The hulls are typically built in two sections, being split at the water line. For the sailing vessels, this approach allows the servos and all lines to the masts and sails to be permanently installed in the upper section. Hull sections are fabricated from white pine obtained at the local building supply. The lower hull was built up using the “layer” method since weight below the waterline is not an issue. Converting the ship hull lines to layouts for each layer is done with the aid of the EXCEL spread sheet program.
White pine for the upper section is ripped down to a 1/8″ thickness to minimize weight above the waterline and built up as a set of box structures. The hull sections are connected with brass bolts, which are hidden on the deck with hatch covers, cabins, etc. The seal between the hull sections is provided by closed cell rubber weather stripping, which is compressed about 50% by tightening the bolts. The seal is seen as the black lines in Figure 3. While this method may sound a little radical, it has never resulted in a leak.
Lower hull layers are cut to shape, inside and out, and glued with a water resistant wood glue. The layers are designed to have a seam at the center so that the centerline is always visible during the final shaping process. The outer surface is then shaped with a hand held power planer and a power sander. Final sanding is of course by hand. Interior surfaces were sanded lightly before gluing and needed no further attention.
The upper hull typically consists of a 1/8” thick deck and lower hull interface surface. Interior ribs form a set of box structures for stiffness. The sides are typically made with 1/8” pine sheets. Bow and stern areas, where there was compound curvature, were formed with short “layered” segments. The result is a very rigid structure for the weight, Figure 4.
Waterproofing of the hull sections was accomplished with multiple coats of spray enamel. Five to six coats has been found to be sufficient with the added benefit of covering any scratches left over from the sanding process.
Ballast is fabricated from 1/8” x 1½ “ steel bars. The bars are painted with enamel and fitted into slots previously designed into their respective layers. Any vertical motion of the bars, when under sail, is eliminated with two-sided tape.
Masts, Yardarms and Sails
Several design approaches have been used for the masts and yardarms depending on the specific sail configuration. On some ships the mast is fixed and only the yardarms rotate while on a few such as the Korean Turtle Boat and the Chinese Treasure Ship, both the masts and yardarms rotate as a unit.
For the Sea Witch the two lower sections of the masts are fixed and do not rotate. The lower yardarm on each mast is attached through two brass sleeves soldered at 90 degrees. One sleeve holds the yardarm and the other rotates on the mast. The upper four yardarms are rigidly attached to the top section of mast, which is designed to rotate. The point of rotation is at the upper platform where brass sleeves provide low friction bearings, Figure 5.
Figure 7. Masts, Yardarms, and Bearings
The sails are sewn from light-weight cotton fabric. The ships are sailed with either the square main sails or the jibs, stay sails and spanker. Since stability requires reefing of some of the sails, the above approach helps with both the rigging and servo controls.
Typically all sails are controlled by the sail servo mounted in the upper hull section. In this way, access to the batteries and radio is available without disconnecting any of the rigging or sail control lines. Lines from the sail servo to the lower fore yardarm are routed through the brass sleeves in the deck. The lower yards and the upper yard assembly are all connected together with various lines, Figure 7. The jibs and spanker are typically not actuated but are free to rotate.
The rudder servo is also mounted in the upper hull section and is secured to the rudder after the hull section bolts are tightened.
Nameplates, fore and aft, are computer generated with the spreadsheet program. On the Sea Witch, the background was set in black and the letters in white. The result are then printed on plain paper and waterproofed with a clear acrylic spray, front and back. They are attached to the upper hull with two-sided tape for a highly waterproof installation, Figure 6. Cabin windows and doors are generated in a similar fashion, with the spreadsheet adjusted to obtain the correct sizes. Appropriate colors are then selected and the results printed and coated with acrylic spray.
Figure 8. Sea Witch Lettering
Appropriate flags and banners are available on the Internet. On the Sea Witch, a 30 star flag flies from the mizzen mast, as appropriate for a ship of the late 1840′s. The flags are copied, reduced to the correct size, printed, and waterproofed as described above with clear acrylic.
Various smaller parts are purchased including; the wheel, the water barrels, the deadeyes, the belaying pins, and the stairs. Pin striping is used to produce the trim lines below the rails.
Thrust is provided by a 1 1/4” diameter propeller connected to a speed 600 motor and speed controller. Nicad or nickel-hydrid provide power and contribute to the ships ballast, Figure 9.
Figure 9. USS Kearsarge Motor and Speed Control