Architecture Bulk carrier

1 architecture

1.1 machinery
1.2 hatches
1.3 hull

architecture

a bulk carrier s design largely defined cargo carry. cargo s density, known stowage factor, key factor. densities common bulk cargoes vary 0.6 tons per cubic meter light grains 3 tons per cubic meter iron ore.

the overall cargo weight limiting factor in design of ore carrier, since cargo dense. coal carriers, on other hand, limited overall volume, since bulkers can filled coal before reaching maximum draft.

for given tonnage, second factor governs ship s dimensions size of ports , waterways travel to. example, vessel pass panama canal limited in beam , draft. designs, ratio of length-to-width ranges between 5 , 7, average of 6.2. ratio of length-to-height between 11 , 12.

machinery

the engine room on bulker near stern, under superstructure. larger bulkers, handymax up, have single two-stroke low-speed crosshead diesel engine directly coupled fixed-pitch propeller. electricity produced auxiliary generators and/or alternator coupled propeller shaft. on smaller bulkers, 1 or 2 four-stroke diesels used turn either fixed or controllable-pitch propeller via reduction gearbox, may incorporate output alternator. average design ship speed bulkers of handysize , above 13.5–15 knots (25.0–27.8 km/h; 15.5–17.3 mph). propeller speed relatively low, @ 90 revolutions per minute, although depends on size of propeller.

as result of 1973 oil crisis, 1979 energy crisis, , resulting rise in oil prices, experimental designs using coal fuel ships tested in late 1970s , 1980s. australian national lines (anl) constructed 2 74,700-ton coal-burner ships called river boyne , river embely. along 2 constructed tnt called tnt capricornia , tnt capentaria , renamed fitzroy river , endeavor river. these ships financially effective duration of lives, , steam engines able generate shaft-power of 19,000 horsepower (14,000 kw). strategy gave interesting advantage carriers of bauxite , similar fuel cargoes, suffered poor engine yield compared higher maintenance cost , efficient modern diesels, maintenance problems due supply of ungraded coal, , high initial costs.

hatches

the sliding hatchcovers of zaira.

a hatch or hatchway opening @ top of cargo hold. mechanical devices allow hatches opened , closed called hatch cover. in general, hatch covers between 45% , 60% of ship s breadth, or beam, , 57% 67% of length of holds. efficiently load , unload cargo, hatches must large, large hatches present structural problems. hull stress concentrated around edges of hatches, , these areas must reinforced. often, hatch areas reinforced locally increasing scantlings or adding structural members called stiffeners. both of these options have undesired effect of adding weight ship.

as 1950s, hatches had wooden covers broken apart , rebuilt hand, rather opened , closed. newer vessels have hydraulic-operated metal hatch covers can operated 1 person. hatch covers can slide forwards, backwards, or side, lift or fold up. essential hatch covers watertight: unsealed hatches lead accidental cargo hold flooding, has caused many bulkers sink.

regulations regarding hatch covers have evolved since investigation following loss of mv derbyshire. load line conference of 1966 imposed requirement hatch covers able withstand load of 1.74 tons/m due sea water, , minimum scantling of 6 mm tops of hatch covers. international association of classification societies increased strength standard creating unified requirement s21 in 1998. standard requires pressure due sea water calculated function of freeboard , speed, hatch covers located on forward portion of ship.

hull

unloaded trillium-class dry bulker @ port of redwood city

bulkers designed easy build , store cargo efficiently. facilitate construction, bulkers built single hull curvature. also, while bulbous bow allows ship move more efficiently through water, designers lean towards simple vertical bows on larger ships. full hulls, large block coefficients, universal, , result, bulkers inherently slow. offset efficiency. comparing ship s carrying capacity in terms of deadweight tonnage weight when empty 1 way measure efficiency. small handymax ship can carry 5 times weight. in larger designs, efficiency more pronounced: capesize vessels can carry more 8 times weight.

bulkers have cross-section typical of merchant ships. upper , lower corners of hold used ballast tanks, double bottom area. corner tanks reinforced , serve purpose besides controlling ship s trim. designers choose angle of corner tanks less of angle of repose of anticipated cargoes. reduces side-to-side movement, or shifting, of cargo can endanger ship.

the double bottoms subject design constraints. primary concern high enough allow passage of pipes , cables. these areas must roomy enough allow people safe access perform surveys , maintenance. on other hand, concerns of excess weight , wasted volume keep double bottoms tight spaces.

bulker hulls made of steel, mild steel. manufacturers have preferred high-tensile steel in order reduce tare weight. however, use of high-tensile steel longitudinal , transverse reinforcements can reduce hull s rigidity , resistance corrosion. forged steel used ship parts, such propeller shaft support. transverse partitions made of corrugated iron, reinforced @ bottom , @ connections. construction of bulker hulls using concrete-steel sandwich has been investigated.

double hulls have become popular in past ten years. designing vessel double sides adds breadth, since bulkers required have double bottoms. 1 of advantages of double hull make room place structural elements in sides, removing them holds. increases volume of holds, , simplifies structure helps in loading, unloading, , cleaning. double sides improve ship s capacity ballasting, useful when carrying light goods: ship may have increase draft stability or seakeeping reasons, done adding ballast water.

a recent design, called hy-con, seeks combine strengths of single-hull , double-hull construction. short hybrid configuration, design doubles forward-most , rear-most holds , leaves others single-hulled. approach increases ship s solidity @ key points, while reducing overall tare weight.

since adoption of double hull has been more of economic purely architectural decision, argue double-sided ships receive less comprehensive surveys , suffer more hidden corrosion. in spite of opposition, double hulls became requirement panamax , capesize vessels in 2005.

freighters in continual danger of breaking backs , longitudinal strength primary architectural concern. naval architect uses correlation between longitudinal strength , set of hull thicknesses called scantlings manage problems of longitudinal strength , stresses. ship s hull composed of individual parts called members. set of dimensions of these members called ship s scantlings. naval architects calculate stresses ship can expected subjected to, add in safety factors, , can calculate required scantlings.

these analyses conducted when traveling empty, loading , unloading, when partially , loaded, , under conditions of temporary overloading. places subject largest stresses studied carefully, such hold-bottoms, hatch-covers, bulkheads between holds, , bottoms of ballast tanks. great lakes bulkers must designed withstand springing, or developing resonance waves, can cause fatigue fractures.

since 1 april 2006, international association of classification societies has adopted common structural rules. rules apply bulkers more 90 meters in length , require scantlings calculations take account items such effect of corrosion, harsh conditions found in north atlantic, , dynamic stresses during loading. rules establish margins corrosion, 0.5 0.9 mm.