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  3. Hydraulic Jacking Units
Offshore · Marine construction

Hydraulic Jacking Units

The pin-and-yoke units that climb a jack-up barge up its legs: a stiffened jack-house base, a fixed and a moving yoke with pin boxes, cylinder brackets and guide pads. We build the steel; the cylinder maker supplies the rams.

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Allmarc 3D model · to scale
Explore the model

How it is built.

Scroll: the camera moves to each part in turn and ends on the exploded view. Drag to turn it round yourself.

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How it climbs

The lower yoke pins into the leg and holds it; the cylinders push the upper yoke up one pitch; it pins in, the lower yoke lets go, and the cycle repeats. The barge climbs the leg a metre at a time.

Scroll to see how it is built · drag to turn it round

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Jack-house base

A deck plate with two stiffened ring decks and knee plates. We build it on a levelled plate so the unit stands square to the leg.

How is it possible at Allmarc?

Used here for: Jack-house base

In 2024 we were the only buyer of Deratech’s 20 kW, 12 m laser.

  • 20 kW
  • 12 x 3 m bed
  • Pallet changer
All our machinery
Manual MIG welding in the Allmarc works

Used here for: Jack-house base

  • Qualified welders, including 6G
All our machinery

03 / 08

Lower yoke

Two thick ring plates joined by inner and outer skins and radial webs, with pin boxes on each pin axis. Braced round while it is welded, as in our shop photo.

How is it possible at Allmarc?
Three-roll pinch cum pyramid plate rolls in the Allmarc works

Used here for: Lower yoke

  • Rolls plate up to 40 mm
All our machinery

Used here for: Lower yoke

In 2024 we were the only buyer of Deratech’s 20 kW, 12 m laser.

  • 20 kW
  • 12 x 3 m bed
  • Pallet changer
All our machinery

04 / 08

Upper yoke

The moving yoke the cylinders push, with the top guide ring above it.

05 / 08

Locking pins

Pins that slide into the leg’s holes and carry the whole barge.

06 / 08

Brackets and guide pads

Clevis lugs for the cylinders, and wear pads in steel shoes that keep the leg centred.

07 / 08

Leg, rams and access

The leg section it climbs, the cylinder maker’s rams, and a platform for pin maintenance.

08 / 08

A kit of parts

Base, yokes, pins, brackets and pads: every member numbered, match-marked and packed in erection sequence.

From our works

In our works: leg and jack-house base

A rolled leg section standing on its jack-house base: two ring decks with radial stiffeners, set up on a levelled plate so everything is square before welding.

A jack-up leg section standing on a stiffened ring base in the Allmarc works
From our works

In our works: a yoke ring

A yoke ring with its pin-box openings, braced with a temporary X so it stays round while it is welded out. The bracing comes off only after the ring is checked.

A thick yoke ring with pin-box openings, braced with a temporary X while it is welded
From our works

In our works: pin-box openings

The two ring plates, the skins between them and the rectangular pin-box openings the locking pins pass through.

A thick double yoke ring with rectangular pin-box openings and a temporary X brace
Photos

In our works, and at sea.

Guide pads on the leg, close upVideo
Welding out a yoke ringVideo
Welding the ring deck of a jack houseVideo
Why Allmarc

Experience you can trust.

We fabricate to your drawings and prove the fit in our own bay before anything ships. Open any line for the detail.

Talk to an engineer
Heavy rolled plate
  • Leg sections and yoke rings rolled from thick plate.
  • Seams welded on the submerged-arc line.
Round and true
  • Rings braced round while they are welded out.
  • Pin holes cut and checked to jig.
Fitted in the works
  • Yokes, guides and leg sections fitted together before dispatch.
  • A 30 m wide bay with 11.5 m under the hook.
To the designer’s drawings
  • Hydraulics, winches and cranes come from their makers.
  • We build the steel they work in.
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We fabricate to your design, from plate to a packed container. An engineer will tell you honestly how we would build it.

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