Navigation in and around ice is a very important topic for vessels destined for the arctic or antarctic waters. The rise of adventure cruising, scientific expeditions, and commercial shipping through these areas is keeping the topic in the forefront of many conversations. Ship operators in these areas are interested not only in detecting and avoiding icebergs but in some cases also knowing how close they can get to ice that is clearly visible above the water. Navigation in such areas is clearly reliant on seaman experience. Since the sinking of the RMS Titanic, engineers around the world have been working on ways to detect icebergs using various sonar technologies. In this blog post, we summarize how FarSounder's 3D sonars can be used to navigate in sea ice conditions and how our obstacle avoidance sonars can be installed on ice classed vessels.
Forward Looking Sonar Uses
The most obvious use of our navigation sonars is to detect singular icebergs ahead of the vessel. Due to the relatively small difference in density between sea water (roughly 1025 kg/m³) and pure ice (roughly 920 kg/m³), typically more than 85% of the iceberg is below the water's surface. This means that icebergs large enough to cause damage to a ship may only have a very small volume protruding above the water. This may be difficult to visually detect and may also be difficult to distinguish with radar. Fortunately, ice tends to be a good sonar reflector. The actual reflectivity of the iceberg depends on the size and shape of the ice.
Icebergs are classified roughly by their size. "Bergy Bits", as classified by the International Ice Patrol, can be 1-5 meters in height and 5-15 meters long, are examples of icebergs that are big enough to cause vessel damage, but small enough that they are difficult to detect visually or with radar. These are actually quite big acoustic targets as compared to large navigation buoys which can be seen without sonars.
Sometimes adventure cruisers want to get close to large icebergs or glaciers. In these cases, they know exactly where the ice is located above the water, but are unsure of the ice extent under the water. In these situations our sonar can be used to easily determine range to the underwater obstacles. The ice will apear on the sonar similar to a coral reef or rock pile.
There are two basic installation techniques for our sonars on board ice classed ships. If the vessel is simply ice hardened and not intended to perform ice breaking (like many explorer yachts and cruise ships), then our standard fixed installation is generally sufficient. Our installation gallery has a number of fixed installation examples. Though they are not all noted as such, some of these are ice classed. In these cases, slighly thicker plates with a little extra reinforcement at the welds were used. For these ships, even if chunks of ice scrape along the hull, the sonar is protected just as it would be from any other in-water debris.
For vessels that plan on performing ice breaking, or for those that may wish for additional protection to the sonar, a hydraulic mounting system can be used. In these cases, the Transducer Module is installed in a small fairing at the end of a host mechanism. When ice breaking, the Transducer Module is retracted into a void embedded into the underside of the hull. The fairing may lay flush to the hull to prevent ice from entering during breaking operations.
We recognize that every vessel is slightly different. Therefore, in both of these installation cases, it is usually most cost effective for the ship yard to fabricate the fairing. We provide an installation design guide, and our engineering team is available to provide advice to naval architects and review installation drawings before fabrication. It is the responsibility of the shipyard/naval architect to secure class approval for the installation and fairing structure. FarSounder sonars have been installed on vessels classed by all the major agencies including, ABS, DNV and, Lloyds.
For those new to the ice classed vessels, there are actually a variety of different ice classifications (and each classification agency has their own variations from one another). For example, DNV supports classification of vessels from ICE-C through ICE-15. In this case, the former is for passage in the lightest of ice conditions and the latter is for the toughest of ice breaking.
The Exploration Continues
Even with the ever expanding global coverage of satelite communication, the ubiquity of freely available aerial photos, and the thousands of years of exploration at sea, the artic and antarctic regions are still a dangerous unknown. FarSounder's 3D forward looking sonars are the latest tool in helping to bring safe passage all over the globe.