SKIPPER DL21 Navigation Speed Logs
The SKIPPER DL21 is a Dual Axis Doppler Speed Log and a Single Axis Doppler Speed Log in one sensor unit. It is working on the Doppler principle, providing longitudinal and transversal ship’s speed (STW and SOG) and distance relative to seawater. The SKIPPER DL21 gives accurate navigation parameters, measured as they happen, and presented in a logical, user-friendly way.
The new DL21 Speed Log is designed for ships over 50.000 GT with a simultaneous and independent measurement of speed through water and speed over ground. This is according to the new IMO resolution MSC334(90).
SKIPPER DL21 Display
SKIPPER DL21 Specification
| Speed Log : | SKIPPER DL21 |
| Number of Axis : | 2 and 3, with 1 axis in addition |
| Speed range longitudinal: | +/- 50 knots |
| Speed range transversal : | +/- 50 knots |
| Water track (from) : | 2 meter |
| Temperature accuracy error : | <1°C |
| Power Supply : | AC : 115-230 V 50/60 Hz |
| DC : 24 V | |
| Power Consumption : | Max 30 W for complete speed log |
| Display : | 9″ Touch and dot LED display |
| Mounting dimensions display : | 124×124 mm. Bracket or panel mounting
190x119x114 mm for touch display
|
| Accuracy : | 0.2 knots or 2% whichever is greater |
| Cable length for display : | None |
| Weight : | 1 kgs for CD402CU-XX
1,5 kgs for JB70D21-XX
1.4 kgs for CU-M001-XX
10 kgs for sensor with 40 m cable
|
| Mounting options : | |
| Speed alarms : | High and low speed limits |
| Power failure | |
| Sensor failure | |
| Outputs : | 3xLAN (IEC61162-450) |
| 8xNMEA0183 (IEC61162-1) | |
| 5xAuxiliary (pulse, limit etc.) | |
| 2xRelay (alarm etc.) | |
| Inputs : | 3xLAN (IEC61162-450) |
| 3xNMEA0183 (IEC61162-1) | |
| 3xAuxiliary (alarm and sync) | |
| NMEA Outputs: | Speed: VBW and VHW |
| Distance: VLW | |
| Others: MTW (Temperature) | |
| Classification: | IMO Wheelmarked |
| CCS on request | |
| RMRS on request. | |
| MED-B |
One full system consist of :
| Displays needed : | SKIPPER DL21 Electronic Unit |
| CU-M001-21-SB for Dual Axis SOG and STW | |
| CU-M001-21-SB for Dual Axis SOG and STW | |
| Sensor options : |
|
| DL21SG-SA for 100 mm Sea Valve | |
| DL21SE-SA for ETNSLB retrofit | |
| DL21SW-SA for Sperry SRD-421/500 retrofit | |
| Electronic Unit : | |
| JB70D21-SA | |
| Bottom housings : |
|
| SB-100-SB Sea Valve for single bottom | |
| DB-100-SB Sea Valve for double bottom |
Types of Speed Logs
Electromagnetic — These devices, also called EM logs, rely on a coil in an electromagnetic sensor. When the AC current energizes the coil, it creates a magnetic field surrounding the sensor. As a vessel moves through water, an electrical field running perpendicular to the magnetic field is produced. The sensor electrodes detect and deliver the resulting signal representing the ship’s speed to a preamplifier, which then converts it to a digital format for viewing. This process is inexpensive and has the advantage of not requiring any moving parts. However, water salinity and temperature can affect calibration. The water flow slows down closer to the hull due to friction, affecting measurements.
Pitometer — Also referred to as a pit log, the instrument uses the principle of differential pressure to determine an object’s speed through the water. It operates by submerging a Pitot tube with an opening at the base in water. While the tube is stationary, the pressure (known as static pressure) remains constant. When the tube starts moving past the water, it creates dynamic water pressure that varies based on the velocity. The effect of static pressure is removed to obtain an accurate measurement of the dynamic pressure for calculating the speed. To achieve this, a second tube is installed near the first with an equivalent static pressure. Movement through water does not generate any dynamic pressure in the second tube. The difference between the pure dynamic and static pressure readings indicates the speed of the moving object.
Doppler — Doppler transducers rely on the Doppler frequency shift effect for estimating the speed of a moving body. A transducer produces high-frequency sound pulses toward both ends of a vessel using two transmitter windows. The reflected pulses are detected by two receiver windows located in the transducer. The time delay between the transmitted signals confirms the receipt of echoes from undisturbed water surrounding the object. The vessel’s fore/aft speed vector is estimated by processing the signal information. A pre-amplifier then transmits this information in a digital format.
Impeller — These logs function by attaching an impeller or paddle wheel to the bottom of a hull. They are employed on small yachts and other such vessels.
GPS (Global Positioning System) — A sensor accesses the GPS satellite signals to pinpoint an object’s speed, in both longitudinal and transverse directions. GPS receivers with integrated rate gyros and an antenna unit calculate the heading velocity, attitude, and course. The heading is then compared in relation to the vessel’s magnitude and direction of motion in the water. The information delivered by the satellites is processed by the system, integrating the velocity data with the longitudinal and transverse ground speeds of the vessel. Speed vectors combined with data related to the rate-of-turn assist in differentiating between the vessel’s translational and rotational movement. These are required for estimating the transverse speeds for both bow and stern as given on the docking display.
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Source: globalspec.com
