Posted on: 15 April 2011   By matthew.zimmerman
Preparing Steel Bulb for Refit of 3D Sonar
Preparing Steel Bulb for Refit
Steel Bulb After Refit of Forward Looking Sonar
Steel Bulb After Refit
FS-3ER Fairing Drawing Excerpt
FarSounder-1000 Fairing Drawing Excerpt
Centerline Installation
Fairing Recessed in Hull on Centerline
Integrating Fairing into Composite Bulb
Integrating Fairing into Composite Bulb
Another Centerline Installation
Fairing Integrated External to Hull

For an end user new to FarSounder sonars, the idea of retrofitting a sonar into an existing hull can seem daunting. However, once the details are examined, the process is relatively straight forward. Approximately 50% of our customer installations are refits to older hulls. Even some of the New Builds that have our sonars have approached integration of our systems as a "refit" when our products have been added to the ship's specifications late in the build process. When beginning to consider one of our 3-dimensional forward looking navigation or diver detection sonar systems, potential customers are often concerned with the installation design process and any potential hydrodynamic impact on the hull. These are important questions to which we believe there are some simple answers. The purpose of this blog posting is to explain the basics of refitting a vessel for our 3-dimensional forward looking navigation and diver detection sonar systems. 

The Installation Design Process

FarSounder's Navigation Sonars consist of a Transducer Module, a Power Module and our SonaSoft™ software. Our Ship Protection Systems utilize multiple Transducer/Power Module pairs. In all cases, the Transducer Module is mounted in a fixed installation fairing while the Power Module is a "black box" mounted somewhere out of the way inside the hull.

We've developed a simple fairing design that can be adapted to all types of hulls. It is essentially a tube with an internal mounting flange that is integrated to the hull. The tube can be integrated internally or kept completely external with only a single cable penetration through the hull. Once the fairing is installed, the Transducer Module itself can be removed and reinstalled underwater by a diver through the use of an underwater wet-matable connector. 

Our engineering department has developed a detailed Installation Design Guide and drawing package which can be provided to customers, shipyards, and naval architects. Though we won't get into all the details here, FarSounder's navigation sonars should generally be installed as far forward and as far deep as possible. The deeper the sonar is installed, the better it will perform in higher sea states. We recommend that the Tranducer Module be installed at least 1 meter (~3 feet) below the water's surface. The faring can be located:

  • directly on the centerline through the stem, 
  • on the centerline but forward of the stem, 
  • to the side of the stem, just off center, or
  • set into the bulb.

Depending upon the hull shape, the rake of the stem, and if the hull has a bulbous bow will determine the optimal location for the unit. Our Installation Gallery has pictures of our sonars installed on a number of different hull types. Can you guess which ones are refit and which ones are new builds? You might be surprised by the answers. 

The technical team at FarSounder is happy to be as involved with this process as the customer would like. Generally, we begin by sending a copy of our Installation Design Guide and Drawing Package to the appropriate parties. The customer (or customer's naval architect, shipyard, or integrator) then sends us a draft of the installation based on our design guide and drawing package. We're happy to provide suggestions for optimal fairing location. In all cases, we request that a copy of the "final" design be forwarded to us before fabrication for review. 

Common Concerns About Fairings

Some customers are initially concerned with adding a sonar fairing for the first time. Just as a radar/antenna mast is commonplace today on a power vessel, one day forward looking sonar fairings will be common on hulls as well. Aside from the valuable navigation and security data our systems provide, our fixed installation approach offers a number of advantages over other sonar technologies.

Fixed Installation Means No Moving Parts - Our system design does not require a hydraulic lift. These mechanical systems require periodic maintenance and limit the depth below keel in which the vessel can operate.

No Hydraulic Lift Means Small Footprint - In a new build scenario, compromises can be made in the vessels interior layout to "save" room for the hydraulic lift machinery that is necessary for other types of sonars. In a refit scenario, this can be difficult and even a deal breaker. The recommended fairing of FarSounder's installation design concept is relatively small. In cases where it is inset into the hull, the required space is often available inside an existing tank. Thus little or no redesign of the interior spaces are required.

We offer complimentary drawing review services. We'll make sure that the installation design is suitable from an acoustics point of view. This also allows us to check for any simple "gotchas" that might not be obvious to designers working with forward looking sonar for the first time. 

We've found that most of our customers' installations follow the same general installation concept. Yet each one is slightly different. Due to these slight variations in design, we don't supply a standard fairing tube. Because the fairing is mechanically so simple it is generally much less expensive to fabricate it at the ship yard than to have our machine shop fabricate the fairing and then send it to the shipyard. Furthermore, since the design is so simple and all the major underwriters including Lloyds, DNV, and ABS are familiar with our systems, customer drawings can easily be reviewed by the ship's underwriter in very little time. Whether you're integrating our sonar into a composite, steel, or aluminum hull, the process is similar. 

We've also received questions about impact on hull performance from adding a fairing. Our sonar looks large when compared with an echosounder, but it is actually relatively small when compared to the size of the ships on which it is installed. Though there is a large perceived impact to the vessel's hydrodynamics (like "aerodynamics" but under the water), in actuality it is quite small and not an issue in practice. We have had no reports of vessel performance changes from before to after installation. In fact, hull finishes can have a much bigger impact on the vessel drag coefficient than our sonar. 

Adding Sonar to Your Ship

Once you've decided to add one of our sonars to your ship, the next step is simple. We generally recommend that customers work with one of our certified dealers/sales reps. These groups will handle the installation, integration, and commissioning of the equipment. They will often work directly with your naval architect/ship yard to make sure that the fairing design process runs smoothly. If requested, FarSounder technicians can also be contracted for commissioning and training.