Why we use box-type mast structures across the line

Open a Velson product sheet and you'll see the same description over and over: mast - box-type structure. From the V2i Myrmax through to the V9 Cisada V+, the mast geometry is consistently a closed rectangular box. This is deliberate.

Why box, not lattice

A drilling mast carries axial pull (the feed force lifting and pushing rod strings), lateral loads (wind, vehicle motion, drill-pipe whip), and torsional loads (rotation reaction from the head). A box section resists all three through a single closed cross-section. A lattice mast resists axial and lateral loads through its members but is weaker in torsion.

For a 6 m or 9 m mast pulling 13,500 kg with a 3.8 kN·m rotary head, torsional loads are not theoretical. Box structures handle them without member fatigue at the welded joints, which is where lattice masts fail first.

Fatigue behaviour

• Box masts distribute stress across the closed perimeter - there are no high-stress nodes at welded joints.
• Lattice masts concentrate stress at member intersections. Each cycle of rotation reverses the bending direction; after 10⁶ cycles the welds start to crack.
• Field-life observation: Velson box masts on V7s in continuous operation for 8+ years show no measurable mast deformation. Comparable lattice masts on competitor rigs typically require weld inspection at 5 years.

Where lattice still wins

On the RC Drill, the mast switches to a heavy-lattice structural-steel construction. The reason: the RC mast is 9.5 m long with a 7.25 m travel length, and the additional length makes the lattice's stiffness-to-weight ratio more attractive. The torsional concern is mitigated by the slower rotation speed (60–140 RPM vs the box-mast platforms' higher RPMs).

For everything else - water well, blast hole, micro rotary - the math favours box. We picked it once, validated it against field-fatigue data, and stuck with it.