Author Archives: pauljackman

AIS now fitted

AIS Transponder on Defiance

AIS Transponder on Defiance

AIS on-board

Defiance has been fitted with an Automatic Identification System or AIS for short.  It is not compulsory for vessels to have AIS. Only larger vessels of 300 tons or more and passenger vessels are required to have it. AIS is an additional safety system on the boat and it has been fitted to improve the safety of passengers on-board.

Uses of AIS

The information can be used in several ways:

  1. Collision Avoidance
    The speed, direction and location of vessels close by can be used to calculate if they are on a collision course with you. AIS receivers have alarms to warn if there is a possible risk to enable early action to be taken. With divers in the water the identity of the approaching vessel can be used to directly call them to avoiding action. A great safety tool.
  2. Vessel Traffic Services, Fishing monitoring and control, Maritime Security
    Not very relevant to smaller craft but large vessels can be monitored and tracked through busy shipping areas.
  3. Aid to Navigation
    Ports, Buoys and other navigation aids such as lighthouses are often fitted with AIS transmitters to aid navigation. These positions will show up on plotters to help with navigation. It is possible for virtual transmissions to be sent to mark points that will show up on the ships plotter
  4. Search and Rescue
    Not only is the last position and data of a vessel recorded to help in search and rescue. The system also identifies ships in the area that can be used to assist in any emergency.
  5. Accident investigation
    The tracks of vessels leading up to a collision or other incident is vital to understanding the actions of the captains and a great help in accident investigation.

How does AIS Work?

The system contains three major parts linked into a box of tricks:

  1. A position location receiver such as a GPS receiver, Galileo or Loran
  2. A VHF Receiver to receive details from other vessels
  3. A VHF Transmitter to send details of the vessel

The system uses the GPS position of the vessel to calculate the speed and direction of the boat. This information is then broadcast by a VHF transmitter to other craft in the area. Likewise all other vessels transmit similar information. So the basic information gathered for all vessels is:

  • Identity including the unique Marine Mobile Identity Service Number (MMSI)
  • Time of message
  • Position sent as latitude and longditude
  • Speed and Heading
AIS track of Defiance during testing. Shown on Marine Traffic Website

AIS track of Defiance during testing. Shown on Marine Traffic Website

This information can be picked up and displayed for all to see. For example on Marine Traffic Website. Applications for moble phones as well as most modern chart plotters can display AIS information. Most systems have some type of display, but this is not actually necessary.

In addition to the basic information the name, size and destination along with much more information is possible.

This information is transmitted regularly by the boat usually every 30 seconds but more complex systems can alter this depending on speed. e.g. at anchor they will only transmit every 3 minutes but at high speed may transmit every 2 seconds, which is as fast as conventional Radar systems. These systems use a special system called SOTDMA ( Self-Organized Time Division Multiple Access) which books time slots when they will transmit data. Simpler systems use carrier-sense time-division multiple-access (CSTDMA) whereby they look for a free slot to transmit just before making their transmission.

AIS uses VHF channels 87B (161.975 MHz) and 88B (162.025 MHz). The Class A transmitters transmit at 12.5W which are the type used on large vessels. Class B transmitters are used on smaller craft and transmit at 2W meaning they can broadcast their information between 5-10 miles. Large vessels are required to have some type of visual display on board, but this is not true for Class B transmitters.

 

 

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Winter Boat Trips

As winter approaches we generally think that it will be dark and grey. However, if we seize those sunny days for a winter boat trip we can see our country at its best. Cold crisp days are ideal for a trip like this one a few days ago. Sea conditions can be be exceptionally good and these are the days to see our beautiful coastline such as the Severn Sisters Country Park and Beachy Head.

Beachy Head

Beachy Head

What makes winter boat trips extra special is the potential for very good visibility which you do not seem to get in the summer months when the heat often gives a haze or mist in the distance. The sun being much lower allows us to see the countours of the coastline highlighted by the shadows. The sun often treats us to much warmer yellow tones in the afternoon making the landscape seem much warmer.

Approaching Beachy Head

Approaching Beachy Head

The retun trip from Brighton to Beachy Head takes about 4 hours. On the way, the activity of Brighton gives way to residential areas of Rottingdean and Saltdean, but before getting there the imposing Roedean School standing alone on the cliff top can be seen. Other notible landmarks such Blind Veterans UK and Rottingdean Windmill can be seen, before crossing the Greenwich Meridian. Following this the port of Newhaven and Seaford Bay is passed before the Seven Sisters cliffs lead up to Beachy Head.

Beach Head Light House

Beach Head Light House


This is a relaxed trip with plenty to see and one of the longer winter boat trips available from Brighton. Alternative shorter trips are along Brighton Seafront which will take about an hour.

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Queue for the Dive Lift

The dive lift is a standard accessory to any good dive boat these days. I had one fitted as soon as I purchased the boat. Just because, I felt it was no longer a luxury but something that should be part of any good dive operation. The first dive lift I came across was in Skin Deep in the days of Andy Smith. Designed by Len Hurdiss it was a revolution to the diving at the time.

The problem is that it now seems too popular at times. Here you see a queue already forming to use the lift.

Divers waiting to get on the dive lift

Divers waiting to get on the dive lift

What is a Dive Lift

Technically a dive lift is a man-over-board recovery device. A dive lift is a platform which can be lowered into the water to recover people from the water. As divers seem very keen on doing this the MOB system seems very useful. For divers it is a stress free way to be picked up out of the water and be raised to deck level for them to step off for an easy return to the boat.

Diver stepping onto the dive lift

Diver stepping onto the dive lift

The platform lowers into the water to a depth of a few feet so a small bend of the knees enables the diver to stand upright onto the dive lift. Once the crew see the diver is stable the lift is raised to the deck level.

Diver on-board

Diver on-board

Once at deck level the diver can walk off the lift to the seating to get unkitted without the fear that the exertion of climbing a ladder could raise issues for of DCS. Te diver ussually has a big smirk on his face at this point, particularly if he has not used a dive lift before.

The best dive lift

This picture shows the commercial dive lifts that lower the diver right down to the wreck. This may be some time off for the recreational diver.

Commercial dive cage

Commercial dive cage

 

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Tagged Black Bream

The Sussex Inshore Fisheries & Conservation Authority (IFCA) has released tagged black bream into the Sussex Coastal Waters. The area of the release is Kingmere Rocks, the newly designated Marine Conservation Zone.

The purpose of taggingthe fish is to gain an understanding of the movement and behaviour of black bream. This information will be used to improve the management of the conservation zone.

The project relies on the information returned for the tagged black bream. The involvement of fishermen to report any tagged fish they may catchis paramount. As an incentive IFCA are running a prize draw to those returning information.

The plastic identification tags are attached next to the dorsal fin (the large fin at the top) and are about 75mm long. They come in three colours: flourescent green, red or blue.  Each tag has a reference number on it, which is used to identify the particular fish. The Green tags are particularly important as the fish has an acoustic tracking device fitted.

It is very important to return all fish unharmed if they are caught. You can download the original document from IFCA which gives further details on what to do if you find a tagged black bream

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Compressed Air Purity for divers

Standard BSEN12021

Compressed air used by divers should conform to BS EN12021. This standard gives the basic parameters for the composition of the air and the limitfor for contaminants that are often found in breathing air. These limits are based on a value that is 10% of the 8-hour time weighted average in the workplace in the UK. (Carbon Monoxide is 8%).

Oxygen

Oxygen (O2) should make 21% (±1%)by volume in dry air.

Lubricants

Lubricants such as oil droplets/mist must not exceed 0.5mg/m³

Carbon Dioxide

Carbon Dioxide (CO2) must no exceed 500ml/m³ (or 500ppm)

Carbon Monoxide

Carbon Monoxide (CO) shall be as low as possible and must not exseed 3.5mg/m³ (or 3ppm)

Water content

for a cylinder pressure greater than 200bar measured at the outlet must not exceed 35mg/m³

Other

The air must be without significant odour or taste.

Air Purity Testing

BSEN12021 specifies that the air purity should be at least tested every 3 months. For clubs operating their own compressor who need not strictly comply with this standard should have the air tested every year as an absolute minimum and again after any work or maintenance that may affect the air purity.

In addition to these parameters the compressor manufacturer may also specify that tests for specific chemicals be carried out. The compressor operator should also test for contaminents in the vicinity that may find their way into the system. A good example may be a test for chlorine if the compressor is located near a swimming pool.

Air Purity Test

Firstly you will need to fill a cylinder from the compressor. The cylinder should be clean, a freshly oxygen cleaned cylinder is ideal, this will minimise any contaminants that may have built up inside a frequently used cylinder. The compressor should be run up to it’s normal working temperature and in normal conditions. The cylinder should be empty to start with and filled to at least 100Bar. The air cylinder should then be emptied again and then filled for testing. Doing this will reduce the contaminants that may have been in the existing air in the cylinder down to a minimal level.

There are many ways to test for air purity. The following is a simple method using gas detection tubes. Most detection tubes require a fixed volume of air to pass through them. This can be done using a fixed volume syringe type pump that will be available from the manufacturer. The following example uses a constant flow valve.

Step 1 – fit flow regulator

Firstly a regulator is fitted to the cylinder that will provide a fixed flow of gas from the cylinder under test.

Flow regulating valve fitted to cylinder

Flow regulating valve fitted to cylinder

Step 2 – Fit gas detector tube

With the test tube in place the regulator is turned on to provide a fixed flow rate that is specified for the tube. The tube will also have a time that the test flow should be allowed to run through the tube. It is very important to allow free flow of gas through the tube and not to restrict the outlet.

Gas detector tube fitted to flow regulator

Gas detector tube fitted to flow regulator

 Step 3 – Take the reading

During the test the reagent in the tube will change colour in proportion tot he amount of contaminent in the sample. At the end of the test the measurement can be read of the scale where the reagent has changed colour.

Colour change in tube during test

Colour change in tube during test

Step 4 – Repeat for other contaminents

Each tube is designed to detect a specific contaminant in a specific range. So the test is repeated with all the relevant tubes necessary.

The instructions with the tube will give the color change as well as the time and flow (or volume) of gas that should be used during the test. |Other parameters such as corrections for temperature and which other contaminants may give rise to a false reading are detailed. Lastly instructions for safe disposal information and first aid for the chemicals in the tubes are included.

Example of test tube

Example of test tube

Further guidance can be found from the Health and Safety Exective Divers Breathing Air Standard

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Cylinder – Hydro Test

A hydro static or hydro test is performed once every 5 years on diving cylinders. Before the Hydro test the cylinder will need to be visually inspected. You may want to read the post on the visual test

Step 1 – Fill with water

The cylinder is filled with water. Liquid is used as it does not compress greatly under pressure. So if a cylinder does fail there is not a great mass of expanding gas to cause damage.

Filling a cylinder with water

Filling a cylinder with water

Step 2 – Fit test adapter

A hydraulic hose is fitted into the cylinder with a connector to attach to the hydraulic pump

Fitting the hydraulic hose

Fitting the hydraulic hose

Step 3 – Connect to Hydraulic pump

The cylinder is dropped into the water jacket and the hose is connected to the hydraulic pump. This is done by a fitting in the side of the water jacket.

Placing the cylinder into the water jacket

Placing the cylinder into the water jacket

The test hose is connected to the hydraulic pump through a fitting inthe jacket

The test hose is connected to the hydraulic pump through a fitting inthe jacket

The lid of the water jacket is then then fitted which has a water tight seal. The jacket is then purged of air with water. The level of the water is set on a graduated tube attached to the jacket.

Step 4 – The Hydro Test

The cylinder is then pumped to the test pressure. This is usually 1.5x the working pressure so 348Bar for a standard 232Bar cylinder. The pressure is then held for 30 seconds.

Pressurising the cylinder

Pressurising the cylinder

As the pressure increases the cylinder will stretch. As it does so the water in the jacket is displaced and the amount of displacement is measured on the graduated tube. When the pressure releases the cylinder relaxes and the water level drops below the initial level. The amount of water displaced during the pressure cycle and after is used to calculate the permanent set of the cylinder.

The cylinder is then removed from the jacket and emptied of water.

Step 5 – Drying

Water inside a cylinder is not good so it must be dried. If left in the cylinder will rust, even a short exposure to the atmophere can cause flash rusting. Once empty the cylinder is inverted over a steam jet. This heats the cylinder and with the addition of chemicals the cylinder can be hot oxygen cleaned. When hot the cylinder is dryed with an air jet and again inspected internally to ensure all the water is removed. The main danger of cold oxygen cleaning of cylinders is the fact that it is almost impossible to dry the cylinder adequately or fast enough.

Drying with an air jet

Drying with an air jet

Step 6 – Stamping the cylinder

This is done with a set of punches. The year and month of the test is put on the cylinder along with the test stations unique identification stamp. A “V” is stamped at the end if the cylinder has just had a mid-term inspection and not a full hyro test.

Stamping the cylinder

Stamping the cylinder

Step 7 – Refitting the valve

The valve is re-inserted into the cylinder with a new O’ring. A tool is inserted into the valve outlet and a torque wrench is fitted so the valve is fitted to the correct setting. If this is done the cylinder does not leak. It is not acceptable to fit the cylinder valve with a spanner and a hammer.

Replacing the valve with a torque wrench

Replacing the valve with a torque wrench

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Cylinder – Visual Test

A visual test or  inspection of a diving cylinder is made before a hydrostatic test is made. It is also done half way between the hydrostatic test cycle to verify the condition of the cylinder.

You may also want to read about the  Hydrostatic test next, or the taking the cylinder valve apart

Step 1 – Checking the threads

The first step is to inspect the threads for damage and to gauge them to see if they are in tolerance.  This is done with a pair of calibrated gauges called the “GO” and “NO-GO” gauge. Simply the GO should wind on or into the thread and the NO-GO should not. Threads are one of the major causes of cylinders to fail and usually it is due to maintenance by non-trained persons.

Gauging the valve thread

Gauging the valve thread

Gauging the outlet thread

Gauging the outlet thread

Gauging the cylinder thread

Gauging the cylinder thread

Step 2 – Visual Inspection

This is done externally and internally. Externally the boot is removed and the general condition of the cylinder is checked. Defective paint will not fail a cylinder. Deep rust marks and damage are the problem. Internal visual inspection is done by using a bright light and endoscope. This can even look back a the shoulder of the valve internally. Deep rust marks are the issue. Cylinders may have a light rusting over the inside. This is not a fail.

Looking inside a cylinder

Looking inside a cylinder

 

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Cylinder Testing – Cylinder Valve

The first part of a cylinder test whether it is hydrostatic or visual is to remove and disassemble the valve.

Step 1 – Remove the handle

This is done with a special flat bladed tool that straddles the centre thread. This one is in fact made from a flat bit. This is done so that it can be attached to an impact driver, as they can become difficult to remove after a couple of years use. The nut once removed allows the spring, then the handle and finally the nylon washer to be removed.

Removing the handle

Removing the handle

 Step 2 – Remove the screw mechanism

Removing the screw mechanism

Removing the screw mechanism

Next the screw mechanism is removed. This is done by unscrewing the nut at the end of the valve. Once removed the spindle should be removed from the cylinder valve. There is a nylon washer on the shaft and o’ring seals at either end of the body.

The screw mechanism

The screw mechanism

Step 3 – Valve Seat

The final step is to remove the valve seat itself. There are various types. Some are all nylon whilst others like the one pictured are brass with a nylon face. This one has a slot in the back that the blade on the spindle fits into. Others are the reverse with the spindle having a saddle that fits over a flat on the back of the seat. All are basically the same.

Valve seat removed with a screwdriver

Valve seat removed with a screwdriver

Step 4 – Remove the cylinder valve

Lastly a tool is inserted into the valve and very delicately loosened with the aid of a large hammer. A-Clamp valves have an adapter that fits over the body to allow the DIN tool to be used. Spanners are not recommended as they will damage the chrome and brass of the valve.

Removing the valve

Removing the valve

These parts are then put to one side, cleaned and serviced with new O’rings. Information on cleaning can be found here which details cleaning of a regulator first stage

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Clan Macmillan

Position – 50 34.78N 0 15.42W

Circumstances of loss

Date of loss – 23 March 1917 sunk by torpedo

Voyage – London – Glasgow with a cargo of Coir

History

The Clan Macmillan was torpedoed by UB39. The ship had returned from Chittagong where she unloaded and then proceded to Glasgow with the remains of her cargo, 50 tons of coir matting. The torpedo struck her starboard side amidships at 0055 and the crew ababndoned ship. A second torpedo then struck. The U boat came alongside the lifeboats where the captain hid. The U boat then departed.

Specifications

Built – 1902 – W Doxford, Sunderland

Owners – W Runcian & Co, Moor Line

Dimensions – 3753 tons 104m x 14m x 7m

Diving Information

The Clan Macmillan lies upright in a general depth of 60m. The Clan Macmillan is often listed as being inshore off Newhaven near the Clodmoor. The two wrecks off Newhaven are both parts of the Clodmoor.

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Clodmoor

Position – 50 43.60N 0 00.62E & 50 43.42N 0 00.64E

Circumstances of loss

Date of loss – 03 May1917 sunk by torpedo

Voyage – Bahia Blanca – Newcastle with a cargo of wheat

History

The Clodmoor was torpedoed in No 2 hold by UB48 at 3:30 and was abandoned 3 hours later. The survibors were taken off and landed at Newhaven. The ship sank at 19:59 that same evening.

The Clodmoor was commissioned by the Admiralty from 24 Feb, 1916 until 20 March, 1916  as HM Collier 1069.  She then transfered to the Italian government until 3 July, 1916 when she returned to the UK for collier duties, followed by a Royal Commission to transport wheat.

Specifications

Built – 1902 – W Doxford, Sunderland

Owners – W Runcian & Co, Moor Line

Dimensions – 3753 tons 104m x 14m x 7m

Diving Information

The Clodmoor lies broken in two in a general depth of 20m. The wreck has often been listed as two wrecks. The Clodmoor and the Clan MacMillan. The Clan Macmillan lies offshore and has now been positively identified.

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