Granite (marble) blocks
|Infobox on Granite (marble) blocks|
|Example of Granite (marble) blocks|
|Stowage factor (in m3/t)||0,77 m3/t (bulk)|
|Humidity / moisture||-|
|Risk factors||See text|
Granite (marble) blocks
Granite is a common type of intrusive, felsic, igneous rock which is granular and phaneritic in texture. This rock consists mainly of quartz, mica, and feldspar. Occasionally some individual crystals (phenocrysts) are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is sometimes known as a porphyry. Granites can be pink to gray in colour, depending on their chemistry and mineralogy. By definition, granite is an igneous rock with at least 20% quartz by volume. Granite differs from granodiorite in that at least 35% of the feldspar in granite is alkali feldspar as opposed to plagioclase; it is the alkali feldspar that gives many granites a distinctive pink colour. Outcrops of granite tend to form tors and rounded massifs. Granites sometimes occur in circular depressions surrounded by a range of hills, formed by the metamorphic aureole or hornfels. Granite is usually found in the continental plates of the Earth's crust.
Granite is nearly always massive (lacking internal structures), hard and tough, and therefore it has gained widespread use as a construction stone. The average density of granite is between 2.65 and 2.75 g/cm3.
Sculptures and memorials.
Granite has been extensively used as a dimension stone and as flooring tiles in public and commercial buildings and monuments.
Engineers have traditionally used polished granite surface plates to establish a plane of reference, since they are relatively impervious and inflexible. Sandblasted concrete with a heavy aggregate content has an appearance similar to rough granite, and is often used as a substitute when use of real granite is impractical.
Shipment / Storage / Risk factors
Conventional shipment of granite blocks
There is an increasing tendency for granite blocks to be stowed mainly in "drop-stow" i.e. in hatch squares, leaving large gaps between the sides of the stows of blocks (three or four high) and the ship's side frames.
A variation upon this is a "pyramid" stow, in which the bottom one or two blocks are floored out, ship's side to ship's side, and then a stepped stow made, ending up five or six high in the hatch square. In addition to being impossible to secure adequately, such a stow also has the effect of concentrating the weight of the stow in the centre of the hold, possibly exceeding the permissible "tonnes per square metre" tank top capacity in that area.
The reasons for such stowage may be due to the time taken to "wing out". Such stowage would also require the use of large capacity lift trucks, which are expensive for stevedores to purchase and operate and are frequently not available. It is far quicker and cheaper for shippers, charterers and stevedores simply to lower most, or all of these blocks into hatch square stowage.
By the very nature of this cargo, a ship loaded with granite blocks will have a large GM and be stiff. When subject to external forces such as beam swell, the ship will have a short period of roll and a tendency to jerk to the upright which may in turn place excessive strain on the lashings.
Hence, masters of ships loading granite blocks are recommended to ensure that:
1. A level, ship's side to ship's side stow is made. On ships fitted with side hopper tanks, the blocks should be stepped out until the upper tier or tiers make contact with ship's side frames, protected by dunnage.
Due to the difficulty in winging out these heavy blocks into hopper tanks or outward flaring ship's side frames, the optimum stowage position is in a centre hold. Stowages in the extreme ends of forward and after holds should be avoided.
2. Any unavoidable large gaps in the stow, due to varying dimensions of the blocks or an insufficient number of blocks to complete the top tier, should be left in the centre of the stow, where they can be securely braced with substantial timber shores.
3. Smaller gaps between individual blocks in the completed stow, as a result of varying dimensions of blocks, should be chocked and wedged with timber, creating a solid, ship's side to ship's side stow.
4. Substantial hardwood timber bearers should be used under the blocks; softwood is not recommended as this will crush and compress under the weight of the blocks. Care must be taken that the dunnage laid between the bottom tier of the blocks and the tank top is adequately spaced to spread the weight of the eventual stow evenly over the tank top, avoiding localised loading between strength members in the double bottom tanks.
The use of round or partially round "pole" dunnage should be avoided. If the blocks do shift as the vessel rolls, these will simply serve as rollers under the blocks, exacerbating any movement.
5. A proper granite stow (as described above) hardly requires securing. This should be necessary only on free-standing blocks (if these cannot be avoided) or across the face of part hatch stows. Shoring or tomming, between outboard blocks and ship's sides is of little use and should not be required if the cargo has been correctly stowed.
Lashing wires should be of at least 16mm diameter, protected from fraying where they are led around the sharp corners of blocks. Rigging screws must be accessible, with sufficient thread capacity remaining to permit re-tensioning on passage. A sufficient number of wire rope clips - minimum three - correctly fitted, should be used on all wire rope joins and at rigging screws.
Cargoes of granite blocks, properly stowed, dunnaged, chocked and secured into a solid, level, ship's side to ship's side block may well be time consuming and costly to stow, but are perfectly safe to carry, if the above guidelines are observed. On the other hand, free-standing, or "pyramid" stows are extremely hazardous. The consequences of several hundred tons of granite blocks of up to forty tonnes individual weight rolling and coming into heavy contact with the side shell of the ship needs no elaboration.
Shipment in containers
Granite (marble) blocks
Following rules apply for shipments of marble blocks in containers:
- Cargo weight must not exceed maximum payload of the equipment.
- Only spreaders may be used to lift the container, use of slings or chains is not acceptable.
Weight of marble blocks has to be distributed evenly on the floor, depending the weight up to a minimum of 6 x 6 inch (15 x 15 cm) square timber. Granite and marble blocks have to be secured by wooden bearers/supports and braced by use of wedges and chains or belts. Depending type/year built the lashing eyes on the flatracks do have a SWL of 2 - 6 Metric Ts.
It is not allowed to use the so-called drop-rings (only SWL 2 Metric tons) for lashing blocks.
Open Top Containers
Weight of granite and marble blocks has to be distributed evenly on the floor, by use of (depending on the weight) minimum 6 x 6 inch square timber. Blocks have to be secured by wooden layers and braced by use of wedges and chains or belts. Please note that the securing rings break load, in the container, is SWL 2.0 Metric Ts wherefore bracing of blocks has to be done in a professional manner.
Note: Loading and discharging of marble blocks in open tops have to be by lifting in and out of the container by use of crane, and NOT through the container doors.
Shipper has to issue a guarantee that blocks will be loaded and discharged by use of crane. Shipper has to be held liable for all loss and/or damages, if any, to the container equipment and related expenses, if above mentioned instructions are not followed.
Marble slabs are allowed in closed dry containers, the weight has to be evenly distributed all over the container floor by use of wooden bearers. The slabs must be properly crated, and the slabs itself must not touch the floor of the container directly.
Only STEEL CONTAINERS to be used.
Marble and granite blocks in dry containers are accepted provided below guidelines are adhered to.
- Only sound units to be used.
- The maximum load per meter (line load) must not exceed 4,2 metric tons/meter, for a 20ft unit or 2,0 metric tons/meter, for a 40ft unit.
- A rule of the thumb as addition: for 20ft containers it is max 1,5 Metric ton per cross member and for 40 ft containers is max 0,75 Metric tons per cross member.
- During stuffing the container must be landed on an even surface and all 4 corner-casting must rest firmly on the ground.
- Blocks to be landed on 2 pieces bearers of (depending their weight) of 6 x 6 inches (15 x 15 cm) wooden layers, of good quality. This is to distribute the weight of the block over the entire length of container floor
- The 6 x 6 inch (15 x 15 cm) wooden bearers must be placed on either side of the container centre line, with a minimum distance, from the centreline, of 0.4 m/40 cm/1'4.
- Blocks must be duly secured around by timber at the bottom to secure the basis avoiding possible shifting when the ship meets adverse weather en-route. Each block must be additional lashed with min. 2 lashings of wires or lashing belts. When wires are being used for lashing so called "edge protectors" to be used avoiding that they are "eating" into the relative soft stones.
- When poly/nylon belts are being used same but this time for protecting belt damages.
- When loading the container with a forklift, the maximum point load of the container must be observed. These are laid down in ISO1496. Newer containers are tested to a maximum axle load of 7260 kg, older to 5460 kg. Forklift trucks with a load-carrying capacity of 2 metric tons have a maximum axle load of approx. 5 metric tons when loaded, and may therefore be allowed access to the container floor. Forklift trucks with a load-carrying capacity of 2.5 tons may exceed the maximum axle load of 5460 kg, but are generally still suitable for access to the container. Problems may arise with battery-powered electric forklift trucks, because of their relatively high dead weight. Such forklifts frequently exceed the maximum axle load.
UNDER NO CIRCUMSTANCES MAY A LADEN CONTAINER BE HANDLED BY MEANS OF WIRE SLING.