Electric Propulsion

According to the United Nations Conference on Trade and Development, 80 percent of the world’s commodities are carried on ships, and this figure is forecasted to increase by 3.8% per year. Unfortunately, most container and cruise ships, oil tankers, and cargo vessels run on heavy diesel oil and produce a huge amount of exhaust gases, including sulfur oxides, nitrogen oxides, soot particles, carbon dioxide (CO2) and fine dust. Combined, the 90,000 ships worldwide burn 370 million tons of fuel each year and produce 20 million tons of sulfur oxide. To reduce these harmful emissions, ship manufacturers will have to convert to electric power.

There are currently three types of electric drives being used in the marine industry:

• Diesel-electric drive: In a diesel-electric drive, diesel generators produce electricity, which then power electric engines that turn the ship’s propeller.
• Hybrid drive: Hybrid drives use on-board batteries in conjunction with an internal combustion engine. The hybrid drive can be switched on for a short time to provide power when needed, or it can store surplus energy from a diesel generator. Hybrid drives allow a ship to sail using nothing but electricity for some time.
• Fully electric drive. Ships that are powered by a fully electric drive system do not have an internal combustion engine on board. Batteries provide all the ship’s energy needs.

© MITRUMEDIA

Cathodic Corrosion Protection

Impressed cathodic corrosion protection (ICCP) systems, which prevent a ship’s steel body from corrosion, are powered by programmable DC power supplies. These systems use galvanic anodes attached to the hull to provide protection. When ships are removed from the water for inspection and maintenance, it is a simple task to replace the galvanic anodes. Smaller vessels such as yachts, with non-metallic hulls, are equipped with galvanic anodes to protect areas such as outboard motors.

Anodes for on-board ICCP systems on ships consist of a relatively inert material such as platinized titanium and are mounted on the outside of the hull. Cables from the anodes are routed through the ship’s hull via a compression seal fitting and connected to the positive terminal of the DC power supply. The power supply’s negative terminal is simply attached to the hull to complete the circuit. ICCP anodes are flush-mounted, minimizing the effects of drag on the ship, and located a minimum 5 ft below the light load line in an area to avoid mechanical damage.

The current density required to adequately protect a hull is a function of the ship’s velocity and must be considered when selecting the power supply and placing the anodes on the hull. Some ships may require special treatment. For example, aluminum hulls with steel fixtures will create an electrochemical cell where the aluminum hull acts as a galvanic anode, making the corrosion worse. In cases like this, aluminum or zinc galvanic anodes can be used to offset the potential difference between the aluminum hull and the steel fixture. If the steel fixtures are large, several galvanic anodes may be required.

Magnetic Silencing – Degaussing

A steel-hulled ship is like a huge floating magnet. As the ship moves through the water, the ship’s magnetic field also moves and adds to or subtracts from the Earth’s magnetic field. Because of its distortion effects on the Earth’s magnetic field, the ship can trigger magnetic-sensitive ordnance or devices that are designed to detect these distortions.

To prevent this from happening, ship manufacturers often install a degaussing system to reduce the ship’s effect on the Earth’s magnetic field. The current flowing through degaussing coils generate a magnetic field that cancels the effect that the ship’s movement has on the Earth’s magnetic field. This, in turn, reduces the possibility of detection by these magnetic sensitive ordnance or devices.

The figure below illustrates how activating the degaussing coils compensate the induced and permanent vertical components of the ship magnetic field (Z zone). As the ship changes hemispheres, the coil current polarity must be dynamically adjusted.

Reference: Federation of American Scientist

Sea Mine – Tracing Vessel’s Magnetic Signature

Modern mines detect what’s called a ship’s magnetic signature. If a mine detects certain signatures, it will trigger a torpedo or mine explosion and give a position and categorization (mainly submarine). To minimize this threat, navies can equip vessels with a built-in degaussing (DG) system. Degaussing systems alter a ship’s magnetic signature, thereby reducing the chance of detection.

Reference: Polyamp: Degaussing Systems

Electrified Submarine

Siemens Marine’s polymer electrolyte membrane (PEM) fuel cells are the wave of the future for external, air-independent electric energy generation in submarines. As the cells need only hydrogen and oxygen as fuel, they can significantly extend a submarine’s dive period. Submarines equipped with these low-temperature fuel cells are far superior to conventional submarines, which must surface fairly frequently to recharge their batteries. These fuel cells are much more efficient than conventional power systems and emit no exhaust whatsoever. The electrochemical reaction creates only water and heat in addition to electricity and is silent, too. Its robust, low-signature and nonmagnetic design was specially created for long-term use and has an expected service life of many years – and all in an effective and affordable life cycle support package.

Reference: Siemens

On-shore cathodic protection

Jetties, harbors and other structures can also benefit from cathodic protection. Different structures require different systems to provide protection. Most designers favor galvanic anodes, but ICCP can also be used. Because there are so many structural geometry, composition, and architectural differences, specialized firms are often required to engineer structure-specific cathodic protection systems. Sometimes, marine structures require retroactive modification to be effectively protected.