Subsea trencher and method for subsea trenching

A subsea trencher for arranging at least partly into the seabed a subsea pipeline laying on the seabed, the subsea trencher comprising:

• at least one cart that separately carries at least one trench tool and is configured to run on the subsea pipeline, wherein the trench tool is configured to work the seabed underneath the subsea pipeline;
• a subsea support frame, that carries, separately from the cart, heavy subsea equipment connected to the trench tool for operating the trench tool, and wherein:
• when the subsea support frame is fixed to the cart, the cart supports the subsea support frame to press down substantially the entire assembled weight of the cart and the subsea support frame onto the subsea pipeline as the assembled cart and the subsea trencher run on the subsea pipeline, and
• when the subsea support frame and the cart are uncoupled from each other, substantially only the weight of the cart presses down onto the subsea pipeline as only the cart runs on the subsea pipeline, wherein, the subsea support frame is configured to be suspended above the seabed or arranged beside the subsea pipeline at a distance from the subsea pipeline sufficient to avoid the subsea trencher from sinking into the seabed as a consequence of the destabilizing effect of the trenching operation caused by the trench tool.