AutoCad Tutorials Representation of a Ship Hull Surface
Using AutoCAD to represent a Ship
Hull Surface using its Offset
Table
Step by Step Tutorials
Tutorial I
“Drawing 2D representation in the form of Lines Plan”
1. Start from Scratch:
When you load ACAD2000 or
any other previous version, a
startup dialog appears
waiting for your orders as
shown in the next figure
Select “Start from Scratch”
button and press Ok
Here you have told the ACAD
to use the default settings in
order to have a quick start
2. Setting the drawing environment:
1. First of all we’ll adjust the units by selecting Units Format>Units
2. In the units dialog box be sure to select decimal in the length type,
0.000 in the precision, then press ok
3. Notice the mouse counter at the most left bottom of the CAD screen, it’s
now have the new precision
Hint: you can also display the Units dialog box by typing units in the
command line
4. Now let’s set our drawing limits by selecting Units Format>Drawing
limits.
5. A prompt at the command line asks you to specify the lower left
corner, type 0,0 in the command line and then press ENTER.
6. Another prompt for the upper right corner; here the maximum length
we have to deal with for ship lines is about 150 m. and the height of the
drawing is the sum of the ship’s depth and half breath plan in addition
to some empty spaces so we type in 200, 90 as our answer to the
command prompt.
1/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
Hints:
1. You can also display the Drawing limits Command by typing
limits in the command line
2. We simply chosen 90 as height because if we plot our drawing
using 1 drawing units = 10 mm this 90 would be equivalent to
90 cm “the width of the paper roll and so the drawing scale
would be 1:100 – to see the boundaries of your drawing space
draw a rectangle with lower left corner 0,0 and upper right
one 200,90
7. Finally in order to see your drawing limits, press the zoom all button
in the zoom fly out located in the standard toolbar, or simply you can
type zoom then all in the command line
3. Start DRAWING:
1. Once you have set up your environment for drawing, you
can start by
i. Drawing the molded base line of the profile using the line
command and specifying the starting and ending points (let’s
say 0, 50 & 200, 50
ii. Drawing the Center Line of the half breadth plan using the line
command and specifying the starting and ending points (let’s
say 0, 20 & 200, 20
Hints:
a. As you sure noticed the two lines are drawn with the same line type
and color, to deal with this problems we have to learn about layers
b. Display the Layer Properties Manager dialog box by pressing the
layers button in the toolbar shown above, or type layer in the command
line:
As you see there is only one layer named “O” with white color and
continuous line type
By pressing the New button a new layer appears with its default name
highlighted waiting for you to change it, try to make the name
expressive; ship center for example.
By pressing enter AutoCAD accepts the new layer’s name and then
give you a chance to make another action (either adding anew layer
or changing a property of any other layer)
2/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
Since this layer represents a center line so it’s a common thing to
change the line type to center; you can set the line type by clicking the
word “Continuous” – a select line type dialog appears but
unfortunately it contains only one type so we have to add the type
we’re looking for by pressing the Load button – now search for the
center line type in the load dialog box and double click it
Repeat the last step to add a Hidden Line Type.
Before you exit the select line type dialog box be sure that the center
line type is Highlighted to assign it to the ship center layer
Press OK to exit the layers dialog box
Now select the center line you have drawn latest and assign it to the
ship center layer by clicking on the O in the layers toolbar shown
above and selecting the required layer then press Esc twice to clear
your selection, notice the changes!
The type line has changed to center but it’s still has to be adjusted, to
do this select the required center line and then type properties – in the
properties dialog box set the line type scale to 0.4 – it’s adjusted now
so close the properties dialog box
iii. Drawing the Center Line of the Body plan using the line
command and specifying the starting and ending points (let’s
say 100, 45 & 100, 70 – as we did before adjust the layer for this
new line as well as the line type scale “I think 0.1 would be good
this time”.
3/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
* The Body Plan Curves
2. Now we can start drawing the curves of the Body Plan:
i. Using UCS (user coordinates system) command, set the location of
the origin to the intersection between the body plan the molded
base line:
Type UCS in the command line then press Enter
ACAD prompts you for a UCS option, type New
Specify the new origin as 100,50,0
Notice the changes to the mouse counter after what
you did
ii. Now you’re going to work with a small area in your drawing “The
right half of the body plan area to draw the forward station
curves” so using the ZOOM command magnify this area to fill
your ACAD screen:
Type zoom in the command line then press Enter
ACAD prompts you for a zoom option, type win
Specify the first corner as –20, -7
Specify the other corner as 20, 25
3. Now preparing for the body plan curves to be drawn set a
new layer named “Stations” & give it a specified color
rather than white to be easily recognized. Also make itthe
current layer.
4/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
4. Start drawing the station curves one by one with the
forward stations to the right of the body plan center line
and the aft stations to the left:
Assume that we have the following data for one of the
forward stations in the offset table:
WL O 0.5 1 2 3 4 5 6 7 8 9
Offset .0956 .4348 .6 .7217 .7652 .7913 .8 .8261 .8609 .9043 .9739
Here the water lines location are presented as ratio of
the water line spacing while the offset values are
presented as a ratio to the half breadth of the vessel
In order to draw this curve in our ACAD drawing we
have to rewrite this table in x-y coordinates that are
represented in m. so the values of the water line heights
should be multiplied by the WL spacing (1.58 m. for this
example) and the offset values should be multiplied by
B/2 (11.5 m. for this example)
Y (m.) O .79 1.58 3.16 4.74 6.32 7.9 9.48 11.06 12.64 14.22
X (m.) 1.1 5.0 6.9 8.3 8.8 9.1 9.2 9.5 9.9 10.4 11.2
5. Every thing is set up now for using the SPLINE Command:
Type SPLINE in the command line or click on the
SPLINE button on the DRAW toolbar
ACAD asks you to specify your first point so you should
enter 1.1,0 then 5.0, .79 for next point, … & so on till the
points are finished press enter without entering any
value to tell ACAD that you have no more points on this
curve.
ACAD prompts you to specify the start tangent with your
starting point located on this tangent so you can specify
any point on the molded base line to the left of the body
plan center line to ensure that your curve will end
tangentially to it “as it should be”
ACAD prompts for the end tangent for this curve and
since we haven’t got a specified one we can simply press
enter to finish the SPLINE command
5/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
6. Repeat Steps 4&5 for the rest of the stations with negative x-
values for the aft stations to be drawn to the left of the body
plan centerline and thus your body plan is completed.
* The Bow & Stern Contours
7. Use the zoom all command to view your drawing limits.
8. It’s time now to draw the aft and forward perpendiculars of
your vessel (remember that your origin is still located
amidships at the molded base line.
Set the a new layer for these line name it “perpendiculars”
and adjust its line type and color
Using the Line command draw the two perpendiculars
using the following data for start and end points:
Aft Perpendicular Forward Perpendicular
Start from To Start from To
-L/2, -50 -L/2,40 L/2, -50 L/2, 40
6/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
9. Assume that we have the following data measured from the
aft perpendicular for the bow contour in the offset table:
WL O 0.5 1 2 3 4 5 6 7 8 9
Offset (m.) 2.0 2.2 2.4 2.7 2.4 1.3 -3.1 -4.9 -5.4 -5.9 -6.1
Here only the values of the WL heights is to be adjusted as
the Y- coordinates because the offset values are already
adjusted in meters
Same steps used in drawing any of the stations curves are to
be repeated after adjusting the origin at the intersection
point of the aft perpendicular and the molded base line
using the UCS command
10. Repeat the last step using the data of the bow contour
* The half breadth Plan Curves
11. Start drawing the half breadth curves one by one all above
the half breadth plan center line, after adjusting the origin
at the intersection point of the aft perpendicular with the
center line of the half breadth plan center line
Assume that we have the following data for one of a
waterline in the offset table:
ST O 1 2 3 4 5 6 7 8 9 10
Offset .3304 .6957 .8870 .9739 1.0 1.0 .9652 .8272 .5706 .2957 .0348
Here the stations location are presented as ratio of the
stations spacing from the aft perpendicular while the
offset values are presented as a ratio to the half breadth
of the vessel
In order to draw this curve in our ACAD drawing we
have to rewrite this table in x-y coordinates that are
represented in m. so the location of any station should be
multiplied by the ST spacing (12.55 m. for this example)
and the offset values should be multiplied by B/2 (11.5 m.
for this example)
Y (m.) 3.8 8.0 10.2 11.2 11.5 11.5 11.1 9.513 6.562 3.4 .4
X (m.) 0 12.55 25.1 37.65 50.2 62.75 75.3 87.85 100.4 112.95 125.5
7/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
Hint: have to find out the end points of each water line using the stern
and bow contours before drawing them.
12. Now work on the Body Plan to find out the offset value of
any desired buttock to be drawn in the profile the distance
command will be helpful in this case
13. Finally finish your drawing using leaders, text tools after
adjusting the drawing boundaries. Prepare for plotting by
adjusting the pen assignment for each color used in your
drawing.
Your final result should look something like this
8/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
Tutorial II
“Drawing 3D representation for the hull surface”
1. Pre-drawing preparation:
Prepare your offset table in the form xyz coordinates; x represents
longitudinal direction, y represents the breadth direction and z
represents the depth direction
Assume that we have the following data for the amidships station:
WL O 0.5 1 2 3 4 5 6 7 8 9
Offset .0956 .4348 .6 .7217 .7652 .7913 .8 .8261 .8609 .9043 .9739
Then our prepared table for this station would be
Z (m.) O .79 1.58 3.16 4.74 6.32 7.9 9.48 11.06 12.64 14.22
Y (m.) 1.1 5.0 6.9 8.3 8.8 9.1 9.2 9.5 9.9 10.4 11.2
X (m.) L/2 L/2 L/2 L/2 L/2 L/2 L/2 L/2 L/2 L/2 L/2
2. Start Modeling:
In order to represent the Hull surface of a ship we shall use here the
3dmesh command there’s so many techniques used in modeling but I’ll
try here to discuss the simplest one.
* The BODY Plan and half-breadth plan Curves as wire frames
Using the same SPLINE command start to plot the body plan curves
one by one as you did before with only one exception you’ll give your
coordinates in xyz coordinates.
Notice that for the same station
curve the x coordinates is the
same.
Repeat for the half breadth plan
curves taking care that the z-
coordinate this time is constant
for the same curve
This net of curves is called wire-
9/10 Eng. Mohamed Salah Ebeida
March 2001
AutoCad Tutorials Representation of a Ship Hull Surface
frames; it gives us an idea of how does the hull look like. But in order
to have better effect, we have to deal with surfaces or 3d mesh
command.
3. Working with surface modeling:
Using the 3d command start to load 3d objects in ACAD and prompts you for the
type of objects you want to create; type mesh and then press Enter
Specify the following corners:
(O, O, O) (L, O, O) (L, O, D) (O, O, D)
ACAD asks for the Mesh size in the M direction > Type the no of waterlines you
have in the offset table, also type the no of stations for the Mesh size in the N-
direction press enter to end this command
To recognize the difference between surfaces and wire frames type Shade in the
command and see what happens – the mesh you have created are now acting like
a plate sheet while the wire frames didn’t change. Press undo to cancel this
shading
So we now have a surface but it’s still a plane one while our hull surface is curved,
to attain this curvature we have make some deformation to our mesh – this is
done by selecting the mesh.
Once the mesh is selected its internal nodes are highlighted by small boxes when
any of them is selected its color turns red and then this node ask you where to
move – specify the right location for each point from your prepared offset table
and when you are done the surface will take the same form as the hull surface for
have of the ship.
By using 3dmirror command you can have a complete ship hull “without the
bottom and the aft most BKHD” a little bit finishing and you should have
something like this.
With my Best Wishes
10/10 Eng. Mohamed Salah Ebeida
March 2001
