Are the systems towed profilers?
How is the system installed?
What locations are suitable for installation of the main winch?
Can a third party power supply be used?
What are the power requirements of the system?
What happens if we lose ship power?
Is the deployment and retrieval operation automated?
What is the best way to deploy the SV and CTD probe during profiling in shallow mode (no tail spool rewinding)?
How do you know the probe depth during a cast?
How do I choose deep or shallow profiling mode with the UnderwayCTD?
Where does the probe surface during retrieval?
Can I use the systems with towfish in the water?
How is the probe recovered back on deck?
How should the probe be stored?
What software do I use?
How many profiles can be stored on the probe?
How does the data compare to a stationary CTD cast or expendable profilers?
How long do the probe batteries last?
How often should the line be replaced?
What is the line type?
How much line can be added to the winch?
How is the line connected to the probe?
What happens if the line becomes twisted?
Does the system need any maintenance while at sea?
How often do the probes require calibration?
Can other sensors be deployed with the UnderwayCTD system?
Can other davits be used with the winch?
Can the UnderwayCTD be used for stationary casts?



No. The UnderwaySV and UnderwayCTD are not towed profilers. Thanks to the low friction winch and free fall probe design, vertical profiles are achieved at the probe drop position. Thanks to the "water pulley" effect, the several hundred meters of vertical line in the water column force the probe to drop vertically and even be pulled vertically upwards for most of the recovery period too.

A key design goal of the UnderwayCTD was to develop a compact system that could be deployed from practically any vessel. As long as 110-240V power is available, it is almost certain that the system can be accommodated on board. The ideal deployment location is in the center of the vessel, with deployment directly over the aft rail but other locations may be possible. The winch and reloader is mounted on a swivel plate with a 4" x 4" square hole pattern; the swivel plate is included with the system. This plate can be attached to a post or rail mount custom fabricated for the survey vessel. Oceanscience can provide designs for mounting options if necessary; call us to discuss your deployment requirements.

Installation of the UnderwayCTD in 4x fast motion Watch the UnderwayCTD system being installed on the Oceanscience vessel.

The winch should ideally be positioned so the arm is pointing directly aft. Deployment over the port or starboard side is not acceptable while underway over about 4kts as the probe will be at an increased risk of hitting the side of the ship upon retrieval. The ideal location is close to the center of the ship; however deployment closer to the corners is acceptable if necessary.

No, the Oceanscience 110/240v to 24v power converter must be used. The winch must be <6ft from the power supply for reliable operation, owing to cable length limitations. The Oceanscience-supplied power cable should also be used.

The power supply can accept any clean ship power from 110V to 240V. A temporary generator can be used if necessary. It is possible to run the main winch and reloader from battery power for short periods, although the cabling for this is not supplied.

In the event of a power failure, the probe can be safely retrieved using the emergency retrieval mechanism. A battery operated power drill can be attached to the main winch to rotate the spool and recover the probe.

No, the current system design requires an operator. The lack of automation allows for a more cost-effective and compact profiling system, and allows the use of non conducting line instead of a cable to tether the probe saving cost and reducing complexity.

The SV probe should always be released from the water surface while being dragged behind the ship, and not dropped "in air" from the deck of the ship when working in shallow water. Deploying the sensor from the water behind the ship allows the transducer face to become fully water wet and results in the best data quality in the top 3m. The CTD probe should be similarly deployed from the water surface in shallow mode which will equilibrate the probe temperature with the water surface eliminating any minor temperature lag effects should the deck temperature be very different to the water surface.

For deep casts where line is loaded on the tail spool, the probe drop speed is constant and accurately known. The probe depth will be equal to the elapsed time x drop speed. For the UnderwayCTD, this is 3.9m/s, giving 230m of vertical drop per minute. For the UnderwaySV, its 5.3m/s drop speed results in 320m per minute. For shallow casts, with no line loaded on the tail spool, the probe drop rate is not constant with depth so depth tables are used to relate probe depth to elapsed time. However, for all deployment modes, the drop rate does not depend on vessel speed. No matter what speed the ship is traveling, the probe will always reach the same depth after the same elapsed time.

As no tail spool rewinding step is needed, shallow mode will be faster for profile depths up to 250m. Deep mode will provide better overall CTD data as it affords a constant flow through the sample cell throughout the profile. This flow stability allows the use of a single lag correction factor to remove salinity spiking.

At 10kts, the probe surfaces over 300m behind the vessel and it can be seen during recovery for several minutes. The probe is then pulled back to the ship along the surface. At 3kts, the probe surfaces about 50m behind the vessel.

The UnderwayCTD and UnderwaySV probes are recovered along the surface when being deployed from a moving vessel. On retrieval, the probe typically does not pass through the area where towfish may be located. During deployment, care may be needed to launch the probe from the appropriate location off the aft deck to maximize the distance between the falling probe and the towfish. The location of the tether line upon recovery can be seen in the photograph below.


Every vessel is different, and each user must determine the best method to safely recover the probe without impact on the vessel. The CTD probe contains a glass conductivity cell and so must not be allowed to hit the ship. Oceanscience recommend using a pole to keep the probe away from the ship while the winch is being rotated during rough conditions.

The CTD and SV probes should ALWAYS be stored in fresh water with detergent added. The detergent keeps the sensor clean and also allows water-wetting of the transducer surfaces to ensure good data in the upper 3m of the profile immediately after the probe enters the water. Ideally, the water should be similar in temperature to the surface water.

Special software from Valeport (UnderwaySV) and SeaBird Electronics (UnderwayCTD) is included to manage the probe communication and setup. CTD data processing is performed using standard SeaBird software used for conventional CTD instruments.

Over 100 profiles may be stored in the UnderwayCTD probe internal memory, enough for the most rapid profiling operations. The UnderwaySV wipes the probe memory automatically after each cast is downloaded and confirmed on the PC so there is no data storage limit necessary. If required, this feature can be disabled and hundreds of profiles may be stored on the probe.

The UnderwayCTD produces data quality of significantly higher accuracy than expendable probes.

	Conductivity (S/m)	Temperature (C)	Depth
UnderwayCTD Accuracy - Processed Data	0.002-0.005	0.004	1dbar
XCTD Accuracy	0.03	0.01	2%
XBT Accuracy	N/A	0.1	2%
SeaBird 911+ Initial Accuracy	0.0003	0.001	0.015%

The batteries of both SV and CTD probe options will last through over 8 hours of continuous profiling and associated data transmission if fully charged. The CTD rechargeable batteries are charged through external terminals; the SV probe accepts standard C cell batteries that are changed when expired.

During intensive surveys, the probe loop splice should be replaced daily, by cutting 50cm of line from the end and re-splicing the termination. This will take just a few minutes. The entire line section should be replaced after 500 deep underway casts, or after about 1000 shallow casts where the reloader has not been used.

Hollow Spectra line of 300lb, 500lb, or 800lb breaking strength.

The maximum amount of line that can be loaded is about 2000m. Typically, 1500m is used however for shallow water surveying 1000m is adequate.

Special splicing techniques are used to create very strong connections between line sections and a loop splice is used to connect the line to the tail spool. Other splicing methods should NEVER be used. The splicing methods are shown in Oceanscience training videos.

The Spectra line may become twisted, especially in shallow mode. To remove twists, pay out the line behind the ship while underway (remove the tail spool and probe first). The tension of the line will pull the twists out.

Little routine maintenance is needed during operation, although cleaning of the levelwind rollers with fresh water and lubricant may be necessary. The line tension control and brake may require adjustment after prolonged use, and periodic lubrication of the drive chain is recommended. All maintenance procedures are available on Oceanscience training videos.

We recommend that the UnderwayCTD probe is recalibrated after every cruise, which will also allow a post cruise calibration to be performed. The calibration is performed at the SeaBird Electronics laboratory. All UnderwaySV probes should be returned to Valeport for periodic re-calibration. It is recommended that third party calibration labs are not used for the UnderwaySV probes. Contact Oceanscience for recalibration information; do not contact SeaBird Electronics directly.

Yes, it is possible to deploy other sensors as long as they match the form factor required for safe deployment and retrieval. Please contact Oceanscience if you would like to discuss special sensor deployments.

No. The Oceanscience davit (arm and block) is specially designed for underway deployment to maximize the safety of the probe recovery.

Yes. As long as the vessel retains a nominal forward motion to prevent entangling of the line in the ship propeller. The maximum profile depth is over 1500m while stationary.