Hydraulic Davit Crane Refurbishment & Load Test, Motor Yacht

The davit crane on a motor yacht refitting at The Boat Works, Coomera, was booked in for a full refurbishment rather than a service. The unit is a Besenzoni hydraulic crane with a static work load of 600 kg on its plate, and it lifts the tender from the aft deck. After years of service the paint, the seals and the hydraulics had all reached the end of their run at once. We removed it, dismantled it to components in the Coomera workshop and sent the five hydraulic cylinders, the valve stack, the slewing swivel and the power unit to A.T. Hydraulics for strip-down inspection. The findings put the job well past a reseal: a dented chrome rod on one cylinder needing a new rod section, corroded fittings and honed barrels on the others, one gland machined to correct wear, and a broken bronze backlash adjuster and worn bearing inside the swivel. All fifteen hydraulic hoses were condition-reported as well. Every one had gone rigid with age, several were kinked or heat-damaged, three were leaking at the fittings, and the report recommended replacing the lot.

The cylinders came back resealed throughout, rod seals to wear rings, and pressure-tested between 2,000 and 2,500 psi with no external or bypass leakage. The power unit was cleaned, resealed, refilled and run up, with its relief valve verified at 175 bar and the valve stack proven on every spool. The structure, boom sections and covers were repainted by Superyacht Solutions at The Boat Works. Reassembly then ran through July and August at the workshop. Pin bushes had picked up overspray and were cleaned back to bare metal before a pin went near them; the slewing pedestal was rebuilt around the overhauled swivel, the power pack and valve block refitted, and the boom, extension arm and boom-head sheaves brought back together on the lift table with the hydraulic lines run through. A new Dyneema lifting line was spliced up, found long on the first fit, and re-made shorter with a little extra taken off to allow for the rope bedding in over time, and the repainted counterweight went back on so it sits snug against the boom head. One setback: the luff cylinder wept oil on the first workshop test, so it went straight back to A.T. Hydraulics, was resealed again and refitted before the crane left the shed.

On 27 August the assembled crane travelled by truck from Coomera to The Boat Works, where Transmarine Cranes lifted it aboard and we bolted it down on the masked and prepared deck footprint. The vessel went back in the water on 3 September, and the next morning we were aboard with water bags and a calibrated crane scale. A 400 kg dynamic test ran the crane through full boom extension and retraction, rope up and down, slew both ways and luff up and down. A 600 kg static test, the plate limit, was then held for three minutes at full extension with the rope fully raised. No movement, no leaks, and the captain was briefed on the results before the written commissioning and load-test report followed. While the crane was out, the same crew reinstalled the flybridge helm wheel with a fresh steering-shaft seal, greased and inspected the deck capstans, and pressure-tested the hydraulic bow thruster before relaunch. The davit went back into service with its test results on paper, which is where an insurer or surveyor will want to find them.

Gallery

From the project

Overhauled cylinders and boom sections back in the workshop, freshly painted Cylinders and job paperwork laid out on the bench before reassembly Pin bush cleaned back to bronze after overspray was found in the bores Slewing pedestal rebuilt around the overhauled rotary swivel Power pack and valve stack refitted to the pedestal, boom pivot in place Boom pivot section lifted onto the pedestal in the Coomera workshop Hydraulic lines fitted along the rebuilt boom Bronze sheaves fitted at the boom head Wrapped boom slung on the chain hoist for fit-up to the pedestal Repainted counterweight with the new Dyneema line spliced through New Dyneema reeved through the boom-head sheave stack Counterweight sitting snug against the boom head after the line was shortened Assembled crane wrapped on the lift table, ready for the truck Deck footprint masked and prepared for the crane to land Crane bolted down on the aft deck in the shed at The Boat Works Davit stowed on the teak before the vessel went back in the water Back to the water in the travel lift, 3 September Water bag on the calibrated crane scale for the 400 kg dynamic test, boom extended over the side 600 kg static test held for three minutes at full extension, the plate limit