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Post by Deleted on Jun 15, 2016 13:57:08 GMT
Rain is free, even if it's a nuisance at times. I'll bet your seastead will have a roof or two, and like anything else on a seastead, once this material is on the seastead, why would you dump it overboard?
Well, yeas, as it runs off the roof it may have bird poo in it, and lizards (if you are lucky enough to have lizards), and some slight salt. But it's nothing any worse than what your garden expects to have anyhow. Plus, it's tons less salt than what your boat is floating in. And it may be tons cleaner too, depending on where you are, it may have zero dangerous chemicals or biohazards. Why let it run overboard, when it's already more than half as clean as your pricey RO system is cranking out? Filtering this rain water is a much smaller load on the system than processing ocean water or water near a sewage outfall pipe is going to be.
And just how much rainwater will you get? I like to use round numbers, so i'll toss out that sort of figure. How about a 900 sq ft roof, which is 30x30 feet, or approximately 45x20 feet, or two 20x20 floaties. An inch of rain on 900 sq feet is 75 cubic feet of water, or 560 gallons. New Orleans has an average annual rainfall of 62 inches, which would deposit 34,700 gallons of desalinated water on your 900 sq ft roof every year. If you could average that water out weekly, that's 660 gallons of water per week, water that your RO system would not need to clean salt (or oil, or fertilisers, or poo from the neighbor's boat) out of.
It's not all shrimp and camelias tho, all water has weight. That free 560 gallons for every inch of rainfall weighs almost 5000 pounds! The good news is it will fit into a tank not much bigger than a 4x4x4 cube, or 18 inches deep in a 8ft kiddie pool (which is where you keep your baby just-hatched freshwater fish, right?). And, fresh water weighs less than salt water. But you will most likely need to add floatation to your 'stead to hold the free water. However, shouldn't you have a week (or a month!) of water aboard anyhow, especially considering you live there, and it's a long way to land for more water if your RO breaks down?
So to recap, rain can provide more water than you might think, it's delivered to you already made far less corrosive than ocean water, cleaning it further is far easier than cleaning ocean water to be drinkable, a garden doesn't need to it be cleaner than it already is, and it's free! It doesn't matter if it runs off your solar collectors before it runs into the rain gutters!
So there it is. If you can put up roof, you are preventing rain water from contaminating the ocean! And you need roof anyhow!
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Post by jeff on Jun 16, 2016 3:15:35 GMT
In order to reduce the need for additional buoyancy, pass the runoff through a filter and into a tough, durable bag and let it float...
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Post by Deleted on Jun 16, 2016 7:36:35 GMT
Floating bags works in calm water, submerged bags would work in deep water (where it's calm). The problem with every material is a limited flexing lifetime.
I remember seeing somewhere, people were sewing together large blue tarps to use as air or water bladders. The tarps aren't airtight as you buy them, but can be painted on the pressurised side to hold air or water.
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Post by thebastidge on Sept 23, 2016 16:46:42 GMT
The tank doesn't have to be flexible to be submerged. Then it is only slightly buoyant. Depending on the overall center of gravity/center of buoyancy of your ship, placement of a 5k gallon tank should not affect the attitude of the vessel/platform much- and since you would endeavour to keep it as full as possible at all times, and only draw it down in emergencies, proper placement just adds stability. Since storing untreated water doesn't make much sense, there'd be no separation from your Water Maker's output, so between nearly-free filtered rain and the water you make, you should always have it nearly full, just plan for it as ballast rather than buoyancy. Putting all the water in the same place just means less energy spent on your water maker, but you would still want a large capacity water maker for dry spells. Water is fairly compact so the increase in wave coupling is within parameters.
Edit: fresh water is 1000Kg/cubic meter. Saltwater averages between 1020 and 1035 Kg/cubic meter. So you get about 30 Kg of buoyancy per cubic meter from having your freshwater tank submerged. My 5k gallon tank is about 18.9 cubic meters, or about 570 Kg of buoyancy, discounting any tank weight. Assuming for the purposes of apples to apples a cubic concrete tank 2.67 m3 and 5 cm thick, that gives us an approximate weight of 2400 kg of concrete. This small tank would be negatively buoyant by about 1900 kg. If one scale up large enough, eventually the buoyancy of the freshwater tank would be positive over the weight of the shell... hmm. Thinking about spar buoy buoyancy now.
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Post by Deleted on Oct 5, 2016 4:39:35 GMT
The tank doesn't have to be flexible to be submerged. It should be if it's shallower than the wavelength of the water waves on the surface. A 50ft long 4ft dia tank (4500 gallons) in the water is going to be pushed around, just less than if it was on the surface. If the tank cannot be allowed to bend (made of brittle concrete, or fatigue-prone steel, or etc), it needs to be braced and stiffened.
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Post by thebastidge on Oct 5, 2016 17:09:43 GMT
A 50ft long 4ft dia tank (4500 gallons) in the water is going to be pushed around, just less than if it was on the surface. If the tank cannot be allowed to bend (made of brittle concrete, or fatigue-prone steel, or etc), it needs to be braced and stiffened. Sure, but you would need a specific engineering purpose to engineer something awkward like that. A squat cylinder makes a lot more sense from the perspective of cost to manufacture and maintain.
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Post by jeff on Oct 5, 2016 18:54:17 GMT
A vertical cylinder, somewhat like a Spar-Buoy should have proportionally less wave action imparted, and could be moored in a tension-leg-platform manner, to further reduce the tendency to move.
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Post by Deleted on Oct 5, 2016 19:54:26 GMT
A 50ft long 4ft dia tank (4500 gallons) in the water is going to be pushed around, just less than if it was on the surface. If the tank cannot be allowed to bend (made of brittle concrete, or fatigue-prone steel, or etc), it needs to be braced and stiffened. Sure, but you would need a specific engineering purpose to engineer something awkward like that. A squat cylinder makes a lot more sense from the perspective of cost to manufacture and maintain. It was an idea of dual purposing spreaders at the bottom of tower legs. I also ran the math on fattening up heave plates to store (drinking) water or (bouyancy) air or (propulsion) machinery, the cost for the flat bulkheads on the ends of the squat cylinders rapidly got out of hand vs the benefits. Fattening the lower legs or leg spreaders for the same purpose, with the same weight of steel, had better payback. And while 50ft is long [ compared to what?], the 4ft diameter offers less resistance to the water moving than a fat cylinder, and more segmentation and contents segregation of the contents, for fault tolerance and placement management.
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Post by thebastidge on Oct 6, 2016 16:48:01 GMT
while 50ft is long [ compared to what?] Compared to a 4ft diameter... Whenever we talk about this, I think of bending moment on a 50 arm. I'm thinking a lot about Flettner rotos now, and how to stabilize them when they are tall enough to really catch a decent air movement, and provide a significant amount of propulsion to a large-ish platform. How to engineer something like that for cheap, that won't burn out bearings, or tear up mounts when force is exerted disproportionately at one end or in the middle. Sure, we have masts that long on sailing vessels now, but they are generally quite expensive, quite heavy/dense/solid, and flex matters very little as long as it doesn't exceed the maximum and break it (which DOES happen). For squat cylinder, I've been thinking in terms of cast (concrete) or molded (polymer). Your other points all make sense.
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Post by jeff on Oct 6, 2016 22:38:03 GMT
I'm thinking a lot about Flettner rotos now, and how to stabilize them when they are tall enough to really catch a decent air movement, and provide a significant amount of propulsion to a large-ish platform. How to engineer something like that for cheap, that won't burn out bearings, or tear up mounts when force is exerted disproportionately at one end or in the middle. I've seen models that had vertical axis wind-turbines mechanically coupled to props., as well as considered them as generators and using electric propulsion... From wikipedia on VAWTs en.wikipedia.org/wiki/Vertical_axis_wind_turbineIn 2011, Sandia National Laboratories wind-energy researchers began a five-year study of applying VAWT design technology to offshore wind farms.[12] The researchers stated: "The economics of offshore windpower are different from land-based turbines, due to installation and operational challenges. VAWTs offer three big advantages that could reduce the cost of wind energy: a lower turbine center of gravity; reduced machine complexity; and better scalability to very large sizes. A lower center of gravity means improved stability afloat and lower gravitational fatigue loads. Additionally, the drivetrain on a VAWT is at or near the surface, potentially making maintenance easier and less time-consuming. Fewer parts, lower fatigue loads and simpler maintenance all lead to reduced maintenance costs." A 24-unit VAWT demonstration plot was installed in southern California in the early 2010s by Caltech aeronautical professor John Dabiri. His design was incorporated in a 10-unit generating farm installed in 2013 in the Alaskan village of Igiugig.[13] Dulas, Anglesey received permission in March 2014 to install a prototype VAWT on the breakwater at Port Talbot waterside. The turbine is a new design, supplied by Wales-based C-FEC (Swansea),[14] and will be operated for a two-year trial.[15] This VAWT incorporates a wind shield which blocks the wind from the advancing blades, and thus requires a wind-direction sensor and a positioning mechanism, as opposed to the "egg-beater" types of VAWTs discussed above.[14] 4 Navitas (Blackpool) have been operating two prototype VAWTs since June 2013, powered by a Siemens Power Train, they are due to enter the market in January 2015, with a free technology share to interested parties. 4 Navitas are now in the process of scaling their prototype to 1 MW, (working with PERA Technology) and then floating the turbine on an offshore pontoon. This will reduce the cost of offshore wind energy.[citation needed] The Dynasphere, is Michael Reynolds' (from Earthship fame) 4th generation vertical axis windmill. These windmills have two 1.5 KW generators and can produce electricity at very low speeds.[16]
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Post by Deleted on Oct 7, 2016 2:38:17 GMT
What will likely bite them all is what happens when a wave quickly lifts a corner or a side of a tall rotor. If the lower bearing mount isn't flexable to allow out of position operation, and the tall structure isn't flexably and well guyed, pricey things will get broken, and pricey things will be relocated to the ocean bottom.
Remember the "sea snake" generator. It suffered constantly from broken or worn out joints between segments.
It seems basic geometry and physics are often overlooked in floaty things. And there's a tendency for people to think they can dominate the moving water, so they try that, instead of designing so the water can do it's thing and the floatie can mostly do as the designer would prefer. For the VAWT on a boat, best you can do is have the control systems suggest the axis be vertical regardless of what the boat is doing, and design the mechanicals to allow such operation with no harm to the system. It's not difficult.
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Post by jeff on Oct 7, 2016 3:24:56 GMT
... or use passive/active stabilization, like that that was retrofitted to at least one Ramform
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Post by Deleted on Oct 7, 2016 4:06:46 GMT
If you are on the side of a 30ft wave, you will be happier if your VAWT is actively and smartly stabilised also, regardless of the hull stabilization systems.
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Post by thebastidge on Oct 7, 2016 19:20:57 GMT
What will likely bite them all is what happens when a wave quickly lifts a corner or a side of a tall rotor. If the lower bearing mount isn't flexable to allow out of position operation, and the tall structure isn't flexably and well guyed, pricey things will get broken, and pricey things will be relocated to the ocean bottom. It seems basic geometry and physics are often overlooked in floaty things. And there's a tendency for people to think they can dominate the moving water, so they try that, instead of designing so the water can do it's thing and the floatie can mostly do as the designer would prefer. For the VAWT on a boat, best you can do is have the control systems suggest the axis be vertical regardless of what the boat is doing, and design the mechanicals to allow such operation with no harm to the system. It's not difficult. The taller it is, the more acceleration it experiences at the top during roll and pitch, for sure. That's what I've been mostly thinking about. It either has to be very robust at the mount, or flexible somehow. I have been thinking about the "gate" a the top and how multiple rotors might be attached with a lightweight deck or framework at the top to form the gate as well as provide stability. You still want pitch and roll control simply for comfort too.
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Post by Deleted on Oct 12, 2016 4:25:29 GMT
Torque couplings like this: can be misaligned in all 3 dimensions, as well as axially, at the same time, without rpm interruptions. I have not studies specs on them, but i bet some tolerate 45 degree offsets, and you can use more than one. Being your VAWT is slow rpm, this coupling can be built with solid drag links instead of springs, and built by any skilled machinist. I always called them "drag link couplers", but i don't know the real term for them. The tower itself can be held by any huge conventionally-looking universal. The rest of your powerplant below deck would be fairly conventional. Computerised hydraulics can be helpful to guy the top to keep it vertical no matter how the hull is tilted, and if so controlled, the top weight is less of a concern. Consider how fast the computerised suspended cameras move over a sporting arenas.
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