## Methods of reducing waterline angles

If the conventional rudder arrangement is dispensed with, the inflow angle of the waterlines in the stern post area of single-screw ships can be effectively reduced by positioning the propeller post further aft. The following arrangements may be advantageous here 1. Nozzle rudder with operating shaft passing through the plane of the tips of the propeller blades. The nozzle rudder requires more space vertically than the nozzle built into the hull, since the propeller diameter to be accommodated...

## Recommendations for bilge radius

The bilge radius R of both conventionally formed and very broad ships without rise of floor is recommended to be CK 0.5-0.6, in extreme cases 0.4-0.7. This formula can also be applied in a modified form to ships with rise of floor, in which case CB should relate to the prism formed by the planes of the side-walls and the rise of floor tangents, and be inserted thus in the bilge radius formula. where A is the rise of floor. The width of ships with trapezoidal midship sections is measured at...

## Main dimensions and main ratios

The main dimensions decide many of the ship's characteristics, e.g. stability, hold capacity, power requirements, and even economic efficiency. Therefore determining the main dimensions and ratios forms a particularly important phase in the overall design. The length L, width B, draught T, depth D, freeboard F, and block coefficient CB should be determined first. The dimensions of a ship should be co-ordinated such that the ship satisfies the design conditions. However, the ship should not be...

## Advice on designing the stern underwater form

Attention should be paid to the following 2. Minimizing the suction effect of the propeller. 3. Sufficient propeller clearance. Separation at the stern is a function of ship form and propeller influence. The suction effect of the single-screw propeller causes the flowlines to converge. Figure 2.25 Transom stern with flared profiles This diminishes or even prevents separation. The effect of the propeller on twin-screw ships leads to separation. Separation is influenced by the radius of curvature...

## Designing the midship section

Today, nearly all cargo ships are built with a horizontal flat bottom in the midship section area. Only for CM < 0.9 is a rise of floor still found. Sometimes, particularly for small CM, a faired floor side-wall transition replaces the quarter circle. The new form is simpler since it incorporates a flat slipway surface and a less complicated double bottom form (Fig. 1.20). A flat bottom can be erected more cheaply on a 'panel line', and manufactured more economically. The desired CM is...

## Ship Design for Efficiency and Economy

OXFORD BOSTON JOHANNESBURG MELBOURNE NEW DELHI SINGAPORE OXFORD BOSTON JOHANNESBURG MELBOURNE NEW DELHI SINGAPORE Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier pic group First published 1987 Second edition 1998 H. Schneekluth and V. Bertram 1998 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or...

## 52 Weight of equipment and outfit EO

Because ships have increased comfort, weight of E& O has increased. Despite smaller crews, the weight of outfit has increased because 1. Greater surface area and space required per man. 2. The incombustible cabin and corridor walls in use today are heavier than the earlier wooden walls. 3. Sanitary installations are more extensive. 4. Air-conditioning systems are heavier than the simple ventilation devices formerly used. 5. Heat and vibration insulation is now installed. The weight of some...

## Weights of superstructure and deckhouses

The method (M ller-K ster, 1973) is based on the requirements of the classification societies. Scantlings for superstructure and deckhouses are commonly bigger than specified for reasons of production. Therefore, it is recommended to add a further 10 -25 to the result of the calculation. The volumetric weight of a forecastle is For ships with L > 140 m Cforecastle 0.1 t m3 For ships with L 120 m Cforecastle 0.13 t m3 The values apply to a forecastle height of 2.5-3.25 m and a length of up to...

## 210 Lines design using distortion of existing forms

When designing the lines by distorting existing forms it usually suffices to design the underwater body and then add the topside in the conventional way. The bulbous bow is also often added conventionally. Thus a knowledge of the conventional methods is necessary even in distortion procedures. Advantages of distortion over conventional procedures 1. Less work there is no need to design a sectional area curve. Even where there is a sectional area curve, no checking of its concurrence with the...

## Computation of weights and centres of mass

All prediction methods should be calibrated using data from comparable ships. This allows the selection of appropriate procedures for a certain ship type (and shipyard) and improves accuracy. The prediction of weights and centres of mass is an essential part of ship design. A first, reasonably accurate estimate is necessary for quoting prices. A global price calculation is only acceptable for follow-up ships in a series, otherwise the costs are itemized according to a list of weight groups. In...

## 33 Economic basics for optimization Discounting

For purposes of optimization, all payments are discounted, i.e. converted by taking account of the interest, to the time when the vessel is commissioned. The rate of interest used in discounting is usually the market rate for long-term loans. Discounting decreases the value of future payments and increases the value of past payments. Individual payments thus discounted are, for example, instalments for the new building costs and the re-sale price or scrap value of the ship. The present value...

## Roughness

The friction resistance can increase considerably for rough surfaces (Naess, 1983). For newbuilds, the effect of roughness is included in the ITTC line or the correlation constant. The values of the correlation constant differ considerably between different towing tanks depending on the extrapolation procedures employed and are subject to continuing debate among hydrodynamicists. In general, correlation allowances decrease with ship size and may become negative for very large ships. For...

## National regulations Germany

National regulations usually follow the above international regulations, but may impose additional requirements. German rules are given here as an example. In 1984 the SBG (Seeberufsgenossenschaft German Mariners' Association) issued new regulations for intact stability which consider ship type and cargo type (SBG, 1984). These recommendations refer to the righting arm curve. Table A.5 gives the minimum required values. Ships with L < 100 m and 50 < 00 < 60 h30 0.2 + (60 - 00) 0.01....

## 211 Computational fluid dynamics for hull design

CFD (computational fluid dynamics) is used increasingly to support model tests. For example, in Japan no ship is built that has not been previously analysed by CFD. CFD is often faster and cheaper than experiments and offers more insight into flow details, but its accuracy is still in many aspects insufficient, especially in predicting power requirements. This will remain so for some time. The 'numerical towing tank' in a strict sense is thus still far away. Instead, CFD is used for...

## 42 Overlapping propellers

Where two propellers are fitted, these can be made to overlap (Pien and Strom-Tejsen, 1967 Munk and Prohaska, 1968) (Fig. 4.1). As early as the 1880s, torpedo boats were fitted with overlapping propellers by M. Normand at the French shipyard. The propellers turned in the same direction partially regaining the rotational energy. Model tests in Germany in the 1970s covered only cases for oppositely turning propellers. Better results were obtained for propellers which turned outside on the...

## 27 Problems of design in broad shallowdraught ships

Ships with high B T ratios have two problems 1. The propeller slipstream area is small in relation to the midship section area. This reduces propulsion efficiency. 2. The waterline entrance angles increase in comparison with other ships with the same fineness L V1 3. This leads to relatively high resistance. 1. Multi-screw propulsion can increase propulsion efficiency. However, it reduces hull efficiency, increases resistance and costs more to buy and maintain. 2. Tunnels to accommodate a...

## 15 Midship section area coefficient and midship section design

The midship section area coefficient CM is rarely known in advance by the designer. The choice is aided by the following criteria (Fig. 1.18) Figure 1.18 Section area curves with constant displacement and main dimensions, but different midship area coefficients Figure 1.18 Section area curves with constant displacement and main dimensions, but different midship area coefficients Increasing CM while keeping CB constant will usually have the following effects C Increased run length decreased...

## Vp 7Rt Lpbptp

Even without the hydrostatic curves, the change in fullness of the design can be estimated as a function of the draught variation. A change in CB changes other characteristics 1. Forebody A flared stem alters Lpp. The stem line should be corrected accordingly (Fig. 2.42). 2. Aftbody There is a change in the ratio of propeller well height to draught. A change of this kind can be used to adapt the outline to the necessary propeller diameter or to alter transom submergence. Lwl changes, Lpp does...

## Freeboard and sheer

The problems associated with freeboard include the 'distribution of freeboard' along the ship's length. The sheer produces a freeboard distribution with accentuation of the ship's ends. It is here (and particularly at the forward end) that the danger of flooding caused by trimming and pitching in rough seas is most acute. This is why the freeboard regulation allows reduction of the freeboard amidships if there is greater sheer. Conversely the sheer can be decreased or entirely omitted,...

## Stern bulb

Hollow waterlines in the vicinity of the upper propeller blades to reduce thrust deduction. Large propeller aperture to reduce propeller induced vibrations. Very broad stern to accommodate a stern ramp in ro-ro ships or to increase stability. V sections in the forebody of containerships to increase deck area. Compromises in the location of the shoulders to increase container stowage capacity. The first two items improve propulsive efficiency. Thus power requirements may be lower despite higher...

## 11 The ships length

The desired technical characteristics can be achieved with ships of greatly differing lengths. Optimization procedures as presented in Chapter 3 may assist in determining the length (and consequently all other dimensions) according to some prescribed criterion, e.g. lowest production costs, highest yield, etc. For the moment, it suffices to say that increasing the length of a conventional ship (while retaining volume and fullness) increases the hull steel weight and decreases the required...

## Criticism of the freeboard regulations

The freeboard regulations have been criticized for the following reasons 1. For small ships, the dependence of the freeboard on ship size results in smaller freeboards not only in absolute, but also in relative terms. Seen in relation to the ship size, however, the small ship is normally subjected to higher waves than the large ship. If the freeboard is considered as giving protection against flooding, the smaller ship should surely have relatively greater freeboard than the larger ship. The...

## 35 Special cases of optimization

Conditions for series shipbuilding are different from those for single-ship designs. Some of the advantages of series shipbuilding can also be used in repeat ships. For a ship to be built varying only slightly in size and output from a basis ship, the question arises 'Should an existing design be modified or a new design developed ' The size can be changed by varying the parallel middlebody. The speed can be changed by changing the propulsion unit. The economic efficiency (e.g. yield) or the...

## The International Load Line Convention of 1966

The International Load Line Convention of 1966 (ICLL 66) has been recognized by nearly every seafaring nation. The first international freeboard regulations took effect in 1904. They were modelled closely on the freeboard restrictions introduced in Great Britain in 1890 on the initiative of the British politician and social reformer Samuel Plimsoll (1824-1898). The idea of using a freeboard index line to mark this was also based on the British pattern. One particularly heavy area of...

## 31 Introduction to methodology of optimization

Optimization means finding the best solution from a limited or unlimited number of choices. Even if the number of choices is finite, it is often so large that it is impossible to evaluate each possible solution and then determine the best choice. There are, in principle, two methods of approaching optimization problems Solutions are generated by varying parameters either systematically in certain steps or randomly. The best of these solutions is then taken as the estimated optimum. Systematic...

## 36 Developments of the 1980s and 1990s

Concept exploration models (CEMs) have been proposed as an alternative to 'automatic' optimization. The basic principle of CEMs is that of a direct search optimization a large set of candidate solutions is generated by varying design variables. Each of these solutions is evaluated and the most promising solution is selected. However, usually all solutions are stored and graphically displayed so that the designer gets a feeling for how certain variables influence the performance of the design....

## Approximate formulae for initial stability

To satisfy the variety of demands made on the stability, it is important to find at the outset a basis that enables a continuing assessment of the stability conditions at every phase of the design. In addition, approximate formulae for the initial stability are given extensive consideration. The value KM can be expressed as a function of B T, the value KG as a function of B D. A preliminary calculation of lever arm curves usually has to be omitted in the first design stage, since the...

## Decomposition of resistance

As the resistance of a full-scale ship cannot be measured directly, our knowledge about the resistance of ships comes from model tests. The measured calm-water resistance is usually decomposed into various components, although all these components usually interact and most of them cannot be measured individually. The concept of resistance decomposition helps in designing the hull form as the designer can focus on how to influence individual resistance components. Larsson and Baba (1996) give a...

## Criteria for the practical application of bulbous bows

Writers on the subject deal with the bulbous bow almost exclusively from the hydrodynamic point of view, ignoring overall economic considerations. The power savings of a bulbous bow should be considered in conjunction with the variability of the draught and sea conditions. The capital expenditure should also be taken into account. The total costs would then be compared with those for an equivalent ship without bulbous bow. Selection methods such as these do not yet exist. The following approach...

## 45Kort nozzles

The Kort nozzle is a fixed annular forward-extending duct around the propeller. The propeller operates with a small gap between blade tips and nozzle internal wall, roughly at the narrowest point. The nozzle ring has a cross-section shaped as a hydrofoil or similar section. The basic principle underlying nozzle operation is most simply explained according to Horn (1940) by applying simple momentum theory to the basic law of propulsion. This postulates that, for generation of thrust with good...

## Historical development

Today the bulbous bow is a normal part of modern seagoing cargo ships. Comparative model experiments show that a ship fitted with a bulbous bow can require far less propulsive power and have considerably better resistance characteristics than the same ship without a bulbous bow. The bulbous bow was discovered rather than invented. Before 1900, towing tests with warships in the USA established that the ram stem projecting below the water decreased resistance. A torpedo boat model showed that an...

## 29 The conventional method of lines design

Lines design is to some extent an art. While the appearance of the lines is still important, today other considerations have priority. Conventionally, lines are either designed 'freely', i.e. from scratch, or distorted from existing lines, see Section 2.10. The first stage in free design is to design the sectional area curve. There are two ways of doing this 1. Showing the desired displacement as a trapezium (Fig. 2.37). The sectional area curve of the same area is derived from this simple...

## Development of stern for cargo ships

In discussing stern forms, a distinction must be made between the form characteristics of the topside and those of the underwater part of the vessel. The topside of the cargo ship has developed in the following stages Fig. 2.22 1. The merchant or elliptical stern. In addition there are numerous special forms. Before about 1930, the 'merchant stern', also known as elliptical or 'counter' stern, was the conventional form for cargo ships. Viewed from above, the deck line and the knuckle line were...

## 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...

## 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...

## 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...

## 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...