Trailer · 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 not yet in the 6,000 lb 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.
The north cap carries the large windows; the south cap holds part of the bath strip.
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.
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.