Resources : Diving Plan
The diving plan below was provided to each member of the dive team and is included here so that it can be reused and adapted for later projects on similar sites.
The site is exposed from east, south and west and waves from the south-west can travel over many miles. The wreck lies on a flat, soft clay seabed in 37m depth plus height of tide. The tides are directed parallel to the coastline running north-west to south-east and vice versa, with the ebb tide being the strongest.
- At spring tide the current reaches 1kt in an east-west direction over the site and the tide height is between 1.0m and 5.5m above LAT, a range of 4.5m
- At neap tide the current reaches a maximum of 0.5 kt and the tide height is between 2.1m and 4.5m above LAT, a range of 2.4m
- The time of slack water is three hours before and three hours after high water at Devonport
- The prevailing wind is from the south-west and the site is exposed from that direction so is affected by significant wave action
- Underwater visibility on site varies between zero and 10m depending on weather during the preceding days
Rules for Dive Team Members
Participation in the A7 project is subject to a number of rules listed below. Failure by a team member to observe these rules will result in their removal from the license to visit the A7 submarine site and may incur extra penalties imposed by the Ministry of Defence if the license terms are breached.
- The license issued for the work is only applicable to divers named on the license so only named divers can visit the site. No guests or visitors will be allowed to dive on the site
- No dives will be undertaken on the site without permission of the project manager
- No attempts will be made to access the inside of the submarine
- Any human remains, clothing or personal effects seen on the site are not to be touched and are to be reported to the project manager, who will report them to the MOD
- No objects of any kind are to be removed from the site without the permission of the project manager. The project manager will obtain any necessary permissions from the MOD
- All photographs and video taken on site or on the dive boat are the property of the A7 Project. No photographs and video from project fieldwork is to be published by any means without the permission of the project manager
- No information, photographs, interviews or other contact with the media is to occur without the permission of the project manager
Each diver will ensure that they have:
- A copy of their diving qualifications logged with the project manager
- A copy of their diving medical logged with the project manager
- A copy of their Nitrox diving qualification logged with the project manager
- A copy of their rebreather qualifications logged with the project manager if a rebreather is to be used
- Signed the A7 Project release and waiver (see Appendix 2)
- Dived to 40m within 1 month of a dive on the site for the Project
- Dive teams will be managed by a Dive Supervisor, nominated by the Project Manager
- A dive team will consist of two divers, the Task Diver and the Safety Diver
- The Safety Diver will provide dive support for the Task Diver who will be undertaking a recording task
- The Safety Diver is responsible for dive management for that dive including dive time, depth, decompression, gas monitoring for both divers. The Task
- Diver will also monitor their own dive time, depth and gas
- The Safety Diver may also be responsible for providing lighting for the Task Diver
- A single dive team of three divers will be allowed where it is not desirable to operate as two separate teams, such as some filming and photography tasks
Dives will be undertaken from the SHIPS Project’s 6.5m RIB Seahorse or In Deep’s dive vessel Seeker
Tide and Currents
Dives will be done at slack tide so water movement on site will be minimal
If divers find that there is a current at the time they are due to dive then the dive is to be aborted.
A dive is to be aborted if the visibility on site is less than 2m
Both divers in a team will each carry a main and a spare torch
The dive is to be aborted in the event of the failure of two of the four torches
Abandoned Fishing Gear and Nets
If abandoned monofilament net is found during a dive then the dive is to be aborted, see note on the First Dive below
Dive Times, Gas Mixes and Decompression
Project dives on the A7 submarine using open circuit SCUBA will use Nitrox 27 (EAN27).
A planned dive to 42m with a maximum 20 minute bottom time (start of descent to start of ascent) on EAN27 requires 15 minutes of stops at 6m. Maximum ascent rate will be 10 metres per minute so ascent time will be 4 minutes.
Total run time for the dive will be 38 minutes.
Actual decompression done by each dive team will be managed by the diver’s own dive computers:
- Each dive computer will be set to the bottom mix of EAN27
- Where possible, each team will be allocated divers using similar types of computer
- If the computers in one team are different then the one computer will be used for controlling decompression times
- The computer used for controlling decompression will be decided before the dive starts
- Divers in a team will undertake the same decompression schedule based on the one selected dive computer
- The type of computer used by each diver will be noted on the Project release form
The seabed depth of the A7 submarine is 37m plus tide height, so the actual depth of water on the site varies between 38m and 42m. The PO2 for open circuit dives on this project is 1.4 bar, and EAN27 has a maximum operating depth (MOD) of 42m at this PO2. With EAN27 the equivalent air depth at 38m is 34.4m and at 42m it is 38.1m.
- Decompression gas will be Nitrox 40, provided in a drop tank deployed at 6m on the mooring line
- Decompression will be done with the dive computers set to EAN27 rather than EAN40 allowing an additional margin of safety
- Divers will carry EAN27 in their pony cylinders rather than the decompression gas EAN40
The pony cylinders will be filled with EAN27 because the pony may need to be used at 42m and the PO2 for EAN40 at this depth is beyond the 1.4 bar limit allowed for dives on this project.
For simplicity, the deeper depth will be assumed for all dives so dives shallower than 42m have an additional safety margin. This avoids the need to tailor gas mixes and decompression according to the state of the tide.
Access to and from the wreck will be via the mooring line installed on the site. Any ascent not using the mooring will be treated as an emergency and the emergency plan will be started, see below.
The support team on the surface will deploy a drop tank full of decompression gas and attach it to the mooring line so it is suspended at 6m depth. The drop tank will have a regulator with two second stages attached to it so the divers should carry out their stops using the gas in this tank. The drop tank regulator will be pressurised but switched off so the divers will need to switch on the gas supply before use.
For timing purposes the end of the dive is the time arriving at the bottom of the mooring, not the time leaving the work area, so the travel time between the two needs to be allowed for.
Dive Computer Failure
Each diver will carry a waterproof card which has the decompression schedule printed on it. The card will be used in the event of failure of all dive computers carried by a dive team so decompression has to be controlled by a dive timer only. The decompression schedule on the card will include additional decompression as a safety factor.
At a rate of 20 litres per minute for light work the volume of gas used for a 20 minute dive plus decompression will be 2300 litres (GAP calculation).
A 15 litre tank filled to 220 bar provides 3300 litres, allowing a 50 bar reserve it provides 2550 litres.
A 2 x 10 litre tank filled to 220 bar provides 4400 litres, allowing a 50 bar reserve it provides 3400 litres.
Actual gas consumption by the divers in the team will be established during the work-up dives.
Time on site uses 20 l/min x 5.2 bar = 104 litres per minute
For 16 minutes this uses 1664 litres
So descent, ascent and decompression uses 626 litres, approximately 42 bar from a 15 litre cylinder.
This suggests that divers using 15 litre cylinders should leave bottom when 90 bar is reached.
There are a number of built-in safety factors:
- A reserve of 50 bar in the main cylinder has been included
- The diver is carrying an additional emergency supply of gas in a 3 litre pony cylinder
- Decompression gas will usually be provided by the drop tank on the mooring, or in the event of a problem a second drop tank attached to the divers delayed SMB
Closed Circuit Rebreathers
Closed circuit rebreathers will be used on the project. Divers wishing to use this equipment must be suitably qualified and experienced in their use.
Dive teams should not get separated underwater. The Safety Diver should concentrate on supporting the Task Diver and should not wander off. In the event of divers becoming separated underwater:
- The divers should spend a minute looking for their buddy but still remaining in visual contact with the wreck
- If the divers are not reunited they should make their way to the bottom of the mooring and wait one minute
- If the divers are still not reunited they should make their way to the surface independently using the mooring, completing any necessary decompression stops
- If a diver loses sight of the wreck then they will send up a delayed SMB and surface up the SMB line, see Uncontrolled Ascents below
Uncontrolled and Emergency Ascents
Normal access to and from the wreck will only be via the mooring line installed on the site.
Any diver or dive team unable to ascend via the mooring line will send up a delayed SMB and surface up the SMB line. The support team on the surface will deploy a drop tank full of decompression gas and attach it to the divers’ marker buoy line so it is suspended at 6m depth. The drop tank will have a regulator with two second stages attached to it so the divers should carry out their stops using the gas in this tank. The drop tank regulator will be pressurised but switched off so the divers will need to switch on the gas supply before use.
If any divers do an uncontrolled ascent and are unable to complete their decompression stops then this is considered to be an emergency. If just one diver fails to complete their stops then the other divers in the team must complete their stops. The dive team on the surface will recover the divers, administer oxygen and contact the emergency services.
In the event of an emergency, all divers will be recalled to the surface. The surface team will let off two thunderflash pyrotechnics in succession, one to alert the divers and the second as confirmation. On hearing this signal any divers on the site will stop work immediately and return to the surface via the mooring line undertaking any required decompression.
A temporary mooring will be installed on the site, preferably located 5m from the bow. This will mean that the entry and exit point to the site will be the same for each dive. It avoids the first divers having to find the sub each time and avoids any accidental damage to the hull by dropping a shot weight on it.
The seabed depth of the A7 submarine is 37m plus tide height, so the actual depth of water on the site varies between 37m and 42m. The mooring will consist of a 25kg steel weight backed up with one or more ground anchors. The mooring line will be 46m long with a large can buoy attached on the surface. A small float will be attached to the mooring rope 5m above the bottom if required to keep the rope away from the submarine at low tide.
The mooring sinker will be installed close to the bow of the submarine with a rope leading from the mooring to the submarine.
The crew of the Coastguard lookout station on Rame Head will be approached to see if they will keep an eye on the mooring buoy for us (01752 847387).
The Marine management organisation will be notified about the deployment of the temporary mooring.
The first dive on the site will need to be done with caution. It is not possible to tell from the sonar images if the wreck is covered in monofilament net. This type of net is a hazard to divers as they can get very tangled in it very quickly. So for the first dive the team will assume the wreck is netted until they can prove otherwise. The risk to divers will be assessed by the first divers on the site. We may be able to remove or tie up a small amount of net so it is no longer a hazard. If we find the site is wrapped in a large amount of net then this will be left in place and diving abandoned.
The first divers will also be tasked with looking for any visible human remains, clothing or personal effects. The type and location will be noted and reported to the dive supervisor and project manager.
Human Remains, Clothing and Personal Effects
A significant point to remember during all operations on this wreck is that it is a war grave and must be treated with respect.
- No intrusive activity will be undertaken. In particular no attempt will be made to enter the hull or to record the interior of the vessel. All photographs and video will be taken from outside the hull.
- If any images taken from outside the hull inadvertently record any human remains these images will not be put into the public domain and will be restricted in circulation to MOD and English Heritage.
- If, in the unlikely event, that human remains are encountered outside the hull the composition and location will be recorded and the matter referred immediately to MOD for further direction. ProMare will then implement the further directions received from MOD at no cost to MOD.
It is not anticipated that ordnance will be found. It is assumed that the torpedoes present on site will be exercise torpedoes which remain within the hull. If any torpedoes are encountered outside the hull they will be recorded but, in accordance with the Project’s ‘no recoveries’ policy, no intrusive activity will be directed at them.
- The existence of any environmental risks encountered e.g. leaking oil, lubricants etc. will be reported to the Project Manager
- Large conger eels live in the submarine so care is needed when working around any holes in the hull
Each diver will ensure that they are carrying the following equipment on each Project dive:
- Dive knife
- Secondary independent air source, such as a pony bottle
- Dive computer plus dive timer or second dive computer
- Delayed surface marker buoy, orange colour
- Underwater torch plus one spare
- Net cutters
- Decompression schedule on a waterproof printed card
- Tools required for the allocated task
- Diving cylinders used on the project must be in test
- Diving regulators used on the project must have been serviced within 12 months
- Rebreathers used on the project must have been serviced within 12 months