Cone and cell units come under microscope
Cone and cell type rubber fender units have become a hot topic in the industry through instances of water filling leading to fender or structural damage.
The damage may be attributable to hydraulic "lock up" of cone and cell fenders fitted in tidal areas where they may fill with water.
Mike Harrison, of SystemFender Consulting Ltd says the problem arises from drainage vents too small to allow the rapid expulsion of water during impacts. Resulting loads are estimated to be up to several times the nominal-rated reaction of the fender.
"This extra load increases stresses in the fender panel and structure, excess hull pressures and can even burst the fender. The larger concern is that some manufacturers continue to ignore this phenomenon or have neglected to rectify past installations.
"Ports and harbours with cone and cell fender installations should consider the effects to personnel and structural safety from this potential latent defect," he warns.
The claimed performance of pneumatic fenders has also come into question recently. Dry air when compressed has a predictable behaviour and the increasing pressure from fender deflection can be calculated and modelled.
However, says Mr Harrison, most fenders are not filled with dry air and performance can differ significantly from that expected.
"Hydropneumatic (submarine) fenders which are partially filled with water are an obvious example, but even conventional pneumatic fenders are often filled with partially or fully water-saturated air that behaves quite differently to dry air when compressed," he says.
