Design hints
An improvement in the hydrodynamic performance must be demonstrated to justify the application of Kort nozzles. In a seaway the efficiency of a propeller with nozzle is less reduced than for a non-ducted propeller due to the more axial inflow. The nozzle efficiency increases in a seaway due to the increased thrust-loading coefficient. In total, the nozzle thus decreases the efficiency losses. When considering if it is worthwhile to install a nozzle, nozzle construction and initial costs play a...
Historical perspective Raholas criterion
Rahola 1939 analysed statistically accidents caused by defects in stability and included the results in recommendations for 'safe stability'. These recommendations are based on the criterion of a degree of dynamic stability up to 40 angle of heel. The dynamic stability can be represented by the area below the stability moment curve, i.e. as the integral of the stability moment over the range of inclination Fig. A.1 . This quantity equals the mechanical work done, or energy used, in heeling the...
212 References
BERTRAM, V. 1992 . CFD im Schiffbau. Handbuch der Werften Vol. XXI, Hansa, p. 19 BERTRAM, V. 1994 . Numerische Schiffshydrodynamik in der Praxis. IFS-Report 545, Univ. Hamburg BERTRAM, V. and JENSEN, G. 1994 . Recent applications of computational fluid dynamics. Schiffstechnik, p. 131 DANCKWARDT, E. 1969 . Ermittlung des Widerstandes von Frachtschiffen und Hecktrawlern beim Entwurf. Schiffbauforschung, p. 124 ECKERT, E. and SHARMA, S. 1970 . Bugw lste f r langsame, v llige Schiffe. Jahrbuch...
14 Block coefficient and prismatic coefficient
The block coefficient CB and the prismatic coefficient CP can be determined using largely the same criteria. CB, midship section area coefficient CM and longitudinal position of the centre of buoyancy determine the length of entrance, parallel middle body and run of the section area curve Fig. 1.15 . The shoulders become more pronounced as the parallel middle body increases. The intermediate parts not named here are often added to the run and the entrance. Figure 1.15 Section area curve. LR...
Combination of devices
Devices to improve propulsion have also been successfully combined. However, savings given for individual systems will not add up completely for combinations of systems. The estimates of total efficiencies which can be obtained given below are just guidelines. Also, in practice such combinations are rarely found as the high complexity of the systems introduces additional initial and sometimes operating maintenance and repair costs. Designers therefore generally favour at least in times of...
The Grim vane wheel
The Grim vane wheel consists of a relatively small propeller driven by the engine plant and a freely revolving propeller fitted on the downstream side, the inner part of which behind the engine-driven propeller acts as a turbine and the outer part as a propeller Fig. 4.17 Grim, 1966, 1980, 1982 Baur, 1985 Tanaka et al., 1990 Meyne and Nolte, 1991 . This propulsion system has the following hydrodynamic advantages over normal single-propeller drive 1. Substantial recovery of rotational energy. 2....
62 Power prognosis using the admiralty formula
The 'admiralty formula' is still used today, but only for a very rough estimate The admiralty constant C is assumed to be constant for similar ships with similar Froude numbers, i.e. ships that have almost the same CB, CP, V L, Fn, V, etc. Typical values for C in t2 3 kn3 kW are These values give an order of magnitude only. The constant C should be determined individually for basis ships used in design. Volker 1974 gives a modified admiralty formula for cargo ships with smaller scatter for C rD...
Effects of bulbous bows on ships characteristics
The effects of a bulbous bow can extend to several areas of the ship's design, construction, manufacture and operation, e.g. 1. Effective drag total resistance and characteristics at various draughts. 5. Course-keeping ability and manoeuvrability. a Possibilities for installation. 8. Construction, manufacture and building costs of bow section. 10. Anchor-handling apparatus and operation with respect to danger of anchor striking bulbous bow. 11. Accommodation of sounding devices on fishing and...
65 References
ALTE, R. and BAUR, M. v. 1986 . Propulsion. Handbuch der Werften, Vol. XVIII, Hansa, p. 132 BALES, S. L., LEE, W. T., VOELKER, J. M. and BRANDT, W. 1980 . Standardized wave and wind environments for Nato operation areas. DTNSRDC Report SPD-0919-01 BERGER, G. 1983 . Untersuchung der Schiffsrauhigkeit. Rep. 139, Forschungszentrum des Deutschen Schiffbaus, Hamburg BLENDERMANN, W. 1993 . Parameter identification of wind loads on ships. Journal of Wind Engineering and Industrial Aerodynamics 51, p....
Schneekluth method for containerships
The method Schneekluth, 1985 is based on the evaluation of systematically varied ship forms and sizes of a containership type corresponding to the level of development at the early 1980s. To isolate the influence of the main data and ratios on the hull steel weight, the construction and building method was kept as uniform as possible over the entire variation range. Checked using statistical investigations, this corresponds reasonably consistently to practical reality and the building method...
Schneekluths method for drycargo ships
The method was developed by Schneekluth 1972 . The hull steel weight is first determined for individual section panels which then form the basis for plotting a curve of steel weight per unit length. The advantages over other methods are 1. Provides a wider range of variation, even for unusual ratios of cargo ship main dimensions. 2. Type of construction of longitudinal framing system is taken into account. 3. Efficient and easy to program. Initially, the method was developed for dry-cargo ships...
Hollenbachs method
Hollenbach 1997, 1998 analysed model tank tests for 433 ships performed by the Vienna Ship Model Basin during the period from 1980 to 1995 to improve the reliability of the performance prognosis of modern cargo ships in the preliminary design stage. Hollenbach gives formulae for the 'best-fit' curve, but also a curve describing the lower envelope, i.e. the minimum a designer may hope to achieve after extensive optimization of the ship lines if its design is not subject to restrictions. In...
Procedures for calculating steel weight
By far the greatest part of the hull weight is made up by the steel weight. For this reason, more precise weight calculation methods are applied to better determine this quantity, even though the weight group 'equipment and outfit' may only be approximated. The procedures to calculate steel weight are based on the steel weights of existing ships or on computed steel weights obtained from construction drawings produced specially for the procedure. Both cases require interpolation and...
Preface
This book, like its predecessors, is based on Schneekluth's lectures at the Aachen University of Technology. The book is intended to support lectures on ship design, but also to serve as a reference book for ship designers throughout their careers. The book assumes basic knowledge of line drawing and conventional design, hydrostatics and hydrodynamics. The previous edition has been modernized, reorganizing the material on weight estimation and adding a chapter on power prognosis. Some outdated...
Grothues spoilers
Cross-flows are often, but not always, observed in model tests investigating the ship flow near the propeller. This phenomenon decreases with distance from the hull. In addition, bilge vortices appear Fig. 4.19 . The cross-flow usually has a thickness comparable to that of the boundary layer. Cross-flows appear predominantly in ships with stern bulb, high B T, high CB and low speed. Cross-flows disturb the propeller inflow and reduce the propeller efficiency. Figure 4.19 Cross-flow and bilge...
28 Propeller clearances
The propeller blades revolving regularly past fixed parts of the ship produce hydrodynamic impulses which are transmitted into the ship's interior via both the external shell and the propeller shaft. The pressure impulses decrease the further the propeller blade tips are from the ship's hull and rudder. The 'propeller clearance' affects 2. Vibration-excitation of propeller and stern. 3. The propeller diameter and the optimum propeller speed. Vibrations may be disturbing to those on board and...