SKIF · Shell and section
A twelve-sided frame with a smooth, rounded skin
The structure is a polygon because straight 2×4s and flat gussets are cheap and easy to build accurately. The outside is not: curved lath on crescent spacers fills out the angled pieces so the covering, and any later metal hull, sits on one fair curve. Both ends are rounded and blunt.
The section
Shape
A 48 in floor flat, then two lower pieces on each side, about 28 in long, at 45° and then 75°. Vertical walls run 53.9 in, from 46.8 to 100.7 in above the bottom. The upper pieces and the 27⅓ in top flat are unchanged at 60° and 30°. The result is 102 in wide and 138 in (11 ft 6 in) tall.
The wide floor flat sits between the deck's fenders, and the steep lower pieces climb over them: at the inner fender edge the finished skin is about 12.5 in above the body bottom, leaving roughly 3–6 in over an estimated 29–31 in fender top. Fender heights are estimated from tire size and need measuring on the chosen deck.
What it buys
- About 9 ft 7 in from the floor to the center of the ceiling, room for a raised bunk or high storage later.
- An 84 in wide service floor 18 in above the bottom, with full 93 in counter-height width above the knee walls.
- Road height of 13 ft 6 in with the 2 in roof solar rows as the only roof equipment.
The cost: the perimeter grows from about 364 to 404 in, about 11% more frame, covering, insulation and lining per foot than the 10 ft section. That mass is now in the weight budget.
The skin, outside in
| Layer | What it does |
|---|---|
| Covering | Canvas or muslin stretched over the lath and finished with cold rosin and raw linseed oil. It sheds rain on a smooth surface with no trim to caulk. With the metal hull upgrade it becomes the fair bearing surface under cork and wool felt. |
| Curved lath | Lengthwise wood strips a few inches apart, standing on the crescent spacers so together they follow the curve. On the walls, floor flat and top flat the lath lies straight on the rib. |
| Crescent spacers and fill | Shaped wood on each rib's angled faces, zero at the rib corners and up to about 2.8 in deep mid-piece, with loose wool between the ribs. |
| Rib polygon | Seven twelve-sided 2×4 rings on 25½ in centers with paired plywood gussets and silicon-bronze bolts. Every frame piece stays straight. |
| Insulation and lining | Wool batts between the ribs and removable upholstered cabin panels on their inner faces: about 4½ in from the outside of the frame to the cabin face. |
The earlier base-build price assumed straight battens and a faceted cloth skin. The lath, spacers and crescent fill are not yet in that price.
Rounded, blunt ends
Each 25½ in end cap follows a blunt superellipse: it keeps nearly the full section until close to the end, then rounds off on every edge, so there is no flat end wall and no sharp corner to catch the wind. The cap section shrinks toward the middle of the body height, so the top and bottom round off as well as the sides.
Each cap is framed as twelve gores: curved studs run from the twelve corners of the rib polygon to a small twelve-sided ring at the centre. Every gore carries one window shaped like it, narrow toward the centre, and the disc inside the ring is opaque. At the north end the TV hangs on that disc; at the south end, behind the bath, the gore windows have privacy glass.
Open: a blunter nose is wider close to its tip (about 97 in at 12 in back, against 86½ in for a plain ellipse), so the turning-clearance estimate in the carrier note has to be redone for this shape. Cap framing, lath bending at the tighter radii, and window frames in a doubly curved surface are not designed yet.
Windows
Gore windows in both caps
Twelve per cap, between the studs, from about 4 in outside the centre ring to the shoulder of the cap, with 2½ in of stud on each side. The wall gores are the largest, about 11 in wide at the centre end and 44 in at the shoulder; the bottom gore runs about 10 to 28 in and the rest about 8 to 21 in. The lowest gores stop 4 in above the cabin floor, so the bottom three windows are shorter.
At the bath end the washer/dryer stands in front of most of the west lower windows and the toilet in front of about half of the two east lower ones; all twelve there are privacy glass.
Windows along the sides
Each 25½ in rib bay of the vertical side walls has one tall rounded-rectangle window: 20 × 41 in glass with 5 in corners in a 21 × 42 in opening, centred about 57 in above the floor. The ribs run unbroken down the wall except at the door and the bath windows, so each bay window is framed by two ribs plus a header and a sill, with 1½ in to each rib.
10 in all: 6 on the west wall and 4 on the east. On the east wall the three bays between the bath and the 32 in main door all carry full windows, the first above the sink: the cooktop/oven folds against the bath partition instead of the wall, and the sink counter sits at 34½ in, under the sills. In the bath a privacy window spans each wall from the cap shoulder to the partition: 19 × 21½ in above the raised washer/dryer, and 19 × 47 in behind the toilet, whose sill drops to 31 in, the bottom of the straight wall where the lower wall starts to curve in. Each crosses the rib at the cap root, which is cut and carried by a header and sill as at the door, and its south end follows the cap as the skin starts to curve in. The folded workbench and desk cover the lower part of the windows behind them until lowered.
Open: flat glass in a doubly curved gore needs a faceted frame or formed acrylic; window frames, seals and the stud joints at the ring are not designed; the extra openings are not yet in the weight or cost.
Frame and materials
Ribs: seven twelve-sided 2×4 rings on 25½ in centers over a 153 in straight midbody, with paired plywood gussets and silicon-bronze bolts at each corner. Floor: paired 2×8 rails and 2×4 joists under ¾ in plywood. A test bay with its lath and covering is to be road-tested before the whole frame is covered.
Metal hull, upgrade: non-magnetic nickel-phosphorus outer backing and a nickel-iron inner backing that transitions into soft iron, carried on the lath covering. Wall thickness and design pressure are still open; a non-circular section suits a sealed, slightly pressurized hull, not a high-pressure one.