New ship will remain stable by creating its own inner waves
A model of the Offshore Accommodation Vessel, riding out the waves in a test tank (Photo: SINTEF)
When offshore oil drilling rigs are being installed, serviced or dismantled, the workers typically stay in cabins located on adjacent floating platforms. These semi-submersible platforms are towed into place (or travel under their own power) and then their hulls are partially filled with water, allowing them to remain somewhat stable in the pitching seas. Now, a ship is being built to serve the same purpose, but that will be a much more mobile alternative. It will keep from rolling with the waves by generating its own waves, inside its hull.
Called the Offshore Accommodation Vessel, the ship will have water-filled tanks built into the bottom and sides of its hull. In cross-section, the tanks will have a U shape, hence their being known as “U-tanks.”
Air valves located at the top of each U-tank will control the direction and rate at which the water inside sloshes back and forth. The idea is that by setting the motion of the water in the tanks to counteract the motion of the waves in the surrounding ocean, the rolling of the ship will be minimized. As can be seen in the following video of a model in a test tank, the concept does indeed appear to work.
The ship will also be equipped with six pod-like azimuth thrusters, each of which can rotate independently to allow the vessel to hold its position relative to the rig. This will be particularly important as workers are walking back and forth between the two, via the ship’s telescoping 55.5-meter (189-ft) gangway. Those thrusters will also provide the forward propulsion while the ship is in transit.
The 155-meter (509-ft) Offshore Accommodation Vessel was designed by Norway’s Salt Ship Design and MARINTEK, which is a division of the SINTEF research group. It is being built by Hyundai Heavy Industries under contract for Edda Accommodation. Once completed in June 2015, it will be able to accommodate 800 people. Along with cabins and office space, it will also feature a gym, sauna, two swimming pools, conference rooms and an auditorium.
A second similar vessel may also be on the way.
Sources: MARINTEK, Edda Accommodation
About the Author
An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.
All articles by Ben Coxworth
So basically a hydraulic version of a tuned mass damper? What took them so long?
Heaven help the users if the 'waves' and the waves ever get in synch! Like the TV weather forecasters called "a confused swell". Remember those cars that tried to pioneer 'active' suspension, pumping oil from left to right sides, good until speed overtook the capacity to react.
There was one steamship, before WW1, that was built with a lengthwise tank partially full of water. The tank could roll back and forth to dampen motion.
It worked but only in sea conditions where the wave period was long enough for the internal tank to stabilize between waves. When the waves got too large and/or too close together, the system made the roll worse.
Also look up the Steamship Eastland. It was built top heavy and after the Titanic sinking, more lifeboats were added, making it even more top heavy. With all the ballast tanks full it was stable but the draft increased. It capsized in 1914 at dockside while loading passengers. It was refloated, the upper decks removed and converted to the gunboat Willmette. With the top weight removed and a crew of only 375, stability was no longer a problem, but the refit was completed too late to see service in the Great War. (It wasn't WW1 until WW2 started.)
Ideal also for Submersible launching & Submarine Rescue
Tender to offshore rigs, Medevac Use
Fireboat to offshore rigs
Exploration research ship type.
I think gyroscopic stabilization would work better as it does not have to be synced to the wave motion.
This is not a new idea, but might be a new implementation. I've sailed on ships that had active stability tanks that used large pumps with stability tanks going from side to side.
I've seen a similar strategy used to stabilize transmission monopole masts. Tanks are mounted inside the tubular mast with tune-able baffles. Ethylene Glycol (antifreeze) is used as the liquid and the system is tuned so that the mast's natural vibration in the wind is counter-balanced by the sloshing of the fluid. The system is passive and has no power supply.
Auckland's Sky Tower uses this technique for example.
Over 160,000 people receive our email newsletter
See the stories that matter in your inbox every morning