HULL HULL FRAMING FRAMING SYSTEMSSYSTEMS

Modern ships vary Modern ships vary considerably in the details of considerably in the details of their construction, according their construction, according

to their size and type, but to their size and type, but almost all conform to one of almost all conform to one of

three basic systems of three basic systems of construction construction

►The sketches, here, The sketches, here, merely illustrate the main merely illustrate the main features of each system features of each system and are kept as simple as and are kept as simple as possible, for purposes of possible, for purposes of comparison. comparison.

Transverse Transverse SystemSystem

►Wooden ships were always Wooden ships were always built on this system, built on this system, because closely spaced because closely spaced transverse frames were transverse frames were needed to hold the planks needed to hold the planks together so that the seams together so that the seams could be caulked. could be caulked.

► It was also necessary to It was also necessary to use it because sailing ships use it because sailing ships needed considerable needed considerable transverse strength to transverse strength to enable them to resist the enable them to resist the racking stresses set up by racking stresses set up by the masts and rigging. the masts and rigging.

►Longitudinal strength Longitudinal strength was less important in was less important in these ships because they these ships because they were comparatively small were comparatively small and hogging and sagging and hogging and sagging stresses were not large.stresses were not large.

►This system is not the most This system is not the most efficient for steel steam ships, efficient for steel steam ships, but it has continued in general but it has continued in general use until recently. This was use until recently. This was partly because it was cheap to partly because it was cheap to build and served its purpose; build and served its purpose; and partly because a suitable and partly because a suitable alternative was not available for alternative was not available for many years.many years.

Longitudinal Longitudinal Systems Systems

►With the coming of With the coming of steam ships, racking steam ships, racking stresses became less stresses became less important, but hogging important, but hogging and sagging stresses and sagging stresses became more serious as became more serious as ships grew longer. ships grew longer.

►It soon became obvious It soon became obvious that more longitudinal that more longitudinal strength could be achieved strength could be achieved by running the frames by running the frames longitudinally (fore and aft), longitudinally (fore and aft), provided that reasonable provided that reasonable transverse strength was transverse strength was maintained. maintained.

►Various attempts were Various attempts were made to do this during made to do this during the 19th century, but all the 19th century, but all had serious had serious disadvantages and none disadvantages and none were generally adoptedwere generally adopted

►Early in this century, a Early in this century, a satisfactory system of satisfactory system of longitudinal framing was longitudinal framing was invented, which came to invented, which came to be called the 'Isherwood be called the 'Isherwood System', after its System', after its inventor. inventor.

► This has longitudinal frames This has longitudinal frames at the bottom, sides and at the bottom, sides and decks, supported by widely decks, supported by widely spaced transverse web frames, spaced transverse web frames, called 'transverses'. It gives called 'transverses'. It gives great longitudinal strength and great longitudinal strength and is much used for oil-tankers is much used for oil-tankers and other types of bulk carrier.and other types of bulk carrier.

►A few dry cargo ships were built A few dry cargo ships were built on this system in the past, but it is on this system in the past, but it is not now used for them because not now used for them because the transverses interfere too the transverses interfere too much with the stowage of cargo. much with the stowage of cargo. A dry cargo ship of this type is A dry cargo ship of this type is shown in the sketch, however, shown in the sketch, however, because it serves as a good because it serves as a good illustration of the system.illustration of the system.

►Combination Combination SystemSystem

Combination System-Combination System-This was introduced to This was introduced to overcome the overcome the disadvantages of the disadvantages of the longitudinal system for longitudinal system for dry cargo ships. dry cargo ships.

► The longitudinal frames are The longitudinal frames are retained in the bottom and retained in the bottom and under the strength deck, where under the strength deck, where they give great longitudinal they give great longitudinal strength; but transverse frames strength; but transverse frames are fitted on the ship's side, are fitted on the ship's side, where the longitudinal stresses where the longitudinal stresses are smaller. are smaller.

► Plate floors and heavy Plate floors and heavy transverse beams are transverse beams are fitted at intervals to give fitted at intervals to give transverse strength and transverse strength and to support the to support the longitudinals.longitudinals.

►This system was not widely This system was not widely used for riveted ships, used for riveted ships, although a number were although a number were built in this way, but it came built in this way, but it came more into use with the more into use with the coming of all-welded ships. coming of all-welded ships.

►This was partly because it was This was partly because it was found that, if these ships were found that, if these ships were built on the transverse built on the transverse system, their- decks and system, their- decks and bottom tended to corrugate bottom tended to corrugate under hogging and sagging under hogging and sagging stresses: whereas the stresses: whereas the longitudinal frames prevent longitudinal frames prevent this from happening. this from happening.

►Lloyds' Rules now require Lloyds' Rules now require longitudinals to be fitted, in longitudinals to be fitted, in general, in the bottoms and general, in the bottoms and under strength decks of all ships under strength decks of all ships of over 120 metres long: so it of over 120 metres long: so it seems that this system will seems that this system will eventually replace the transverse eventually replace the transverse one for all larger dry cargo ships.one for all larger dry cargo ships.

►The combination system is The combination system is also often used for small to also often used for small to medium-sized oil tankers medium-sized oil tankers and for some other types of and for some other types of bulk carrier, for which it has bulk carrier, for which it has certain slight advantages.certain slight advantages.

CantileverCantilever

framing framing

►This is really only a This is really only a modification of the modification of the combination system, but is combination system, but is included here because of its included here because of its special features. It has been special features. It has been developed for some modern developed for some modern types of ship, which have very types of ship, which have very long and wide hatchwayslong and wide hatchways

►In these ships, there is too In these ships, there is too little left of the decks and little left of the decks and beams to give the necessary beams to give the necessary strength to resist longitudinal strength to resist longitudinal and transverse stresses; so and transverse stresses; so the strength has to be made the strength has to be made up in other ways.up in other ways.

►Transverse strength is Transverse strength is maintained by using very strong maintained by using very strong hatch end beams wherever hatch end beams wherever possible and by fitting special possible and by fitting special web frames, called 'cantilevers', web frames, called 'cantilevers', at frequent intervals abreast of at frequent intervals abreast of the hatchways.the hatchways.

►To give longitudinal strength, To give longitudinal strength, the sheer strake and deck the sheer strake and deck stringer plate are much stringer plate are much heavier than normal; whilst heavier than normal; whilst the hatch side coamings are the hatch side coamings are extra deep and are often extra deep and are often made continuous throughout made continuous throughout the ship. the ship.

►Sometimes, the hull is Sometimes, the hull is also extended upwards at also extended upwards at the sheer strake, to form the sheer strake, to form a strong box girder in a strong box girder in place of the ordinary place of the ordinary bulwark or rails. bulwark or rails.

►If the ship is of the 'twin -If the ship is of the 'twin -hatch type' (with two hatch type' (with two hatches abreast), a deck hatches abreast), a deck girder or longitudinal girder or longitudinal bulkhead is also fitted at bulkhead is also fitted at the centre linethe centre line