Egret design
When Harwich Haven Authority was looking to replace its 27-year-oldsurvey vessel, a starting point was recognising that, because of thevaried nature of the survey work involved, one launch could not totallyfulfil the authoritys survey requirements.
“We recognised that biasing the launch at any one type of survey work would have a detrimental effect in other areas,” says HHA chief executive Stephen Bracewell.
However, bearing in mind that the new vessel would have a 25-year lifespan, a key priority was to maximise usage of the vessel, thereby minimising the need for outsourcing.
The use of multi-beam technology was considered an essential and, in order to accommodate it, provision was made for a moonpool, through which a multi-beam echo sounder could be deployed.
The choice of VT Halmatic’s Cara 52 hull form gave the best space for the moonpool arrangement and gave an important reduction in draught compared with the old launch.
As a result, the 16.13 metre Egret is something of a groundbreaker.
“It is innovative to have a moonpool in a vessel of this size and the design gives us a number of important benefits,” says Mr Bracewell.
The 686 mm diameter free-to-flood moonpool enables the multi-beam sonar head and the tidal current profiler to be deployed beneath the keel line of the vessel. The advantages of this compared with an over-the-side mounted bracket or towed system include less likelihood of damage to the equipment and greater launch manoeuvrability, while the survey process is less affected by the launch’s motion, and unaffected by propeller wash.
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