I've seen an excavator undercarriage that was set-up to run under saltwater while connected to a "mother ship". Power and controls were above water and extended hydraulic hoses were run down to power the track drive motors. There are a number of places close to shore where where there is gold on the ocean floor and this is the kind of rig needed to get it. I'd like to use a 7,000 to 10,000lb machine undercarriage like from a Hitachi EX35 or EX40, or Yanmar or equal. Could it be as easy as taking off the cab, engine and controls and making the hydraulic lines longer? How about the track motors- are there any vents on them that water would leak into? Are the shaft seals good for external pressure from the water as well as from the internal pressure? Are the rollers sealed well enough to keep out the water? I think this is a case of "the devil is in the details", and anything you guys can suggest to watch out for is most appreciated.
The quick answer is, yes. Extend the hoses and it should work. Excavators can survive immersion in water, it's just a matter of how long for. I would guess that if an undercarriage were in saltwater every day, after a few months you would have nothing but a rusty lump of scrap. You could probably prolong it's life by washing it every night with clean water. Rubber tracks may be a good option, but if you cut one and expose the wires, it will rot out before your very eyes...
I would look into zink or some other means of actively preventing electrolosys
I think I'd use a suction dredge set up. That excavator isnt going to last long in salt water immersion.