NDBC's Coastal Buoy

A 2.3-meler-diurneter meteorological and ocean-measuring buoy for semi-protected waters is under development at the National Data Buoy Center. Two pre-prototype Coastal Buoys are being fabricated with interchangcuble underhull structures to evaluate hydrodynamic characteristics, including WUL’E motion response favorable for wave nreasuremenl capability. The underhull structures include a fixed, courrterweiglited, hoop design as well as the traditional center pipe design. The Coastal Buoy, ofclosed cellfoam andniur-ine aluntinum construction, is lighter, more economical, and easier to handle than previous small iiuoys. This paper presents the design criteria guidelines, pre-prototype designs, arid expectedi7erformance. INTRODUCTION The Coastal Buoy project was initiated to develop a low.cost, reliable, moored buoy for semi-protected and coastal waters. This buoy will have the ability to provide metcorological and ocean surface measurements, with Ihe data processed on board and transmitted to the GOES satellite for dissemination 011 standard National Weather Service circuits. NDBC will use the Coastal Buoy to measure waves, air, and water tempcraturc in coastal regions and relay the measurements to NDBC Coastal-Marine Automated Network (CMAN) meteorological stalions via direct data link communications. The Coastal Buoy will also be integrated into the moored buoy system at selected stations. The buoy is ideally suited to support scientific experiments and environmental monitoring projects of short duration, and is also suitable for some subsurface measurements. An illustration of the Coastal Buoy is shown in Figure 1. Two pre-prototype Coastal Buoys are being fabricated for test and evaluation. They will be instrumented to measure wave motion response as well as metcorologicaliocean sur€ace measurcments, and will be deployed at various test locations including NDBC’s Ocean Test Platform south of Gulfport, Mississippi. Figure 1. Illustration of Coastal Buoy. DESIGN GUIDELINES AND REQUIREMENTS The Coastal Buoy is suitable for meteorological, ocean temperature, and wave measurements. The meteorological package includes a barometric pressure sensor within the hull and sensors for wind speed, wind direction, and air temperature at a 3-meter elevation. The mast can be cxtended to an elevation of 5 meters, if desired. Since NDBC’s NOMAD and 3-meter buoys measure wind and air temperature at 5 meters, this is the preferred height. Any of NDBC’s payload configurations can fit in the payload compartment, which is 0.91 meter in diameter and 0.82 meter high. Payload weight is being constrained to less than 227 kilograms. This (constraint should be easily attainable because NDBC is shifting from primary batikry power systems to a lighter weight hybrid solariprimary battery system, with the expectation that most payloads will be less than 136 kilograms. Because magnetic compasses will be part of the payloads, the Coastal Buoy is being fabricated of nonmagnetic materials. The Coastal Buoy is a platform capable of being maintained and serviced at sea in calm weather. Required maintcnance can be expected to call for meteorological sensor change-out and access into the top of the electronic payload compartment. While at-sea servicing is possible; the normal procedure will be for servicing on board or along side the servicing vessel. Other design features are: * A truck can transport the buo:y without special routing or permits. * The buoy can be handled easily and safely without special equipment or procedures. * The buoy can be serviced by an 1 I-meter vessel, and configurcd to be placed on deck of a suitable servicing vessel. Swap-out of buoys on station can also be accomplished by the same servicing vessel. The buoy’s outfitted weight is less than 615 kilograms. The hull life is in excess of 6 years, and estimated production costs in lots of 10 or more is $3,500 (not including sensors, electronics, or mooring). The Coastal Buoy is vandal-resistant whcre feasible. The primary form of vandalism experienced presently by NDBC is damage to buoy hulls from small arms gunfire. Since these Coastal Buoys will be in semi-protected waters where they will be more exposed to vandalism than the deep-ocean buoys, closed cellar foam is used to minimize thc possibility of catastrophic damage from small arms fire. TENTATIVE OPERATILNG ENVIRONMENT In the NDBC standard Meteorological Monitoring Configuration, the Coastal Buoy will have at least a 1-year unattended life with the rollowing operational and survival environmental conditions: Operational Survival Wind Speed (knots) 5 0 75 Significant Waves Height (meters) 5 8 Surface Current (knots) 2 4 COASTAL BUOY DESIGNS The hullform was selected to provide sufficient buoyancy, stability, wave motion response, and ability to function in strong water currents. Mathematical simulation analysis and scale model testing of discus hullform buoys indicated a hull 2.3 meters in diameter would provide the appropriate wave motion respouse for the range of wave conditions expected. This limited synopsis should be supplemented with appropriate considerations presented in a paper by Teng et al.[l]. The curved hull chine was selected for performance in currents[2], reduced wave slope, and nautlcal 1406 appearance. The hullform has sufficient freeboard to provide in excess of 200% reserve buoyancy based on a maximum expected deployed displacement of 790 kilograms, including 140 kilograms of payload and 180 kilograms of static mooring load. The selected buoy hullform height also falls within an increment for economical production of the flotation collar since two collar heights can be fabricated from the 1.37 metcrs of raw material. Principal access to the meteorological sensors will be by a folding upper mast configuration, although stability is sufficient for a person to climb the mast in calm water and change out the highest sensor. The metacentric height is 0.67 meter with an assumed 180kilogram static mooring load attached directly under the payload compartment, and 0.57 meter without a mooring. These values are based on a 7-kilogram sensor suite at lhe top of the mast. The practical mooring and underwater instrumentation weight limil is 700 kilograms with an appropriate mooring designed for the survival conditions. The hull displacement curve is provided in Figure 2 . The hull structure is marine grade aluminum with a closed cell foam flotation collar closely fitted around the payload compartment. Thecentral hull structural component is the payload compartment shell, shown in Figure 3. Two variations of the structural interface between the tripod superstructure and the payload compartment shell are being evaluated. The first is a triangular structure fitted around the payload compartment circumference, shown in Figure 4.