Every regular user of the ShipShape package will find their own working methods and the software allows freedom to work in the most comfortable mode. Included in this section are some tips and hints on working methods.
There are several tips to allow ShipShape users to understand and obtain the maximum from the program.
Order Of Working
The process of creating curves, fairing and building the curve network can be carried out in many ways, each of which may be best suited to a particular application. A suitable fairing sequence might be: 1. Digitise all the section curves and create dummy longitudinal curves.
2. Fair the stem profile, transom and midship sections and enter them into the network.
3. Enter the keel, deckline and bilge/knuckle longitudinals into the network and connect them to the faired sections from stage (a).
4. Fair this set of longitudinals.
5. Insert the remaining set of sections into the network and fair them.
6. Insert the remaining longitudinals into the network. At this stage, the only fairing option which preserves the coordinate data of each curve is the adjustment of curve end conditions. The end
conditions should now be faired.
7. It may be that minor changes need to be made to the actual points on the curves. Bear in mind that any change to a section point will be reflected in the intersecting longitudinal point. Any further fairing is a repetition of the process to date but should be confined to movement of a small number of carefully selected points on the network, chosen near areas of residual unfairness.
8. When the hull is considered to be sufficiently fair, the network must be complete prior to generating interpolated curves for a lines plan or generating hydrostatic data.
9. It is worthwhile to check the hydrostatics early on, so that necessary adjustments to displacement, LCB etc. may be made before too much effort is made in the fairing process.
Half Sidings
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1. Decklines, knuckle lines and keel lines form natural longitudinals.
2. Between these features, additional longitudinals are required to define sections properly. The nodes on each section should be placed at a smoothly varying spacing. They should be closest for regions of high section curvature and furthest apart on straighter portions.
3. It is a good idea to place a longitudinal along the line of the bilge corner or similar curvature feature on the hull.
4. On nearly vertical sided parts of the hull topsides, the longitudinals will naturally take on the appearance of waterlines, whilst on nearly horizontal lower surfaces, they will resemble buttock lines. No attempt should be made to force the longitudinals to conform to either waterlines or buttocks.
5. The final placing of longitudinals will be determined by the fairing process. It is not necessary to place a great effort on getting them correct at the input stage.
6. Regions of exceptionally high curvature may best be treated as a 2 point circular arc segment joining longer curves on either side. Typical examples include bilge corners, fillets between hull and skegs and bow rounds.
Breaks Of Longitudinal Continuity
The program suite treats longitudinals and sections in analogous ways, so that longitudinals may join at a section part the way across the net of curves, as well as vice versa. There may be a requirement for a step in a deckline or a mild slope discontinuity at the leading edge of a propeller tunnel, or some other feature. This is accomplished by using the same general principles as described for forming knuckles and chines in sections.
Break to create a forecastle
As shown in the figure above, all of the network grid points do not have to have sections or longitudinals connected to them. Such 'holes' in the network can be useful for defining discontinuities such as steps in the deckline and multiple hull entities (e.g. multihulls).
Knuckle Line Features
Knuckle lines are formed by defining separate sections above and below the knuckle. Two special features of knuckles are worthy of comment:
1. Fading a knuckle line can be accomplished by extending a section across the longitudinal forming the knuckle. The result is a knuckle which fades out between the last pair of sections ending on the knuckle line and the first continuous section which crosses the line. Thus, knuckles do not need to run the full length of the hull.
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2. It is possible to create a chine with a spray rail. This is achieved by defining a rail by two longitudinals representing the inner and outer chines, with the inner chine forming the upper edge of the hull lower surface and the outer chine forming the lower edge of the topsides. The best method of defining such a rail is to create and fair one chine (e.g. the inner one) and
subsequently form the other chine by making a copy of the first and editing the (y,z) data to obtain the desired rail dimensions.
Straight Sections
Straight lines can most easily be defined as two-point curves, defined only by their end points. For example, a chine hull with straight sections between the chines can be developed by, first, defining the longitudinals for the keel, chines and deck edge, putting points at the same x values on all curves. Secondly, define a set of dummy sections with two points each, sufficient to define all of the straight- line section segments on the hull. Link all of the longitudinals into the network, to fix their positions, and then link the dummy sections between the longitudinals. The sections will then take on the co- ordinates of the longitudinals at their end points and, if their end curvatures are zero, define straight sections between those points.
End Slopes
The slope at the end of a curve is a vector with x,y and z components equal to dx/du, dy/du and dz/du. Thus it has both a magnitude and a direction. Altering the direction of the vector by changing the relationships between dx/du, dy/du and dz/du modifies the direction of the end of the curve. This is analogous to holding the end of a batten at a fixed angle. Altering the magnitude of the vector without changing the relationships between the components is analogous to changing the length of a batten thus varying the fullness of the curve. The following figure illustrates the effect of varying one slope vector component whilst keeping the other fixed.
S1 S2
S3 S4
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YE Curve A Slope B ZE Curve A Slope B
S1 2 0.000 0.000 2 0.000 0.000
S2 2 0.000 0.000 2 0.000 2.000
S3 2 0.000 0.000 2 0.000 4.000
S4 2 0.000 0.000 2 0.000 6.000
In this illustration, the A end is free (zero curvature), the y-slope at the B end is set to 0 and the z-slope at the B end gradually increased from 0 to 6. When the z-slope assumes a positive value, the B end of the curve has a vertical tangent. As the z-slope is progressively increased, fullness is induced into the curve and the B end tangent remains vertical.
Bow Round Theory
h h A R
α
δ
xδ
y New location oflongitudinal end point
Original location of longitudinal end point
Exact Circular Arc
α
= half angle of entrance from longitudinal end slope data 1Required arc radius 2
Single Segment approximation End tangent vector length 3
Method of Constructing Bow Round
1. Fair main fore body with longitudinals squared off to true stem profile.
2. On main longitudinal, change end point x and y-co-ordinates using the Edit Values route and calculated
δ
x = -h cosα
,δ
y = h sinα
.3. For end rounding segment, calculate tangent vector length T and set segment end conditions via Edit Values such that
dx/du = T cos
α
, dy/du = -T sinα
at tangent with main longitudinal anddx/du = 0, dy/du = -T on centreline at stem profile.
Increasing Speed
ShipShape can be reasonably computationally intensive and thus on some slower computers can seem to run slowly. Most of the operations are quite repetitive so if the user can reduce the number of
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repetitions ShipShape can run quicker. Refreshing and drawing can also slow ShipShape down so there are options associated with this that can help to resolve any speed issues.
Speed is quite strongly related to the number of interpolated points that ShipShape has to calculate so some of the tips in Reducing Memory Overhead also apply here.
i) There are numerous options associated with each view of the ship (i.e. Ship View window and Edit Curve window). Turning off some of the curves that are non-essential to the users operation in the View Options dialog can rapidly increase the refresh rate of the views.
ii) Turn off the Auto Interpolate option on the Interpolate Parameters Tab of the Interpolator Setup dialog. This will prevent ShipShape from re-interpolating the ship every time the construction curves are altered in any way. If you need to recalculate the interpolated curves on the ship at any time you can use the Recalculate command.
ii) Reduce the plot density in the View Options dialog. This has the effect of reducing the number of interpolated points to draw and also the number of derived points to calculate.
iii) Lower the plot density of Sections, Longitudinals, Buttocks, Inclined Planes and the Intermediate Spacing on the Interpolate Parameters Tab of the Interpolator Setup dialog. This has the effect of reducing the number of interpolated points to draw on each interpolated curve and also the number of derived points to calculate.
All these options are aimed at reducing the number of interpolated points over a ship. In general if these options are used wisely then there should be no speed problems associated with ShipShape.
Reducing Memory Overhead
ShipShape is written to be as memory ‘friendly’ and non-aggressive as possible such that it does not require a large memory overhead to run. To give an insight into ShipShape and its use of the computer’s memory it is best to describe the breakdown of allocation of memory, at what point is allocated and what affects the memory overhead.
ShipShape first of all has memory associated with the executable program and the static data within that program. Examples of this are toolbars, permanent dialogs, windows and internal settings. All other memory is allocated dynamically when needed and thus deallocated when not needed. For example most dialogs and their associated memory are created when needed and when the user closes the dialog, the memory for that dialog is destroyed leaving more memory space for other dialogs and objects.
A large amount of the dynamically allocated memory is associated with construction curves and the derived interpolated curves from the ship. All of these require memory and the more points associated with these curves the larger the memory overhead. Once curves are created, including derived interpolated curves they are generally stored in memory until the user changes the memory requirement (i.e. adds more points or curves). These are stored in memory for viewing and calculating data such as hydrostatics. This allows ShipShape to rapidly recalculate derived data without the need to calculate the
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is to close any other programs that are running on the machine. If this is not possible then the next step is to reduce the amount of memory ShipShape is using, this can be done by several means:
1. Reduce the plot density in the View Options dialog. This has the effect of reducing the number of interpolated point to reduce the total memory required to spline curves.
2. Lower the plot density of Sections, Longitudinals, Buttocks, Inclined Planes and the Intermediate Spacing on the Interpolate Parameters Page of the Interpolator Setup dialog. This has the effect of reducing the number of interpolated points on each interpolated curve.
3. Lower the number of interpolated sections, longitudinals, buttocks or inclined planes in the Orthogonal Planes and Inclined Planes Page of the Interpolator Setup dialog.
4. Turn off the interpolated sections, longitudinals, buttock, inclined planes, intermediate sections or intermediate longitudinals on the Interpolate Parameters Page of the Interpolator Setup dialog.
5. Turn off the offset table on the Interpolate Parameters Page of the Interpolator Setup dialog. 6. Remove any construction curves that are not required using the Curve Delete command.
All the above tips are aimed at reducing the number of interpolated points over a ship. In general if the options available to the user are used wisely then there should be no memory problems associated with ShipShape.
Digitizer Setup and Configuration
ShipShape uses its own drivers via the COM ports on your machine to communicate with digitizer tablets. It does not require WinTab or any other similar drivers and these should not be loaded.
Digitizer settings are accessed via the Digitizer Setup dialog this has various options to match the settings on the digitizer tablet.
As ShipShape expects a constant stream of information from the digitizer tablet the information from the digitizer should be setup to be streaming constantly rather then when a digitizer pointer button is pressed.
Importing and Using DXF Files
1. The DXF Translator will only load sections if they are planar in the x-direction (i.e. have a constant x value) within a tolerance defined by the user on the Import DXF Options Dialog. When the LFH file is saved it will specify only one x value being the x value of the first point of the section. The Import DXF Options Dialog has several filter options that can aid the accurate import of a DXF file.
2. The Wolfson Unit packages are sensitive to the spacing defined in the LFH file and it is useful to consider this when using another package to create the DXF file. Refer to the other manuals for more details on section spacing, numbers and intervals.
3. It is best to keep the DXF file simple with ideally sections just defined. This will lower the chances of any spurious lines being read and translated as sections.
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4. The maximum number of points per curve or line is 255 and the maximum number of curves or lines are 255. The DXF translator will notify the user if the DXF file exceeds this.
5. The co-ordinate system is a Cartesian (x,y,z) system. The axis system is placed with its origin on the centreline, at a convenient longitudinal datum (e.g. amidships) and a convenient vertical datum (e.g. baseline or design waterline). Longitudinal or x-values are positive forward, vertical or z-values are positive up and transverse or y-values are positive to starboard.
6. Sections defined in a DXF file must be a continuos line with no breaks, for example a the line above and below a chine must be part of the same polyline.
7. The resolution of the definition of the hull created in the DXF is directly related to the resolution of the resolution exported in the DXF file. It is therefore important to have enough points on a section such that straight lines between the points will adequately model the shape
of the hull.
8. DXF files must be in ASCII and 3-D format for further information see File Types and Formats.
Printer and Page Setup for Plotting
To use the Plot Setup window a printer must be setup under Windows as the page created accesses the current printers page settings. Therefore even if the computer you are working on does not have a printer it is necessary to install a dummy printer to enable the Plot Setup window to work.
Auto Saving and File Backup
The auto save facility allows the current ship file to be saved at regular intervals. The purpose being if a problem occurs either on the computer or within ShipShape a backup file, saved at the last auto save
interval, will be available on your computer. When ,in normal operation, ShipShape closes, the auto save file will be deleted as the user will have the latest wanted version of the ship saved to the normal .HFG file. Should an auto save file need to be loaded the user should select all files in the Open dialog file type and search for the name of the file with the .AH~ extension instead of the normal .HFG extension.
A backup of a file is also created when a file is saved. This file is created and is the version of the file before the current saved one. This way a copy of the file before the one saved is always available. Should a backup file need to be loaded the user should select all files in the Open dialog file type and search for the name of the file with the .HF~ extension.
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GLOSSARY
B Min, B Max, the minimum and maximum Y co-ordinates of the hull, B Max - B Min equals the total beam of the hull.
buttock, a derived curve that has a constant y value.
CAD, Computer Aided Design.
CB, block coefficient = (submerged moulded volume) / (reference length * reference beam * (waterline - keel position)).
CM, midship section coefficient = (area of reference section) / (reference beam * (waterline - keel position)).
CP,prismatic coefficient = (submerged volume) / (area of reference section * reference length).
CW, waterplane coefficient = (area of waterplane at waterline) / (reference length * reference beam).
construction curve, a curve defined by the user to produce the shape of a ship.
curvature,second derivative with respect to U. e.g. d2X/dU2,. d2Y/dU2,. d2Z/dU2
derived curve, a curve derived from construction curves by interpolating a defined orthogonal plane, inclined plane or intermediate curve.
dialog, a window with input and output.
full displacement, the displacement of the ship including the shell thickness in weight units. It is the enclosed volume plus the shell thickness multiplied by the specific gravity of water.
girth, the full distance around a transverse section travelling on the surface to the waterline.
GZ, righting lever, the transverse distance between the centre of buoyancy and the centre of ravity.
heel, the rotation angle of the ship in degrees around the X axis of the ship.
immersion, the amount of displacement increment per unit increase in draught at the particular displacement waterline.
inclined plane, a plane that is defined with a constant x-value, y-value or z-value to derive a section, buttock or waterline respectively.
intermediate curve, a derived curve that is iso-parametric over the ships surface. In the girthwise or longitudinal direction.
interpolated curve, a derived curve.
keel position, the position used to calculate the minimum point of the draught (i.e. draught = waterline - keel position).
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KMl, longitudinal metacentric height, relative to the keel position.
KMt, transverse metacentric height, relative to the keel position.
LCB, longitudinal centre of buoyancy, relative to X=0.
LCF, longitudinal centre of flotation, relative to X=0.
link, fix a curve to its location in the network, This defines the relationships between the three- dimensional network curves. Co-ordinate data are transferred at points where the curves are already