Spar Buoy House

Discussion in 'Boat Design' started by Portager, Aug 11, 2002.

  1. Portager
    Joined: May 2002
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    Location: Southern California

    Portager Senior Member

    Well this isn't really a boat, but it would float and it could even move (very slow). This concept has been rattling around inside my head for 25 years, so I finally decided to share it before it falls prey to Alzheimer's.

    The concept is that a vertical spar is both an efficient structure and a stable platform. Since it has a small waterline area relative to the total mass, it reacts very slowly to waves, so it hardly respond to small waves. In large long wavelength waves it rides over them.

    The spar buoy structure is a 10 foot diameter steel pipe 200 feet long. My calculations indicate that a 1/2" wall thickness would provide a factor of safety of 8 to 10 and weigh 10,556 lbs. Near the waterline the hull would be protected from biofouling and corrosion by SPLASHTRON® . Since SPLASHTRON® isn't cheep and I want the spar to be a living vertical reef (like oil platforms legs do here in Southern California), the hull above and below the normal waterline, would be protected from corrosion by a minimum 1" thickness of concrete with fine aggregate. This method has demonstrated a useful life of greater than 50 years with no bottom paint and no maintenance. I have allowed for the weight of 1.5" thickness to allow for application variations and assure the minimum is >1". To improve stability, lightweight concrete would be used above the waterline and conventional concrete would be used below the waterline. Since biofouling will build-up over time and increase the mass, I have allowed 125,000 lbs of excess buoyancy in the form of water ballast to allow for mass growth. The lowest 22.6 feet of the spar would be filled with 300,000 lbs of high density concrete for stability. This makes the center of gravity 45 feet lower than the center of buoyancy.

    The house would be built around the top of the spar, 40' above the waterline. Simulations show that this is adequate to ride 100' waves without contacting, which exceeds the 100 year wave height in my area. The house is in three levels, the lowest level is primarily for utilities (generator, watermaker, fuel tanks, water tanks, storage, ...) the second level is for bedrooms and the top level is living areas. The living areas view should be pretty good at 68' above sea level. The two upper levels provide 2,300 sq ft of living space. The roof is a deck and the very top is a helicopter pad. I figure even if I never own a helicopter, I would still have the helipad just encase someone needed a medical evacuation. The house is designed to survive 150 mph hurricane winds, even though we don't get hurricanes in Southern California.

    I have planned to put water-tight bulkheads in the spar every 10 feet, so there are 14 separate water tight compartments. A small elevator runs from the top deck down to the 60 foot depth. Waterlocks would be located at 30' and 60' for SCUBA diving to the outside. Heater tape would be built into the door and door jams to periodically heat the doors high enough to prevent biofouling on the doors. I also plan to provide an external platform at the 60' level for kelp to attach to.

    I estimate that this house could be built for $400,000 to $500,000 US.

    So what have I forgotten? Well one think is the dock and boat house. Any brilliant ideas? I welcome any comments you want to provide.

    Mike Schooley

    Attached Files:

  2. tspeer
    Joined: Feb 2002
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    tspeer Senior Member

    What did your simulation say about the natural frequency and damping ratio? You only have the ring around the shaft plus the wetted area for damping. Given the mass, I wouldn't be surprised to see it build up some pretty large amplitudes at low frequencies.

    Depending on how it's anchored, it might also have some interesting motion as it fetches up against its restraints.
  3. Portager
    Joined: May 2002
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    Location: Southern California

    Portager Senior Member

    Natural Frequency

    Thanks, I appreciate the feedback.

    The natural frequency is 0.333 Hz so the period is 3 seconds. Deep water waves of this period would have a velocity of 4.67 m/s and a wave length of 14 meters. Since the maximum wave height to length ratio is 1:7 the maximum wave height with a 3 second period is 2 meters.

    I tried a range of dampening coefficients and I found that it wasn't very sensitive and motion was minimal. It moves so slow that it doesn't build up very much momentum. My initial concept was going to have a cone and a larger diameter below water, but the simulation indicated that it wasn't necessary, so I went with the simpler, lower cost structure.

    Ideally I think the mooring lines should be attached at the center of gravity so snubbing loads don't cause a disturbing moment so to speak:). I think the lines could run through eyes at the CG and then up to the utility level where the mooring winches would be located. I would use three Seaflex moorings with large float balls so that peak loads would cause the balls to temporarily submerge instead of jerking the spar buoy.

    Mike Schooley
  4. lockhughes
    Joined: Jun 2002
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    Location: Wards Island Toronto north shore, Lake Ontario

    lockhughes ElectricGuy

    wow. I can't comment on any technical aspects. It just makes me go wow.

    With my extremely limited vocabulary... are you guys tapping about this bobbing around? In which case, could "flopper stoppers" be of use? If you're building a platform for kelp anyway, maybe three or four "flapper valves" type thingees spaced around the perimeter of the platform?
  5. Mike D
    Joined: Sep 2002
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    Location: Canada

    Mike D Senior Member

    I like the idea of watching the world drift by, it’s boring watching grass grow :)

    I have only skimmed very quickly over the sketch and maybe you could explain a few points to me that I don’t understand.

    On the sketch you give the weights of Whouse = 50,000#, Whull = 10,555# and Wballast = 294,628# which totals 355,183# and the sea water ballast at 125,000# would make the total weight 480,183#. The sea water ballast would be slowly discharged to compensate for growth so it should be included in the weight. There is no mention of variable loads such as food, people etc but these are small in proportion so I have ignored them. But the displacement is given as 363,926# It is a floating object and weight must equal buoyancy – unless Archimedes shouted “Oh, Hades” in his bath and not “Eureka”. ;)

    Then I noticed that the Whull was only 10,555# which struck me as odd. Steel plate weighs 40.8#/sq. ft./inch so a tube 10’ diameter would weigh about 200 x 10 x Pi x 20.4 call it 128,200# and this ignores any internal stiffening structure and decks etc. which I would expect to add another 30 or 35% for an all up steel weight of about 170,000# This ignores the outer aggregate but a perimeter of say 31.4 feet at only 100#/cu.ft and 200 ft high would be 78,500# at 1.5” thick.

    The depth of the Spar occupied by sea water ballast is not given but I eye-balled it as three of the 10’ tween deck spaces. The Spar is 120’ immersed so 120/30 x 125,000# is 500,000# and the displacement is given as 363,926# Then I checked the buoyancy using 10’ dia and 10.25’ dia at 35 cu. ft/Long ton (the standard marine value for ships etc). The first value is Pi/4 x 10^2 x 120/35 x 2240 = say 603,200# and the second is say 633,700#

    In the notes you state that the centre of gravity is 45’ lower than the centre of buoyancy but the sketch gives it as 82.11’ below the waterline of 120’. The C of B is half the draft so C of G seems to be 22.11’ below C of B.

    As you can appreciate, this is only a cursory overview. I have not looked at behaviour in waves, strength, stability and all those other weird things that nav archs get up to. The following did cross my mind though. The 100’ wave is a singular event in a confused sea of about 35 feet significant wave height so you could be riding out these “small” waves when this SOB comes out of nowhere so I doubt that it is not impacting on the topsides. One last thing, have you taken account of the helicopter weight on top, not good for stability.

    If you would clarify my concerns I could take a quick look at some other features.
  6. gymfuzz
    Joined: Mar 2006
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    Location: Wilsonville, OR

    gymfuzz New Member

    Are there spar buos out there that could be purchased and modified? Is anyone still working on this idea?

  7. Guillermo
    Joined: Mar 2005
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    Guillermo Ingeniero Naval

    What about wind effect?
  8. Ari
    Joined: Jan 2006
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    Location: Port Dickson, Malaysia

    Ari Patience s/o Genius

    I do like your idea and concept Portager but for that amount of money maybe you can get used oil rig / platform.There is a company in Malaysia that bought an oil rig and turn it into a scuba live aboard hotel..they are located in Sabah,East Malaysia / Borneo Island.Anyway your sketch do looks like ex Shell storage vessel named Brent Spar..Sakhalin gas project do utilised something like your is workable.:)
  9. KDB
    Joined: May 2010
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    Location: Washington DC

    KDB Junior Member

    I joined the forum because this dead old thread is relevant to my interests.
    I am wondering if the original poster was inspired by this.

    It is a spar buoy used as a research station.
    It is called the "The Flip" because it travels (is towed) vertically and shifts ballast to upend itself
    It has a crew of 6, houses 11 passengers (the scientists) and needs resupplied once a month.
    It has been in service 40 years and the crew swears there is no safer place to be in rough seas.

    Add a lawn like spiral island
    and you are at home, sweet home in international waters.

    This summer I am going to start experimenting with a small (10x10ft.) platform mounted on a spar bouy.
    Anyone wanna help design or at least answer a few stupid questions?
  10. Tug
    Joined: Aug 2007
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    Tug Junior Member

    I am interested in this idea as well...
    But i am not a engineer and unfortunately would only ask questions not provide answers...
    10x10 feet would be a great starting much wieght do you plan on having on this platform...
  11. KDB
    Joined: May 2010
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    Location: Washington DC

    KDB Junior Member

    Hey tug,
    Well, not only am I also not an engieneer but reading this forum I often have to google common nautical terms (Which one is starboard again?)
    My goal is a 10x10 ft platform that can hold about 1000 lbs. (5 swimmers and a picnic basket) and sits 10-12 ft. off the surface.
    Depending on the materials I can get the best price on that looks like about 1 to 1.5 cubic meter of displacement.
    I am trying to keep the weight of the thing under 1000 lbs. but that is looking unlikely at this point.
    I'll post more numbers as I get them.
  12. Luckless
    Joined: Mar 2009
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    Location: PEI, Canada

    Luckless Senior Member

    I see that this is a rather old thread, but still an interesting idea.

    One of the biggest challenges I see is how do you easily Get on and off it, if it is designed to be so free in the water with large sized waves?
  13. KDB
    Joined: May 2010
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    Location: Washington DC

    KDB Junior Member

    Portager put a 'copter pad on top of his.
    My budget is more like a rope ladder down to a rowboat.
    Also, as far as materials I am considering bamboo.
    I simply drill holes to fill some segments of the bamboo with ballast.
    Holes at top of each segment I want to fill with water, holes at the bottom of segments I want to use as pneumatic shocks and no holes for buoyancy.

    Does anyone know how long treated bamboo will last in sea water?
  14. KDB
    Joined: May 2010
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    Location: Washington DC

    KDB Junior Member

    Well I came back to admit my shame: summer has passed me by and I got no farther than pricing materials. (I wanted something I could put on top of the car and priced myself out of business by thinking PVC rather than wood and concrete) Plus, I already have a job.

    The spar house is still a possibility and those nuts (er,us nuts) over at are all over it. In fact they are planning a 1 acre spar structure called "Club Stead" . Basically they plan a few city blocks in international waters so they can do all the things that every country on earth has agreed are bad ideas. In short: a floating casino/whorehouse/IDon'tEvenWannaKnow.


    Worst/best part is: than already have over $1 million towards the $5 million pricetag of constructing this fateful pleasuredome. The guy who started Paypal is in on it.

    The rest of the community (the little people, the scum, the nobodys) are using the floating neutrions as a template and desiging huge rafts to keep the rogue waves off their tomatoes.

  15. rdmiller3
    Joined: Apr 2011
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    Location: Muskego, WI US

    rdmiller3 New Member

    Modern Spar Design

    I came across this thread yesterday when it occurred to me that a "Tiny House" on top of a spar might be a workable way to live at sea.

    Some things stood out to me, having just read the first couple chapters of "Living Aboard"...

    - I didn't see any mention of a life raft. Maybe that just goes without saying.

    - You mention "utilities" without any mention of the head (toilet).
    I got the impression that storage and disposal of septic waste is one of the major issues for those who live aboard boats.
    You might not get in trouble dumping sewage from a moving vessel at sea (because you probably won't get caught) but dumping from a tethered spar could be a different matter.

    - Mooring arrangements for boats could be tricky. I've been wondering how to deal with that one. Maybe mooring buoys tied to the spar's anchor line(s). That would have the added benefit of providing a convenient way to weigh anchor and be towed.

    As far as spar design, my googling showed me that modern spar platforms use a design called a "cell spar".

    - The upper part of the buoyancy hull is a bundle of tubes rather than a single tube so there's not just a single point of failure.

    - Tubes are straked with spiral vanes to prevent vortex turbulence induced by current flow past the spar.

    - Several tubes continue deeper than the bundle and are joined by horizontal "heave plates" to damp vertical motion.

    - The main ballast mass is attached to the lowest heave plate at the bottom of those longer tubes.

    I'd put the artificial reef and kelp shelf on a separate spar at a safe distance.

    Also, the length-to-diameter ratio for most oil platform spars is about 1:10 (rather than the 1:20 which you suggest).
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