178 Ship Design for Efficiency and Economy

5.4 Weight margin

A reserve or design margin is necessary in the weight calculation for the following reasons:

1.Weight tolerances in parts supplied by outside manufacturers, e.g. in the thickness of rolled plates and in equipment components.

2.Tolerances in the details of the design, e.g. for cement covering in the peak tanks.

3.Tolerances in the design calculations and results.

A recommended weight margin is 3% of the deadweight of a new cargo ship. If the shipbuilder has little experience in designing and constructing the required type of ship, margins in weight and stability should be increased. This is particularly the case if a passenger ship is being built for the first time. If, however, the design is a reconstruction or similar to an existing ship, the margin can be reduced considerably. Smaller marginal weights are one advantage of series production.

Weight margins should be adequate but not excessive. Margins should not be applied simultaneously to individual weights and collective calculations as it is more appropriate to work with one easily controllable weight margin for all purposes.

It is also advisable to create a margin of stability with the weight margin by

placing the centre of mass of the margin weight at around 1:2KG above the keel. The weight margin can be placed at the longitudinal centre of mass G.

New regulations and trends in design lead to increasing weights especially for passenger ships.

5.5 References

CARREYETTE, J. (1978). Preliminary ship cost estimation. Trans. RINA, p. 235

CARSTENS, H. (1967). Ein neues Verfahren zur Bestimmung des Stahlgewichts von Seeschiffen. Hansa, p. 1864

DUDSZUS, A. and DANCKWARDT, E. (1982). Schiffstechnik. Verlag Technik, p. 243

EHMSEN, E. (1963). Schiffswinden und Spille. Handbuch der Werften, Vol. VII. Hansa, p. 300 EHMSEN, E. (1970). Schiffsgetriebe, Kupplungen und Verstellpropeller. Handbuch der Werften,

Vol. X. Hansa, p. 230

EHMSEN, E. (1974a). Schiffsantriebsdieselmotorenwinden und Spille. Handbuch der Werften, Vol. XII. Hansa, p. 220

EHMSEN, E. (1974b). Schiffsgetriebe. Handbuch der Werften, Vol. XII. Hansa, p. 250 FABARIUS, H. (1963). LeichtgutÐLadegeschirr. Handbuch der Werften. Vol. VII. Hansa, p. 168

HARVALD, S. A. and JENSEN, J. J. (1992). Steel weight estimation for ships. PRADS Conference, Newcastle. Elsevier Applied Science, p. 2.1047

HENSCHKE, W. (1952). Schiffbautechnisches Handbuch. 1st edn, Vol. 1, Verlag Technik, p. 577 HENSCHKE, W. (1965). Schiffbautechnisches Handbuch. 2nd edn, Vol. 2, Verlag Technik, pp. 465,

467

HOLLENBACH, U. (1994). Method for estimating the steeland light ship weight in ship design. ICCAS'94, Bremen, p. 4.17

¨

KERLEN, H. (1985). Uber den Einfluß der V¨ olligkeit auf die Rumpfstahlkosten von Frachtschiffen. IfS Rep. 456, Univ. Hamburg

KRAUSE, A. and DANCKWARDT, E. (1965). Schiffbautechnisches Handbuch. 2nd edn, Vol. 2, Verlag Technik, pp. 97, 467

MILLER, D. (1968). The Economics of Container Ship Subsystem. Report No. 3, Univ. of Michigan

¨ ¨ , . (1973). Ein Beitrag zur Ermittlung des Stahlgewichts von Aufbauten und

MULLER-KOSTER T

Deckshausern¨ von Handelsschiffen im Entwurfsstadium. Hansa, p. 307

Computation of weights and centres of mass 179

MURRAY, J. M. (1964±1965). Large bulk carriers. Transactions of the Institution of Engineering and Shipbuilding Scotland, IESS, 108, p. 203

N. N. (1975). Winterschiffahrt und Eisbrecherhilfe in der nordlichen¨ Ostsee. Hansa, p. 477 PROTZ, O. (1965), Diesel oder Turbine bei Großtankern, Hansa, p. 637

SATO, S. (1967). Effect of Principle Dimensions on Weight and Cost of Large Ships. Society of Naval Architects and Marine Engineers, New York Metropolitan Section

SCHNEEKLUTH, H. (1972). Zur Frage des Rumpfstahlgewichts und des Rumpfstahlschwerpunkts von Handelsschiffen. Hansa, p. 1554

SCHNEEKLUTH, H. (1985). Entwerfen von Schiffen. Koehler, p. 281

SCHREIBER, H. (1977). Statistische Untersuchungen zur Bemessung der Generatorleistung von Handelsschiffen. Hansa, p. 2117

WANGERIN, A. (1954). Elektrische Schiffsanlagen. Handbuch der Werften. Hansa, p. 297 WATSON, D. G. M. and GILFILLAN, A. W. (1977). Some ship design methods. The Naval Architect, 4;

Transactions RINA, 119, p. 279

WEBERLING, E. (1963). Schiffsentwurf. Handbuch der Werften, Vol. VII, Hansa WEBERLING, E. (1965). Schiffsentwurf. Handbuch der Werften, Vol. VIII, Hansa