October 21, 2008 at 5:06 am #716
I contacted Cliff Goudey about the thruster he used in his mobile aquaculture experiment because it was very efficient. He told me these are off the shelf mixers used in the waste-water treatment industry and cost about $20,000 each. On just 6.2 hp these 8 foot diameter propellers get 760 lbs of thrust. I setup a wiki page with more info and links to info on his experiments and fun underwater video.
With some solar panels these could really work out well. If I was building a prototype seastead today this is the thruster I would want to use. Anyone ever find anything better?October 21, 2008 at 4:36 pm #3995
I think several of the seastead designs we already have could be made as prototypes large enough to live on. And I have another design I want to make that I think will be the most stable so far. Basically I will replace the ball floats in the WaterWalker with 3-inch diameter PVC pipe about 1.5 feet long and tie the end of the tripod to the pipe. So the tripod will be down in the water partway and the PVC pipe vertical with 1/2 to 1/3rd out of the water. The smaller water-line-area (less than 1/4th of the ball) should make it less sensitive to waves (sort of have spars in the corners instead of balls). A fat rope between the tripod legs will be down in the water and can act like a heave plate, or maybe I will put some cloth at the corners to reduce heave. Anyway, it should work very well.
One thing that we have not really explored is thrusters. But the stuff I found already makes me think this will not be a problem (760 lbs thrust on 6.2 HP, wow!). So I think a real working prototype is something within reach in the next year or two.October 21, 2008 at 9:23 pm #3996
Excellent idea with the pipes. I guess hanging the corners of the structrure from below the pipes would be the easiest and most robust attachment, avoiding torsion from the pipes to act on the structure. The structure will float lower in the water though, with the corners below the flotation, so you´ll have less room to build on if you want to stay on the same height above sea level.
Those Flygt mixers look very efficient. They are even designed to be mounted on rails so you can hoist them up for maintenance. See PDF here: http://www.flygtus.com/724490.pdf
I guess what is needed in general is a large propeller with low pitch and low speed. I was thinking about buying a large used ship´s propeller and turning it very slowly with gearing but I really doubt that would be competitive with these mixer units in the long run, with running costs included.
Here is a couple of other manufacturers of mixers:
Product name “Amaprop”:
Product name “JPX”: http://www.jmikorea.com/e_prod_010.htm
A search for “submersible mixer” turned up some good results.October 22, 2008 at 1:04 pm #4003
>Excellent idea with the pipes. I guess hanging the corners of the structrure from below the pipes would be
>the easiest and most robust attachment, avoiding torsion from the pipes to act on the structure. The
>structure will float lower in the water though, with the corners below the flotation, so you´ll have less
>room to build on if you want to stay on the same height above sea level.
Yes, I think there can still be plenty of room. Having part of the tripod underwater increases water drag but reduces wind drag. At the slow speed we will do the water drag is probably ok. The maximum wind drag probably determines the size of the thruster we need, so reducing it could be good.
>Those Flygt mixers look very efficient. They are even designed to be mounted on rails so you can hoist
>them up for maintenance. See PDF here: http://www.flygtus.com/724490.pdf
>I guess what is needed in general is a large propeller with low pitch and low speed. I was thinking
>about buying a large used ship´s propeller and turning it very slowly with gearing but I really
>doubt that would be competitive with these mixer units in the long run, with running costs included.
Amazon sells some windmill blades cheap that I have looked at for making something. But for initial tests it is probably better to just pull the structure around with a boat guzzling fuel and to fully demonstrate the seastead concept I think we want an electric engine that is very efficient and reliable. So I don’t think I will be trying to make my own thruster.
>Here is a couple of other manufacturers of mixers:
Cool. I suspect we don’t really need 760 lbs of thrust and could get by on a thruster costing less than $20,000. On the other hand, it is nice to have reserve thrust for when it gets windy and you are near land. Given the cost of the living quarters I don’t think $20,000 will seem like much. Probably we will buy two.
After looking at thrust ratings on available thrusters I am now more motivated to measure how much pull it takes to move my models. This would let us know how much thrust we need for a certain speed (say 2 MPH) for a certain type of seastead.
— VinceNovember 9, 2008 at 7:28 am #4206
West Marine sells Lewmar bow and stern electric thrusters from 3hp / 92 pounds thrust at $1.5k to 14.5 hp / 550 pounds thrust for $6.6k. That’s immediately less efficient than the mixer-as-prop, but less expensive for the same thrust. The thrusters may not be rated for continuous use however. I suppose the market is medium-sized yachts.
Adding some notes to the Thruster wiki entry.December 19, 2009 at 7:01 pm #8950
years ago on some tv show (can’t remember which one) some scandinvian or dutch (I think) inventor came up with a simple genious wave powered truster which he fitted to an old rowboat for testing.
it was a neutrally bouyant flipper mounted and hinged subsurface on a support strut. as the boat moved up and down on the waves the water resistance on the flipper actuated it’s motion, causing forward propusion for free.
refine and scale it, and it could be great for low speed propusion and or station keeping.
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