On Friday 02 February 2007 20:18, Craig Jungers wrote: > Looking at the photos of a drill rig under construction reminded me of > my days in the 70s working offshore. In the 1970s I was assigned to work > on the Hughes Glomar Explorer which was (ahem!) to explore the ocean > bottom looking for nodulese mangles or some such. At any rate, the only > mangle it pulled up was (so the story goes... I'm not admitting to > anything) was a sunken Soviet submarine. That must have been interesting, Craig! But Soviet subs do not grew on trees, so you'd have to have something fancy! Actually I saw something about the operation on Discovery - don't remember seeing you, though :-)! (snip) > But the most interesting thing about semi-submersibles is their ability > to remain relatively stable in a very heavy seaway. In fact, I was > aboard the 709 in the North Atlantic with sea heights of 70-feet. It may > interest some of you to learn how they do it. > > A semi looks to most people like a platform because it rests on several > (six or more) columns that appear to the unitiated to be "legs" are > connected to hulls 40 (or more) feet below the water. So a semi is > actually a form of catamaran! The shipyard I worked for went from, in about ten years time ships, to one floating diock (the world's biggest), to jack-ups, to semisubmersibles: first a few accomodation platforms, then some drilling platforms, Balmoral, a big production platform, and the last two were diving platforms. I was often heliguard, even had a chopper crash upon me (at least that was my impression at the time), with the chopper balancing on the edge of the net, surrounding the helipad. The water 20 meters below was freezing so they were damned lucky that the engine exploded just before touch down. No-one was seriously hurt, but one guy had to take early retirement, and one had nightmares years after. Anyway, semis (the submersible kind) work great as long as the hulls are under the water surface, or nearly so, and the platforms themselves over. During testing normally the two hulls are truely semi-submerged, so that the hulls can be used as wharves (sp?) for smaller supply ships and when transporting the shipyard crew back and forth, as there are normally too many people onboard during daytime to sleep onboard during testing. Once during the a test trip with a Norwegian drilling platform, while we were anchored just a few miles from the shipyard, an unplanned hurricane approached, rapidly. Due to the bad weather there was no way the smaller ships could get out to us, so a helicopter shuttle line was established, using Longrangers and Siouxs, but then after a few trips to shore, the wind proved to much for them too, so a lot got stranded onboard for the night. An added problem was that the electrics for the sensors involved in the trimming of hulls fused, so the rig got stuck in top position, and leaned a lot in the 80 knot gale. Scary, really scary when you saw the look of the really experienced North Sea guys - if they were worried things were quite bad, and it was. I myself and a handful others got off the rig by being hoisted off the rig, dangling over a foamy sea, onto a Norwegian offshore ship that backed in under us as far as the skipper dared, but after just picking up a handful he called it quits - never seen bigger waves in my life. and that was inshore - God knows how it would have been out in the North Sea. Well, we got safely to shore, the rig didn't topple and a hundred extras were forced to stay the night, the laundry with its dirty linen became a popular place to snatch a few hours sleep - some teams worked through the night, as they didn't find anywhere to sleep. The semis that came to the shipyard were sometimes really beaten up, usually by waves that had banged the bottoms of the platforms into intersting new shapes. To fix their problems some needed extra legs to float higher, while others got their legs thickened. So, while semisubmersibles stand a lot of seas, many a sailor will tell you that sleeping in accomodation platforms can be very scary, especially when the waves slap into the bottoms of the platforms, just as a ride in a catamaran with a deck between the hulls can be when the waves are of the wrong size and form. And it is these huge waves that sometimes wrench the platforms away from their eight (sometimes more!) gigantic anchors, and snap the man-thick, specially hardened, chains like they were made of thin plastic! The last mile, or so, is thick steel wire, and the winches are humongous, equipped with both disc brakes and band brakes, the latter having better locking power. In short semisubmersibles are highly complex, and highly vulnerable to damage from colleages that has come adrift, or from supply ships that venture too close, but they are very seldom lost. Fire, as usual with sea vessels of all kinds, is their worst enemy, by far! Yours, Tord *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
On 2/2/07, Tord Eriksson <tord_at_tord.nu> wrote: > > > That must have been interesting, Craig! But Soviet subs do not grew on > trees, so you'd have to have something fancy! Actually I saw something > about the operation on Discovery - don't remember seeing you, though :-)! I was playing table tennis under the helo deck at the after end of the ship when some of those videos were shot. And just playing that game on a moving ship is interesting. During testing normally the two hulls are truely semi-submerged, so that > the hulls can be used as wharves (sp?) for smaller supply ships and when > transporting the shipyard crew back and forth, as there are normally too > many people onboard during daytime to sleep onboard during testing. All the offshore rigs I worked on were self-propelled and dynamically positioned and not anchored. Unlike most semis (which are towed by ocean-going tugs) we would bring the hulls up to the surface, aim all the thrusters aft, and drive to the next location. However when the weather got too bad we would have to ballast the hulls down to keep the rig stable. This slowed our speed from about 10kts down to 2 or 3 knots. > An added problem was that the electrics for the sensors involved in the > trimming of hulls fused, so the rig got stuck in top position, and leaned > a lot in the 80 knot gale. Scary, really scary when you saw the look of > the really experienced North Sea guys - if they were worried things > were quite bad, and it was. The ballast control panel on the semis I worked aboard was located at the bridge and often directly behind the dynamic positioning control panel. About 20 years ago the Ocean Ranger took a wave directly into the bridge which shorted out that panel and led to the loss of the rig and all aboard her (off Newfoundland where I had been working only a few years previously). So, while semisubmersibles stand a lot of seas, many a sailor will > tell you that sleeping in accomodation platforms can be very scary, > especially when the waves slap into the bottoms of the platforms, > just as a ride in a catamaran with a deck between the hulls can be > when the waves are of the wrong size and form. I have several years of sleeping aboard semis with only a steel plate separating my room from the waves (as opposed to most of the hull on a ship-shape). As far as comfort goes the semi wins hands down. The greatest disadvantage to a semi is that in cold weather the deck is very, very cold. And one must watch stability closely. > And it is these huge waves that sometimes wrench the platforms > away from their eight (sometimes more!) gigantic anchors, and snap > the man-thick, specially hardened, chains like they were made of thin > plastic! The last mile, or so, is thick steel wire, and the winches are > humongous, equipped with both disc brakes and band brakes, the latter > having better locking power. Dynamically positioned semis (and drill ships) do not anchor as the weight of the chain and cable to anchor them in 8,000-plus feet of water would sink them (especially the semi which has a very limited load-carrying ability). Equipment (then made exclusively by Honeywell) would interpret signals from beacons placed on the sea floor to control thrusters which would pivot and thrust to drive the vessel in such a way as to counteract the effects of current, wind and wave action and keep it over the well-head. I was an officer (Chief Mate at one time) on the Discoverer Seven Seas (a ship-shape) when we set a world record for drilling in deep water back in the 1980s. Something over 8,000 feet. (I wonder where my plaque has gone.) Interesting work and from what I read in the news it's getting active again due to high oil prices. Craig Jungers Royal City, WA *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************
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