The Challenges of ROV Operations in the Southeastern United States – Tantangan Operasional dari ROV di Amerika Serikat Bagian Tenggara

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The Challenges of ROV Operations in the Southeastern United States

by Chris Ritter, Global Foundation for Ocean Exploration
November 18, 2019

Imaged by its camera sled ROV Seirios, ROV Deep Discoverer explores some interesting, yet potentially dangerous, geology on the Pourtalès Terrace during Dive 10 of the 2019 Southeastern U.S. Deep-sea Exploration.

Imaged by its camera sled ROV Seirios, ROV Deep Discoverer explores some interesting, yet potentially dangerous, geology on the Pourtalès Terrace during Dive 10 of the 2019 Southeastern U.S. Deep-sea Exploration. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2019 Southeastern U.S. Deep-sea Exploration. Download larger version (jpg, 304 KB).

 

Whenever NOAA Ship Okeanos Explorer plans to explore off the southeast coast of the United States, we know there will be challenges. No matter how much we anticipate and plan for them, it’s always disappointing when we’re unable to deploy the remotely operated vehicles (ROV) and share the wonders of the deep with scientists and other dedicated followers who join us live online. The 2019 Southeastern U.S. Deep-sea Exploration cruise has certainly had its fair share of challenges and lost dive days. Here’s a little insight into the factors that have been guiding our dive/no dive decisions.

 

The Dangers

Potentially dangerous situations are inherent in ROV operations during launch and recovery and while operating at depth. During launch and recovery, deck crew and ROV engineers are on the back deck of the ship assisting with operations. In rough weather (i.e., wind over ~25 knots or 29 miles per hour and waves over ~6 feet), the ship motions could become so extreme that the deck crew could lose footing on deck, or the ROVs could swing unsafely while being lifted by the crane. It’s part of the dive supervisor’s job to help minimize the operational risks for personnel on deck.

The dangers of operations are not limited to launch and recovery. While descending and ascending in the water column, the cable that attaches the ROVs to the ship can become entangled in the ship’s propellers or rudders if the ship is not making proper forward way through the water. On the seafloor, there are concerns that the currents could push the vehicles into geological features. The dive supervisor helps manage ship speed and movements so that both the ROVs and ship are not harmed during operations.

 

The Decision-Making

There is no formula that we can use to decide whether or not it’s safe to dive. When preparing for a deepwater ROV dive, the navigator, dive supervisor, and ship operators study the three major forces acting on the ship. These major forces are the wind, the seas (i.e., the waves), and the currents.

At most dive locations around the world, the wind and seas are the predominant forces. If these two forces are minimal, the dive supervisor and commanding officer usually give the “green light” for a dive. This is not the case in the waters of the Atlantic off the Southeastern U.S. because of the Gulf Stream, which is a strong ocean current that brings warm water from the Gulf of Mexico into the Atlantic Ocean and extends along the eastern coast of the United States and Canada.

The Gulf Stream direction and magnitude is modeled by the U.S. Navy Coastal Ocean Model (NCOM), which is a high resolution model that offers ocean current data at a 2 nautical mile (2.3 mile) resolution every 24 hours. The navigator, dive supervisor, and ship operators use this model output to very roughly estimate expected currents at each dive site. Image courtesy of NOAA Ocean Prediction Center.

The Gulf Stream direction and magnitude is modeled by the U.S. Navy Coastal Ocean Model (NCOM), which is a high-resolution model that offers ocean current data at a 2 nautical mile (2.3 mile) resolution every 24 hours. The navigator, dive supervisor, and ship operators use this model output to very roughly estimate expected currents at each dive site. Image courtesy of NOAA Ocean Prediction Center. Download larger version (jpg, 344 KB).

For almost all the ROV dives during the 2019 Southeastern U.S. Deep-sea Exploration, the Gulf Stream has been the predominant force on the ship. Surface currents such as the Gulf Stream affect the ship’s ability to hold position during a dive and affect how the vehicles stream behind the ship during launch and recovery when the vehicles are in the water column. Since the Gulf Stream is such a large, consistent, and high-magnitude force, there are also subsurface currents that affect the ROVs during their descent, ascent, and throughout the dive while on bottom.

The ROV team on the Okeanos Explorer uses an acoustic Doppler current profiler (ADCP) to estimate surface and subsurface currents. The figures below show readings from the ADCP taken at a dive site that was deemed unsafe for dive operations on the day we were there. The figure on the left displays the surface current direction and magnitude and the figure on the right displays the subsurface current profile throughout the water column. Although the 2.2 knots (2.5 miles per hour) of surface current are much higher than seen at a typical dive site, this alone did not lead to the decision to cancel the dive. With a bottom depth of about 500 meters (1,640 feet), the subsurface current profile shows about a 0.5 meter/second (~ 1 knot, or 1.7 miles per hour) current close to the bottom. This situation isn’t safe for the ROVs, and thus we made the difficult decision to cancel the dive.

The conditions on November 14, 2019, were unfavorable for diving. The readings on that day from the acoustic Doppler current profiler show the surface current direction and magnitude (left) and the subsurface current profile throughout the water column (right).

The conditions on November 14, 2019, were unfavorable for diving. The readings on that day from the acoustic Doppler current profiler show the surface current direction and magnitude (left) and the subsurface current profile throughout the water column (right). Image courtesy of the NOAA Office of Marine and Aviation Operations. Download larger version (jpg, 277 KB).

 

Why It’s Worth It

The Gulf Stream isn’t all bad though! It’s a big reason why these dive sites are so valuable to the scientific community (and so interesting for those who follow the dives online). The warm Gulf Stream currents bring nutrients and help sustain life like that found among the deep, dense, and diverse coral communities that we’ve been documenting throughout this expedition. With some of the imagery, samples, and data that have been collected at these dive sites, it’s easy to see why diving near the Gulf Stream can be worth its challenges.

Marine life was both abundant and diverse on the Central Blake Plateau, an area through which the Gulf Stream passes, during Dive 06 of the 2019 Southeastern U.S. Deep-sea Exploration.

Marine life was both abundant and diverse on the Central Blake Plateau, an area through which the Gulf Stream passes, during Dive 06 of the 2019 Southeastern U.S. Deep-sea Exploration. Image courtesy of the NOAA Office of Ocean Exploration and Research, 2019 Southeastern U.S. Deep-sea Exploration.Download larger version (jpg, 1.4 MB).

Terjemahan Bebas oleh Ir. Russel Effandy, Dip. CII.:

Tantangan Operasi ROV di Amerika Serikat Bagian Tenggara

oleh Chris Ritter, Yayasan Global untuk Eksplorasi Laut
18 November 2019

 

Imaged by its camera sled ROV Seirios, ROV Deep Discoverer explores some interesting, yet potentially dangerous, geology on the Pourtalès Terrace during Dive 10 of the 2019 Southeastern U.S. Deep-sea Exploration.Digambarkan oleh kereta luncur kamera ROV Seirios, ROV Deep Discoverer mengeksplorasi beberapa geologi yang menarik, namun berpotensi berbahaya, di Pourtalès Terrace selama Penyelaman 10 dari Eksplorasi Laut Dalam AS Tenggara 2019. Gambar milik NOAA Office of Ocean Exploration and Research, 2019 Southeastern U.S. Deep-sea Exploration. Unduh versi yang lebih besar (jpg, 304 KB).

 

Kapanpun Kapal NOAA Okeanos Explorer berencana untuk menjelajah di lepas pantai tenggara Amerika Serikat, kami tahu akan ada tantangan. Tidak peduli seberapa besar kami mengantisipasi dan merencanakannya, selalu mengecewakan ketika kami tidak dapat menggunakan kendaraan yang dioperasikan dari jarak jauh (ROV) dan berbagi keajaiban yang mendalam dengan para ilmuwan dan pengikut berdedikasi lainnya yang bergabung dengan kami secara online. Pelayaran Eksplorasi Laut Dalam A.S. Tenggara tahun 2019 tentu saja memiliki banyak tantangan dan kehilangan hari menyelam. Berikut adalah sedikit wawasan tentang faktor-faktor yang telah memandu keputusan kami untuk menyelam/tidak menyelam.

 

Bahaya

Situasi yang berpotensi berbahaya melekat dalam operasi ROV selama peluncuran dan pemulihan dan saat beroperasi di kedalaman. Selama peluncuran dan pemulihan, awak dek dan teknisi ROV berada di dek belakang kapal untuk membantu operasi. Dalam cuaca buruk (yaitu, angin lebih dari ~25 knot atau 29 mil per jam dan gelombang lebih dari ~6 kaki), gerakan kapal bisa menjadi sangat ekstrim sehingga awak dek bisa kehilangan pijakan di dek, atau ROV bisa berayun tidak aman saat diangkat oleh derek. Merupakan bagian dari tugas penyelia selam untuk membantu meminimalkan risiko operasional bagi personel di dek.

Bahaya operasi tidak terbatas pada peluncuran dan pemulihan. Saat turun dan naik di kolom air, kabel yang menghubungkan ROV ke kapal dapat tersangkut di baling-baling atau kemudi kapal jika kapal tidak bergerak maju dengan benar di dalam air. Di dasar laut, ada kekhawatiran bahwa arus dapat mendorong kendaraan ke fitur geologis. Penyelia selam membantu mengatur kecepatan dan pergerakan kapal sehingga ROV dan kapal tidak terluka selama operasi.

 

Pengambilan Keputusan

Tidak ada rumus yang bisa kita gunakan untuk memutuskan aman atau tidaknya menyelam. Saat mempersiapkan penyelaman ROV laut dalam, navigator, pengawas selam, dan operator kapal mempelajari tiga gaya utama yang bekerja di kapal. Kekuatan utama ini adalah angin, laut (yaitu, ombak), dan arus.

Di sebagian besar lokasi penyelaman di seluruh dunia, angin dan laut adalah kekuatan utama. Jika dua kekuatan ini minimal, supervisor dan komandan selam biasanya memberikan “lampu hijau” untuk menyelam. Ini tidak terjadi di perairan Atlantik di bagian tenggara AS karena Arus Teluk, yang merupakan arus laut kuat yang membawa air hangat dari Teluk Meksiko ke Samudra Atlantik dan memanjang di sepanjang pantai timur Amerika Serikat dan Kanada.

The Gulf Stream direction and magnitude is modeled by the U.S. Navy Coastal Ocean Model (NCOM), which is a high resolution model that offers ocean current data at a 2 nautical mile (2.3 mile) resolution every 24 hours. The navigator, dive supervisor, and ship operators use this model output to very roughly estimate expected currents at each dive site. Image courtesy of NOAA Ocean Prediction Center.

Arah dan besarnya Arus Teluk dimodelkan oleh US Navy Coastal Ocean Model (NCOM), yang merupakan model resolusi tinggi yang menawarkan data arus laut pada resolusi 2 mil laut (2,3 mil) setiap 24 jam. Navigator, pengawas selam, dan operator kapal menggunakan keluaran model ini untuk memperkirakan arus yang diharapkan secara kasar di setiap lokasi penyelaman. Gambar milik NOAA Ocean Prediction Center. Unduh versi yang lebih besar (jpg, 344 KB).

Untuk hampir semua penyelaman ROV selama Eksplorasi Laut Dalam AS Tenggara 2019, Arus Teluk telah menjadi kekuatan utama di kapal. Arus permukaan seperti Arus Teluk mempengaruhi kemampuan kapal untuk mempertahankan posisi selama penyelaman dan mempengaruhi bagaimana kendaraan mengalir di belakang kapal selama peluncuran dan pemulihan ketika kendaraan berada di kolom air. Karena Arus Teluk adalah gaya yang begitu besar, konsisten, dan berkekuatan tinggi, ada juga arus bawah permukaan yang memengaruhi ROV selama penurunan, pendakian, dan selama penyelaman saat berada di dasar.

Tim ROV di Okeanos Explorer menggunakan profiler arus Doppler akustik (ADCP) untuk memperkirakan arus permukaan dan bawah permukaan. Gambar di bawah ini menunjukkan pembacaan dari ADCP yang diambil di lokasi penyelaman yang dianggap tidak aman untuk operasi penyelaman pada hari kami berada di sana. Gambar di sebelah kiri menampilkan arah dan besaran arus permukaan dan gambar di sebelah kanan menampilkan profil arus bawah permukaan di seluruh kolom air. Meskipun arus permukaan 2,2 knot (2,5 mil per jam) jauh lebih tinggi daripada yang terlihat di lokasi penyelaman biasa, ini saja tidak mengarah pada keputusan untuk membatalkan penyelaman. Dengan kedalaman dasar sekitar 500 meter (1.640 kaki), profil arus bawah permukaan menunjukkan arus sekitar 0,5 meter/detik (~ 1 knot, atau 1,7 mil per jam) yang mendekati dasar. Situasi ini tidak aman untuk ROV, dan karena itu kami membuat keputusan sulit untuk membatalkan penyelaman.

The conditions on November 14, 2019, were unfavorable for diving. The readings on that day from the acoustic Doppler current profiler show the surface current direction and magnitude (left) and the subsurface current profile throughout the water column (right).

Kondisi pada 14 November 2019 kurang mendukung untuk kegiatan diving. Pembacaan pada hari itu dari profiler arus Doppler akustik menunjukkan arah dan besaran arus permukaan (kiri) dan profil arus bawah permukaan di seluruh kolom air (kanan).
Kondisi pada 14 November 2019 kurang mendukung untuk kegiatan diving. Pembacaan pada hari itu dari profiler arus Doppler akustik menunjukkan arah dan besaran arus permukaan (kiri) dan profil arus bawah permukaan di seluruh kolom air (kanan). Gambar milik Kantor Operasi Kelautan dan Penerbangan NOAA. Unduh versi yang lebih besar (jpg, 277 KB).

 

Mengapa Itu Layak?

Arus Teluk tidak semuanya buruk! Ini adalah alasan besar mengapa situs menyelam ini sangat berharga bagi komunitas ilmiah (dan sangat menarik bagi mereka yang mengikuti penyelaman online). Arus Arus Teluk yang hangat membawa nutrisi dan membantu mempertahankan kehidupan seperti yang ditemukan di antara komunitas karang yang dalam, padat, dan beragam yang telah kami dokumentasikan selama ekspedisi ini. Dengan beberapa citra, sampel, dan data yang telah dikumpulkan di lokasi penyelaman ini, mudah untuk melihat mengapa menyelam di dekat Gulf Stream dapat menjadi tantangan yang sepadan.

Marine life was both abundant and diverse on the Central Blake Plateau, an area through which the Gulf Stream passes, during Dive 06 of the 2019 Southeastern U.S. Deep-sea Exploration.

Kehidupan laut berlimpah dan beragam di Dataran Tinggi Blake Tengah, area yang dilalui Arus Teluk, selama Penyelaman 06 dari Eksplorasi Laut Dalam A.S. Tenggara 2019.
Kehidupan laut berlimpah dan beragam di Dataran Tinggi Blake Tengah, area yang dilalui Arus Teluk, selama Penyelaman 06 dari Eksplorasi Laut Dalam A.S. Tenggara 2019. Gambar milik NOAA Office of Ocean Exploration and Research, 2019 Southeastern U.S. Deep-sea Exploration. Unduh versi yang lebih besar (jpg, 1.4 MB).

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