MOTHERBOARD/Per Platou and Amanda Steggell, with Annesofie Norn, Neptun Sports Diving Club and the people of Husoy, Træna.


The 8th Sister is an art project that investigates the practical and contextual implications of creating an underwater sculpture in which its "true" form is manifested as an image on an ultrasound/echosounder display.

See project website for full description/documentation:

The 8th Sister was sunk 10 m beneath the sea in Træna, an archipelago of more than 1000 islands and skerries on the actic circle, 50 km off the north-west coast of Norway, 01-07.07.05.


When writing the project description "Mind, the Gap" I had several discussions with my supervisor Laura Beloff as to whether The 8th Sister could be included. Her concern was that it is disputable as to whether an art work comprising of a physical object that should be viewed via an echosound display could be considered in terms of synaesthesia. Her concern was that:

01: the visual rendering of the sonic signal is not simultaneous as echosounders work by projecting sound waves under water and using dtat derived by the returning echo to render an image. In other words, there is a delay between the audio and visual rendering.

02: when people view the image of the physical object via the echosound display they cannot hear the sound that is generating it.

In relation to the question of whether The 8th Sister project can be considered relevant, or successful in terms of synaesthesia - my answer, from an artmaker point of view, is yes! Echos are with us constantly and almost everything we hear has an echo. As the echo that renders the visual image is sound, I do not consider the question of simultaniety as a hinderance in describing The 8th Sister as a syn-aesthetic work. Additionally, any computational process takes time, even if the result is perceived as being simultaneous.

However, I have to admit that only a person with the condition of colour/sound synaesthesia would experience both sound and imagery simultaneously when viewing the sculpture via an echosounder display (hearing colour). A bit of a paradox! That the artwork does not produce an audible soundscape when viewed (or received) by the public may be a debatable issue. This may be a digression, but one can just as well argue as to whether people hear Munch's "silent" Scream.

But wait!

I viewed The 8th Sister on one echosounder that also emitted sound as the visual imagery on the display changed. The experience of The 8th Sister depends on the state of the technology one has to experience her by. Different types of echosounders render depth differently, and the angle, distance and speed of the boat in relation to the object anchored to the sea bed also play a role in her manifestation, as do environmental conditions, such as temperature and current. (2) Additionally, echosounders can be calibrated to give different renderings of depth.

Two versions of The 8th Sister on different echosounders
[click on images for higher resolution]

One eye-witness said:

The first time I sailed over her with the echosounder she looked like an angel. The second time, she looked like a mermaid. If you look down at her into the water, you can see something glittering but you can't see her form.
- Fisherwoman and shopkeeper, Husøy, Træna

Another comment:

Technically speaking, you can't see her without an echosounder. I think the idea's great since I work with electronics. You never can tell how she will reflect. If you sail over her in one direction, you'll see the whole of her body, but if you choose another direction, you may not see her at all. It's all about reflection!
- Electrician, Husøy, Træna

There are many factors that influence the way the public experienced The 8th Sister in addition to echosounder issues, such as:

- previous knowledge of the project via the press,
- rumour spreading by eye-witnesses and involved parties in Træna,
- local knowledge of the area,
- knowledge of the Legend of The 7 Sisters,
- degree of involvement in the project,

and so on. In such a small community news travels fast and these factors contributed to making The 8th Sister a site-specific Live Art performance rather than an art object. While the connection to the synaesthetic notion may not lie on the surface of their conciousness in relation to this project, many of the people in Træna rely on echosounders as depth- renderers and fish-finders in their everyday lives. They are familiar with the technology, and this played a strong role in the way they perceived and adopted The 8th Sister.

If the project had been carried out in the Oslo fjord I think that the perception of the artwork on the part of the public would have been quite different.

Depth has become profound even as it has become increasingly superficial. The idea that the deep harbours the truth is an old one; surfaces have prevaricated since the Greeks, appearances deceive, and it is foolhardy to trust the eyes.
- Judith Roof.


1) The 8th Sister was initiated and produced by Motherboard in co-operation with Erlend Mogård-Larsen (Træna Festival).

It was constructed with Annesofie Norn, Neptun Sports Diving Club (Sandenessjøen), and the people of Husøy, Træna.

2) Single beam sonar sensors utilize sonar (sound navigation and ranging) technology to collect measurements of the seafloor. These sensors collect point or raster data derived from the strength and time of the acoustic return. Single beam sensors consist of a transducer, mounted on or towed by a boat, that feeds into a signal processor and display device. The transducer emits a single sound pulse with a narrow footprint into the water column at specific intervals directly below the transducer. The sound wave bounces off the seafloor and the return is captured by the transducer.

Single beam sonar data are collected along transect lines and typically cannot provide continuous coverage of the seafloor. The output resolution of the data are determined by the footprint size, sampling interval, sampling speed, and distance between transects.
Different systems analyze the returns of the sound waves very differently - some systems only analyze the first return to measure bathymetry, while others use one or more returns to derive classifications of the seafloor or subsurface sediments.

Depth and "footprint"

The footprint of a single beam transducer is determined by water depth. It is smaller in shallower water and larger in deeper water. For example, one type of transducer (a 6-degree transducer) has a footprint that is one-tenth the depth, so in water that is 10 meters deep, the sensor's footprint is approximately 1 meter.

How boat speed influence the data
The density of data points is dependent on boat speed because the sensor emits pulses at specified intervals (e.g., 1 pulse every second or 1 pulse every 5 seconds). Slowing down or speeding up the boat changes the number of points collected along the transect.
If the boat is traveling too fast, an air pocket can form around the transducer that interferes with the transducer's ability to detect the returns. In addition, the boat can be traveling too fast for the sensor to pick up the return.

If a boat is stationary or traveling extremely slow, it may be subject to wave action and the boat may rock from side to side. When a boat rocks, the transducer sends pulses at angles towards the seafloor and not directly below the transducer. This changes the area of the seafloor that the sensor is viewing and may alter the return signal.

Taken from Remote Sensing for Coastal Management
URL: http://www.csc.noaa.gov/crs/rs_apps/sensors/

3) Judith Roof "Depth Technologies", p21 in "Technospaces - inside the new media" by Sally R. Munt (ed), Continuum 2001. ISBN 0-8264-5003-2.