RhinoCentre Training Approach

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Fonts and notations

• Executed Rhino commands in exercises are displayed in a bold with an underscore in front. For example:   _Polyline
• Command options are written in brackets with the access key underlined.
• For example (PersistentClose=No). Typing [P] [Enter] will toggle 'Yes' or 'No' of the 'PersistentClose' option.
• Keys will be written in square brackets like [TAB].
• Keys to be pressed one after another are written with a greater-than sign in between like [P] >[Enter]
• Keys to be pressed together (holding the first one and press the second) will have a plus sign in between like [Ctrl]+[S].
• Mouse buttons are written in capitals: LMB (left mouse button), MMB(middle mouse button) and RMB (right mouse button)
• Key-Mouse combinations (press and hold the key and mouse click) are written with a plus sign in between like [Ctrl]+LMB.

Tip icons indicate a more efficient way of doing something or a technique that might not be obvious.

The Caution icon is used when the described operation can cause problems if it's not done carefully.

The Note icon is used to draw attention to an important concept or something fundamental for understanding the subsequent material.

Prepare the GA

Exercise 2: Prepare the GA 

• Start Rhino with a new file from the "Large Objects - Millimeters" template
• Create a picture frame with the image "M1R2-AHTS vessel-Drawing.png"
• Move the picture frame from the 'Aft Perpendicular' (Fig. 3) of the Main deck on the drawing to '0' in Rhino

[caption id="attachment_9566" align="alignnone" width="700"] Fig. 3: 'Aft Perpendicular' of the Main deck[/caption]

• The length between perpendiculars (Lpp) is 67.4 m. This is used to scale the drawing to the correct size
• Select the picture frame and run _Scale:
  • Origin point is 0
  • For the first reference point drag the cursor to the right, hit [TAB] and click at the current 'Fore Perpendicular' (Fig. 4)
  • For the second reference point type 67400 > [Enter]

[caption id="attachment_9521" align="alignnone" width="700"] Fig. 4: 'Fore Perpendicular' of the Main deck[/caption]

• Save the file as "M1R2-AHTS vessel-GA exercise.3dm". Create a ‘Work In Progress’ folder on your desktop when you don’t have one already. In the save dialog, mind you to toggle 'save textures', which will save the PNG image in the file.

Scale an existing hull to the GA

Exercise 3: Scale to the basic dimensions

• Open the file "M1R2-AHTS vessel-Practice". This file shows an existing ship hull based on loft curves
• Attach the prepared GA file: "M1R2-AHTS vessel-GA oriented.3dm". Notice the picture frames cutting through the ship hull
• Scale the front part of the ship hull to the correct length using _Scale1D on all loft curves in the "Front" viewport (Fig. 5). Origin point is 0. For the first reference point drag the cursor to the right, hit [TAB] and click at the stem loft curve top point. For the second reference point, move the mouse to the top of the stem of the AHTS vessel. Notice it displays an 'x' value of about 71000 mm, therefore we type 71000 > [Enter]

[caption id="attachment_9522" align="alignnone" width="700"] Fig. 5: Scale to the correct length[/caption]

• Scale1D the overall height of the hull to the curve just below the B-Deck height (13250 mm). Again the origin point is 0
• In the top view scale the hull to the correct breadth. The GA mentions a molded breadth of 17.5 m (check the 'Info' layer). As only port side is modeled the half breadth is 8750 mm.

Exercise 4: Stem and bow

• Shape the stem curves according the GA in the "Front" viewport with 'Project' turned on
• If you have difficulties to examine the hull while editing the control points set the viewport display mode to X-ray
• Turn off all layers of the attached GA file except the layer 'Main deck'
• Validate the breadth of the hull with the Main deck picture frame. It looks accurate in the aft ship and mid ship

The bow however is too slender on the main deck height (Fig 6). We will fix that at a later time. [caption id="attachment_9523" align="alignnone" width="700"] Fig. 6: The bow is too slender[/caption]

• For now turn off the GA 'Main deck' layer. We'll tackle the breadth problem later.

Shape a deck line

Exercise 5: Shaping the sheer strake knuckle [caption id="attachment_9524" align="alignnone" width="700"] Fig. 7: The upper part of the stem is blunt[/caption]

• Turn on the layer "B-deck" from the GA and notice the hull is too wide. Furthermore the upper part of the stem has a blunt shape (Fig 7)
• Turn on the picture frame "Starboard profile" layer for reference as it shows that the sheer strake knuckle shape declines in the most forward part near the stem from Point-1 to Point-2 (Fig. 8)
• Edit the shape to meet the shape of the picture frame using the "Top", "Front" and "Perspective" viewport. Hint: The stem is not extrapolated and trimmed later, therefore it has to start in Point-2.
• Turn off both GA layers when done.

[caption id="attachment_9525" align="alignnone" width="700"] Fig. 8: Sheer strake knuckle declines[/caption]

Tracing the waterline curves of the GA

Exercise 6: Preparing reference objects

• Turn on picture frame layers "Tank top", "Tween deck", "Main deck" and "A-Deck"
• Compare the fore ship of the 3d hull with the picture frames.

• Turn off all GA picture frame layers except the layer "Tank top"
• Turn off layer "Loft curves" and "Loft surface" (just the one picture frame should be visible now)
• Create a new sub layer in the layer "Ship hull design" called: "Reference curves"
• Set the layer color of this new layer to orange
• Trace the port side hull contour with the _InterpCrv command in the top viewport (Fig. 9). Be careful not to use too many control points. Hint: Turn on 'Ortho' when you start at the flat of side in order to have a straight line.

[caption id="attachment_9526" align="alignnone" width="700"] Fig. 9: Trace the port side hull contour[/caption]

• Put the new curve in layer "Reference curves"
• Make sure that the contour curve is positioned to the proper height which is the same height as the picture frame
• Turn off the picture frame layers "Tank top".

Reference Ribbons

Exercise 7: Create a reference ribbon

• Create a sub layer of the layer "Reference curves" with the name "+175 mm" and set the layer color to orange
• Create another sub layer of the layer "Reference curves" with the name "-175 mm" and set the layer color to green
• Select the "Tank top" contour and run the _Ribbon command.
  • Set the offset distance to 175 mm
  • Click outside the hull in the "Top" viewport to determine the 'Side to offset' (Fig. 10)

[caption id="attachment_9527" align="alignnone" width="700"] Fig. 10: Click outside the hull in the "Top" viewport[/caption]

• Change the layer of the ref-rib (the newly created ribbon surface) to the "+175 mm" layer
• Again select the "Tank top" contour and run the _Ribbon command.
  • Offset distance should still be 175 mm
  • This time click inside the ship hull In the "Top" viewport for the 'Side to offset'
• Change the layer of this ref-rib to the "-175 mm" layer
• Turn on layer "Loft surface" to see how the ribbons interfere with the hull surface
• Turn off the layer "Loft surface" and "Reference curves".

Exercise 8: Reference ribbons for all decks

• Trace the contours of "Tween deck", "Main deck" and "A-deck"
• Move the contours to their proper heights
• Create the ref-ribs of each contour
• Put all objects on their proper layers

• Lock the layers with the reference curves and ref-ribs
• Turn off the GA layers with picture frames
• Turn on layer "loft curves" and "loft surface" and notice the deviation of the loft surface to the ref-ribs (Fig. 11).

[caption id="attachment_9528" align="alignnone" width="700"] Fig. 11: Deviation of the loft surface to the ref-ribs[/caption]

Display Mesh

Exercise 9: Adjust the Display Mesh

• Check whether the object display mesh settings of the loft surface is set to acceptable values. When you think you have the proper settings ask the trainer to take a look at your settings.

Transforming the hull

Fairing checklist

1- Curvature of loft curves

2- Control point distribution

3- Isocurve density

4- Display Glossy for fairing

5- Gaussian curvature display

6- Lines plan

Exercise 10: Fit the loft surface to the original GA within tolerance and fair

• Turn on the layers "Reference curves", "+175 mm" and "-175 mm"
• Start editing the bulb shape loft curves as that part is most off from the ref-ribs. use _Move, _Scale, _Nudge, etc. whatever is convenient to you. Add loft curves if needed
• Remember to use the checklist above regularly while editing
• For gaining extra experience, also model the aft ship to reference ribs that you first have to create yourself.
• Save your file in the WIP folder on your desktop.

When you send us this file as one of the tasks for receiving a certificate of completion, you will receive in return, an example of a fair and accurate result. Otherwise you can also ask for the file by sending an email request.

• Regarding NURBS definition
  • Curve and surface degree
  • Amount of control points vs. control point weight
  • Knots; uniform vs. non-uniform objects
• Single loft curves vs. poly loft curves
• Single surface / poly surface
• Chines and knuckles approach
• Transverse loft curves vs. longitudinal loft curves
• Loft Styles:
  • Why loose?
  • When straight sections?
  • Why not normal style?

NURBS

• The order of an object defines the character of the object. The order is the 'degree plus one'. As Rhino uses degree in commands the following degrees exist for both curves and surfaces:
  • Degree 1 objects are straight lines and polylines with straight line segments. This makes it 2nd Order (Degree 1+1).
  • Degree 2 objects are circles and arcs. This makes it 3rd Order (Degree 2 + 1).
  • Degree 3 or higher degrees are most free-form curves. This makes them 4th or higher Order.

• A set of control points is used to manipulate the position and shape of the object of a certain degree. The amount of control points is at least the Degree +1 point. A straight line contains degree 1 +1 = 2 control points which define the start and end position of the line.
  • Degree 1; lines and polylines contain at least 2 control points
  • Degree 2; circles and arcs contain at least 3 control points for an arc
  • Degree 3; free-form curves contain at least 4 control points
  • By moving control point positions the position and shape of a curve or surface can be defined.
  • If the desired shape cannot be realized then adding control points to the object allows more control.
  • Control points are always either connected directly to the curve/surface, or act as if they were connected by a rubber band

• The rational part of the definition is the ability to set a weight to an individual control point. The weight determines how strong a control point pulls to a curve or surface like a rubber band. Instead of adding control points for more control, setting another weight might also be a solution to get to the desired shape. In the level 1 Hull Design and Fairing training module this was used to model the desired bilge radius. When the control points of a curve all have the same weight (usually 1), the curve is called non-rational and otherwise the curve is called rational. Some objects like arcs, circles, and ellipses are always rational.

• When the amount of control points of an object is larger than the Degree+1, knots are automatically added to the curve or surface. The knot structure can be uniform or non-uniform in Rhino. When a control point has to be added without changing the shape of a curve it is best to insert a knot. Most likely this will lead to a non-uniform knot structure. When it is important to maintain a uniform knot structure, it is better to insert a control point although the shape will change then.

Curve and surface degree

Exercise 11: Examine the curve degree [caption id="attachment_9532" align="alignright" width="409"] Fig. 15: Object Description dialog[/caption]

• Open file "M1R2-NURBS.3dm" and notice three lines
• Make sure that the Top viewport is maximized
• Turn on 'Project' in the Osnap toolbar

 

• Select the straight line at the bottom (01-Line) and click 'Details' in the object properties panel. Notice in the "Object Description" dialog (Fig. 15) that it is a line with a start, end and length
• Check the object description of the middle curve (02-Polyline A) and notice that this is an open polyline with three points
• Dismiss the dialog and turn on the control points of the polyline and notice their positions
• Hit [Esc] to turn off the control point display

 

• Turn on layer "Degree 2". Notice the arc (04-arc) [caption id="attachment_9533" align="alignright" width="192"] Fig. 16: Rebuild the L-shaped curve[/caption]
• Examine the object description of the arc and read that it is called an Arc with a certain start, end, center, radius and angle
• Turn on the control points of the arc and notice that all points are at the same position as the 1 degree polyline
• Now run _Rebuild and select the L-shaped curve (02-Polyline A)
  • Set the Degree to 2 and Point count to 3 in the "Rebuild" dialog and press OK (Fig. 16)
  • Notice that the shape changes to a large arc that runs through the middle control point of the original polyline

 

• Turn on the control points of the new arc and notice the midpoint is far out
• Move this point to the middle control point of the white arc (make sure to turn on "point" snap). Now notice that the shape is different than the original arc. We will fix this later
• Examine the object description of the new arc and read that it is a degree 2 object

 

• Turn on layer "Degree 3" and notice a white freeform curve (05-Curve A) on top of the black kinked polyline (03-Polyline B)
• Examine the object description of the freeform curve and read that it is an open NURBS curve with a degree = 3
• Turn on the control points of both the polyline and the curve and notice they are on top of each other. So apparently only the degree is responsible for the shape and not the amount and position of the control points

• Select the the kinked polyline (03-Polyline B) and run _ExtractPt 4 points are added at the control point locations
• Run _Rebuild and select the kinked Degree 1 polyline (03-Polyline B) in order to convert it into a freeform curve
• Set the Degree to 3 and Point count to 4 in the "Rebuild" dialog and press OK. Notice that the shape changes to a freeform curve

The rebuild command tries to match the original curve as good as possible which leads to this shape that runs through the second and third control point

• Turn on the control points of the curve and notice that the second and third points are far out in order to match the shape as good as possible
• Move the second and third point to their extracted respective points of the kinked curve

Notice that the shape is the same as the white freeform curve so apparently an original Degree 1 curve can be rebuild to a freeform curve. On the other hand the white freeform curve of Degree 3 can also be rebuilt to a Degree 1 polyline with the _Rebuild command. Try this yourself without deleting the original white curve

• Turn on layer "Degree 5" and notice another freeform curve (06-Curve B) above the 3 degree curve. The leader mentions: 5 degree 6 control points [caption id="attachment_9534" align="alignright" width="320"] Fig. 17: Different control point positions[/caption]
• Examine the object description and validate that it is indeed a Degree 5 curve with 6 control points
• Turn on the control points of this Degree 5 curve and notice their positions
• Now copy the 5 degree curve on top of the lower Degree 3 curve. Notice that the shape is nearly the same
• By turning on the control points of both freeform curves the difference in their positions can be examined (Fig. 17)

 

• Turn on layer "Compare 3/5 degree". Notice a white straight line (08-Curve Degree 5) [caption id="attachment_9535" align="alignright" width="320"] Fig. 18: A Degree 5 curve is 'more relaxed' than a Degree 3 curve[/caption]
• Click at the curve and notice that one black curve (07-Curve Degree 3) and one white curve (08-Curve Degree 5) are on top of each other
• Turn on the control points of both curves
• Move the points at Dot-2 upwards 20 millimeters. Notice that the white curve seems more 'lazy' than the black curve
• Move the points at Dot-4 downwards 10 mm
• Examine the object description of both curves and discover that the black curve is Degree 3 and the white curve is Degree 5. So apparently a Degree 5 curve is 'more relaxed' than a Degree 3 curve (Fig. 18)

 

• Hit [Esc] to turn off the control point display
• Now move the white curve 60 mm. to the right
• Turn on the curvature graph of both curves by running _CurvatureGraph
• Set the scale to 115 and notice that besides more curvature, the Degree 3 curvature graph is not perfectly smooth as somewhere midway (between Dot-2 and Dot-4) there is a kink (Fig. 19)

[caption id="attachment_9536" align="alignnone" width="640"] Fig. 19: Curvature difference of 3 and 5 degree curves[/caption]

• Turn off the curvature graph analysis

As you can see a 3 degree curve can have kinks. Although it is possible to get rid of these kinks through control point editing it will be very hard to keep the shape the same while doing so. So if a perfectly smooth shape is required it’s advisable to work with 5 degree curves right from the start.

Adding Control Points

Exercise 12: Adding Control Points [caption id="attachment_9537" align="alignright" width="320"] Fig. 20: Notice the difference in the shapes[/caption]

• Turn on layer "Degree 3, 1 knot" and notice again a freeform curve of the same shape as seen before
• Click at the curve and notice that one black curve (10-Curve A is a copy of 05-Curve A) and one white curve (09-Curve C) are on top of each other
• Examine the object description of the white curve and discover that it is a Degree 3 curve and now contains 5 control points instead of four
• Turn on the control points of both curves and notice that the original black curve contains the four points as the white curve indeed contains 5 points. Surprisingly the shape is the same
• Now move the control points of the right curve end to Dot-5 and notice the difference in the shapes (Fig. 20)

[caption id="attachment_9538" align="alignright" width="320"] Fig. 21: Notice the difference in the shapes[/caption]

• Turn on layer "Degree 3, 2 knots" and notice again a freeform curve of the same shape as seen before
• Click at the curve and notice that one black curve (12-Curve A is a copy of 05-Curve A) and one white curve (11-Curve D) are on top of each other
• Examine the object description of the white curve and discover that it is a Degree 3 curve and now contains 6 control points instead of four
• Turn on the control points of both curves and notice that the original black curve contains the four points as the white curve indeed contains 6 points. Again the shape is the same
• Now move the control points of the end point at the right hand side to Dot-6 and again notice the difference in shapes (Fig. 21)

Control point weight

Exercise 13: Edit Control Point Weight

• Pan and zoom to the arc (04-arc) in "Top" viewport
• Turn on the control points of the white arc
• Run _Weight and select the middle control point of the white arc
• Read in the "Set Control Point Weight" dialog that the weight of this point is not 1 but 0.707107
• Now examine the object description of the black arc shaped curve in the object properties menu
• Read that it is a Degree 2 curve [caption id="attachment_9539" align="alignright" width="425"] Fig. 22: Edit Control Point Weight[/caption]
• Turn on the control points of this black curve
• Run again _Weight and select the middle control point
• Read in the "Set Control Point Weight" dialog that the weight of this point is 1 (Fig. 22)
• Change the value to 0.707107 and press OK. Notice that the shape became exactly the same as the arc
• Examine again the object details of the black curve in the object properties menu. Read that it now became an elliptical arc

 

• Turn on layer "Set weight" and notice a freeform curve (13-Curve A) which is a copy of the curve to the left (05-Curve A)
• Examine the object description and read that it is a Degree 3 curve, non-rational with 4 control points
• Turn on the control points and run _Weight on the second control point
• Read that the current weight is 1
• Move the slider to adjust the weight and see how it affects the shape of the curve.
• Set the value to 10 and press OK
• Now also do this for the third control point
• The conclusion is that both Degree 3 curves with only 4 control points at the same position have a totally different shape (Fig. 23)

[caption id="attachment_9540" align="alignnone" width="640"] Fig. 23: Same degree and point count but different shape[/caption]

• See the object description of the curve and find out that the curve became rational

 

• At last turn on Layer "More control points" and notice a white curve (14-Curve E) on the same location that has the same shape
• Examine the object properties discover that this curve is a 'normal' Degree 3 curve, non-rational, with 6 control points
• Finally examine the weight of the 6 control points. Do they all weigh 1? Does that make it a rational or non-rational curve?

Single loft curves vs. poly loft curves

Exercise 14: Single loft curves

• Open file "M1R2-Strategy"
• Run _Explode on the loft curves visible on screen and find out that they can't be exploded as they are single curves
• Turn on the control points of the main frame curve to see their positions
• Examine the object description of the main frame loft curve. Find out that it is a Degree 3 curve with 7 control points with rational behavior. The rational behavior means that one or more control points have another weight value than 1. This is correct as one of the control points of these loft curves where weighed to match the bilge radius
• Turn on layer "Exercise > Single loft curves > Loft Surface"
• Switch to display "Glossy for Fairing" and see the nice smoothness of the hull
• Turn off layer "Exercise > Single loft curves"

Exercise 15: Polycurve loft curves [caption id="attachment_9541" align="alignright" width="320"] Fig. 24: No smooth transition from the bilge radius to the bow[/caption]

• Turn on layer "Exercise > Polycurve loft curves"
• Again run _Explode on the loft curves and read: Exploded 6 curves into 18 segments
• Undo the Explode command
• Turn on the control points of the main frame curve to see their positions
• Examine the object description of the main frame loft curve. Find out that it is an open polycurve with three curve segments:
  • Segment 1 is a Degree 1 line with 2 control points
  • Segment 2 is an Arc
  • Segment 3 is again a Degree 1 line with 2 control points
• Turn on layer "Exercise > Polycurve loft curves > Loft Surface"
• Switch to the "Glossy for Fairing" display mode (if it's not still active) and notice that there is no smooth transition from the bilge radius to the bow area. It shows with a crease which is not acceptable (Fig. 24)
• Switch the display mode back to "Shaded"

 

• Explode the loft surface (ignore the "History Warning") to find out that it actually is a polysurface made from three surfaces: One bottom part, a bilge part and a ship side surface
• Undo the Explode command
• Turn off layer "Exercise > Polycurve loft curves"

Single surface vs. poly surface

Exercise 16: Polysurface hull

• Turn on layer "Exercise > Polysurface hull"
• _Zoom (All Extents) to take a look at some loft curves
• Create a hull surface with _Loft/Loose (don't forget to activate History recording)
• Change the layer of the created surface to "Exercise > Polysurface hull > Loft Surface"
• Turn on the control points of the hull surface. Rhino mentions: "Cannot turn on points for polysurfaces"
• Examine the loft surface object details and find out what type of surface this is. It appears to be a polysurface made of three surfaces
• _Explode the hull surface (ignore the "History Warning")
• Turn on the control points of the hull surfaces
• Undo the explode action
• Turn off layer "Exercise > Polysurface hull"

Exercise 17: Crease Splitting [caption id="attachment_9542" align="alignright" width="320"] Fig. 25: Control point display of a single, kinked hull surface[/caption]

• Run _CreaseSplitting and set (SplitAlongCreases=No)
• Turn on layer "Exercise > Crease Splitting". The appearing loft curves are identical to the ones from the last exercise
• Again create a hull surface from the loft curves using _Loft/Loose with History recording enabled
• Now turn on the control points of the hull surface and see that it is possible (Fig. 25)
• Try to explode this hull surface to find out that Rhino mentions: Cannot explode single surfaces
• Change the layer of the created surface to "Exercise > Crease Splitting > Loft Surface"
• Run _CreaseSplitting and set (SplitAlongCreases=Yes)
• Turn off layer "Exercise > Crease Splitting"

Chines and Knuckles

Exercise 18: Hard chines [caption id="attachment_9543" align="alignright" width="320"] Fig. 26: Use Intersect to check if the tunnel cuts the hull[/caption]

• Turn on layer "Exercise > Hard chines". This shows an exact copy of the hull we created in the previous exercise
• Turn on layer "Exercise > Hard chines > Tunnel" which shows two magenta curves: one large arc and one very small line
• Use these two curves to create a tunnel surface with Loft/ Straight Sections (with record history). This makes it easy to update the shape of the tunnel when the hull surface is edited. Notice that the tunnel doesn't intersect the hull properly.

   

If you have difficulties selecting the tiny tunnel loft curve for the Loft or Move command just right-click the layer "Exercise > Hard chines > Tunnel > Curves tunnel", choose 'Select Objects' and hit [Enter].

[caption id="attachment_9544" align="alignright" width="320"] Fig. 27: The resulting soft chine[/caption]

• Move the tunnel curves down until the tunnel surface fully intersects the hull surface visually
• Use _Intersect to check whether the tunnel surface cuts the hull surface well. It should create one single curve along the tunnel (Fig. 26)
• Delete the intersection curve
• Trim the surfaces with each other. This delivers a "hard chine". Note that trimming breaks the History connection
• Join the surfaces together
• Make sure the layer of the joined polysurface is set to "Exercise > Hard chines > Loft Surface"
• Use the _FilletEdge command to create a fillet on the joined edge with a radius of 50 mm. This delivers a soft chine (Fig. 27)
• Examine the result with the display Glossy for Fairing to see if it looks nice

 

• Turn off layer "Exercise > Hard chines"

Exercise 19: Soft chines

• Turn on layer "Exercise > Soft chines ". This shows exact the same loft curves as seen with the previous hulls
• Turn on the control points of one loft curve. Notice that they are positioned at each corner
• Copy the second loft curve from the stern 300 mm aft wards
• Create a hull surface with _Loft/Loose (as usual don't forget to activate Record History)
• Change the layer of the hull surface to "Exercise > Soft chines > Loft Surface"
• Change the degree of the three aft ship curves from degree 1 to degree 3 using _ChangeDegree (Deformable=No)
• Turn on the control points of these three aft ship loft curves and notice that Rhino has added two control points at each strake
• Turn on layer "Exercise > Soft chines > Ref. Points"
• Insert control points at (A), (B) and (C) with _InsertControlPoint
• Move the control point at (A) upwards to (F) in order to create the tunnel shape. Notice that the tunnel shape is not very pronounced
• Move the two adjacent control points (of point A) to (D) and (E). This makes the tunnel shape wider but still not very pronounced. (Fig. 28)

[caption id="attachment_9545" align="alignnone" width="640"] Fig. 28: Move the adjacent control points to (D) and (E)[/caption]  

• In the Right viewport, add one extra control point to the left of (D) but very close (Fig. 29). Repeat this at (E) but then to the right

[caption id="attachment_9546" align="alignnone" width="640"] Fig. 29: Add one extra control point to the left of (D)[/caption]  

• Move the control points at (G) and (H) very close to (B) (Fig. 30)

[caption id="attachment_9547" align="alignnone" width="640"] Fig. 30: Move the control points at (G) and (H) very close to (B)[/caption]  

• Repeat this for the two adjacent points of (C)
• Add two extra control points very close to (B)
• Repeat this by adding two extra control points very close to (C). Notice that the tunnel shape is more pronounced now
• The render mesh of the hull surface is not very smooth. So edit the render mesh settings to show a smooth hull surface in the tunnel region.
• Turn off layer "Exercise > Soft chines > Ref. Points"
• The chine from the bottom strake to the tunnel is now described by two control points in each curve. In order to make the transition from the bottom strake to the tunnel even more pronounced add a third control point at each position
• Turn off layer "Exercise > Soft chines"

Transverse loft curves vs. longitudinal loft curves

Exercise 20: Longitudinal Loft Curves [caption id="attachment_9548" align="alignright" width="388"] Fig. 31: Loft with longitudinal curves[/caption]

• Turn on layer "Exercise > Work Boat". Notice the transverse loft curves
• Turn on layer "Exercise > Work Boat > Loft Surface transverse"
• Duplicate all longitudinal edges of the hull surface with _DupEdge
• Create layer "Loft Curves longitudinal" as a sublayer of "Exercise > Work Boat"
• Change the layer of the longitudinal curves to this new layer
• Turn off layer "Exercise > Work Boat > Loft Curves transverse" and "Exercise > Work Boat > Loft Surface transverse"
• Create a hull surface using _Loft/ Straight Sections with the longitudinal loft curves (don't forget to activate Record History) (Fig. 31)
• Create layer "Loft Surface longitudinal" as a sublayer of "Exercise > Work Boat" and change the layer color to white
• Change the layer of the new hull surface to this layer
• Turn on layer "Exercise > Work Boat > Loft Surface transverse" and notice the shape is identical
• Turn off layer "Exercise > Work Boat > Loft Surface transverse"
• Save the file as "M1R2-Strategy-finished" in the WIP folder on your desktop.

Dynamic Sections

Exercise 23: Dynamic Sections

• Open file "M1R2-Analysis"
• A well-known hull surface and its loft curves is visible on screen
• Create a _Polyline in the Top viewport from "0,-1000" to "0,15000" to "r2500,0" to "r0,-16000" and then "r2500,0"

• Run _ExtrudeCrv with the option (BothSides=No) and (DeleteInput=Yes) to create a surface from the polyline with a height of 20000 mm. Also here we create a large margin in case the design changes radically
• Select the extrusion and move it 1000 down (-Z) and 5000 backwards (-X)

• Run _Array while the Top viewport is active and select the previously created polysurface. For the "Number in X direction" type 15, the "Number in Y direction" stays "1" and also the "Number in Z direction" stays "1". For the "X spacing" type 5000 and make sure (Preview=Yes). The preview shows that 15 copies are not enough so change the "XNumber" to "20" to be sure to have some extra freedom in case the ship hull needs to be longer later. Press [Enter] to finish the Array command (Fig.32: The stations reference object)

[caption id="attachment_9549" align="alignnone" width="640"] Fig. 32: The stations reference object[/caption]

• Window select the extrusions and run _Join

 

• Create a new layer called "Lines Plan" as a sublayer of "Exercises > Dynamic Sections"
• Create a layer called "Stations" as a sublayer of "Lines Plan" and change the layer color to red
• Create another layer called "Reference" as a sublayer of "Stations"
• Change the layer of the joined extrusions to "Reference"

• Make sure "Record History" is turned on and run _Intersect
• On the "Select objects to intersect:" prompt, select the hull surface and stations reference object and press [Enter]
• The station curves have been generated
• Change the layer of these new station curves to "Stations" and lock this layer
• Turn off layer "Reference"
• To witness the dynamics of these stations, move the two bow loft curves significantly forward (For example 5000 mm). If all is well the red station curves should update now

Exercise 24: Curve deviation [caption id="attachment_9550" align="alignright" width="320"] Fig. 33: The deviation values reported in the command prompt.[/caption]

• Turn on layer "Exercises > Curve deviation > Original Reference" which shows an orange station curve in the fore ship area
• Unlock layer "Exercises > Dynamic Sections > Lines Plan > Stations"
• Run _CrvDeviation and select both the red and orange curve at this position. Rhino reports the maximum deviation in the command prompt (Fig. 33). If desired you can keep the marks indicating the maximum deviation (KeepMarks=Yes). Press [Enter] to finish the command
• If you later need to read again the maximum deviation press [F2] to bring up the "Command History" panel
• Turn off the layers "Exercises > Curve deviation" and "Exercises > Dynamic Sections"

Forefoot Continuity

Exercise 25: Forefoot Continuity [caption id="attachment_9551" align="alignright" width="320"] Fig. 34: The problem-area at the forefoot[/caption]

• Turn on layer "Exercises > Forefoot Continuity" and take closer look at the forefoot of this hull
• For a realistic presentation of this area the starboard side off the hull is mirrored with Record History turned on
• Do you notice that the bottom strake shows twist and the forefoot shows a kink?
• Run _CurvatureAnalysis, select both hull surfaces and adjust the Analysis Mesh for a smooth display
• Switch to Style: "Min radius" and press 'Auto Range'. Now a nasty area becomes visible in the forefoot region (Fig. 34)
• Rotate around this area to investigate the shape of the forefoot
• Turn off Curvature analysis

 

• Maximize the Front viewport and zoom in at the forefoot
• Turn on layer "Exercises > Forefoot Continuity > Ref. Objects"
• Turn on the control points of the loft curves and notice the points of Ref-1/2/3 are not inline which creates the kink at Ref-2
• To get that fixed select the control point at Ref-3 and run _Move
  • On the "Point to move from:" prompt, snap to Ref-3
  • On the "Point to move to:" prompt, type _AlongLine (or go to Tools > Object Snap > Along Line in the main menu) [caption id="attachment_9552" align="alignright" width="320"] Fig. 35: The fixed forefoot[/caption]
  • On the "Start of tracking line:" prompt, snap to Ref-1
  • On the "End of tracking line:" prompt, snap to Ref-2
  • Now move the control point along the constraint till you are satisfied with the shape
• Rotate around the forefoot in Perspective viewport to find out the surface doesn't appear to be twisted anymore (Fig. 35)
• Turn off layer "Exercises > Forefoot Continuity".

 

As you might wonder the bottom strake has a triangular shape but does contain four edges as the edge between Ref-1 and Ref-2 is part of the keel line which is defined by a loft curve that starts at Ref-1. Therefore the bottom strake has currently a rectangular contour. By moving the control point at Ref-1 to the position of Ref-2, the surface becomes really triangular but Rhino also converts the bottom and adjacent strake into a single surface then. The problem is that this cannot be exploded or unrolled to an expanded contour for manufacturing. Therefore it might be a solution to minimize the distance between the control points at Ref-1 and Ref-2 and avoid again a singularity.

Developability

1. Check if the surface is straight in one direction
2. Locate areas with significant twist
3. Analyze the surface with _CurvatureAnalysis > Style: Gaussian
4. Unroll developable surfaces and examine the result

Exercise 26: Developability [caption id="attachment_9553" align="alignright" width="320"] Fig. 36: Locate areas with significant twist[/caption]

• Turn on layer "Exercises > Developability". The hull and curves visible are the exact ones from the last exercise
• The first developability-check is whether the hull strakes are straight in one direction due to proper input.
• Apparently this hull is modeled with lofted straight sections and longitudinal freeform curves. So that is promising
• The second check is to examine the overall hull and locate twisted areas
• Apparently the upper bow area bulwark seems to be heavily twisted (Fig. 36)

  [caption id="attachment_9554" align="alignright" width="320"] Fig. 37: CurvatureAnalysis[/caption]

• Select the PS hull surface and run _CurvatureAnalysis using style: "Gaussian". Set the range from +1e-08 to -1e-08 (Fig. 37).

                  [caption id="attachment_9555" align="alignright" width="295"] Fig. 38: Curvature analysis mesh settings[/caption]

• Check the analysis mesh settings of the curvature analysis and adjust them if necessary (use the settings shown in Fig. 38 as a reference). Blue areas might be twisted too much for accurate unrolling to planar contours for manufacturing
• Explode the PS hull surface

            [caption id="attachment_9556" align="alignright" width="425"] Fig. 39: Unroll area difference in the command history[/caption]

• Run _UnrollSrf and select the upper bulwark strake. In the Top viewport a black surface shows the planar expansion. More important is to read the command history (Fig. 39) by pressing [F2].
• There you can read that the unrolled area is 0.09% bigger after unrolling.
• Let's try to minimize this to a maximum value of 0.05%. An area less than 0.05% bigger or smaller seems okay for most manufacturing purposes (Note: No rights can be derived from this advice!)
• _Undo the _Explode

As the proper settings for Gaussian analysis depend on the size of the hull, they have to be smaller when the hull size increases. This means that a proper setting for a small hull of let's say 10 m. long, might be for example +1e-08. For a larger hull of let's say 100 m. long, it might be for example +1e-09 or even +1e-10.

 Another way to check whether the unrolling is accurate is to measure the lengths of edges and projected frames on the original 3d surface and unrolled planar surface. They have to be more or less the same values.

• Turn on control points of the topmost loft curve
• Move the first control point at the bow aft wards with Nudge and see what happens with the Gaussian curvature display. Proceed until the point is at the same X location as the second control point of the loft curve

Notice that the Gaussian analysis color is now green at center line but remains blue more aft wards. Select both points and move them both forward in front viewport with Nudge. Now you'll notice that the Gaussian analysis color turns into green. This is the way to go!

• When you're satisfied with the bow bulwark shape, right click in the layer manager on the layer "Exercises > Developability > Loft Surface" and choose "Duplicate layer and objects" from the menu [caption id="attachment_9557" align="alignright" width="449"] Fig. 40: Area difference is within tolerance[/caption]
• Rename this new layer into "Hull surface". Find out that this hull surface doesn't update when loft curves are edited. Apparently the Record History is not maintained when copying history objects
• Turn off the layer "Exercises > Developability > Loft Surface"
• Explode the copied hull surface
• Run _UnrollSrf (Labels=Yes), select the upper bulwark strake again and press [Enter}. Read in the command prompt: Area difference is within tolerance (Fig. 40). This is good!

Also notice the numbered labels indicating which edge belongs where.

Notice the option of the _UnrollSrf command to select curves on the surface to unroll with it. This is useful for unrolling frame curves, window openings etc. with the shell expansion.

[caption id="attachment_9558" align="alignright" width="320"] Fig. 41: Contour curve and labels of the unrolled surface[/caption]

• In the Top viewport, move the unrolled surface to a position that doesn't interfere with other geometry
• Run _Ungroup to ungroup the unrolled surface and labels
• Run _DupBorder to extract a contour curve of the unrolled surface
• Delete the unrolled surface
• In the Top viewport, rotate the contour and labels more or less in the same direction as the ship hull (Fig. 41)

• Unroll the other strakes and orient these contours below the top bulwark strake. Make sure the accuracy is within 0.05%. Apparently even the bottom strake is within accuracy of 0.05%. This means that the Gaussian curvature range setting is apparently not an absolute value.
• Turn off Curvature Analysis
• Create a layer "Unrolled Strakes" as a sublayer of "Exercises > Developability"
• Change the layer of all contour curves and labels to this layer. Use _SelDot to select the dots at the 3d hull surface
• Turn off layer "Exercises > Developability"

Curve and surface direction

Exercise 27: Curve and Surface Direction

• Turn on layer "Exercises > Curve and Surface Direction ". Four loft curves are visible
• Run _Dir, select the upper loft curve and press [Enter]. Notice the white arrows indicating the direction from aft ship to fore ship
• Click at the curve to flip the direction
• Click again at the curve to switch back to the original direction from aft ship to fore ship. Press [Enter] to finish the _Dir command
• Now also examine the direction of the other loft curves. Find out that the 'keel' curve shows a direction from the fore ship to aft ship. Cancel the _Dir command to make sure you don't flip the direction of the keel curve.
• Turn on layer "Exercises > Curve and Surface Direction > Loft Surface"
• Run _Dir again and select the surface. Notice the arrows pointing inward
• Click at the surface to flip the direction and press [Enter]. A "history break warning" mentions that history between the loft curves and loft surface is lost when the flipped direction is accepted
• Undo the flipping of the surface direction

[caption id="attachment_9559" align="alignright" width="320"] Fig. 42: The hull surface is destroyed and twisted[/caption]

• Select the keel curve and flip its direction. Notice that the hull surface is destroyed and twisted (Fig. 42). This is no solution
• Delete the hull surface
• Loft the curves again (make sure Record History is turned on)
• Change the layer of the hull surface to "Loft Surface"
• Analyze the surface normal with _Dir. Notice the arrows point outwards (Fig. 43). This is good for Orca3d analysis

[caption id="attachment_9560" align="alignright" width="320"] Fig. 43: All loft curves have the same direction[/caption]

• Mirror the hull surface (remember to Record History)
• Analyze the direction of the mirrored hull surface. Do the arrows also point outwards?
• In case the surface normal point inwards, select all loft curves with _SelCrv , run _Dir and click the option (FlipAll).
• Try this and undo the operation.

 

Edge Analysis

Exercise 28: Edge Analysis [caption id="attachment_9561" align="alignright" width="320"] Fig. 44: The 'Edge Analysis' dialog[/caption]

• Turn on layer "Exercises > Edge Analysis". A developable hull is visible now
• Run _ShowEdges, select both hull surfaces (PS- and SB side) and press [Enter]. The 'Edge Analysis' dialog pops up (Fig. 44)
• Click at "Naked Edges" and notice some magenta edges at center line, deck and open transom
• Join PS- and SB side together, neglect the History Break Warning and notice that the center line edge is not magenta anymore. Apparently the center line is watertight now
• Undo the join operation

Use the Zoom button to find very small Naked Edges

Homework:

• Find out in the Rhino help what a non-manifold edge is

Exercise 29: Faces and Edges Display

• Import the custom display file "Faces and Edges.ini" the same way you did it with the "Glossy for Fairing" display mode in "Hull design and fairing Level-1"
• Switch the "Perspective"viewport to this new display and notice:
  • Surfaces show the direction positive in grey and negative in blue. This means that the outside of an object should show in grey
  • Joined edges show black and naked edges show magenta
  • Isocurves show Red in U-direction and Green in V-direction
• Switch back to "Shaded" display
• Save the file in the WIP folder on the desktop