REPLACING A GULF STEAM TURBINE 

 

The Wet Submersible and Diver Safety 

            Unlike the mass installations of the Gulf Stream Turbines that can be performed without anyone getting wet, SCUBA divers will be needed to service and replace the Gulf Stream Turbines when they are at their operating depths.  Because the Gulf Stream’s velocities are considerably greater than the speed that a SCUBA diver can swim, a vehicle will be needed to transport the divers to their work. 

Most conventional small submersibles that are used for scientific and personal use have been of the “dry” type.  The operators of these subs remain dry and at one-atmosphere of pressure inside a watertight compartment.  These subs are normally very heavy because their structures must withstand the great hydrostatic pressures at depth and because they must carry heavy ballast to neutralize the buoyancy resulting from the displacement of a large volume of water by the air-containing compartments. 

There is another type of dry sub that has been developed by Deep Flight Submersibles.  It is called the Deep Flight Aviator and it is both much lighter and faster than the conventional dry subs.  In these subs, the occupants are encapsulated in individual low-pressure hull accommodations and the remainder of the sub’s hull is flooded.  Although these dry subs are much faster than the conventional dry subs, like all dry subs, their occupants cannot work outside their pressure-tight capsule.

            Unlike the typical dry sub with its watertight structure, a wet sub’s hull completely floods.  Because they fill with water, the hydrostatic pressures inside and outside the hulls remain in balance, making it possible for them to be much lighter than the typical dry sub.  Because the water pressures inside and outside are equal, the SCUBA divers are able to work outside. 

Obviously, any wet submersible that would be used to service the Gulf Stream Turbines must be faster than the current.  Although the current’s velocities may normally be in the 5-mph to 6.9-mph range, on rare occasions they might reach speeds near the surface of more than 8 mph.  In order for the sub to be able to move latterly across such a current, its top speed should probably be greater than 10 mph.  To reach such speeds with low power requires a clean design.  Because the inside and outside pressures of the flooded submarine will be balanced, the sub can have a streamlined fiberglass hull that can slip through the water with a minimum of drag.

The Omer 4 is a man-powered wet sub that won the 2003 International Submarine Races held at the Naval Warfare Center’s Carerock facility in Bethesda, Maryland.  The Omer 4 proved that it is possible to achieve relatively high speeds with very low power.  Powered by just two hard-pedaling Virginia Polytechnic University students, this craft reached a speed of 8.276 mph.  The maximum power that these students would have been able to produce would probably be less than ¼ horsepower (137.5 foot-pounds per second).  In contrast, those submersibles servicing the Gulf Stream Turbines could be powered by an electric motor of 10 to 20-kW, which would equal 13 to 26-hp.  

There are some important differences between designing a winged underwater craft and an airplane.  An airplane uses the lift produced by its wings to support its weight.  The winged submersible will use its buoyancy to support its weight and use its fins for stability and control.  

Mini-subs usually have neutral buoyancy in order for the pilot to maintain control of the sub when it is moving very slowly.  Some subs are controlled with movable fins, others by small propellers that can be directed in any direction, allowing them to hover.  Because the submersible servicing the Gulf Stream Turbines will be in currents of between 3.5 and 8 mph, their slowest speed would not need to be slower than about 3.3 mph.  Instead of having neutral buoyancy, these subs could have a small amount of positive buoyancy, which could be easily overpowered by those downward forces produced by the sub’s movable hydrofoils.  In other words, instead of the “wings” supporting the sub’s weight to keep the sub from sinking lower, they would counter the weak lifting forces produced by the slight positive buoyancy to prevent the submersible from moving higher.   

Because the submersible will serve as an underwater truck to transport objects of varying weights and densities, it should be equipped with two buoyancy-compensating tanks, one located forward and one aft.  Although the forces produced by the hydrofoils should almost always be more than enough to overpower some negative buoyancy if a heavily loaded sub is moving, those hydrodynamic forces will become weak at slow speeds and disappear at no speed.  Locating the buoyancy-compensating tanks forward and aft would allow the divers to adjust the sub’s buoyancy to allow good control at very low speeds.  Also, should there be a power failure, having slightly more positive buoyancy in the forward buoyancy-compensating tank would allow the pilot to “glide” the sub back to the surface while under full control.

Because other wet submarines normally have neutral buoyancy and are slow, they usually have their front horizontal fins located far forward to provide a long moment arm to increase the ability of the fins to vertically rotate the sub.  A forward placement of the hydrofoils on the much faster submarines that would service the Gulf Stream Turbines could cause control problems however.  This is because they would cause the entire sub to rotate very quickly.  This rotation would further increase the hydrofoil’s angle of attack, which would further increase the rotational force. The result would be that the pilot would be constantly fighting to keep the sub from pitching up and down.  For better stability and control, the front hydrofoil should be located amidship, slightly forward of the of centers of gravity and buoyancy.  These forward fins would be able to rotate in opposite directions to control banking and roll.  The horizontal rear fins would work together to control the sub’s vertical movements, as do the elevators do for an airplane.  

The designers of the submersibles must not only consider the sub’s performance, but how they should be equipped.  Because the pilots will frequently not have any physical reference points outside their cockpits, they could easily become disorientated without the same instrumentation that are used for instrument flying.  The instruments must indicate direction, depth, rates of climb and descent, speed, and attitude (artificial horizon).  In addition, there could be sonar to help the pilots locate the submerged turbines, which, incidentally, should always be approached from the rear.  The sub should also have headlights, floodlights, an acoustical phone system, compartments to carry a collapsed inflatable float and tools, and have a “docking hook” that would allow the sub to be “towed” while positioned for the crew to work.  In addition to supplying enough air to the divers during long decompression stops during ascents from extended times at depth, the air tanks should supply compressed air to power pneumatic tools and to purge water from its buoyancy-compensating tanks.

If the compartments containing the batteries, motors and other electronic gear are strong enough to withstand high hydrostatic pressures, the only thing that would limit a wet sub’s depths would be the absorption of nitrogen by the divers that can cause nitrogen narcosis (rapture of the deep) at depths.  Just as there is considerable individual variation in tolerance to alcohol, there is also a good deal of difference in susceptibility to nitrogen narcosis.  A few divers may be seriously hampered at depths as little as 100 feet, while most divers, though somewhat impaired, can function reasonably well in the 125 to 175 foot range.  Narcosis can be a treacherous problem since divers may become quite drunk without realizing it.  Although time at depth is not an important factor, the greater the depth, the more intense the effect.  When oxygen-helium mixtures are used instead of compressed air (which is 70% nitrogen), it is possible for trained SCUBA divers to go as deep as 2,000 feet.  Although the oxygen-helium mixture will eliminate the dangers of narcosis, it does not reduce the dangers of decompression sickness (the bends), caused by too rapid ascents.  During deep and prolonged dives, the body tissues can become completely saturated with the dissolved gases.  Depending on the level of gas saturation, the decompression times can be extremely long.  For example, if a diver descends to 190 feet and remains at that depth for only 5 minutes, his total ascent time would be 3 minutes and 10 seconds (190 seconds) while ascending no faster than 60 feet per minute.  However, if he were to remain at that depth for 40 minutes, his total ascent time should be 103 minutes and 10 seconds (6,370 seconds), including four decompression stops.  To reduce the absorption of gases that can cause decompression sickness, divers must reach their working depths quickly.  This is because a diver’s bottom time starts when he leaves the surface and ends only when he starts his direct ascent to the surface. 

Because the following wet submersible is clean, it should easily reach speeds of more than 12 mph from less than 20 kilowatts (26.8 hp) of power.  In addition to carrying a large tank of compressed air for the crew to breath during long ascents, that air can be used for operating the pneumatic tools and for inflating floats to lift bottom weights when recovering those Gulf Stream Turbines using them.  In addition to the large air tank, each diver should have personal SCUBA gear readily accessible to provide backup should anything go wrong with the sub’s air system.


 

The submersible in the drawing has twin rudders so that the vertical tail fins will not interfere with an inflating float’s bag, which would be ejected from the top of the sub’s hull.  These fins are short to permit the sub to get close to the valves that are located in the belly of the Gulf Stream Turbines’ buoyancy tanks, behind the rotors.  The protective shield shields the rear diver from the full force of the current while working.  The shield is retractable and can be locked at various heights.  The sub also carries a vacuum tank for removing moisture from those junction boxes that have been re-assembled underwater. There could also be a tank for helium-oxygen mixtures for dives deeper than 200 feet.

                Although the preceding drawings and text contain ideas that can be used in those subs that would be used for servicing the Gulf Stream Turbines, these mini-subs should be designed by marine engineers with experience in this field.  Hawkes Ocean Technologies at www.deepflight.com, has its design and engineering office located in the San Francisco Bay area and their innovative mini-subs demonstrate that they should have the necessary talent to do a good job.  This company is headed by Graham Hawkes, a marine engineer who has created the Deep Flight series of winged submersibles. Other possibilities include Silvercrest Submarines, a British company at www.subarines-ros.com, Global Submarines Oy, Ltd. at www.globalsubmarines.com, and International Venture Craft Corp at www.ivcorp.com.

Removal of Individual Gulf Stream Turbines for Servicing and Repair

If the proper equipment is used, the removal and replacement of the individual Gulf Stream Turbines should not be difficult. (Two drawing from the previous section are repeated here because it would otherwise be difficult to understand the replacement process without referring to them.)  Using a wet sub to reach the submerged machine, the divers must first turn off the power at the waterproof switch that is located on the electricity collecting cable assembly.  This will disconnect the unit’s generators from the collecting cable and cut the current from the grid that has been energizing the generator’s stators, killing the generator’s ability to produce electricity.  The waterproof junction box between the electricity collecting cable assembly and the electricity extension cable is then separated into its two parts.  The connection between the anchor line and the ring that supports the electricity collecting cable segment is then unhooked.



With the electricity extension cable disconnected from the electricity collecting cable and the electricity collecting cable segments unhooked from the anchor line, there will no longer be any physical connection between the Gulf Stream Turbine and the rest of the submerged generating system.  Because the machine will no longer be producing electricity, its two rotors will spin freely, which will result in a reduction in drag and the proportional downward vector force.  If the Gulf Stream Turbine is not being held down by a bottom weight, this reduction in the downward vector force will allow the Gulf Stream Turbine to ascend to the surface, still attached to its anchor line. 

For those machines that are using bottom weights, an additional lifting force will be required.  The best way to do that is to increase the buoyancy by adding external flotation. Because the volumes of a gas are inversely proportional to their pressures, a balloon-like float would work beautifully for this purpose because it will become increasingly buoyant as it is ascending into decreasing pressures.  Another advantage of the inflatable floats for lifting the floats is that, when deflated, they can be folded into a small volume, much like a packed parachute, for stowing in the submersible.

            Projecting downward from the bottom of the inflatable float would have a tube with a spring-loaded check valve that would open only if the float’s interior pressures exceeded the outside pressures.  There would be a fitting located between this check valve and the float’s bag to which an air hose can be attached to inflate the float.  When the compressed air is being released into the float’s expanding bag, it will expand and will start lifting the bottom weight off ocean floor.  After the inflating float has lifted the bottom the weight from the bottom and has started to slowly rise to the surface, the compressed air hose can be disconnected.  Then, as the float continues to rise higher and higher, the resulting decreasing water pressures will cause the air inside the bag to expand to further increasing the float’s buoyancy sufficiently to lift the Gulf Stream Turbine, its anchor line, and the suspended bottom weight to the surface.


Returning Individual Units to Service

When returning an individual Gulf Stream Turbine, it must be pulled down to its operating depth with a bottom weight and a bottom weight line of the proper length.  Once the unit is at operating depth, the electricity collecting cable assembly is reconnected to the anchor line.  This job would be difficult if the electricity extension cable were not already secured to the side of the anchor line extension.  Because the extension cable is attached to the anchor line extension, the two parts of the junction box will be where they can be easily joined.   

The re-hooking of the connection between the anchor line and the electricity collecting cable segments would also be difficult without a good plan and the proper equipment.  One way to pull the electricity collecting cable forward to re-establish the linkage would be to use a block and tackle that is combined with a pneumatically powered winch.  Working from his wet sub’s cockpit, the diver would first attach the device to the anchor line.  Then the sub could be backed off far enough for the diver to attach the opposite end of the device to the ring that is used for supporting the electricity collecting cable segment.  When the two ends of the device are connected to the anchor line and the collecting cable segment, the diver attaches an air house to power the pneumatic which pulls the two ends of the device close together.  After they are close together, the diver re-hooks the connection and removes the device.

After the two parts of the junction box have been re-joined and tightened, it will be full of water.  Projecting downward from the bottom of the junction box are two small pipes, each having a valve and a capped end.  The caps are removed from the pipes’ ends and a compressed-air hose is connected to one of the pipes.   Both the valves are then opened and the compressed air drives all the water from the other pipe.  Both valves are then closed and the air hose is replaced with a hose connected to a tank that has a strong vacuum.  The valve to that hose is then re-opened and the vacuum sucks out any remaining water and moisture, and lowers the box’s internal pressure to a fraction of one atmosphere.  The valve is again shut and, the hose removed, and the two caps returned to ends of two pipes.  The vacuum inside the sealed junction box should cause the remaining moisture inside the box to vaporize and prevent any condensation from forming on the box’s interior surfaces.  The underwater switch can than be turned to the “on” position, which will put the Gulf Stream Turbine back in business. 




 

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