Dive support vessel

Discussion in 'Boat Design' started by Adhithya, Jun 27, 2014.

  1. Adhithya
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    Adhithya Junior Member

    I'm a student of Naval Architecture have been assigned a project to design a dive support vessel, but at present i have no access to any database, so could any one of you possibly having access to a marine database, provide me with the details for about about 20-30 DSVs above 90m length?
    I'd be grateful for any help provided.
     
    Last edited: Jun 28, 2014
  2. rxcomposite
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    rxcomposite Senior Member

    Consult workboats magazines. It is not a specific type of boat but can belong to a tug category retrofitted as Dive Support Vessel. The first thing that has to be fitted is a decompression chamber which can be a unit that is bolted to the deck. Larger vessels have their own gas generating system.

    Next would be a davit or crane to lower submersibles. Larger ones have a channel in the middle of the boat like a big deep endless well for lowering a submersibles. More complicated ones have a Dynamic Positioning System (DPS).
     
  3. Yobarnacle
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    Yobarnacle Senior Member holding true course

    I have sailed as captain on dive support vessels, one 220 ft another 230 ft long, others close to 200ft. As Mr RX says above, DP is the current technology, but all DSV, even DP equipped DSV, have 4 point anchor systems. Some have 5 anchors and winches for each.
    you need a number of control rooms with panoramic visibility. The normal bridge for navigation of course. And in addition, an aft bridge for setting stern anchors or mooring to oil platforms or other offshore structures. Both bridges need unobstructed 360 degree views.
    You need a survey office adjacent to the main bridge, for two surveyors and all the computers and positioning equipment the surveyors install for a project. Surveyors are contract crew and bring their own proprietary equipment and programs, including sat phones and internet. You need space on the deck above for large communications domes they bring with them.
    You need another separate aft bridge for the dive supervisors, called the dive shack. Inside the dive shack is the gas mix control valve board and communications equipment between divers, tenders and supervisors, and they need a clear unobstructed view aft, of the work deck, about a third of the vessel at the stern. The dive shack needs desks and chairs for at least 6 people and satellite telephone and internet. They need a large open deck area adjacent for the bottle racks of dive gasses. Quite a large quantity of gas bottles. And ability to load offload bottle racks by crane. No overhead obstructions. Frequently the aft maneuvering bridge is the deck above the dive shack and the gas deck just forward of the dive shack.
    You need another bridge called the observation room, as an office for the bosses. Desks tables easy chairs and sofas for at least eight people, with sat fone and internet and large screen TV for display from underwater camera feeds. They need to see work deck, but prefer 360 degrees. the observation room is often the deck below the main bridge.
    You need several cranes and space for a habitat and dive bell for saturated diving. And not just one decompression chamber, but at least 4, and at least one air lift able by helicopter. There is always twice as many divers as tenders, plus a project boss and a minimum of two dive supervisors.
    Non-sat deep diving frequently allows only 45 minutes a day on bottom with 4 hour decompression ascent, divers jerked to surface last 50 feet, gang tackled, stripped and hustled into decompression chamber, pressurized to 100ft, and 4 MORE hours decompression. Divers jump in pairs or multiples of two. Two men on bottom, around the clock, with 45 minute work time at depth, needs a minimum of 8 divers per 3 hour period. That is 64 divers for 24 hour operation, with no extras but you have a few, 32 tenders, at least 3 bosses, so figure 100 man dive crew. This is NOT the vessel crew. Every undersea pipeline near the project, will have a pipeline rep from the owning company aboard. The company chartering the boat will have a "COMPANY MAN" aboard. He is the client, the BIG boss. Needs private office and lots of luxuries.
    The Galley needs to seat and feed at least 50 people at a time. Needs walk in freezers and chill boxes for a couple tons of fresh and frozen groceries. All these people expect to eat like KINGS.
    You need bedrooms and heads and laundry facilities for 150 people. You need at least one rec room for movie watching and card playing. The galley dining area is just for eating. Which when one meal is finished the next soon begins. Four meals per day, one every six hours.
    You are going to need lots of generators including clean power generators for the chambers. Clean power means dedicated and not powering anything else.
    well, I scratched the surface of what's required. :)
     
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  4. rxcomposite
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    rxcomposite Senior Member

    Whew Yobarn, that is a true Dive Support Vessel!:!: Makes a toy out of some of the ships I boarded. But one really stands out. A true DSV. Rows and rows of tanks in the engine room, enough berth for 150 men, several levels of dining saloons. I was wondering at the time what the heck do they need 150 men. Now I understand.

    Said vessel is captained and crewed, all Indians. Probably registered in India. The OP should not have any problem looking that up in the register.
     
  5. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Thanks Mr RX. I don't like DSVs. The captain is still responsible by law, but not really in charge. the project boss (dive crew top man) and the COMPANY MAN run the ship.
    The captain is a chauffer more or less. I only take a DSV job if I'm hungry and nothing else available. I MUCH prefer deep sea towing ! :D Just me and my crew.
     
  6. rxcomposite
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    rxcomposite Senior Member

    Like having the ship's owner ride with you during the voyage.:rolleyes:
     
  7. Yobarnacle
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    Yobarnacle Senior Member holding true course

    This is probably not an option in your design project, but you might run it by your professor and maybe get credit for original thinking.
    If I was going to design a DSV, it would be an ITB or ITU. Integrated tug and barge.
    The DSV is the barge and has a barge captain and hotel crew to care for the divers, bosses and guests. A hotel crew doesn't need seamans papers. Cheaper employees. And the barge captain doesn't need mates. The tug has a tug captain and small crew.
    I mentioned some DSVs have 5 anchors. The standard 4 points anchors spread, and one MORE anchor abeam on weather side. This 5th anchor requires a tug to set. The tug can set it. Don't need an out company tug hired. I'll explain a 4 point set in a moment. but the ability for the tug to break out of the notch and leave the barge can be a great asset. If somebody needed to leave or board at sea, and you didn't have a helipad on the DSV, the tug can run over to a nearby oil rig or manned platform, and the chopper flight arranged. Also the tug can go on tow and take some strain off the anchors in bad weather. Avoids having to pick up and reset. Lost time. Some of the time, it could do this if weather wasn't very very TOO rough.

    Four point spread. Surveyor and captain and pipeline reps agree on a anchor pattern sufficiently wide to stabilize DSV and not endangering any subsea structure or piping. Your anchor winches have a bit more than 3000 feet of wire each winch. on final location, each of the 4 anchors will be about 1500 feet away.
    Surveyors are not navigators. they have charts of the BOTTOM and it's pipelines valves risers, junctions ect. These are industrial secrets.
    The surveyor sends the plot to a electronic chart type screen at the helm. The captain maneuvers to the first bow anchor target, up weather. Anchor is dropped in target center. Captain slides vessel sideways down weather to second bow target and drops other bower. There is a target position in the middle of this spider web, where the DSV will eventually park to work. The captain maneuvers astern and sideways to this center target. Not quite at the center, lock up the bow winches and full astern, to straighten the bow anchor wires. Pull any mud loops out. Back into center target slacking wires as needed but keeping them taut. Chain hitch lift bags to the two bow wires. These will float the wires and prevent the wires from dragging and snagging something on the bottom at this center location. There is SOMETHING down there you are planning to dive on. breaking a high pressure gas valve on the sea floor isn't fun. 6000 psi pressure escapes at mach two. It turns the sea into froth, which doesn't float ships, and at mach two, usually erupts into a 2 mile square fire ball when it reaches air. Not a good day for the DSV and it's people.
    after installing lift bags, head for down weather stern anchor drop. It's a bit difficult to maneuver because two bow wires are pulling against your bow and your rudders are at the stern. After the 3rd anchor is down, head up weather to final stern anchor target. 3 wires pulling against you, I found it easiest to aim my bow at last drop and DRIVE there. Near target I spin the vessel, plop the stern on target, drop anchor. and stop engines. Heave in on weather bower. pick up slack as available on lee bower. slack as required two stern anchors. When abeam but up sea of final position, heave in on lee bow and stern and pay off weather bow and stern and gently move to center of web. remove lift bags, tighten up. start anchor watch. Call in tug for beam weather 5th anchor if you use one. TADA! It's safer and less likely to bust an anchor loose moving down weather to final location. Winching upwind and up sea, might rquire you to pick up everything and start all over, if your 1st anchor, your weather bower lost its bite and broke out.
    Oh! Forgot to explain being beam to sea and wind. divers like to work on lee side. So we set up so the vessel provides a lee. Beam on.
     
  8. rxcomposite
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    rxcomposite Senior Member

    Attached Files:

  9. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Nice big DSVs. Which of the pictures is the one you were on?

    I guess Adhithya wanted 20 or 30 different ship's sets of blueprints rather than sea stories. :D
     
  10. kerosene
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    kerosene Senior Member

    I think he wanted his homework done for him... Annoyingly common these days.

    Thx Yobarnacle for sharing your stories btw, very interesting read
     
  11. rxcomposite
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    rxcomposite Senior Member

    Yobarn- Didnt find it as some pics don't have names but it is very similar to the first pic. The second pic is a modern one.

    Might as well look at my old notebook/scratchpad to remember the name.
     
  12. rxcomposite
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    rxcomposite Senior Member

    If s/he did read Yobarnacle's post, the salient design points are there.

    DPS
    4 (5) Point mooring
    Saturation diving

    Plus from my contribution, if there is saturation diving, there must be a decompression chamber and gas storage/production.

    Now the question is how deep is the operation going to be and is the helideck an option or integral part? Helideck design is partly governed by FAA so the search goes deeper.

    I agree, some people just like to throw some seeds around and come back later to see if it indeed grow, others nurture it, checking everyday the progress and asks intelligient questions. Others, well, they just like to see their avatar in the net and see who bites.
     
  13. Yobarnacle
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    Yobarnacle Senior Member holding true course

    You have to decompress for longer and longer periods as the stages get shallower.

    http://www.deep-six.com/page87.htm
    Look on your decompression table for 140' for 80 minutes. If you did that dive you would have major stops on the ascent. You would have to stop at 40' and hang out there for 10 minutes. Ascending at 1 foot per second you would have another stop at 30' for 23 minutes. At 20' you would have to stop for 41 minutes, and then 79 minutes at 10'. The total time for ascending would be 155 minutes and 20 seconds! That ascent time was the result of an 80 minute dive! " (excerpt from above link)

    This is a shallow dive of 140 ft. The diver has to wait 79 min at the 10 ft from surface mark for this ascent.
    These longer and longer decompression stages tie up equipment. Time is money on project. With decompression chambers, they jerk the man straight up from 50 ft and throw him in a chamber to decompress the next 4 hours.
    And they need chambers as treatment if a diver gets bent. One chamber, a flyable light weight self contained/self powered chamber, is always kept empty, ready for use by a diver complaining of the bends. Worst, is a nitrogen bubble in the spinal column. can paralyze you for life, if you live.

    Saturation diving is for very deep dives like 1000ft and the divers don't decompress.
    They work two hours on and two hours off. 4 men, working in pair, but they stay on bottom 12 hours. A diving bell hooked to a crane on DSV, stays on bottom those 12 hours. Trip down and ascent only takes 10 minutes or so since no decompression stages.
    The pair of divers resting for their two hour break, rest inside bell, which has cots and toilet and food and drink and a supply of paper back novels.
    Working under pressure is very exhausting. and damaging to the body. A day in sat takes a year off your life, they say.
    The divers resting in bell, are also available to assist in an emergency, the two men outside.
    4 men on bottom is minimal for sat. Rotating every 2 hours, the 4 divers do their twelve hour hitch.
    Then they are brought to surface in the pressurized diving bell.
    The bell is then connected to a pressurized habitat on board the DSV.
    They enter the habitat through airlocks and 4 other men that were in habitat previous 12 hours, enter the bell for the ride to the bottom.
    So 4 are in habitat and 4 on bottom 24/7 operation. This is minimal. There are larger habitats and bells.
    These 8 men remain saturated at bottom pressure until the job is finished.
    After project completion, the 8 men remain in habitat together another week, slowly decompressing.
    THAT is sat diving. :D
    "
     
  14. Yobarnacle
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    Yobarnacle Senior Member holding true course


  15. Adhithya
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    Adhithya Junior Member

    I'd like to thank yobarn and RX for their insights into the operational requirements for a DSV, but what I required were the dimensions and the form factors of modern DSVs, based on which I could do a preliminary parametric estimation and proceed on to design the hull, and then do a preliminary GA and so on.

    and Mr. Rx, the DB you have cited requires a subscription of $2000 which I do not have at my disposal, and if you, or any one else is a member, i sincerely request him to provide me with the details I'm searching for.

    the specs of the DSV i'm working on are: < 6m draught, DP, Sat dive upto 300m, max 19kts.

    P.S., I'm not trying get my homework done here but asking for data that I require which I can not access or afford....
     
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