Vessel Grab/Marine Grab/Clamshell Grab for Ship Cranes

Type: Clamshell Grab for Ship Cranes

Capacity: 0.5m³ ~ 15m³ (customized design supported)

Number of flaps: 2 petals (symmetrical structure)

Applications: bulk materials such as coal, sand, grain, fertilizer, scrap steel, slag, etc.

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Overview

Features

Parameter

Application

Overview

Marine grab is a specialized attachment powered by a marine crane (or quay crane/STS crane) for the efficient grabbing, handling, and unloading of bulk solid materials. Essentially, it's a "mechanical arm" of the crane.

The basic working principle of a clamshell marine grab: The clamshell marine grab operates using two sets of wire rope systems on the crane. The specific working steps are as follows:
1.Support rope/lifting rope: Responsible for the overall lifting and lowering of the clamshell grab.
2.Opening and closing rope: Controls the opening and closing of the grab's jaws through a pulley system.
3.Grabbing process: The clamshell marine grab, in its open state, falls onto the material pile → the opening and closing rope is tightened, the jaws close, and the material is dug in → the grab is lifted to a full capacity.
4.Unloading process: The full grab is moved above the unloading point → the opening and closing rope is released, and the jaws open under their own weight and the pressure of the material → the material is unloaded.

Double-jaw grabs, also known as clamshell grabs, are simple and robust in structure, widely applicable, and easy to maintain. They are mainly used for grabbing bulk materials such as coal, ore, grain, fertilizer, and sand. Multi-jaw grabs, also known as orange peel grabs, are primarily used for grabbing scrap steel, large pieces of ore, construction waste, and household waste.

Features

Clamshell Marine Grabs typically refer to double-jaw grabs, named for their clam-like opening and closing motion. This is one of the most classic and widely used grabs in ship and port loading and unloading. The core advantages of clamshell (double-jaw) grabs lie in their simplicity, robustness, versatility, and economy. They are the "main force" in port bulk materials handling and the first choice for operations requiring high reliability and low overall cost, especially when handling common bulk cargo.

Clamshell grabs are simple and reliable in structure.

The clamshell grab mainly consists of two jaws, a central hinge, a pulley system, and an outer shell, without complex hydraulic or electrical systems (basic model). It features a low failure rate, easy maintenance, highly interchangeable spare parts, and high tolerance to harsh working conditions (dust, humidity).

Clamshell grabs for port cranes have extremely wide applicability.

By adjusting the shape of the jaws, bucket capacity, and material, the marine grab can be adapted to handle a variety of bulk cargoes, from coal and ore to grain, fertilizer, and sand. This "one-machine-for-all" approach reduces the hassle and cost of grab replacement for docks or ships that need to handle multiple materials.

Clamshell grabs are relatively lightweight and have a high grabbing ratio.

Compared to multi-jaw grabs (orange peel grabs) or hydraulic grabs of equivalent capacity, their structure is simpler and their weight is lighter. With the crane's rated lifting capacity remaining constant, clamshell grabs can grab more effective cargo, improving the economy of a single cycle.

Clamshell grabs are a perfect match for standard cranes.

Designed specifically for the most common twin-drum wire rope cranes, no additional modifications to the crane are required. Clamshell grabs for ship cranes can be directly installed and used on almost all port ship cranes and quay cranes, offering extremely high compatibility.

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Parameter

Parameter category	Parameter range/description
Model capacity	0.5m³ ~ 15m³ (customized design supported)
Applicable materials	Medium and low density bulk materials such as coal, sand, grain, fertilizer, scrap steel, slag, etc.
Rated load	1 ~ 30 tons (matching with grab bucket capacity and crane)
Drive mode	Hydraulic drive/wire rope mechanical drive (optional)
Number of flaps	2 petals (symmetrical structure)
Material	Main body: high-strength wear-resistant steel
Applicable crane	Gantry crane, bridge crane, port fixed crane, etc. (need to match lifting weight and opening and closing mechanism)

Key Technical Parameters and Selection Considerations for Clamshell Grabs Used in Port Cranes and Ship Cranes

1. Clamshell Grab Capacity:
The volume of material (cubic meters) the grab can hold when fully loaded. Selection is based on crane capacity, ship hatch size, and operational efficiency requirements.
2. Clamshell Grab/Marine Grab Weight:
The weight of the grab itself. The grab ratio (weight of grabbed material / grab weight) is a key indicator of its performance; a higher ratio is more economical.
3. Compatible Cranes:
Must be compatible with the lifting capacity, wire rope system (single rope, double rope, electro-hydraulic), and working radius of port cranes such as STS cranes and ship cranes.
4. Bulk Material Characteristics:
Specific Gravity: Determines whether to choose a light, medium, or heavy-duty grab.
Particle Size and Flowability: Determines the jaw shape, capacity, and leak-proof design.
Abrasiveness/Corrosivity: Determines the steel material and the use of wear-resistant plates (such as Hardox steel).

Application

1. Bulk Material Port Handling: Unloading: Unloading cargo from arriving bulk carriers (such as Capesize bulk carriers) onto the dock. Loading: Loading cargo from the storage yard onto export vessels. 2. Vessel-Owned Loading and Unloading: Many large engineering vessels (such as self-unloading sand dredgers and grab dredgers) and some cargo ships are equipped with cranes and grabs for self-loading and unloading or dock operations without shore-based equipment. 3. Waterborne Transshipment: Transferring cargo between two vessels (such as from a large ship to a barge). 4. Intra-Dock Transfer: Transferring cargo between storage yards, warehouses, and trucks.