User:Vincecate/Pipe Spar

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Looking at Red Hawk Spar and thinking about using standard commercial pipes to make a spar. Could have 1 pipe or maybe a group of 3 or 7 pipes.


First lets look at a single 36 inch sched-40 stainless steel pipe. This is probably 0.375 inch thick (we will call it 1 cm). The density of stainless steel is about 8000 Kg/m^3 or 8 grams/cc. At 36 inches diameter it is about 287 cm in circumference. If we have a pipe 150 meters long this is 8*287*150*100=34440000 grams or 34,440 Kg. Stainless costs around $5/Kg with a pipe being a bit more than this.

If we have 20 meters above the water then we have 130 meters underwater. Displacement for 3 foot diameter pipe is 1.5*1.5*3.141592 = 7.069 cubic-feet per foot of pipe. With 426.5 feet underwater and each cubic foot of water is 60 lbs, then 7.069 * 426.5 * 60 = 180,885 lbs or 82,048 Kg.

After taking out the weight of the pipe, we have 82,048-34,440= 47,608 Kg for ballast and living space. If we use half for ballast then we have 47,608/2 = 23,804 Kg for living space. Would want a LightTopHull.

Detail with migration

If we use migration to reduce maximum wave height we could use a shorter pipe. If maximum wave height, measured from trough to crest, is 30 feet, then we really only need to be 15 feet above the average water level. So 1/4th the pipe length and 1/4 the cargo capacity, or 1/2 the pipe length and 1/2 the capacity are also interesting.

Detail Options

Could use a thicker pipe and still have interesting size living space. Can also brace the joint between the pipe and the living space. Lots of lift really.

If it is necessary to be able to take on some seawater when there is not much weight on the spar, I would have tanks for this under the living area. I would not have any method where any human or computer could cause the ocean to flow into the main spar.

There is more on this idea in the forum. If the strength of the pipe is not sufficient, then some combination of the following options should work:

* Less weight on top 
* Thicker wall pipe
* Larger diameter pipe
* Require a minimum air pressure inside pipe (say 100 PSI, keeps pipe sides out so it does not buckle)
* Multiple pipes (say 3 or 7) grouped together
* Shorter pipe (less stable but harder for water to get leverage to break in half)
* Longer pipe (reduces maximum tilt and strength needed at that time)
* Switching from stainless steel to aluminum pipe


Using PVC pipe a scaled model can be tested to see:

* Stability in waves, in particular maximum tilt
* Period of swinging back and forth
* Force needed to move it
* How it compares to other designs

There is used pipe for sale at such reasonable prices that even a full scale prototype could be affordable (steel but not stainless steel).

Energy Storage

The pipe is closed off with an air valve so we can use the pipe as a huge air tank for Compressed Air Energy Storage. Can use solar to power air pump. Generator runs on air pressure. Plenty of energy storage for a family. Some energy is lost making cold air, but we probably can use the cold air to cool the house instead of an air conditioner.

If there was rough weather coming might want to keep high pressure in the tank. The high pressure air can give the spar extra strength by keeping the pipe from ever buckling.

A computer will measure air going in and out of the tank and sound an alarm if the pressure is changing from what it should be. Would also want the computer to monitor the height of the house above the water and sound an alarm if it ever started going down.

Stainless steel is good for holding high pressure air, but aluminum is not. So this is probably not an option if aluminum is used for the spar.

Requirements Analysis

  • Safety
    • Stainless steel does not have cracking problem that cement might.
    • No controls/valves that would let a human or computer put water into spar, so safe
    • More engineering evaluation needed on strength of spar and what type of pipe(s) needed
    • Use kite and sea anchor for migration to avoid hurricanes and storms
    • Something like this should be a safe design
  • Comfort
    • Should have a gentle motion on normal days but significant response to large waves.
  • Cost
    • This should be one of the cheapest designs. Mostly using commercial pipe. Regular steel pipe could be cheaper. Aluminum pipe could be cheaper. Might even be able to get used pipe that was reasonable. It's a very simple design.
  • Pretty
    • Looks nice.
  • Modular
    • Can make individual family sized units. Could have cable under a line of these so they floated together if you connected a sea anchor at one end and a large kite at the other.
  • Cargo
    • Crane by living space to lift stuff off cargo boats.
  • Free Floating
    • Yes, could anchor also.
  • Scalable
    • A single 36" pipe is one of the smaller spar buoy designs. Might do a fatter and shorter pipe. Could scale up with larger pipe or multiple pipes (say 3 or 7).
  • Standards
  • Mobile
    • Could lift it up and put in on a barge for long distance transport. Could also use a floating dry dock for transport. Would not move fast or easy in vertical position. For short distance positioning thrusters could be used. For long distances a big kite could slowly pull it.
  • Draft
    • Very deep draft.

Modeling experiment

I had 5 lbs on the bottom of this 10 foot 2-inch diameter schedule-40 pipe and a 2.5 lbs weight on top, but it touches the bottom of the harbor in the deepest part. So I had to take the 2.5 lbs weight off. I also had a T on the top that I cut through to make a flat place to attach stuff.

Below is the video of the test, with about 2.5 feet out of the water. When it is leaning toward the end of the video it might have hit bottom (not sure). The video is slowed down by a factor of 4 (though really at 1:25 it should be slowed by 5 I can't get Windows Movie Maker to do 5).

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