Global-Mariner

                                       "The Ships"

                                                                    - featuring SKA 4 - page three -

                                                  - incl. her sister ships, crew and Greenland -

A good picture of what it is all about - - -

The four SKA boats would usually sail side by side keeping a fixed distance from each other, - one of the boats being the leader, taking care that the correct position was maintained by reading the signals from the transmitter on the known position on the island - - -

How did the other boats keep the correct distance from the leader?

Well,- it was done extremely primitive compared to modern days satellite navigation, simply by having somebody watching the neighbour boat through an optical distance measuring device, - a sort of prism -, where you would see two images of the next boat if the distance was not correct - - -

Then you would advice the helmsman to go closer or further away, until you saw only one image in the handheld prism.

One image was the indication, that the distance was correct - -

At certain intervals, the lead boat would advice the other boats to draw a vertical line on the echo sounder print, - and mark it -, so that later it could be identified and compared with the lines from the other boats taken at exactly the same time.

Then later again, - when new charts was going to be made in Copenhagen -, the rolls of echo sounder paper from the four boats was compared, and the data from each boat taken at the same time, could be plotted into the chart - - -

On the picture above, you clearly see the echo sounder print with several such vertical lines - - -

Also take note of the curve the echosounder is drawing on the print. It is quite a dramatic picture of the sea bottom below, showing a wall coming up from the deep - - -

Take note of the look out in the front of SKA 5 - - -

This is because the echo sounder was mounted about mid ships, and therefore reading only the depth from that point.

However,- the details of the Greenland sea bottom is quite dramatic, with holes, valleys and vertical walls, and the depth could actually go from 100 meters to 0 meters just within a few meters - - -

Therefore the boats often ran aground even though the echo sounder showed plenty of water under the keel - - -

And therefore a look out was very often the best solution in waters still not surveyed - - - Old fashioned???? Yes indeed it is,- but it works - - -

I remember that two different distance measuring systems were used to determine our position, - the "raydist"- and the "hydrodist" system.

The "raydist" stations we erected on small islands and rocks were basically tall radio masts, and the principle was that these antennas would continuously emit different signals which could be received on the leading SKA boat.

Depending of the distance from the transmitters, the signals would have a difference, and when those different signals were compared, it was possible to calculate how far the SKA boat was from the base station.

The other system, - "hydrodist" -, could measure the exact distance between two points. What exactly the principle was with "hydrodist" I cannot remember anymore, but I am quite convinced, that the instrument that Walseth "plays" with on above picture is a "hydrodist" - - -

This was the end of page 3 - - - Please continue to page 4 - - -