Amphibious excavators propel themselves by track action against the bed. That mechanism has limits, and they are reached sooner than most buyers assume.
The failure mode
In water deep enough for the machine to float substantially, track contact with the bed becomes light. In soft bed material the tracks then churn without generating propulsion. The machine has buoyancy but no mobility, which on an open water body is a serious situation.
What determines the limit
- Pontoon volume relative to machine weight. Greater buoyancy means less track loading on the bed.
- Bed consistency. A firm sand bed provides traction at depths where soft silt provides none.
- Attachment weight and position. A loaded attachment forward alters weight distribution and can lift the rear tracks.
Solutions, in order of preference
- Correct class selection. Choosing a machine whose configuration suits the actual depth costs nothing extra at specification stage.
- Pontoon extensions. Added buoyancy and footprint, at the cost of transport width.
- Spud poles. Hydraulic legs that anchor the machine to the bed for digging. They solve holding position, not travel.
- Working from a barge. Beyond the practical depth for amphibious work, this becomes the correct answer.
What to measure beforehand
Maximum depth across the working area, not average. Seasonal variation. Bed consistency at depth — probe it rather than assuming from the bank. And whether depth is likely to increase as material is removed, which on dredging work it usually is.