This blog was written by Neil McLennan, Engineering Advisor of the Littelton Port Company.
The safe navigation of vessels using the dredged channel requires the swell to be measured. This and other inputs allows dynamic under-keel clearance statistics to be calculated.
An offshore buoy also allows the sea and wind state close to the pilot on/off boarding zone to be assessed. Decisions that influence the safety of these transfers are made using this information.
We purchased a Sofar Ocean Spotter wave buoy in 2019 to serve as a short-term substitute when our much larger main wave buoy was brought in for routine maintenance. The Spotter has now been deployed for extended periods.
The Spotter has been providing sea and swell spectral wave data that meets the requirements of our OMC International DUKC® system. The inferred wind speed and direction information is also proving sufficient for our pilotage decisions.
The larger buoy requires heavy moorings that are much more expensive to maintain. The logistics of bringing it in for annual or unplanned maintenance are demanding and expensive.
The Spotter must be lightly moored to achieve its designed wave responsiveness, but this has significant upsides including reduced cost of providing the mooring components and the floating plant for servicing. Smaller and faster vessels can take the equipment to site and to recover the buoy.
We have incurred damage to the larger wave buoy due to recreational fishermen mooring to it and damaging aerials. While the risk of damage to the Spotter buoy or its moorings cannot be eliminated, the geofencing function provides early warning that there may be an issue.
The purchase and operating cost of the Spotter is much lower than the large buoy so we are now using it as our primary offshore wave data source and have purchased a second Spotter to allow them to be regularly swapped over while moorings are checked and biofouling removed.
Deployment of the buoy is easy. The Sofar website is easy to use and reliable. Accessibility of data for third party users is simple to set up. Support from the Sofar representative in New Zealand is of a high standard.
Bigger has not proved to be best for our application.
