Find why a small spacing edit removes a whole row
A planner sees ten Australian square pallets on a twenty-foot dry-container drawing. After adding a small inter-pallet gap, the quantity falls. The change is not necessarily an error: rectangle fit is controlled by dimensional thresholds. Two nearly floor-wide loads can lose their two-across arrangement when only a few millimetres are added. Use explicit row arithmetic to understand the change before asking the engine to search for another candidate. Record the required spacing and its operational source instead of assuming every zero-gap drawing is usable.
The site exposes two different geometric controls. Gap is separation between modeled pallet rectangles. Wall clearance removes a band from the perimeter of the modeled floor. Neither control measures the correct handling, airflow or restraint allowance for your shipment. Those requirements must be supplied by the relevant operation or carrier. The model then answers whether the rectangles fit under the supplied spatial conditions. This guide’s numeric allowances are examples for arithmetic, not recommended loading distances.
Use the row formula with gaps only between neighbors
For n identical footprints with side a along a row and gap g between neighbors, occupied length is n × a + (n − 1) × g. There is no added gap beyond the last footprint. If usable length is L, the maximum whole n for that uniform row is floor((L + g) / (a + g)). For equal clearance c at both ends, replace L with L − 2c first. Apply the formula independently to both directions for a uniform rectangular grid, then multiply the two integer counts.
Take a 2352 mm floor width and two 1165 mm square footprints. With zero gap they require 2330 mm, leaving 22 mm total. With a 10 mm band at each wall, usable width is 2332 mm. A two-millimetre gap yields a 2332 mm row and consumes the entire modeled width; a three-millimetre gap yields 2333 mm and does not fit. This threshold explains why a one-millimetre change can remove a whole pairwise row configuration. It does not establish that the exact-threshold arrangement can be loaded operationally.
| Wall band at each side | Gap between loads | Required / usable width | Pair fits geometrically? |
|---|---|---|---|
| 0 mm | 0 mm | 2330 / 2352 mm | Yes |
| 10 mm | 0 mm | 2330 / 2332 mm | Yes |
| 10 mm | 2 mm | 2332 / 2332 mm | At the modeled threshold |
| 10 mm | 3 mm | 2333 / 2332 mm | No |
| 15 mm | 0 mm | 2330 / 2322 mm | No |
Count longitudinal gaps before interpreting spare length
On a forty-foot floor length of 12032 mm, ten 1200 mm footprint lengths occupy 12000 mm. Nine neighboring gaps remain, not ten. With g = 3 mm, the row occupies 12000 + 9 × 3 = 12027 mm and leaves five millimetres before end clearance. With g = 4 mm, it occupies 12036 mm and fails. A ten-millimetre band at both ends leaves only 12012 mm usable length, so even the three-millimetre-gap row fails that different input record.
For the 630 inch trailer example, thirteen 48 inch lengths occupy 624 inches. Twelve half-inch gaps add six inches and exactly reach 630 inches. Adding any positive end band prevents that particular thirteen-row arrangement. This is a comparison of a specified grid with a specified rectangle, not proof that the overall count must fall by two. A mixed-orientation candidate may redistribute space. Review the engine’s result and coordinates rather than translating a failed uniform grid directly into a global maximum claim.
Do not confuse a gap with a larger loaded footprint
Suppose a nominal 1200 × 800 mm pallet is wrapped to a maximum envelope of 1230 × 830 mm. Entering a 30 mm gap around nominal rectangles does not generally reproduce those larger footprints. A gap exists only between neighboring rectangles, while the larger load also extends toward the walls and changes rotation geometry. Use the measured 1230 × 830 mm footprint and enter any additional agreed separation separately. Otherwise the model can understate the perimeter space required by the cargo.
A rectangular envelope is a simplification when protrusions vary with height or position. It may be a conservative screen, but it cannot describe how corners nest or how an upper-level board approaches a wall during loading. Do not shrink the entered dimensions merely because the engine returns a more convenient count. Record which physical features define the envelope, and obtain a separate detailed drawing when those features materially affect the handling process or final arrangement.
Interpret the finite search after a constraint changes
The algorithm handles identical rectangles, with right-angle rotation optionally allowed. It enumerates strip arrangements and uses multiple MaxRects heuristics, validates final placements and retains the best candidate found. This finite search is broader than the two uniform grids but not an exhaustive solution of every rectangle packing. If the result says best found, keep that status. A zero-gap verified fixture does not prove optimality for a new clearance or loaded footprint, even if the count happens to remain unchanged.
For a quick bound, usable floor area divided by one footprint area gives an upper limit on identical positions. It disregards the shape of residual space and usually cannot establish a usable count by itself. Adding gaps can weaken the usefulness of that bound further, because required separation consumes space outside the bare footprint area. The meaningful evidence is a valid set of coordinates under the entered boundaries and spacing, together with any supported proof condition reported by the engine.
Run a controlled spacing comparison
Use the twenty-foot dry preset with 1165 × 1165 mm loads, rotation enabled, zero gap and zero wall clearance. Keep all dimensions fixed while changing wall clearance to 10 mm, then test gap 0, 2 and 3 mm. Hand-check the two-across width with the table. Record each returned quantity and status; if a count changes, inspect the drawing to identify which rows or orientations changed.
Write your own input record beside this example: equipment identifier; dimension source and date; actual loaded footprint; rotation; gap; wall clearance; loaded height; result count and proof status. Retain the record with the layout.
Represent the actual spatial requirement honestly
An instruction to leave extra room at the door only cannot be represented exactly by a uniform wall clearance at all four sides. Reducing length may represent that reserved end zone more faithfully, but the record must explain the resulting boundary and how the remaining region is used. Nonuniform access channels, refrigeration machinery and irregular obstructions may need a drawing beyond the full rectangular floor model. The program cannot infer a reserved region from equipment class, product type or an empty optional field.
Likewise, a returned final-position gap says nothing about whether there is enough room to insert the last pallet or install securing materials. Coordinates do not trace motion. Discuss the loading sequence, fork direction and restraint plan with the team that will execute it. The result’s purpose is to support that review with reproducible geometry. It should not replace the review by assigning a generic percentage reduction, calling the remaining residual a safety margin or asserting that tight packing prevents cargo movement.
Primary sources and scope
Hapag-Lloyd twenty-foot Standard: Example floor width, with fleet variation explicitly acknowledged.
CMA CGM equipment specifications: Standard, pallet-wide and reefer examples must retain their own dimensions and equipment conditions.