Showing posts with label Diving helmets. Show all posts
Showing posts with label Diving helmets. Show all posts

Monday, March 31, 2014

Wooden Ship wheel

Ship's wheel

ship's wheel is used to change its course. Together with the rest of the steering mechanism it forms part of the helm. It is typically connected to a mechanical, electric servo, or hydraulic system. In some modern ships the wheel is replaced with a simple toggle that remotely controls an electro-mechanical or electro-hydraulic drive for the rudder, with a rudder position indicator presenting feedback to the helmsman.
Helmsmen on older ships used a tiller (a horizontal bar fitted directly to the top of the rudder post) or a whipstaff (a vertical stick acting on a tiller).
Early ships' wheels (c. 1700) were operated to correspond to the motion                                          of The design of ships' wheels probably influenced that of the modern steering wheel.
the tiller, with a clockwise motion (corresponding to a right tiller motion) turning the rudder and thus the ship to the left. Eventually the control direction of the wheel was reversed to make it more consistent with the action of a motor vehicle's steering wheel.
A traditional ship's wheel is composed of eight cylindrical wooden spokes (though sometimes as few as six or as many as ten) shaped like balustersand all joined at a central wooden hub or nave (sometimes covered with a brass nave plate) which housed the axle. The square hole at the centre of the hub through which the axle ran is called a drive square and was often lined with a brass plate (and therefore called a brass boss, though this term was used more often to refer to a brass hub and nave plate) which was frequently etched with the name of the wheel's manufacturer. The outer rim is composed of four sections each made up of stacks of three felloes, the facing felloe, the middle felloe, and the after felloe. Because each group of three felloes at one time made up a quarter of the distance around the rim, the entire outer wooden wheel was sometimes called the quadrant. Each spoke ran through the middle felloe creating a series of handles on the outside of the wheel's rim. One of these handles/ spokes was frequently given extra grooves at its tip which could be felt by a helmsman steering in the dark and used by him to determine the exact position of the rudder—this was theking spoke and when it pointed straight upward the rudder was dead straight. The wood used in construction of this type of wheel was most often eitherteak or mahogany.
The steering gear of earlier ships sometimes consisted of a double wheel where each wheel was connected to the other with a wooden spindle that ran through a barrel or drum. The spindle was held up by two pedestals that rested on a wooden platform, often no more than a grate. A tiller rope or chain (sometimes called a steering rope or chain) ran around the barrel in five or six loops and then down through two tiller rope slots at the top of the platform before connecting to two sheaves just below deck (one on either side of the ship's wheel) and thence out to a pair of pulleys before coming back together at the tiller and therefore the ships rudder. Movement of the wheels (which were connected and moved simultaneously) caused the tiller rope to wind in one of two directions and shifted the tiller left or right. In a typical and intuitive arrangement, a helmsman turning the wheel counterclockwise would cause the tiller to move to starboard and therefore the rudder to swing to port causing the vessel to also turn to port.

Wednesday, March 19, 2014

Nautical Compass - Maximus International -


compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the Earth. The frame of reference defines the four cardinal directions (or points) – north, south, east, and west. Intermediate directions are also defined. Usually, a diagram called a compass rose, which shows the directions (with their names usually abbreviated to initials), is marked on the compass. When the compass is in use, the rose is aligned with the real directions in the frame of reference, so, for example, the "N" mark on the rose really points to the north. Frequently, in addition to the rose or sometimes instead of it, angle markings in degrees are shown on
the compass. North corresponds to zero degrees, and the angles increase clockwise, so east is 90 degrees, south is 180, and west is 270. These numbers allow the compass to showazimuths or bearings, which are commonly stated in this notation.
The magnetic compass was first invented as a device for divination as early as the Chinese Han Dynasty (since about 206 BC). The compass was used in Song Dynasty China by the military for navigational orienteering by 1040-1044, and was used for maritime navigation by 1111 to 1117.The use of a compass is,This was supplanted in the early 20th century by the liquid-filled magnetic compass.
recorded in Western Europe between 1187 and 1202, and in Persia in 1232.The dry compass was invented in Europe around 1300.

Types of compasses

There are two widely used and radically different types of compass. The magnetic compass contains a magnet earth's magnetic field and aligns itself to point to the magnetic poles.[14] Simple compasses of this type show directions in a frame of reference in which the directions of the magnetic poles are due north and south. These directions are called magnetic north and magnetic south. The gyro compass (sometimes spelled with a hyphen, or as one word) contains a rapidly spinning wheel whose rotation interacts dynamically with the rotation of the earth so as to make the wheel precess, losing energy to friction until its axis of rotation is parallel with the earth's. The wheel's axis therefore points to the earth's rotational poles, and a frame of reference is used in which the directions of the rotational poles are due north and south. These directions are called true north andtrue south, respectively. The astrocompass works by observing the direction of stars and other celestial bodies.                                                                           
There are other devices which are not conventionally called compasses but which do allow the true cardinal directions to be determined. Some GPSreceivers have two or three antennas, fixed some distance apart to the structure of a vehicle, usually an aircraft or ship. The exact latitudes and longitudes of the antennas can be determined simultaneously, which allows the directions of the cardinal points to be calculated relative to the heading of the aircraft (the direction in which its nose is pointing), rather than to its direction of movement, which will be different if there is a crosswind. They are said to work "like a compass", or "as a compass".
Even a GPS device or similar can be used as compass, since if the receiver is being moved, even at walking pace, it can follow the change of its position, and hence determine the compass bearing of its direction of movement, and hence the directions of the cardinal points relative to its direction of movement. A much older example was the Chinese south-pointing chariot, which worked like a compass by directional dead reckoning. It was initialized by hand, possibly using astronomical observations e.g. of the Pole Star, and thenceforth counteracted every turn that was made to keep its pointer aiming in the desired direction, usually to the south. Watches and sundials can also be used to find compass directions. See their articles for details.
A recent development is the electronic compass which detects the direction without potentially fallible moving parts. This may use a fibre optic gyrocompass or a magnetometer. The magnetometer frequently appears as an optional subsystem built into hand-held GPS receivers and mobile phones. However, magnetic compasses remain popular, especially in remote areas, as they are relatively inexpensive, durable, and require no power supply.

Magnetic compass
The magnetic compass consists of a magnetized pointer (usually marked on the North end) free to align itself with Earth's magnetic field. A compass is any magnetically sensitive device capable of indicating the direction of the magnetic north of a planet's magnetosphere. The face of the compass generally highlights the cardinal points of north, south, east and west. Often, compasses are built as a stand alone sealed instrument with a magnetized bar or needle turning freely upon a pivot, or moving in a fluid, thus able to point in a northerly and southerly direction.
The compass greatly improved the safety and efficiency of travel,
especially ocean travel. A compass can be used to calculate heading, used with a sextant to calculate latitude, and with a marine chronometer to calculate longitude. It thus provides a much improved navigational capability that has only been recently supplanted by modern devices such as the Global Positioning System(GPS).

Thursday, January 30, 2014

Diving helmet - Maximus International -

Diving helmets are worn mainly by professional divers engaged in surface supplied diving, though many models can be adapted for use with scuba equipment.
The helmet seals the whole of the diver's head from the water, allows the diver to see clearly underwater, provides the diver with breathing gas, protects the diver's head when doing heavy or dangerous work, and usually provides voice communications with the surface (and possibly other divers). If a helmeted diver becomes unconscious but is still breathing, the helmet will remain in place and continue to deliver breathing gas until the diver can berescued. In contrast, the scuba regulator typically used by recreational divers must be held in the mouth, otherwise it can fall out of an unconscious diver's mouth and result in drowning[2] (this does not apply to a full face mask which also continues to serve air if the diver is unconscious).
Before the invention of the demand regulator, all diving helmets used a free-flow design. Gas was delivered at a constant rate, regardless of the diver's breathing, and flowed out through an exhaust valve. Most modern helmets incorporate a demand valve so the helmet only delivers breathing gas when the diver inhales. Free-flow helmets use much larger quantities of gas than demand helmets, which can cause logistical difficulties and is very expensive when special breathing gases (such as heliox) are used. They also produce a constant noise inside the helmet, which can cause communication difficulties. Free-flow helmets are still preferred for hazardous materials diving, because their positive-pressure nature can prevent the ingress of hazardous material in case the integrity of the suit or helmet is compromised. They also remain relatively common in shallow-water air diving, where gas consumption is of little concern, and in nuclear diving because they must be disposed of after some period of use due to irradiation; free-flow helmets are significantly less expensive[citation needed] to purchase and maintain than demand types.
Most modern helmet designs are sealed at the neck using a neoprene "neck dam" which is independent of the suit, allowing the diver his choice of suits depending on the dive conditions. When a neck dam is installed into a drysuit, however, the entire body is isolated from the surrounding liquid, giving an additional degree of warmth and protection. When divers must work in hazardous environments such as sewage or dangerous chemicals, a helmet (usually of the free-flow type or using a series exhaust valve system) is sealed to a special drysuit (commonly made of a fabric with a smooth vulcanised rubber outer surface) to completely isolate and protect the diver. This equipment is the modern equivalent of the historic Mark V "Standard Diving Dress".

We at Maximus International india manufacture replica of diving helmets and many other nautical reproductions.