- Brief Overview
- The Project
- The Sussex Marine Trust
- Socio-Economic Impact
- Environmental Impact
- Contact Us
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Simply opening the sea cocks to scuttle the vessel would result in a prolonged 'free surface effect' which would almost certainly result in the capsizing of the vessel. This has the potential to trap air in the ships upturned hull, which may cause the ship to become a floating hazard to shipping. Even if the ship sunk to the seabed without presenting a hazard to shipping, it should be noted that an inverted ship offers a lesser habitat for colonisation by marine life and is less attractive to scuba divers.
The scuttling will therefore have to be achieved with the use of explosive cutting charges to open holes in the ship's hull at strategic locations at fractionally different times during the scuttling process in order to achieve equal and stable flooding of the vessel in order to drop the ship in an upright attitude onto the sea bed.
Complex computer fluid dynamics software will be used to model the flow of water into the different ships compartments from the scuttling holes. These computer models will be used to calculate the best locations, number and sizes for the scuttling holes to be used to create a balanced and stable scuttling.
Explosive Cutting Charges: There are a number of techniques/technologies available for explosively cutting steel. The most efficient use some means of focussing the energy from the detonating explosive so that it cuts or rips the target material in two.
Estimates: The following assumptions have been made about the ship in question, based on data from the Batch 1 Type 42 Destroyers disposed of in 2008 and that gathered from the Scylla Project with allowances being made for the larger nature of a Type 42 Destroyer over that of a Lender Class Frigate like HMS Scylla:
- The hull is mild steel and less than 15mm thick at the keel/10mm thick immediately below the waterline.
- Copper Linear Cutting Charges of 267grams/metre have been used on similar projects (Scylla) to cut the 15mm Mild Steel hull.
- 30 Large diver access holes will be pre-cut in the upper hull of the ship.
- 20 Large diver access holes will be partially pre-cut above the water line*.
- 20 Medium diver accessible scuttling holes will be explosively cut immediately below the waterline.
- 15 Small non-diver accessible holes will be explosively cut below the waterline (engine room)
* using small lengths of cutting charge to complete the partially pre-cut holes, pre-cut holes sealed against water ingress from wave action, using commercial sealant.
This represents a requirement to cut approximately 130 metres of hull steel, using an appropriate cutting charge system. An additional 8 kg of detonating cord and detonators will be required to connect up and initiate the firing sequence.
Eight different explosive options have been proposed and need to be assessed on cost and environmental grounds.
The detonation of explosives near water will result in some water borne shockwaves being generated; if these shockwaves are sufficiently strong they can adversely affect the marine environment. The lower the total explosive mass used, the less affect it will have on the marine environment.
The 267gram per meter (1200 grain per foot) linear cutting charges, as used on HMS Scylla , have been used as a baseline. Using the same type of cutting charges would result in 43 kg of explosive being required to scuttle a Type 42 Destroyer.
Design of Efficient Cutting Charges and Initiation Systems: A number of experimental firings have already been carried out by Live Action FX Ltd at zero cost to the project to establish a baseline for linear cutting charge performance, these firings utilised a series of specially fabricated linear cutting charges (see figures 9 and 10).
These fabricated charges could be developed for proper use on the SinkOne4Sussex project and may provide cost savings and lower shock wave characteristics than using commercially available charges. However, this development work would cost approximately £2,000.
Validation of the Best Explosives Techniques – Performance: The explosive performance (steel cutting capability) and mass of explosive required for each of the eight options has been estimated using the product manufacturers claimed performance figures against a standard Mild Steel target.
Before any of these options can be employed to scuttle a ship a more accurate assessment will be needed to establish true performance figures for the different products against representative targets (the same thickness and type of steel as used in the hull of the ship). This work needs to be carried out on a suitable high explosives firing range and would be expected to cost £8,000.
Environmental Impact of Explosive Techniques: If the environmental impact of the explosives is a concern for the project, this can be assessed.
Once the eight different explosives options have been assessed for performance, a preferred set of up to three options can be down selected for more specific testing, which can assess the shockwaves that are likely to be transmitted through the ship's hull into the surrounding water.
This assessment work needs to be carried out on a suitable high explosives firing range and will require simulated sections of ship's hull to be constructed and backed with water; through which the shockwaves can be measured using high strain transducers. This will also test the chosen options in the configuration that would be used for the actual scuttling, there by establishing complete confidence in the final cutting technique to be used for the project.
Assessing the environmental impact of three (3) different options in this manner is estimated at £9,000.
General Planning, Design and Management: This elements of the scuttling includes the following:
- Determination of Explosive & non-explosive scuttling/access holes.
- Design the blast plan for detonator timings to achieve uniform flooding.
- Site Management of scuttling team.
- Organise: transport, delivery and storage of the explosives.
The total cost of this General Planning, Design and Management of the explosive scuttling element is likely to be in the region of £25,000.
Pyrotechnic/Firework Display to Accompany the Scuttling: As high explosives do not provide a crowd pleasing effect when they are fired (a small flash, a loud bang and some grey smoke) it is usual to enhance such a public spectacle using various pyrotechnics and fireworks.
This could be used for publicity with a VIP or some competition winner pressing the plunger – Live Action FX Ltd has an 1800's functional wooden plunger box that can be made available. The cost of the described pyrotechnic/firework sequence is estimated at £3,000.
Explosives Inspection of Reef Immediately After Scuttling: Before the artificial reef can be checked and declared safe to dive, it must first be declared free from explosives. This will involve the checking of each explosives site to ensure that the charges have functioned correctly. With any remaining charges being made safe and recovered back to a pre-designated area where they can be disposed of.
This inspection can take place within approximately half an hour after the ship has been scuttled and is expected the cost £20,000.
Contingency Plan: The scuttling plan (how many holes, where, of what size and when they open) and blast design (types of cutting charges used, ring main and detonator connections, etc.) will ensure that the ship sinks and settles on the seabed.
However, insurers are always looking at the risks and worst case scenarios. The project insurers may require a contingency plan to be in place in order to deal with the unlikely circumstance of the prevailing conditions nullifying all of the careful calculations and causing the ship to 'turns turtle' – i.e. it capsizes, but remain afloat due to air trapped in the hull.
This unlikely scenario would obviously present a major hazard to shipping and would need to be dealt with quickly.
The proposal is to have two heavy duty sets of linear cutting charges prepared and ready for use on a separate boat. Should the need arise these can be deployed onto the upturned hull of the ship and fired to open holes, allowing the trapped air to escape and sending the ship to the seabed.
Having this contingency plan prepared and ready for use on the scuttling day is estimated at £4,000. Dealing with such a situation without a contingency plan is likely to cost over 6 times this figure!