I agree, they might look big enough to float but MJ is right, way too much weight for that size displacement. They strap them to barges to do deepwater work.
And yes, they are all "longbooms" to reach out beyond the widetracks...
Massey Ferguson 5465, Kubota M5040, Farmall H (2), Minneapolis Moline R, Case 530CK, Cat 416C
What about one of these? Definitely doesn't float..
Underwater excavator
The construction of a 1200 km long gas pipeline is underway at a depth of up to 1000 metres on the ocean bed between Norway and the United Kingdom. A ship measuring more than 350 m in length and housing a pipe-laying system is being used at surface level. Two custom-designed excavators work at depths of up to 1000 metres to make ready and level out the ocean bed. Important components such as the boom and undercarriage have been designed using the know-how and technology of Switzerland's own Menzi Muck. Designed in St. Gallen (Rheintal) and featuring corrosion-resistant materials such as titanium and aluminium, these have proved vital to the implementation of the project.