Short answer: For hull surveys, use two Diver Magnet - 140s, one in each hand. For hull work in one location with tools attached, use the Diver Magnet - 200 or Diver Magnet - 250.
Why 200–250 kg suits hull work
Rated pull is measured on clean, thick, flat steel with a straight pull. Underwater, paint, growth, rust, gaps, thin plate and side-loading all reduce it, often a lot. That's why we recommend a magnet rated at least 2–3× the load. A 250 kg magnet still gives a solid working hold on a coated hull, while a much larger magnet adds weight without adding much for visual or thickness surveys.
By task
UWILD / class hull surveys Two Diver Magnet - 140s, one per hand Holds well on painted hulls; easy to reposition along the survey line Hull cleaning, propeller polishing 200–280 kg, most often Diver Magnet - 250 Resists tool reaction forces Light visual checks, short dives Diver Magnet - 115 or 140 Compact and light Heavily corroded or uneven steel Diver Magnet - 500 Rust and uneven steel cut the hold a lot, so size upWhat reduces holding on a hull
- Paint, marine growth and corrosion (the largest factor)
- Thin plate: full rated pull needs about 10 mm of steel
- Pull angle: a 45° pull detaches the magnet far more easily than a straight pull
What it is not for
A diver magnet is a personal positioning and tool-holding point. It is not lifting equipment. Always attach it to your harness with a lanyard.
From our own work: “On hull surveys I prefer two Diver Magnet - 140s, one in each hand: together they give plenty of stability, yet each releases easily enough to keep moving along the hull.”
Related: Diver Magnet - 200 · Diver Magnet - 250 · How to choose the right diving magnet · Magnet pull force explained
