Now that we’ve merged the small flipper into the creature, and have rebuilt and deleted history, we’ll duplicate and mirror to get the other side of the creature. Select all of the surfaces and Group (Ctrl + G) them together. Grouping them automatically places the pivot point at the origin, which if you’ve been following along, should be at the center point of the creature. Simply type -1 in the Scale X channel in the Channel Box.

You can use many methods in creating the larger fin on the creature’s back. This tutorial will use a Birail. You could use a Boundary, Loft, or any number of other methods with equal results. There are three different types of Birails: Birail 1, Birail 2, and Birail 3+. The different types refer to the number of curves involved. A Birail 1 uses three curves. A Birail 2 uses four. And a Birail 3+ uses five or more. The number in the name refers to the number of Profile Curves. In addition to the profile curves, you will always have two Rail Curves, hence the name “Bi-Rail.” For the dorsal fin, we’ll use a Birail 1. This method uses two Rail Curves and one Profile Curve.

In the Side View, using the CV Curve Tool, draw a curve following the contours of the dorsal fin in the drawing from the body to the tip (Fig 54). This will be Curve1. Draw another curve from the body to the tip along the bottom edge of the fin (Fig 55). This will be Curve 2. These two curves will act as our Rail Curves. The next curve we draw will be our Profile Curve, and must be snapped to the ends of the Rails. So, holding the “C” key to turn “Snap to Curve” on, LMB and drag along Curve 1 to the end closest to the body. This will be the initial CV for Curve3. Switch to the Front View and draw a curve arcing toward Curve2. For the last point, switch back to the Side View and again, hold the “C” key to turn on “Snap to Curve” and LMB and drag the CV along Curve2 to the end closest to the body. Press enter to finalize the curve. You should have something similar to Fig 56 and 57.

Now, before creating the Birail surface, we need to check the curve spans. My spans are as follows:

• Curve1: 9 Spans
• Curve2: 6 Spans
• Curve3: 3 Spans

As in the Boundary, the curves that are opposite each other need to equal each other’s spans. For comparison, let’s keep the spans as they are and perform the Birail. Go to Surfaces > Birail > Birail 1 > Options. In the options, Edit > Reset Settings. The way the Birail tools work, you first select the profile curve (Curve3 in my example) and then select the two rails (Curves 1 and 2). I get the following result (Fig 58). Once again, not very efficient geometry. Delete the Birail surface’s history and move it to the side, out of the way.

Now, let’s rebuild the Curve 1 and 2. Select both, and go to Edit Curves > Rebuild Curve > Options. In the options, use the following settings:

• Parameter Range: 0 to #Spans
• Keep: Ends
• Number of Spans: highest in the pair (9 in my example)

It’s also a good idea to rebuild your profile curve using the “Keep” Setting of Ends and CVs, in order to optimize its settings.

In a comparison (Fig 59) you should be able to see, as in the boundary surface, the difference when the spans are equal.

You can delete the unwanted Birail surface. Rebuild the new one with optimization settings and delete its history. You can delete the curves used to create it. In order to get the other half of the fin, we’ll duplicate it and mirror to the other side. To do this, select the fin surface, go to Edit > Duplicate > Options, and Edit > Reset Settings. Duplicate. In the Channel box, input -1 in the Scale X channel. The duplicated half fin should flip to the other side. Now, we’ll attach the two halves together. RMB on each and select “Isoparm” from the menu items that appear. LMB on an isoparm on the left surface and drag it to one of the edges where the two surfaces will meet. Hold Shift and do the same on the other surface. Edit NURBS > Attach Surfaces > Options. Make sure “Blend” is selected and “Keep Originals” is unchecked. You should get a result similar to Fig 60. The surface is still un-attached on the opposite end, but because it is only one surface now, the Attach Surfaces action won’t work. Select the surface and Edit NURBS > Open/Close Surface > Options. In the options, try the V direction and Apply. If it doesn’t work, undo, and try the U direction. Your surface should close. Rebuild with optimization settings and delete the surface’s history.

Now, if your fin is like mine, it has a hole in the tip. To remedy this, insert an isoparm at the tip of the fin (Fig 61). Select the Hull at the very tip and scale it down until the hole is practically invisible (Fig 62). Rebuild with optimization settings. You should get a result similar to Fig 63.

For texturing later, move the seam to a more desirable position, by selecting an isoparm where you want the seam to move and Edit NURBS > Move Seam.

Because this creature has two dorsal fins, we’ll duplicate the one we’ve created to use for the other as well. Move the duplicate down, out of the way. We’ll come back to it later.

Because of the detachment needed to merge the small flippers to the creature, the current location for the dorsal fin doesn’t allow for an optimal merging location. I’m going to move the fin up as I have in Fig 64. Your changes will more than likely vary, but I applied the following changes:

• Translate Y: 2.1
• Translate Z: -.2
• Rotate X: 7.8