Gemmak, the engineering division within Rope and Sling Specialists (RSS), has completed a scope of work aboard Helwick Light Ship LV91, issued by Swansea Museum.
Designed and built as a light vessel, her hull shape and form were specifically developed to remain anchored to mark a navigation hazard in all weathers and sea states.
Following a site survey by RSS to replace the mast tensioners, it was discovered that both 87-year-old masts were in poor condition, so replacing the mast tensioners may have caused undue stresses and strains.
Due to the proximity of the boat to a pedestrianised area, it was noted that the likelihood of failure and potential collapse onto that area would greatly increase with new wire tensioners acting on the masts.
“We were then contracted to undertake thickness testing on the masts to estimate the material loss due to corrosion and the affect that would have on the stability of the masts. Sections of the masts were tested and found to be in some locations between 40% and 60% of the assumed wall thickness. The recommendation based on health and safety was to remove the masts and to land them both on the ship so that any possible future works will still have the original equipment in one place,” said Matthew Edwards, engineer Gemmak Engineering.
Both masts were estimated to weigh between 900kg and 1,000kg; they were approximately 12m tall and measured 270mm in diameter. Pipework was estimated to weigh 700kg, but during the lift the crane was reporting near 900kg for the front mast and near 1,000kg for the rear mast.
A local rental company provided a 35t capacity Terex AC 35 L crane and led on the lift plan and selection of below-the-hook equipment; a Skyjack SJ66T (22m) was used to fit 1-ton capacity, 1m-long slings to the masts. Despite the length of the masts, centre of gravity wasn’t a concern because the masts were landed on the boat, then re-slung to create a horizontal lift.
“The existing mast tensioners were kept attached to the masts and tied to each mast during the lift,” added Edwards.
A safe working area was created for the one-day duration of the works.
