Marine Seismic Surveying with Towed Components Below Water's Surface

Abstract

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. Seismic streamers have head floats supporting the streamers. Each of the floats has adjustable buoyancy preconfigured to counterbalance the weight in water of the towed component that the float supports. Acoustic signals from a transceiver at the vessel find locations of the towed components. A towed fish at a lower level than the towed components also uses acoustic signals with a transceiver to further refine the locations of the towed components.

What is claimed is: 
     
         1 . A marine surveying vessel for towing seismic equipment with at least one equipment cable and at least one tow cable, the vessel comprising:
 at least one skeg mounted on the vessel and extending at least below a waterline of the vessel, the at least one skeg having at least one passage along which the at least one equipment cable passes; and   at least one shuttle movable along the at least one skeg adjacent the at least one passage and supporting the at least one tow cable.   
     
     
         2 . The vessel of  claim 1 , wherein the at least one shuttle comprises at least one tow point disposed on the at least one shuttle and configured to couple to the at least one tow cable. 
     
     
         3 . The vessel of  claim 2 , wherein the at least one tow point supports the at least one equipment cable with the at least one tow cable coupled to the at least one tow point. 
     
     
         4 . The vessel of  claim 2 , wherein the at least one tow point comprises at least one eyelet connector disposed on the at least one shuttle. 
     
     
         5 . The vessel of  claim 2 , wherein the at least one tow point comprises at least one pulley disposed on the at least one shuttle. 
     
     
         6 . The vessel of  claim 1 , wherein the at least one skeg mounts on a stern of the vessel. 
     
     
         7 . The vessel of  claim 6 , wherein a distal end of the at least one skeg extends below the stern to at least a keel of the vessel. 
     
     
         8 . The vessel of  claim 1 , wherein the at least one passage comprises a separation separating the at least one equipment cable in the at least one passage from the at least one shuttle. 
     
     
         9 . The vessel of  claim 1 , wherein the at least one skeg comprises a rail extending along the at least one skeg, the at least one shuttle being movable along the rail. 
     
     
         10 . The vessel of  claim 9 , wherein the at least one shuttle movable along the rail adjusts a depth of the towed seismic equipment in the water. 
     
     
         11 . The vessel of  claim 1 , wherein the at least one skeg comprises at least one pulley moving the at least one shuttle along the at least one skeg. 
     
     
         12 . The vessel of  claim 1 , wherein the at least one shuttle comprises at least two shuttles movable along the at least one skeg, each of the at least two shuttles supporting at least one of the tow cable. 
     
     
         13 . The vessel of  claim 12 , wherein the at least two shuttles are movable together along the at least one skeg. 
     
     
         14 . The vessel of  claim 12 , wherein the at least two shuttles are independently movable along the at least one skeg. 
     
     
         15 . The vessel of  claim 1 , wherein a distal end of the at least one skeg extends vertically from the vessel and comprises a base plate disposed horizontal to the at least one skeg.