How the Charts are made

This is the portable survey craft used for shallows and small bays on Corrib, and any other lakes.

It has both sidescan and conventional sonar aboard, and independent power supplies with solar backup.

And "Burlesque", a fully kitted survey craft now, with computer systems, sidescan and conventional sonar, DGPS and conventional GPS.

Equipment used .



The primary sounding equipment is a Lowrance HDS unit installed on both my survey boat, Burlesque, and in the inflatable,  with  Structurescan modules. These utilise two transducers; both mounted on the transom (over the side on the inflatable), although the sidescan transducer is dismountable for use on a towed 'fish'. The towed setup is not used on Corrib due to the nature of the geography, I'd do more damage and spend more time hauling it in and out than gaining any benefit.

The maximum depth (so far) on Corrib is 167ft, and the unit is very capable of giving excellent returns at that depth. Initial passes are made at 3-4kts on a "planned" grid (it doesnt often work out that way though) with the unit set onto 300ft range and 450khz frequency. This gives me a great overall picture of what is happening within 2-300 feet either side of the vessel. If anything interesting or unexpected is seen then a more 'in depth' survey at higher frequency (less range) is carried out. This is how I found "Trevors shallow" and the wrecks depicted on this site.

For what may be archaeology or interesting geology I then use the Burlesque's onboard underwater video system, and starting in 2014 she now has an onboard ROV which can be operated from within the cabin.


The positional data for the Lowrance HDS is acquired with 2 GPS units (one for backup/check) which utilise EGNOS and standard differential corrections. The units update positional information approx 5 time per second. This data is is all collected, a days data amounts to several gigabytes and is analysed using Sonarviewer software from where it is exported as CSV data for further numbercrunching. Sidescan mosaics are constructed using DrDepth which has been found to be very capable.

If something interesting and shallow pops up on the sidescan, I find somewhere safe to anchor and launch the inflatable for a close grid survey. Once the limits of a shallow or obstruction have been determined I then carry out a sidescan survey around it using either the inflatable or Burlesque.


Lightweight lake surveying using a Garmin GPSMap60Csx with high gain antenna


For rocky, shallow or previously poorly surveyed areas of the lake, and smaller lakes, I use an HDS unit and a Garmin GPSMap60Csx connected with a home made cable to a Garmin Intelliducer (0183). This is done through a  power supply/distribution box which I constructed, and contains a large rechargeable LIon battery, a recharging socket, a fuse, a rocker switch and three RS232 connections – one supplies power and NMEA data to the the GPS, another receives the NMEA signal from the transducer and carries power to the transducer, and another is a NMEA Tx with no power connections for connecting a small Panasonic Toughbook computer.
The transducer is mounted onto a pivoting and fully adjustable/removable mounting bracket which started life as a metal artists easel.

The system also has solar power backup, which now enables the unit to run almost indefinitely. It has been logging every day for up to 7 days without recharging, logging depth data onto the GPS. The Toughbook runs for 8 hours and can be recharged from the car or via the solar panel, tracklogs are downloaded onto the netbook every hour during surveys.


A sidescan unit is also installed on the inflatable, with a battery pack system giving 10 hours imaging time, and mounted on an overside unit from