under heavy cyclic loading.

• Deck Surface Preparation: Flame-cut the deck opening using the official semi-flush template to accommodate the 24" x 30" mounting ring flange footprint, then grind the perimeter smooth and clean to bare white metal to remove all rust, mill scale, and slag.
• Welding & Distortion Control: Tack-weld the semi-flush deck ring flange into the cutout, utilizing a staggered welding sequence to prevent thermal warping of the machined sealing seats, and complete the continuous structural fillet weld according to AWS D1.1.
• Handle Pocket Inspection: Verify that the recessed handle pocket is completely free of weld spatter, debris, or water pooling prior to final assembly to ensure the drop-handle functions smoothly through its full range of motion.
• Debris Inspection & Cleaning: Thoroughly inspect the interior seat and seal channel for weld spatter, slag, or grinding grit before inserting the gasket or attempting to close the hatch plate.
• Gasket Seating & Torque Sequence: Verify the Buna-N gasket is seated flat and uniform within its groove without twists, then hand-tighten all 24 bolts before applying final torque in a progressive star/cross-weave pattern to ensure uniform mechanical compression.
• Vessel Class Compliance: Cross-reference all final weld profiles, positioning, and NDT requirements with the vessel designer's specifications and governing class society rules (e.g., ABS, Lloyds, DNV) prior to pressure testing.