IALA endorses Calmar

Mobilis has supplied the marine industry with robust, IALA compliant and cost-effective navigation, mooring and zone marking buoys for more than 20 years. Mobilis, which is exclusively distributed in the UK by Hydrosphere UK Ltd, developed the numerical catenary mooring line calculator to enable quick and easy evaluation of all the environmental forces acting on a moored buoy.

Many people around the world still use ‘three times the depth’ rule, explained David Henry, Naval Architect for Mobilis. “The rule of thumb does not take into account the various drag forces exerted on the buoy and mooring by maximum site environmental conditions or the linear mass of the chain, both of which make a considerable difference to the necessary catenary length.”

As a result, moorings have often ended up being too short when weather conditions deteriorate.

Based on Mobilis’ mooring calculation bank, the new IALA approved software integrates more load parameters than other calculators and takes into consideration maximum depth of water, surface wind generated current, current drag on the mooring line, drag force caused by wave height drift, increasing drag coefficient due to biological fouling on the buoy hull and chain and buoy immersion and drag increasing as the mooring load increases. This allows for the exact equilibrium of buoy displacement, lifted catenary chain loads and horizontal drags to be calculated.

“Considering that full chain moorings are generally still used for most aids to navigation at sea, Mobilis decided to develop a general tool using this calculation method, to very simply and quickly calculate a reliable catenary mooring line for most conditions,” added Mr Henry.

“At Mobilis we have been calculating moorings using a full analysis method for more than 20 years and have not experienced a single buoy mooring line breakage over several thousand buoy mooring specifications.”

The Calmar software allows users to input or use libraries of buoy models, build their own buoy model for calculation and compare the results between two different buoys or two different buoys’ mooring lines.

By Jake Frith