# The right angle in a crane's jib is the whole machine

> A gantry crane's jib runs as one hard diagonal and its hoist drops as one hard vertical, and every other part of the machine exists only to stop that angle moving.

August 19, 2026 · https://justog.club/stories/harbour-crane-diagonal

A gantry crane, side-on, the jib one hard diagonal from lower left to upper right. Hook and block
hang from the jib tip on a single vertical line. The legs are open lattice underneath. SWL 40 T is
stencilled along the jib.

Take away either line — the diagonal or the vertical — and there's no crane left, just a shape.

## Why is the jib drawn as one diagonal instead of a more literal crane shape?

Because the diagonal is the actual load path, not an artistic choice.

A jib carries its load along its own length, out from the tower to the point where the hook hangs,
and drawing it as a single hard line follows that path exactly. Anything closer to a photograph —
girders, bolts, walkways — would be decoration sitting on top of the one line that's doing the
work.

## What is the right angle between the jib and the hoist actually for?

It's the entire machine, and everything else on a crane exists to stop that angle moving.

The jib sets where the load sits out over the ground. The hoist, dropping straight down from the
jib tip, sets how high it sits. Between them, those two lines are the whole geometry of a lift —
the lattice legs, the counterweight at the back, the rails underneath are all there to keep that
diagonal and that vertical from shifting under whatever's hanging off the hook. It's the same crane,
more often than not, that lowers [a stack of containers](/stories/shipping-container-stack)
into place a box at a time — the diagonal does the same job whether what's on the hook is a net or
a forty-foot box. [A trawler's derricks angled out and down](/stories/trawler-side-on-heavy-line)
are a smaller-boat version of the same idea: a diagonal boom, a vertical pull, a frame built to
resist both.

## What's the actual choice in a crane print — steep jib or shallow, high hook or low?

How far out the hook sits from the tower, mostly, because that's the figure the whole picture is
built around.

A jib closer to vertical reads as a crane lifting straight up beside itself. Laid out closer to
horizontal, it reads as reaching well clear of its own base — the working reach a real gantry crane
is built to cover. The hook's height down that diagonal is the second choice, and it sets whether
the print reads as a load about to land or one only just leaving the ground.

## Can I put a real crane maker's plate or a real yard's marking on this?

Not a specific maker's plate without their say-so, though a load figure stencilled on a jib is
common practice on any working crane and isn't owned by anyone in particular.

A safe working load painted on the jib is there because the person standing underneath needs it,
not because it's decoration — which is exactly why it's normal to see one on any crane, invented or
real. What's somebody's actual property is a named manufacturer's plate: their logo, their model
number, their own printed format. If a real maker's plate is the point, ask them, the same as
licensing anybody else's document. SWL 40 T on this print is invented for that reason, in the right
format but attached to no maker at all.

## Does the diagonal-jib idea work for something other than a harbour crane?

Yes — for anyone whose work is reading a load path rather than looking at a finished shape.

A dock worker, a crane operator, an engineer, anyone who's stood underneath one of these and
watched the jib take the strain as a load lifts clear has a working relationship with that diagonal
that a generic industrial skyline doesn't offer. It reads as well as a gift for somebody retiring
off a crane as it does for somebody just starting on one.

## Isn't a crane a strange, over-technical thing to put on a shirt?

Only if the diagonal and the vertical don't read clearly enough to look deliberate rather than
accidental.

Simplified this far — two lines, an open lattice, one stencilled figure — a crane reads closer to
[a propeller's three blades fanned dead-on](/stories/propeller-three-blade) than to an
industrial photograph: a shape legible as engineering before it's legible as a picture of anything
in particular, which is exactly the register it's aiming for.

## Does it print well?

Yes, if the jib and hoist stay hard flat lines rather than shaded girders.

Cream for the frame against charcoal, with the SWL figure picked out in yellow so it reads as the
one thing on the print meant to be read rather than looked at. [A hard edge on a diagonal this size
survives the weave in a way a shaded, tapering line never does](/stories/bold-shapes-survive-fabric).
Keep the lattice legs open rather than filled and the whole print stays legible at a distance.

## How do I get one made?

Describe the crane at [JustOG](/) — the angle, the reach, whether a load figure shows on the jib.
Pick a direction, drag the crop frame, see it composited on the real garment, and it's made to
order and shipped.

Designs other people have published are in the [shop](/shop).

Take the hook away and the jib is still holding up nothing. That's what the counterweight is for.