1.2 m autonomous boat hull ideas?

That's the other benefit to using a trolling motor, I don't have to have a rudder. As you probably noticed, I've been toying with this idea for a long time. I finally have some time to invest in it and I'm hoping to nail down the design over the next week or so. Unlike most of the projects here, building the boat is only the first stage of the project. The majority of the project will be spent designing custom electronics and sensors.

 

For your velocity I would go with a cylinder and hydrodynamic ends. Elliptical bow and parabolic stern. The cylindrical body makes fitting gear WAAAAY easier with little to no drag differences. I'd make a screw-on bow with a removable inner frame for mounting your hardware. The motor pod could pivot ball-in-socket style for added hydrodynamics (i.e. reduced drag).

So, 4' X up to 1' but 8 - 10" would be better. I think a big variable is how much battery power you need for the motor.

What are your electronic volume requirements?

-Tom

 

At 1.2 meters you are solidly in model-boat territory. There are loads of plans around the net for all kinds of boats this size. You can also get moulded GRP hulls which are of the right size, or even larger.

Power from, say, one or more brushless motors, and either propellors or jets (Graupner do a nice alloy drive which would be suitable). Appropriate ESCs and Lithium-ion batteries are the order of the day.

You can drive RC hobby speed controls and servos from a PC/embedded system using a PWM signal; or a Pololu Maestro for which I have software here - http://openpilot.cvs.sourceforge.net/viewvc/openpilot/Servo/maestro/

On the basis that I have built 2ft (600mm) racing powerboats down to 0.9Kg (all-up), you should have no problem with building a 4ft boat for less than 5Kg, without instrumentation.

Best of luck,

Tim B.

 

That's the direction I initially was thinking, but the time and costs to build it started to get to a point where it became unmanageable. That's why I've come back to a simple stitch and glue boat hull and a trolling motor.

 

You're right, but I've looked high and low for a 1.2 - 1.8m RC boat that wasn't either a scale model or a high speed racer. If you look at the boat I linked to above, I think you'll see it looks an awful lot like a v-hull racer you might pick up at hobbyking. But again, I've not found anything that had the carrying capacity I'm looking for.

And yes, I've thought about RC gear and have a bit of experience in that area myself. The problem again is that most are designed for moving light weight at fast speeds. I could add a reduction gear, but now we're adding to the complexity and cost when a $150 - $200 trolling motor would do all that plus have thrust to spare.

 

You kinda lost me there. I don't think the time or monetary costs are going to be too high.

How many antennas on top? Can any be "hidden" under the surface of the vessel?

I'd go with Fiberglas initially and move to epoxy in later builds if applicable.

How autonomous will this rig be? Daily runs, one hour, weeks? Would a molded solar cell be of appreciable benefit or too costly?

I think you need to sit down and figure out what you need it to do and how your budget fits your priorities. For example: will the cost of high end batteries justify the gains (space, weight, performance). How did you decide on 2 - 3 knots for your target speed?
What is the total weight of your payload? Is it variable? Knowing this kind of stuff will help design an over all size BEFORE building begins.

-Tom

P.S. Are you in Washington State?

P.P.S. I wouldn't use a speed controller. Pick a single target velocity and design around it (i.e. design to it). What I mean is use your battery voltage output to fix the speed of your motor and arrange your parallel/series connections accordingly to achieve that.

 

"That's the other benefit to using a trolling motor, I don't have to have a rudder."

You could easily do this with a water jet too.

-Tom

 

What's the diameter on that trolling motors prop? Two blade? Do you already have it? You may be able to sell the speed controller to recover some costs. You could also make your own propeller (stainless steel) for $10 worth of steel and about an hour of grinding, but you'd have to design it first on JavaProp. You'd end up with about 80% efficiency vs. 60-70% from the trolling motor prop.

-Tom

 

Don't know what you have in mind then. Perhaps you could explain your idea a bit better?

Several. Probably not. I plan on adding an antenna tower as radio waves (especially higher freq) are detrimentally effected by water.

True, I could use polyester resin instead of epoxy. I'm just real familiar with WEST epoxies, been using it for years.

It would only run for hours at a time. Not entirely autonomous either, it will always remain within sight of the operator who will be able to intervene and take control at any time necessary.

Ideal speed for the sensors is 5 kts but 2.5 is acceptable.

It's a test platform so will be variable.

No, North Carolina.

That's probably a good idea. Still need to be able to remotely start/stop the motor and I'm not sure what the cost difference of an RC brushed speed controller would be versus an RC power switch would be.

Good idea.

 

Okay, this is spiraling a bit here.

Not sure I can explain much better, a lot depends on your requirements/needs. Not completely autonomous but also R/C and always in sight. That changes a lot.

An antenna tower's not great for what I had in mind. I thought you were looking to reduce windage.

WestSystem's great, I thought you wanted to reduce costs.

If ideal sensor speed is 5 knots then I would attempt to design for 5 knots...

What would the payloads vary from and to?

If on/off is okay it'd be way better from a weight/space/efficiency/cost point of view.

The only draw-back is you'd have to spend the time designing the prop. Are you familiar with JavaProp?

So, I have another idea given the changes. It's more of a SWATH but with only one submerged hull and one surface hull. I'll have to find the web-site but it's right up your alley and it's being marketed successfully right now but in a much larger version. I'm not proposing you buy one, just look at the idea.

Tomorrow...

 

What I was getting at was that there was a lot of existing knowledge on boats of this size. Gearboxes (for single reduction ratio) are not that hard to find or build, and the ESC/Motor/Servo technology is plug and play these days (and ESC is REALLY preferable to an on/off switch for numerous reasons, not least control and reliability (these days there's little weight difference)). There is significant choice of drive systems and propellers, which are "off the shelf".

Also have a look at the hull weights that people are building to for this size of boat, and the construction techniques they are using. The model world (both maritime and aeronautical) are good at making stiff, light structures.

If you are struggling for displacement, I suggest you do a quick sum for a cargo-ship hull-form with block coefficient of say, 0.8, to see what overall size of boat you would need. V-hulls and catamarans are not designed for high payloads.

If I were trying to do this project, I would probably start with a ready-to-run model about 2-3 feet long, just to get a platform for the basic autopilot. Once I was happy with that, then I would start adding sensing gear, and at that point I would design and build a specific platform.

Hope this is of some help,

Tim B.

 

One of the possibilities for the boat: Scrounge around to find a used kiddie kayak. If not a kiddie yak then the smallest standard one you can find. That would be a painless way to get afloat without a lot of building time or money.

If your pickup truck has post sockets in the bed, you can easily make a simple frame to hold the longer boat up above the bed of the truck. That way you can make the boat as long as you like. If the truck has no sockets, then a few sticks will build a rectangular frame work that fits into the bed of the truck, a simple box frame with no skin. This has worked quite nicely for several pickup trucks that have hauled my laser, sunfish, kayaks.

 

BigK:

There is a used kid's freestyle at 5' 3" length about 10 down on this site if you decide to go that route:
http://www.kernriver.com/usedkayaks.htm

You can use a model air prop under $10 with a cheap resistor troll motor and probably achieve your target speed: http://www.boatdesign.net/forums/boat-design/efficient-electric-boat-27996-17.html

Porta

 

Oops, look at post #252 by McDenny on the second link.

P.

 

Nope, can't find it.

Looks like you got busy with something else anyway.

-Tom