The ProSILVA 15-4ST is a tracked forwarder designed for very soft ground.
The forwarder has a 15-ton load capacity, but is still able to operate on very soft terrain. The ProSilva 15-4ST BogHopper track-mounted forwarder weighs 35 000 kg when loaded, but its contact pressure is very small. This is due to the design of the tracks and suspension. The contact area of the tracks when making an 8 cm (3.1 in) depression is 7 m2 (75 ft2) when using 800 mm (31.5 in) tracks. The track frames are tilted lengthwise and crosswise, where bent track plates are used to ensure that it is almost unnoticeable where the forwarder has been travelling. The suspension is designed to reduce vibration to the driver and forwarder frames. The forwarder makes use of an active swivel to transfer the pressure to the most supporting part of the terrain. Sensors are used to determine the position of the forwarder on the terrain. When operating on soft ground, the articulated joint is then held straight, which allows cabin movements to be reduced. All of the above allow the forwarder to be used around the year without resulting in soil damage. Source: http://www.prosilva.fi/en/products/prosilva-15-4st