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 wonder how prone to capsizing either a catamaran or trimaran with a wing would be given that, with a regular sail, I would think (just a guess) that capsizes are due to the helmsman not releasing the sail in time in a gust, or catching on the rigging as the sail swings on a run or broad reach (and pitch-poling). The wing has none of these problems.
I'm sticking with a trimaran but with rails jutting out of the bottom of the boat so that I can attach an adjustable keel. I hope to balance the boat using the battery or possibly extra ballast.
I'm still sourcing everything - shops close for a while here thanks to the holidays.
I think my strategy is to find everything I need for the full-scale boat and slowly build it up and swap things for better ones when I can. For example, if I build the central frame that connects to the mast and keel, I can add that to a simple hull with regular fiberglass. When I am able to, I'll make a carbon-fiber hull. The same with the mast - I will start with a simple one and then make it stronger. Finding scale parts for a model is difficult here. The actuators and control equipment are expensive so I'll want to invest in them once.
For the rudder, I will attach gudgeons to the transom and have the tiller arm feed underneath a cover so that it is protected from the elements - this has to attach to a linear actuator. There are marine grade actuators available but it makes sense to have this all protected.
Something I need to work out is how to make the mast foot area waterproof. I will have the mast sticking out of the top and there is the cam system to consider. Possibly something like a neoprene skirt used for kayaking. Of course your catamaran avoids this issue as the mast foot will be sitting between two pontoons.
Capsizing depends on windspeed. knowing rig geometry (area, height of center of pressure) and catamarn righting moment (based on weight/buoyancy of floats and total mass) there can be calculated a "capsizing windspeed", at that windforce it depends on the skil of the sailor to react to wind changes in speed and direction. The normal aproach - for cruising, not race - is to reef the sails to a size that keeps the chance of capsizing low. For a wing sail that means to adjust the tail for a lower wing angle.
However there might be possible a certain situation (sudden change in wind direction + wave motion + boat speed) that for a short moment, before wing moves itself into the wind, when it will give a higher force than desired.
A low weight wing with a small rotation inertia will respond faster to these turbulences. But no matter how light the wing is, there is still needed a nose weight in front of it for aerodynamic balance (like saildrone has), and that weight away from the mast will increase its inertia.
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Here I found an actuator that for a 3-4m, 50-100kg boat at 10kts, seems ok regarding its stroke length, force and speed http://www.robotshop.com/en/6-in-stroke-high-speed-linear-actuator....
The estimation I made from this calculator http://www.aquafax.co.uk/images/aceimages/PDF%27s/HowtoTorque.pdf - for a rudder aprox. 37cm high, 22 cm width, 10kts max speed
However they do not have a position traductor or control, like a RC servo does. Only two wires to the motor.
Hey Guys, General rule of thumb regarding Catamarans and Trimarans to keep in mind is the mast height should be no more than 1.25 times the length of the WATERLINE to help prevent pitch pooling which is a common problem with the design.
Regards,
David R. Boulanger
@David Boulanger
Good to keep in mind. It might be different for wing sails but for a long-distance voyage it is certainly better to play on the safe side.
@Cezar
Good find on the rudder torque calculations.
This page has a possible solution for your flexible mast:
http://www.flatearthkayaksails.com/about/fitting-instructions/
The nice advantage of a catamaran is that it is probably easier to build a frame for the mast and cam system (if you are stull using a cam) and it's just a case of attaching everything you need on top, probably in waterproof boxes.
So that I can position the rudder actuator along the hull-stern axis, I could use a linkage like this:
http://www.flickr.com/photos/shipto/5530020868/
Or...I could put in a rudder with control horn like this:
http://canoeingforcharity.blogspot.com/2011/04/making-kayak-rudder-...
I can then feed the wires in through the body like so:
http://www.kayakrudderkits.com/wp-content/uploads/2011/03/ocean_kay...
And then on the inside loop the wires around a single pulley. If the loop is tight, I should be able to attach the end of the actuator so that as it moves back and forth, the horn moves. If I place a spring tensioner in the wire, I can help to ensure that the wires stay taut:
http://www.agrisupply.com/images/xl/11310.jpg
I also wonder if a small water pump is desirable. I can base this decison on how good I think my boat building skills are :) It could be a lifesaver though. Something like this one only with better solar panels:
http://www.ebay.com/itm/Mini-Firm-Solar-Powered-Water-Pump-Panel-Ki...
Kayak hatches like these will make wires, batteries and the computer accessible.
http://kayaksportfishing.com/rigged_kayaks/submissions/gary_fong/in...
There is a lot to be said for simply using a 2nd-hand sea kayak as a platform.
Advantages:
+ They are the right length
+ They can be fitted with amas
+ They can be fitted with a rudder (although the rudder would need to be larger to be of any use at speed)
+ They have easy-access hatches
+ They have a hole where the mast can be seated
+ They often have large flat areas on top where the solar panels can be
+ Generally well-constructed
+ There is possibly enough space to sit in while testing
+ Much easier for anyone else to build
Disadvantages
- More expensive
- I would still want to place a keel on it for the self-righting capability
- 2nd hand examples are not too abundant where I am
- It becomes a bigger target for thieves
Can you think of reasons why a sea kayak with amas wouldn't be a good choice? It does seem like a good candidate.
The cam mechanism still has to sit out in the open air, but an aluminum frame for this can be bolted on top of the kayak. Plus the solar panels can be attached to the frame.
Regarding a keel, it may be possible to attach one to a kayak without drilling extra holes through the bottom (to avoid causing leaks). Potentially a keel could be strapped on using nylon webbing and stainless steel ratchet buckles with a base plate matching the form of the bottom of the hull. The main problems I see are warping of the hull over time and stretching of the nylon webbing. Even long metal jubilee clips would warp the hull, but the removable keel is an option.
Regarding self-righting ability of a trimaran, mabe a very deep, heavy keel is not needed.
I was caught by the proa-discussions.. thing.
They have a heavy windward outriger (ama), so the risk is to capsize leeward.
In order to recover from that type of capsize some designers put a leeward pod, that's the big.. bump in the upper left corner of the hull in this picture: http://en.wikipedia.org/wiki/File:Lee_pod.gif
So when the proa capsizes to left, that lee pod rights it from 0 degrees (mast horisontal) to some 30-40 degrees mabe. And from that point on, the weight of the ama takes the work of righting everything up.
Now if you get a copy of the image above in a mirror ad put it over the original, hull-over-hull, you get a trimaran with two "righting bumps" and two amas, in both left and right side.
Such trimaran would right itself up from 90 degrees capsize. Now building such righting pod flush with the hull might sound difficult but fortunately it is not needed. Two empty light cylinders (think of an long empty PET bottle) in its place, up on the ama's arms, tightened to it, will do the same thing.
Now there-s still the problem with 180 capsize (turtle). I calculated that a wing that is 3m high and 80wide with and 12cm width, with a NACA 0015 airfoil, will have some 160 liters of volume. If it's watertight - hence buoyant - then nothing but a very heavy boat (heavyer than 150kg) will keep the wing buoyancy to lift the turtled boat up and turn it into 90 degrees capsize, from which it will right itself up as described above.
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Regarding using an off-the shelf kayak as a platform - now, after a lor more reading about boat design and performance I'm not sure about it. I think for trimarans and proas narrow deep hulls should help both performance and righting, since a deep narrow hull, heavy on the bottom, together with the floats (and those high empty pods), will provide righting moment from a capsize, much like a heavy deep keel does.
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But mabe I'm wrong, asserting without testing isnt much worth
proas are really cool the fact they can stop in short distance and reverse direction without actually turning could be usefull. https://www.youtube.com/watch?v=F_CGdsZGAaQ
See at 3:12 how the lee pod prevents a full capsize.
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Here are close details, and view of the hull and leepod. The hull is very narrow, seen from upside, the boat doesnt seem so. https://www.youtube.com/watch?v=n3ZVj--A0xI
I found the "Bionic Broomstick" - it is a 14 (or 16?) feet proa fitted with a Worsley style wing.
The shared experience about its building and sailing is quite interesting. I liked both the wing and boat itself with simple, easy to build hull(s).
The thread starts here http://proafile.com/multihull-boats/discussion-forum/viewthread/290
And continues here (proa forum moved) https://www.proaforum.com/viewtopic.php?f=9&t=39
It's author - Skip Johnson - also uploaded a few youtube clips https://www.youtube.com/watch?v=DFVv5w5NtQw
Oh, I forgot to add: Which autopilot system?
I read that the ArduRover/ArduPilot might be too responsive for a long boat as it was intended for smaller RC boats and is not easy to reset.
However, this is a great project and does what we need:
https://www.youtube.com/watch?v=-nA6wo9PXls
Note that he is using two Megas but could probably be squeezed down to just one.
I'd like to try and work on the electronics side and figure out the power requirements.
I dont know either which autopilot to use. Arduino based ones have the advantage you can find alot of boards designed to - more-or-less - plugin into arduino type boards. That means that if you have a future need you have more chances to find, if not the right board at least one that can be modded or .. I dont know. Much third party work, tutorials, including on youtube, and possible help with arduino. That's its big plus.
Pixhawk has much more memory and processing power. I dont know yet if these will be needed, most certainly not in a basic, simple pilot, but it's cool to know you got them if you ever need them.
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APM Mega pilot software (that followed from Ardupilot) supports both Arduino and Pixhawk, so probably it's not that difficult, if you start development on Arduino-based APM, to compile / modify it later for Pixhawk. But I haven't studied them thoroughly so I dont really know how easy it is to port code from one to another.
The movie (with the arduino on the yacht) also shows a linear actuator and rudder. It uses just a long shaft to push-pull the rudder's arm, Seen from above, the arm is 90degrees to the rudder. I guess it's hard to imagine a simpler way.
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