Choosing the best marine hull for an autonomous boat

Motors are 300g each, electronics and solar panels will go up to 0.7kg while batteries depends if the hull keel can host them, otherwise I'll also need to add the weight of a leaded bulb.

The calculations about solar panels daily production now give a very negative estimate, however I think sea tests will give much more meaningful data to work on. Interestingly the SolarSurfer prototype was running a 120W solar panel array while the two motors consumption, blue thruster T100, is well above 100W each, yet they still managed to travel autonomously from California to Hawaii.

Going to the boat shape, a drawing I am considering right now is this one here, even if I am not sure how reliable the proportions are
SimScale https://www.simscale.com/projects/screamingon2go/apotheosis/

 

Just use a skinny monohull with a huge keel weight (battery).
Again, the R/C world: a very skinny sailboat hull.
Flat deck with zero shadowing on the panels.

 

The panels will get salt film on them and be less efficient.

So you will program it for a route that it will follow by itself? How long will it travel for, weeks or months?

 

That flat transom will create more drag than a double ended shape.

 

Having a curved top deck water spills will not evaporate on top of panels, but some salt film will definitely accumulate over weeks of navigation. First tests will last a couple of hours but I expect to deploy the boat for months-long missions.

I got suggested to use Marblehead RC yatch, whose main drawback is a very limited space on the deck, leading to less solar cells being hosted and overall less power available. The same applies to sailboat hulls.

 

I would suggest a sphere. The top half covered in solar panels. The bottom half bisected vertically by a thin square keel that terminates in a very long rudder that extends... I donno. Maybe half the diameter of the main body. The pivot for this "rudder" is connected by a cam mechanism to a fairly robust stepper motor. This provides steerage and propulsion by flapping back and forth fish-like. This would greatly simplify mechanical and electrical design (at the expense of programmatic complexity).

Yes, its ride quality would be completely unacceptable for a manned craft, but unless you intend to take aimed pictures or use a star tracker, drones don't care.

 

Anelito, interesting project. Your max power (246W) seems way too high. At this power I can push a 14ft skiff with two people and the weight of another small person in batteries, at about the same speed at which I can row continuously. No need to waste time printing propellers, there are plenty of model boat props available at reasonable prices, and you can experiment with different sizes. If you don't anticipate weed problems use model airplane propellers; they are more efficient. Brushless motors are much lighter and slightly more efficient than brushed, and no more difficult to use. You might recover more thermoelectric energy from the solar panel than from the motor, and if it works it would make the solar panel more efficient. Panels are available with an aluminium backing; an ideal flat surface to recover waste heat from.

 

Agreed, flex panels over slightly cambered decks would allow self cleaning.
Wet panels produce more power than dry.

R/C has adjustable pitch propellers for airplanes that are the most efficient available for your purposes.
And, you can tune them.

What is your target speed?

 

I'm guessing you are not looking to create something new so much as get experience in an emerging field. There's no reason to reinvent the wheel, so melding existing design ideas used on successful boats will give you experience and a working boat/experimental platform and I believe it's the way that designing and building is done. "Bernard of Chartres used to compare us to dwarfs perched on the shoulders of giants. He pointed out that we see more and farther than our predecessors, not because we have keener vision or greater height, but because we are lifted up and borne aloft on their gigantic stature." That and, "Monkey see, monkey do".

This configuration has some good stuff going for it, the batteries and motors are all in the keel pod, putting that weight low. I'm not sure about the deck hanging over and being all winglike, it looks perfect for capturing the wind on a wave top and then having problems of navigation and the course having to be constantly corrected. Maybe flipped over, but unlikely with a heavy enough keel and self up righting if it did flip.


Those lines in the hull above are the thin templates mentioned below...

With those templates in place, you can saw off the bigger pieces with a knife or hand held hacksaw blade, and then take a board with rough sandpaper stuck to it and you sand down to those templates, somewhat like drawing by connecting the dots. That's a fast easy way to do it, but maybe you want to use the cnc to gain experience.

You can get the foam plug close enough by handwork, because when you glass it that kind of roughs up the surface and somewhat negates the cnc accuracy. It's like the cnc is over qualified for the job. After glassing it's all handwork anyway, unless you want to cnc the fiberglass too.



These guys went ahead and made a two piece mold for multiple hulls, but ended up not using it. Instead they just scooped the foam out of the plug and used it.

They used a very simple U shape for the hull that would be easy to duplicate, it looks submarinish, but the size of the U s , or the size of the hull, are determined by how much weight it has to support.

Hulls displace water. (Volume displaces weight) If you put 10 kgs of weight in a hull, it sinks enough to displace 10 kgs of water. So you have to have enough volume in the hull to displace every bit of weight that hull carries, which is itself and all equipment. Plus added size so it floats with the topsides above the water however much you want.

 

Those guys are very open about that and newer versions. They show how to make the power pod and other parts.
Blog-Beiträge http://www.seacharger.com/build-blog/previous/2
SeaCharger build blog: see the latest progress on the project http://www.seacharger.com/build-blog
SeaCharger Oceangoing Autonomous Boat - Home http://www.seacharger.com/

This site is called SeaCharger also, but a different boat. It could be the same folks. I think it is.
SEACHARGER SOLAR POWERED AUTONOMOUS ROBOTIC BOATS UNMANNED DAMON MCMILLAN http://www.bluebird-electric.net/artificial_intelligence_autonomous_robotics/SeaCharger_Autonomous_Robotic_Boat_Unmanned.htm
They are dedicated to 'open source' shenanigans, so there is a lot of stuff I would use if I were doing this type project.



***Spaghetti-os are not part of the pod***

 

Or are they...

Could be they've given away the proverbial "secret sauce". Literally.

 

Propellers will eventually get tangled with continuous use as autonomous vessel is my opinion. That includes folders, weedless, maybe even jet props- I would think. May need to withstand collision with a speedboat and storm conditions?

PC

 

That is why I suggested the fin, fluke, scull rudder thing.

 

Thank you all for the replies, apparently autonomous boats is a hot topic

The SeaCharger is on overall a nice project but hull-wise it doesn’t seem well engineered as that huge panel must generate a lot of drag due to wind and currents.

I like the idea of batteries and motor in the bulb but the model I’m working on atm is too small, maybe in the future it can be a nice addition and it would easily solve thermal dissipation needs.
Strangely they used AA-sized LiPo batteries which usually have a very low discharge rate, much lower than what a brushless usually needs.

Going to propeller, I am actually discussing with ArduPilot team (a firmware for autonomous drones) to include a seaweed removal manoreuvre already developed by the SolarSurfer, now BlueRobotics. A folding propeller could be useful to avoid damage during storms, when the boat will go in sleep mode.

For now I will try a sailboat hull, maybe adding fixed trim fins to increase stability.

Lastly, good point about solar panels heat recovery, I will test a bit with temp sensors and monitor the temperatures on motor and panels.

 

You'll want to eliminate catch points.
Like reverse bows, bulb/strut connections, and on deck as well.
A 10 degree slant on your vertical strut attaching to the very front of your bulb would do it.
Nothing should stick out, everything needs to be flush.

Cylinder doming your top deck slightly would aid aerodynamics.
And with an MPPT, you'll benefit from doming.
Keep your Lifepo4 battery small.
It doesn't matter if it doesn't make it through the night.

If roll proves an issue in sea-trials, you could incorporate a control-surface in the lower section of the strut as a roll stabilizer.
A canard.
R/C has cheap gyro-servos that will do just that.

I think stabilizing fins a bad idea.
Too much added wetted surface area.
Simply make your keel fin deep and high aspect ratio.
Motor and battery are awesome ballast in a skinny, long bulb.