The Sentrylog is a multi-zone corrosion monitor with data logging capability.  Used as a monitor, an LCD display and LED’s provide indication of the vessel’s level of cathodic protection. Used as a data logger, the corrosion history of the boat or structure can be recorded and examined.  Corrosive events, which may be short lived, can be detected. The multizone capability of the Sentrylog allows different zones on a vessel to be simultaneously monitored. For example, the external hull may represent one zone, other zones may include the insides of sea chests, ballast tanks, water jet tunnels etc. Each zone requires a reference electrode to be installed. Up to 3 zones can be monitored with one Sentrylog .

The Sentrylog(2000) provides extended data storage allowing for up to 2,000 sets of data to be gathered.

The Sentrylog kit comprises a Sentrylog monitor, mounting screws, 3 AA batteries, an earth lead, a serial data cable for computer connection and a software disk. 

Sentrylog kit


Note: Reference electrodes are purchased separately. Refer to: Reference electrode installation and Order information


  1. The Sentrylog can be bulkhead mounted in any convenient location such as in the engine room or in the vessel’s bridge/pilot house.  The box dimensions are 115 mm x 65 mm x 40 mm deep.
  2. Drill two 3.8mm diameter holes at 83.5 mm by 52.5 mm centers on the hull bulkhead or other suitable mounting location. See the schematic drawing of the Sentrylog below.
    Schematic of Sentrylog with wiring and installation details
  3. Remove the Sentrylog lid taking care to keep it supported. Mount the Sentrylog box using the two 8g x 12 mm self tapping screws provided. 
  4. Insert the 3 AA batteries supplied. Refasten the Sentrylog lid.
  5. Connect terminal E to the hull with the earth lead provided.
  6. Connect terminals 1 up to 3 to reference electrodes.

Monitor operation

Press the test button. The LEDs will light and LCD milli-volts will display.  The Sentrylog will commence reading zone 1. After a few seconds the Sentrylog will cycle to zone 2 and so on. To conserve battery life the Sentrylog operates normally in ‘power down’ mode. The Sentrylog will auto power down after one minute.  

For a particular zone, a reference electrode must be connected to the corresponding terminal on the Sentrylog and it must be in contact with sea water. Only then will the Sentrylog indicate the cathodic protection level correctly.  

Data logger setup 

Note: Images and descriptions contained within this section are for illustration only and may vary slightly depending upon the version of the software that you are using.  Detailed operating instructions are provided with each logger.

  1. Connect the Sentrylog to a spare serial port (COM1 or COM2) on the back of your PC or laptop using the data cable provided.
  2. Run the software by inserting the floppy disk into the disk drive. Run Windows Explorer, select a: drive and double-click on the program sealog.exe. Alternatively, copy sealog.exe from the floppy disk to a suitable directory and run it from there. The Settings menu, see below, is the default menu.
Settings menu
  1. From the dropdown list provided at the bottom left of the screen, select the serial port being used on the PC.
  2. Ensure that the Sentrylog is powered up and not ‘asleep’.  If asleep, all the lamps on the front of the unit will be turned off. Wake the Sentrylog up by pressing the ‘test’ button for a few seconds. Once the Sentry is awake and connected to your PC running the software, the green CommsActive light on the bottom left of the software display will light. 

If the CommsActive light does not light then check that the Sentry is awake, that the data cable is correctly attached and that you have selected the correct serial (COM) port.

Fill in the menu fields as follows:

  1. Material:    Select aluminum, steel or bronze with the select arrow button.
  2. Zones:       Select 1, 2 or 3.  Depends on the number of reference electrodes installed. 
  3. Reference type:    Select the material corresponding to type of reference electrode material used, either zinc or AgAgCl (silver silver chloride). 
  4. Log interval:  500 (or 2,000) logs per zone are available. If the logging period is set to storing a reading every two hours say, the Sentrylog will take a reading every few seconds during that two hour period. Each reading is compared with previous readings and at the end of the two hour period, the maximum and minimum reading that occurred during that two hour period is stored. This approach to data logging ensures that important corrosion events are not missed.  With the logger set to store data every 6 hours, for example, 4 months of data may be acquired.

    Log interval

    1 min

    5 mins

    1 hour

    6 hours

    12 hours

    24 hours

    Data cycle

    8 hrs

    42 hours

    21 days

    4 months

    8 months

    16.7 months

    Data cycle-2000

    33 hrs

    7 days

    83 days

    16 months

    2.8 years

    5.5 years

  1. Set time    Clicking this button sets the Sentrylog time to the current PC time.
  2. Cyclic logging    Checking this box causes the Sentrylog to continue to take data (overwriting the oldest data) when the data cycle time has been exceeded. For example, setting the Sentrylog to store data every 1 hour will cause existing data to be overwritten when 21 days have passed. If the Cyclic logging box is not checked, then for a 1 hour log interval, the Sentrylog will stop logging after 21 days.
  3. Sentry Name Type in the vessel name or site name (max. 16 characters)
  4. Zone 1 Description  Name of zone 1 reference electrode location (max. 16 characters)
  5. Zone 2 Description  Name of zone 2 reference electrode location (max. 16 characters)
  6. Zone 3 Description  Name of zone 3 reference electrode location (max.16 characters)  

Disconnect the data cable from the Sentrylog .  

Data logger operation  

As a data logger, logging is automatic whenever the batteries are connected . In “power down” mode, the LCD screen will show “Log” when logging. When logging ends (if the option cyclic logging is not ticked), the word “OFF” will indicate logging has stopped. Using the Sentrylog as a corrosion monitor by pressing the “test” button, will override the “Log” or “OFF” messages and the mV readings corresponding to the particular zone will appear on the LCD screen.

Data uploading  

  1. Follow steps 1 to 4 in the Section “Data logger setup” above
  2. Click on the Log data button. The menu shown below will appear.
    Log data menu
  3. With the 'Sentry Ready' indication showing in the Status bar, click on Get Logs-Sentry. It may take around a minute to up load all the data.
  4. Click on Save to File. Save the data as a .txt file in your directory of choice.  

Clear screen clears the data window, but does not delete data stored in the Sentrylog .

Clear Sentry Data clears any data stored in the Sentrylog .

The data can be processed in a number of different ways. 

    • The values may be viewed as a list within the ‘Log Data’ page.
    • The text file can be imported into any standard spreadsheet or word-processor package where it may be further analyzed and/or graphed.

Cathodic protection levels

The Sentrylog has LCD and LED indication of the cathodic protection level. Providing the Sentrylog has been set up for the correct material and reference electrode type, green LED indication shows that the material is protected form corrosion. Red LED indication can indicate under protection or over protection. Under protection indicates corrosion can take place. The rate of corrosion is influenced by a number of variables such as the type of material, the oxide layer present, the quality of the electrolyte and the potential relative to the reference electrode.  Moderate over protection can be accepted but may be uneconomic for steel, bronze and brass.  Over protection can cause problems with aluminum due to amphoteric attack.

LCD readings can be evaluated from the table below for Seaguard zinc electrodes and typical materials in use in the marine sector. For Ag AgCl reference electrodes, subtract 1000 from the numbers below:


Freely corroding


Over protected

Carbon steel




304 Stainless steel (active)


















115 x 65 x 40mm

Battery life

>18 months



Ref. electrode

Zinc or AgAgCl (1, 2 or 3 required)


3 alkaline AA cells

Log capacity(*)

500/2000 readings per zone 

Operating temp.

0 to 500 C

Log time

User selectable (1 to 24 hours)


-1200mV to +1200mV

Data connection

RS232 (cable supplied)


+/- 5 mV


Laptop or PC, 486 or higher



IP 65

Up to 3 zones


‘Sealog’ software supplied. Windows 95, 98, 2000 and NT compatible.


(*) Log capacity for the Sentrylog(2000) is 2,000 readings per zone. 

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