The Assignment is to prepare the shell expansion of any ship on a drawing sheet. To avoid complications the bow and aft part are not drawn.
Shell Expansion Shell expansion is a two-dimensional drawing showing the arrangement of the shell plates, stiffening members, all butts, seams, fillets welds etc. The drawing shows the various plate strakes and their identification number. The purpose of the drawing is to assist in the plate development and subsequently the cutting of the strakes prior to fabrication and erection.
2. PROCEDURE The shell is expanded in the transverse plane, where longitudinal distances are measured relative to the centreline axis. All vertical dimensions in this drawing are taken around the girth of the vessel rather than their being a direct vertical projection. This technique illustrates both the side and bottom plating as a continuous whole. The girth of the main deck, tween deck, double bottom etc. is taken at each station and the ordinates are plotted to get the profile of the shell expansion. Bulkheads are fixed vertically and after that the strakes are decided. Strakes of steel plating are distinguished by letters from the keel onwards, the garboard strake being ‘A’. The plates in each strake are numbered from aft to forward. The girth of the ship decreases towards the ends and so the width of the plate must be decreased in these parts. To save making the plates too narrow, at the ends of the ship, a number of pairs of adjacent strakes are run in to one. This is done by means of a stealer plate. The strakes taken from the midship and primary members are also plotted. The maximum size of the plate is 10m x 3 m and other checks which are done on shell expansion are given below.
The minimum distance between two butt welds is 200mm. The minimum distance between any other two welds is 100mm. The angle between two seams at the joint should be greater than 600. Butts or seams at the position of stiffening member should be avoided.
3. SELECTED SHIP & OTHER DETAILS
The selected ship is a Multipurpose General Cargo Vessel designed under the Lloyd’s Register of Shipping rules and regulations. The ship has a deadweight of about 22000dwt. The vessel should run at a speed of 14.5 knots and its area of operation is from Mumbai– Mombasa – Toamasina – Mumbai. Multipurpose General Cargo Carrier as the name indicates is a ship, which should be able to handle multiple requirements such as the ability to carry general cargo (cargo in granular form, bale form, sacks, etc), palletised cargo (containers or any other similar packing) and heavy loads in general.
LOA LBP B (mld) D (mld) T (mld)
163.7 158.4 24.2 14.75 10.2
m m m m m
Deadweight Speed Radius of Action
The attached body plan has dimensions. 24.2cm x 14.75cm ( the y axis of sed has a scaling of 1:100)
& the shell expansion drawing dimensions are estimated to be. 105.6cm x 26.2cm(the x axis of sed has a scaling of 1:150)
cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm cm
The standard plate dimensions taken are : Keel Strake - 1m x 6m Garboard Strake – 2m x 6m Bilge Strake – 2.5m x 6m Sheer Strake – 2.2 x 6m Other plates are cut keeping in mind the need for minimizing the cutting of plates and the need for continuity or continuous seam length.
Table showing bilge length for drawing the bilge strake :