A skeg mounts from the stern of a towing vessel and extends below the waterline. A channel in the skeg protects cables for steamers and a source (e.g., air gun array) of a seismic system deployed from the vessel. Tow points on the skeg lie below the water's surface and connect to towlines to support the steamers and the source. A floatation device supports the source and tows below the water's surface to avoid ice floes or other issues encountered at the water's surface. The floatation device has a depth controlled float and one or more adjustable buoyancy floats. The controlled float has its buoyancy controlled with pressurized gas used for the air gun source and actively controls the depth of air gun source in the water. Each of the adjustable float connects in line with the controlled float with flexible connections. Each adjustable float has its buoyancy preconfigured to counterbalance the weight in water of the air gun or portion of the source that the float supports.