Saddletanks

Seeing as I was going to open up the long flooding channels in the kit hull (atop the saddletanks), this presented somewhat of a dilemma in the entire build process. With that decision alone, many new things had to be done: creation of an inner pressure hull, extending the saddletank curvature inside the kit hull, and creating the individual ribs within the channel.

Materials

I needed to use the following products & materials for this phase of the project:

  • Sheet styrene
    Long sheet of 0.20" sheet styrene to make the extension pieces & ribbing
  • Styrene rod
    0.10x0.20" flat strip styrene (for weld beads)
    0.40" square strip styrene (for shelves to support the extension pieces)
  • Chemicals
    Liquid cement (I used Tenax 7R)
    Putty (I used Tamiya Putty)
  • Miscellaneous
    Long (16") wooden dowel, 1.25" diameter
    Masking tape
    Oven & oven mitts

Saddletank Inner Curve — Rear

As described in section 2, with the 3 large flooding holes added to the outer hull above rear edge of the saddletank, looking through those holes you should be able to see the curve of the inner part of the saddletank. To represent this, I used Kraftmark™ ProCreate epoxy putty to create a faux section of the saddletank behind the newly-created flooding holes.

Saddletank cutaway Saddletank - epoxy putty

 

Saddletank Curvature — Adding Extensions Inside the Hull

By cutting open the long central flooding channel of the kit, there is no continuation of the saddletank curvature inside the hull. This needed to be corrected to create the illusion of a full saddletank that curved inside and contacted the inner pressure hull.

The easiest way to mimic this was to add a long, narrow curved piece of thin styrene to the inside edge of the kit hull. I used a 1.25" wooden dowel as a form to curve the styrene to the proper shape.

Making the Saddletank Inner Extensions

I made a simple template for the saddletank extension pieces.

Trace the template onto a sheet of 0.20" styrene. Make 2 of them, one for each side.

To give the proper curve to the extension piece, tightly tape the styrene piece along a 1.25" dia. wooden dowel. Use masking tape… not scotch tape.

Positioning the extension piece on the wooden dowel Extension piece ready for forming

Put the dowel in an oven at 300°F and heat it for 5–10 minutes. Allow it to cool, and remove the tape. Carefully remove the styrene extension piece from the dowel. It should now have the proper curvature.

Repeat for the other extension piece, but remember to flip it over so the piece curves the opposite way!

Attaching the Saddletank Inner Extensions

Add short shelves of 0.40" square strip styrene along the flat inner edges of the kit hull where the saddletank extensions will be attached. These shelves will support the extension pieces when you attach them to the kit hull.

Shelves to support the extension pieces

Place the curved side of the extension piece against the inner edge of the kit hull, and cement it in place; I used Tenax 7R. With the extension piece in place there should be a smooth continuation of the curvature of the saddletank. Allow the glue to dry.

Attached extension piece - from the inside Attached extension piece - from the top

Use putty to blend the seam between the kit hull and the extension piece. If you feel ambitious, you can extend the saddletank weld beads to the inner curvature using 0.10x0.20" flat strip styrene.

 

Channel Ribbing

I used pieces of 0.15" sheet styrene to mimic the 42 ribs that are visible inside each long flooding channel.

Before making the ribs, temporarily tape the kit decks to the hull. This will ensure that the now-free part of the kit hull retains the proper shape. If you do not do this, you may unintentionally force the hull into the wrong shape when you add the ribs, and the deck may not fit later on.

Attach top deck before adding ribs

Each rib starts with a dimension of 8x10mm and a bottom edge that is curved to follow the curvature of the saddletank (Ø1.25"). You must trim the side edge of each rib to match the angle of the outer hull. A template can be found here.

Cement each rib in place, making sure to align each rib with a row of vertical rivets (visible on the hull). Each rib should also be perpendicular to the centerline of the hull .

Step 1: Add strip styrene weld lines

Here are side-by-side pictures of the simple ribbing I used for U‑625, and the improved technique I used for U‑673

Ribbing on U-625 Ribbing on U-673