Sonar Domes

Sonar domes are located on the hulls of submarines and surface ships. Their purpose is to house electronic equipment used for detection, navigation, and ranging. Sonar domes on Navy surface ships are made of rubber. On submarines, they are made of steel or glass-reinforced plastic (GRP) with a 1/2-inch rubber boot covering the exterior. Military Sealift Command (MSC) T-AGS Class ships have sonar domes made of GRP. Zinc anodes are fastened to the exterior of steel sonar domes, and are contained within all the sonar domes, for cathodic protection.

Sonar domes can be filled with fresh and/or seawater to maintain their shape and design pressure. Most surface ship sonar domes are initially filled with freshwater, and any water that is lost underway is replenished with seawater from the firemain system. Sonar domes on FFG 7 Class frigates and some MSC ships are filled with seawater. Submarine sonar domes are connected to the sea through a small tube to equalize pressure, but water inside the dome has limited exchange with seawater.

The larger AN/SQS-53 and AN/SQS-26 sonar domes on cruisers and destroyers are located at the bow, and the smaller AN/SQS-56 domes on frigates are mounted on the keel. Submarine sonar domes are located at the bow. MSC T-AGS Class ships have several small sonar domes at various locations on the hull. The T-AGS Class free flood sonar domes have ports which are open to the sea.

A variety of materials compose sonar domes, and components and materials inside sonar domes. Components and materials interior to sonar domes can include piping, sacrificial anodes, paint and the interior material surface of the sonar dome itself. Materials on the exterior surface of the sonar dome consist of the exterior material surface of the dome itself, any paints or coatings applied to the dome, and in some cases, sacrificial anodes. There have been changes in the composition of the rubber material in Navy surface ship sonar domes. Prior to 1985, all sonar domes contained tributyltin (TBT) antifoulant on the interior and exterior, to prevent or minimize marine growth. The TBT was impregnated into the outermost 1/4-inch layers (both exterior and interior) of the rubber. Figure 6 shows the plys or layers of a surface ship rubber sonar dome. Since 1985 rubber sonar domes have been manufactured with TBT only on the exterior surface. This type of sonar dome has been backfitted on older ships when they require sonar dome replacement, and has been installed on all new ships since 1990. Submarine sonar domes do not contain TBT. Instead, the exterior rubber boots are coated with a copper-based antifouling paint.

Sonar domes are emptied for sonar dome maintenance or replacement, and are always emptied when a vessel is in drydock. Some maintenance can be performed pierside. Sonar domes are emptied by first pressurizing them with air, to force as much water as possible through the installed eductor piping. Once this step is complete, eductors are used to remove all remaining water in the dome. The total volume of water discharged exceeds the sonar dome volume because the seawater used to operate the eductors is discharged along with water from the sonar dome. The water emptied from the sonar dome interior is: 1) discharged overboard, if the vessel is waterborne, or 2) collected for proper management ashore, if the vessel is in drydock.

Sonar Type Ship Class No. of Vessels [1999] Dome Material Dome Water Volume (gal, approx.)
AN/SQS-53 CG 47, DDG 51, DD 963, DDG 993 80 Rubber/TBT 24,000
AN/SQS-26 CGN 36, 38 3 Rubber/TBT 24,000
AN/SQS-56 FFG 7 43 Rubber/TBT 5,000
AN/BQQ-5 SSN 688 (through 750), SSN 637, SSN 671 47 GRP or steel 35,000
AN/BQQ-6 SSBN 726 17 GRP or steel 74,000
AN/BQR-7 SSN 640 2 GRP or steel 35,000
AN/BSY-1 SSN 688 (from 751) 23 GRP or steel 35,000
EM100 MSC T-AGS 51 2 GRP N/A (free flood)
EM1000 MSC T-AGS 60 (62 & 63) 2 GRP N/A (free flood)
EM121A MSC T-AGS 60 4 GRP 300
TC-12NB MSC T-AGS 60 4 GRP 25
TR-109 MSC T-AGS 60 4 GRP 75

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