Hi all,
I am interested in long-distance ocean-going drones.
To date, I am aware of only 2 craft that have made it across the Pacific; both WaveGliders. They are the Papa Mau and the Benjamin. Both released at the same time from San Francisco, it took 1 year for the Papa Mau and another 3 months for the Benjamin. They were both solely under wave-power using the SV2 version.
However, 2 more WaveGliders released at the same time failed to make it from SF to Japan.
Another boat, the Honey Badger, is a sailboat and made it from SF to Hawaii in 34 days. This design is different to a regular sailboat, but clearly it works.
Scout was an attempt to go across the Atlantic using solar power and a propeller but got lost about half way across.
The new SV3 version of the WaveGlider is now more of a boat-hull design than a surfboard and now possesses a solar-powered propeller pushing the underwater glider.
BlueRobotics are beginning to produce the T100 and soon the T200 thrusters, with 5lb and 10lb thrust respectively. Two T100s were used to power their SolarSurfer in an attempt to travel up the Californian coast but some weed fouled one of the thrusters (possibly a prop spur would be the right solution?). Plus, when the sun went down, there appeared to be just as much drift during the night than forward motion during the day.
An underwater torpedo glider like SLOCUM or Seaglider needs very little energy, but working at depths complicates things immensely.
And here is my question:
"If you wanted to go from one side of the ocean to the other, which design would you choose? And which route would you choose?"
If I wanted to go westwards across the Pacific, I could potentially use the equatorial currents and use OSCAR (Ocean Surface Current Analyses - Real time) to help catch the best currents but then a couple of days ago I saw a beautiful map at Global Fishing Watch (something Google are involved in) and saw that those same currents are highly fished, and so probably best avoided due to the danger of nets.
I like the SailDrone idea as there is less underneath to catch upon compared with the SolarSurfer and WaveGliders, but the guidance tech on the SailDrone is probably harder to master. Other sailboats don't appear to have much success.
To date, thrusters and props for this size of boat have not proven themselves of this type of endurance. I would like to see how well the T200s fair out at sea.
A good design might include:
- A hull that cuts through the water like the SV3 rather than gets bumped around like a surfboard.
- A glider with a thruster on the glider like the SV3, but with a tether that can be detached in case of emergencies e.g. fishing net entanglement which seems to be the biggest risk.
- A self-righting hull.
- Two or three T200 thrusters attached to the hull of the boat, but with only one in operation at a time as the other two are redundant until one thruster fails (problem: the glider below should be in front of the boat and pulling it along)
Thoughts?
Replies
I found these scale drawings from one manufacturer of horizontal axis wind vane to servo-oar steering systems. It seems the sizes of the oar and wind vane are quite close to each other.
Since the servo oar behaves in water just like a balanced rudder, I assume that for very small boats, the horizontal type of windvane having its area and shape close to the rudder blade, should be able to steer directly the rudder without needing the complication or fragility of a smaller rudder tab and its linkage
Mr.Vane pdf drawing
Hi Geddes, if you have acces to google drive, I uploaded there a few movies to illustrate the above windvane mechanics.
https://drive.google.com/file/d/0B1udbEguLYNuNkgwdDVSak9DTDg/view?u...
https://drive.google.com/file/d/0B1udbEguLYNuRk9rSDZQZDR0a3c/view?u...
https://drive.google.com/file/d/0B1udbEguLYNuenFGMFF6VW5KZWM/view?u...
https://drive.google.com/file/d/0B1udbEguLYNuaGFxLTFZNFZiTkU/view?u...
here-s a take on understanding horizontal axis wind vane pilot. There-s the yellow wing, its vertical push-pull crank system, fixed to a rotating drum ( this one should be rotated 360 deg by an actuator to change sail direction), a (whitish) holding tube under the drum (this gets fixed astern) through which goes down push-pull shaft (bamboo skewer) going down to the rudder.
and here is the left-right movement of the wind flap
crank is pushed down:
crank is pulled up:
here are two possibilities to transfer this vertical movement to the rudder tab. These parts are below the articulated screw that detaches rudder rotation from windvane rotation while allow push-pull vertical forces.
The first idea is the same as bowden cable, but using rigid tube and thick steel wire instead of flexible one. I just tested 2.5mm coat hanger steel wire into 4mm ID PVC tube and friction seem to be reasonable low, one gram or so to move (rotate) the wire 1-2 cm inside the tube. They have to match curvature.
The second idea is a bell crank style:
The two images above do not show the off-center 3-4cm rudder tab rotating arm - that one is pushed not the tab itself
sorry the image is so big, I halfed it but still big..
Now follows the bottom of the vertical shaft, just an idea about how vertical movement allowing horisontal rotation of the part that gets attached to the rudder. It needs to be exactly above rudder hinge axis
Here-s a nice transatlantic attempt of a solar roboat
https://www.youtube.com/watch?v=X7DLqQlfMp8
The site http://gotransat.com shows a lot of info - includes tracking data, hull building.
They found a lot of local sponsors too.
Even being much simpler than a multihull sail boat, they put alot of effort into it
looking into wing coverings, I found polyester fabrics very similar with those used in (ultra)light aircraft. There is Sig Koverall http://www.sigmfg.com/cgi-bin/dpsmart.exe/ProductsV6.html?L+Sig+rsx...
Used in large scale rc models.
And a bit heavier is Ceconite "uncertified light" fabric for manned ultralights http://www.ceconite.com/fabrics.htm
Both work the same way - glue on the wing frame (or foam core), heat shrinked, doped with various resins and painted. The resulting wing is reportedly very strong and rigid.
Much heavier grade is also used as cover for skin-on-frame boats.
I may have found a place here to construct my boat. Yours, however, looks like it is almost ready for the water!
I have been thinking more about the design here:
http://www.faymarine.com/plansite/images/1_SS_aux_rudder.GIF
The 'course setting' mechanism is troublesome in that anything would add to the weight of the rudder assembly. I wrote to this forum but am still looking for the right answer.
http://engineering.stackexchange.com/questions/1763/precise-rotatio...
It could be that a tab on the back of the wind vane is indeed the answer. The apparent wind should always be from the front and so the wind vane doesn't not need to rotate 360 degrees. Because of this, a pair of bowden cables connected to a linear actuator would probably work well. The linear actuator can of course be undercover and waterproofed.
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I did look at a few communications options. The majority reach out a couple of hundred miles into the ocean, but this means many months of complete blackout. This is why I like the 2-way ocean-coverage that the Iridium satellites provide - although of course the cost is higher.
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re: Another method is to have the rotary encoder attached directly to the ruder shaft, that will read directly position of the rudder.
I agree completely. Moving the wind-vane tab to move the rudder tab is all about moving the rudder after all - and then linking this to the direction of the boat.
I did read through all of the "Build Your Own Trim Tab Self-Steering System". There was a line that said "A 5 degree turn on the trim tab should produce a 5 degree turn (in the opposite direction) of the main rudder". I wouldn't expect the same concurrence between the tab of the wind vane and the movement of the rudder. Feedback is essential and something I will read more about.
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That Ceconite woven fabric looks like it would work very well. I did try to find information about how well it stands up to saltwater but I could not find any. I will presume that the fabric would let moisture through to the underlying frame, and so any wood would require treatment. But it looks strongs and stands up to UV light. My fears with a skinned wing is that a mixture of UV and saltwater would eventually degrade it too far, but ceconite might just work.
Regarding foam cutting, you can source the nichrome wire on ebay http://www.ebay.com/bhp/foam-cutting-wire
I've seen some are using guitar strings instead of nichrome.
When I built mine I found harder to source a 300watts transformer, that lowers the mains voltage to some 24V
There is a lot of infos about how to make a wire cutter, including instructables and youtube sites.
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What I found the most difficult is the cutting itself, you need a steady slow moving hand, patience and some practice.
It's very difficult to follow a shape without templates.
I found easyest to make templates from thick cardboard (easy to cut in desired drawn shape with a scissor), then glued aluminium foil stripes on the edges on the cardboard. Thats enough to let the wire slip easyer on the template, and to prevent it to cut into the cardboard, the cardboard being anyway much heat-resistant than the foam.
Most cutting imperfections or wrinkles from the cutting are easily smoothed with sandpaper glued on a piece of wood board. That's how I shaped the pink ama, that's an yet uncovered block of pink XPS foam.
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