Psycrometer

An instrument consisting of two thermometers which is used in the measurement of the moisture content of air or other gases. The bulb or sensing area of one of the thermometers either is covered by a thin piece of clean muslin cloth wetted uniformly with distilled water or is otherwise coated with a film of distilled water. The temperatures of both the bulb and the air contacting the bulb are lowered by the evaporation which takes place when unsaturated air moves past the wetted bulb. An equilibrium temperature, termed the wet-bulb temperature (TW), will be reached; it closely approaches the lowest temperature to which air can be cooled by the evaporation of water into that air. The water-vapor content of the air surrounding the wet bulb can be determined from this wet-bulb temperature and from the air temperature measured by the thermometer with the dry bulb (TD by using an expression of the form e = eSW − aP (TD − TW). Here e is the water-vapor pressure of the air, eSW is the saturation water-vapor pressure at the wet-bulb temperature, P is atmospheric pressure, and a is the psychrometric constant, which depends upon properties of air and water, as well as on speed of ventilation of air passing the wet bulb.

An instrument that uses the difference in readings between two thermometers, one having a wet bulb and the other having a dry bulb, to measure the moisture content or relative humidity of air

A hygrometer, also known as a psychrometer, is an device that is used to measure the humidity in the air. A common way these devices work is by using a material that attracts moisture, and that changes depending on how moist it is. The probably simplest method of these is to use a human hair. The hair will change length, depending on the moisture.

A hygrometer has two bulbs: one wet and one dry. Both bulbs are traditional thermometers, though one is covered with a wet towel. After a period of time, the water on the wet bulb evaporates and at that time, the temperature is measured on each bulb. The difference between the temperatures is noted. Then each is used on a chart to find the relative humidity of that temperature and area. A small difference between the temperature of the bulbs shows a high relative humidity coming from a low evaporation rate. In dry air, evaporation happens faster showing a large difference in temperature thus giving you a low relative humidity.

Example: 30˚C Dry Bulb + 20˚C Wet Bulb = ~40% relative humidity

Preventing Hull Corrosion with ICCP Systems

Although modern hull coatings can provide some protection against corrosion, they seldom offer a complete solution. For this reason, most operators choose to protect their vessels with a purpose-designed impressed current cathodic protection system (ICCP).

Using an arrangement of hull mounted anodes and reference cells connected to a control panel, the ICCP system produces a powerful impressed external current to suppress the natural electrochemical activity on the wetted surface of the hull. This eliminates the formation of aggressive corrosion cells on the surface of plates and avoids the problems, which can exist where dissimilar metals are introduced through welding or brought into proximity by other components such as propellers.

An essential feature of Impressed Current Cathodic Protection (ICCP) systems is that they constantly monitor the electrical potential at the seawater-hull interface and carefully adjust the output to the anodes. Therefore, the system is much more effective and reliable than sacrificial anode systems, where the level of protection is unknown and uncontrollable.

By installing an ICCP system, operators can make significant cost savings in hull maintenance and achieve reductions in fuel costs by having a smooth hull surface. Furthermore, the system will safeguard the owner's investment and ensure greater safety through stronger hull integrity.

Cathelco Ltd. has developed ICCP systems for vessels of every type:

ICCP for container, cruise, tankers, and other ocean-going ships. ICCP for steel-hulled supply, crew, ferries, tugs, yachts, work, fishing, and other

commercial vessels.

ICCP for aluminum-hulled supply, crew, ferries, tugs, yachts work, fishing, and other commercial vessels.

ICCP for military vessels. ICCP for water-jet propulsion systems.

ICCP for container, cruise, tankers & other ocean-going ships

Ships such as container vessels, VLCCs and bulk carriers are usually protected by forward and aft systems.

Forward system. To provide a smooth hull profile, the forward system normally uses circular or elliptical anodes of approximately 100 amps mounted port and starboard. Power can be supplied from a modular or thyristor (SCR) control panel.

Aft system. Linear loop anodes are ideal for installation on large commercial vessels as they provide a high output from a relatively small surface area. Because of their powerful output, one 300 amp anode fitted on each side of the hull gives effective protection. Alternatively, linear anodes can be fitted. Generally, thyristor control panels are used for aft systems on larger vessels, as they are economical and incorporate comprehensive information systems.

ICCP for steel hulled supply, crew, ferries, tugs, yachts, work, fishing & other commercial vessels

The Cathelco Ltd. Minitek System uses the latest technology to protect steel-hulled craft against corrosion. This is achieved by using a compact control panel and an arrangement of anodes and reference cells which are flush mounted on the hull – so there is nothing to interrupt the smooth profile or cause additional drag.

The current to the anodes is constantly monitored and adjusted to provide the "optimum" level of protection at all times. This is far superior to the performance of sacrificial anodes where the amount of protection cannot be easily verified and may be insufficient to prevent corrosion.

Anode life 15 years - unlike sacrificial anodes. Reduced weight in comparison with sacrificial anodes. Flush-mounted anodes to ensure smooth hull profile. No maintenance required. Self-diagnostic system. Operates from 230V or 115V AC. electrical supply. Control panel only measures 500 x 390 x 210 mm for systems up to 40 amps. Lower yard installation costs than recessed sacrificial anodes.

Length,Approximate

SacrificialAnodes

ICCPSystem

WeightAdvantage

25 m 186 kg 40.5 kg 145.5 kg

45 m 465 kg 52 kg 413 kg

60 m 926 kg 85 kg 841 kg

ICCP for aluminum-hulled supply, crew, ferries, tugs, yachts work, fishing & other commercial vessels

Aluminum is generally regarded as a stable material which does not corrode easily. However, when used in conjunction with other metals such as bronze propellers and steel components, serious problems of hull corrosion can arise.

The Cathelco Ltd. Alutek System uses the latest technology to eliminate corrosion on aluminum hulls. Unlike traditional sacrificial anode systems, it uses flush mounted, lightweight anodes and advanced monitoring systems to provide the optimum level of protection. So there is nothing to detract from the smooth lines of your craft or reduce its speed.

Flush mounted anodes keep the hull streamlined.

Reduced weight in comparison with sacrificial anodes. Automatic system - constantly monitors and adjusts output. Operates from 230V or 115V AC. electrical supply. Monitoring electrodes - measure the electrical potential near the dielectric shield Controlling anodes - measure the electrical potential at a remote point on the hull. Shield sensors - detect changes in resistance at the coated aluminum/seawater interface. Lower yard installation costs than recessed sacrificial anodes.

Length,Approximate

SacrificialAnodes

ICCPSystem

WeightAdvantage

25 m 80 kg 52 kg 28 kg

45 m 200 kg 52 kg 148 kg

60 m 400 kg 52 kg 348 kg

95 m 600 kg 52 kg 548 kg

ICCP for military vessels

The Cathelco Ltd. Corrintec Division is a technological leader in the design and manufacture of ICCP systems for naval vessels. Their equipment has been supplied to 22 navies around the world for frigates, guided missile destroyers, fast patrol craft, submarines and fleet auxiliaries.

In addition to a long association with the British Royal Navy, Cathelco Ltd. has supplied equipment to the new generation of high-speed vessels including the U.S. Navy's "X" Craft.

I-Shield and Patroltek by Cathelco Ltd. represent the latest systems in a continuing technological evolution based on the highest levels of product integrity, reliability and performance.

Cathelco Ltd. now protects the USS Missouri. For the full article reprint, please see Cathelco Ltd. Protects Historic Naval Vessel.

ICCP for water-jet propulsion systems

The Cathelco Ltd. Jettek ICCP system provides a unique and highly effective corrosion protection for fast craft. Its reliability has been proved on fast ferries and military high-speed craft around the world, superseding systems solely based on "isolation" methods.

The Problem: Water jet tunnels are particularly vulnerable to corrosion because they are constructed from dissimilar metals, typically aluminum and stainless steel, or high tensile steel and stainless steel. Problems can arise at the interface of these materials resulting in rapid corrosion, which can put the safety and structural integrity of the vessel at risk.

Most high-speed craft are fitted with "isolation" systems to prevent corrosive activity between the dissimilar metals. However, many have a history of repeated failure, indicating that "isolation"’ is not a particularly efficient or successful method of preventing galvanic corrosion.

facsimile recorderIn a facsimile receiver, the device that performs the final conversion of the facsimile picture signal to an image of the object, i.e., makes the recorded copy