A marine survey system can include a first cable including a first end configured to be coupled to a direct current (DC) power supply on a marine survey vessel and a support module coupled to a second end of the first cable and configured to receive power therefrom. A first electrode of towable electromagnetic (EM) source equipment can be coupled to the support module and configured to receive power therefrom. A depth control device can be coupled to the first electrode and configured to control a depth of the first electrode. A first end of a second cable can be coupled to the support module and configured to receive power therefrom. A second electrode of the towable EM source equipment can be coupled to a second end of the second cable and configured to receive power therefrom.