Design for Slow

Hello,

I am an open water swimmer and RC airplane/drone enthusiast. I spend a lot of time during the summer swimming a lake near where I live and have a lot of time to think. Anyways, I am working on a design for a small autonomous boat that I can follow during my swims. This boat would also carry a flag indicating that swimmers are in the water and provide something for swimmers to hang on to if something goes wrong.

The electronics are fairly straight forward. There several opensource platforms that already have that features for ground base autonomy. Ardupilot (Open Source Drone Software. Versatile, Trusted, Open. ArduPilot. https://ardupilot.org/) is one that I would use and have experience with.

Specs:
Hull Length - 5'
Width - 2'
Steering - differential thrust using two small water jet. I figure people will be near and I want to minimize the chance of getting finger damage.
Speed - cruise 1.5 kts, max 5kts
Hull design - ????
Hull - ideally self-righting

I chose the length and width because it seemed like it might be big enough for a swimmer to hang on to. ;-) It also seems like there could be room for a small storage area for water, food etc.

Everything is subject to change. I am really looking for ideas and feedback. I am in my own little world and would hate to start down a path that is doomed.

The big question for me is the hull design. Is there a hull the is optimized for a cruise of 1.5kts?

Thanks for your time.

 

AJC,

Welcome to the forum.

It's possible, somehow, but much easier to tow a flagged float.
Make it the shape of a little boat if you like, keel, mast, orange.

You may want to add a little drag to it for training effect!

 

This is a possibility and something that exists but it definitely isn't as cool. (Orca Openwater Safety Buoy at SwimOutlet.com https://www.swimoutlet.com/p/orca-openwater-safety-buoy-8185022/) Also, with the autonomous boat, I would be able to program different rates, paths and rest points.

This project isn't as much a need as it is something fun to do. ;-)

 

Re the design of the hull, you mention that it has to be capable of letting swimmers hang on to it.
So, how many swimmers, and how much support will have to be provided for each swimmer?
Is it literally just holding on (perhaps a few kg's of displacement) or should a swimmer be able to partially climb on board if they are tired?
Re stability, a catamaran hull form might be useful......

Who is going to be 'driving' (or controlling) the autonomous boat? It would be a bit difficult for you to swim and drive it remotely at the same time?
As Bluebell says, it would probably be easier to just tow it behind you. And a proper boat shape (or a catamaran shape) will probably have the same (or less even) resistance than a swim float, while being much more versatile.

 

You mention open water swimming >>> what maxi waves height you envisage, roughly ? Waves, even small, are an important specification for that size of hull (its resistance, its stability).

 

This sounds an interesting and probably feasible project - I wish the best for it.

I am not an open water swimmer but I can easily imagine that you might prefer to be accompagnied by a small automnonous vessel rather than having to drag a floating marker bouy behind you. I can also see the advantage of having that automonous vessel carry some food and water and presumably a means to signal for help if necessary. Furthermore, I would think that with modern battery technology it might be feasible for this automonous boat to have sufficient power and range that it could tow a distressed swimmer to the nearest safe landing point. It sounds as though you already have sufficient knowledge of electronics to carry out this project, I am guessing that you envisage a tiny electronic device carried on the swimmer's body, the control system within the autonomous boat sensing the position and course of this device (maybe acoustically although if you are swimming crawl stroke perhaps a wrist mounted radio device?) so as to keep the autonomous boat a few meters ahead of the swimmer. Then, pressing a single button on the device carried by the swimmer could be arranged to make the autonomous boat come slowly up to the swimmer.

I don't think hull design needs to be a stumbling block. Self righting is quite easy for an unmanned powered boat because you are not particularly concerned with static stability or motion in waves - hull design gets more difficult when you want to combine self-righting with good static stability or stability to carry sail. For example, a simple axisymetric hull, maybe like a stubby torpedo floating half submerged, with the centre of gravity off the axis of symetry, will be self righting and could at least be a starting point for a design.

Another thought is that a couple of members of the Amateur Yacht Research Society are developing a 'rescue float' for use by beach lifeguards. This is not autonomous (although maybe it could be). The present version is for human power propulsion but one option that is being considered is to have a pair of small electric thruster units (shrouded propellers) on short arms that hinge down from each side of the craft. The idea of the hinge mounts is that whatever way up the craft is floating the thrusters will drop down by gravity so that the propellers stay immersed.

 

Here is an example about in your size objective, with a cata hull , the ARCAB :
An affordable and portable autonomous surface vehicle with obstacle avoidance for coastal ocean monitoring - ScienceDirect https://www.sciencedirect.com/science/article/pii/S2468067219300161

 

Some others there :
Drone marin d'études océanographiques - Tous les fabricants du nautisme et du maritime - Vidéos https://www.nauticexpo.fr/fabricant-bateau/drone-marin-etudes-oceanographiques-44459.html

 

Make it a catamaran as in ARCAB in a previous post. A swimmer holding on may tend to overturn a small monohull. A small autonomous boat may be unable to follow the required course if a swimmer is hanging on to the side. Just some points to consider.

 

Thanks for all the comments and suggestions.

I think this (SL20 | OceanAlpha USV https://www.oceanalpha.com/product-item/sl20/) is something like what I had in my mind.

The boat will be RC/autonomous, meaning that someone could control it like an RC boat but it would have another autonomous mode. In autonomous mode, it would act in a predetermined manner. For example, it could be programmed to follow a particular path at a set rate, then loiter for a while, then start on another path at a different rate. Basically one could program a swimming workout.

I haven't been able to find a simple way for the boat to be aware of the swimmers. This is a hard problem especially when the swimmers are likely in wet suites. For the first round, the boat will follow a specific route to a point then wait for a swimmer to reach it and push a button to start the next leg.

Many swimmers that I swim with pull a buoy with them and I doubt that will change.

The primary purpose of this project is pacing, other features are a bonus.

 

What happens if you are tired or get a cramp? The boat will go to the pre-determined location and leave you behind. Also, you need to prevent the boat from hitting other swimmers and interfering with marine traffic.

 

I would think that would be an interesting project for an electronics engineer, but I am not one of those. I am not all that well up on the latest gadgets but I think you can get waterproof smartwatches that have a built in GPS and which could communicate by Bluetooth with another device within the autonomous boat, that device also having GPS built in. I dont know whether this would give the accuracy needed given that the swimmer and the autonomous boat are probably only two or three meters appart. It probably helps that you dont need an absolute position, just the relative position between a pair of GPS receivers. If the smart watch is worn on the wrist by a swimmer using crawl stroke signal transmission would be intermittent but I would think that suitable software could take care of that. Or the usual way to send signals through water is acoustic. I see that you can get acoustic modems that divers use to send data but they are fairly expensive and maybe too large. I would not think that you actually need to send 'data' - just have a single transmitter/receiver attached to the swimmer's trunks or wetsuit and three of them spaced out on the bottom of the autonomous boat. These would be a bit similar to the transducers used for depth sounders although the required range is somewhat less so perhaps they could be quite compact with low power requirement. Every few seconds the autonomous boat would send out a 'ping' and the unit on the swimmer would then return one so that range and direction can be determined from times of flight. If the autonomous boat does not receive a ping back when expected it would switch off its propulsion and wait, or return to the last recorded position of the swimmer - that way the system is 'fail safe' and if the swimmer is in difficulty he/she just needs to switch off their transmitter, or as a last resort throw it away.

As for hull design, the hull of the autonomous boat you gave a link to looks good but you did say that you would like it to be self righting and this one does not claim to be. (although it may be) Self righting is probably only necessary if you encounter breaking waves. If you don't need self righting then I would agree that a catamaran would be a good option and a cross beam between the hulls could be a useful handle for a swimmer to hang on to. I guess that you would like it to fit in a car boot.

 

The boat that I gave a link to doesn't look self-righting but I think with some changes it could be.

Locating a person underwater is a big challenge. The idea about having a "ping" from the boat and a response from some apparatus the swimmers ware is likely the best idea.

Again, the purpose of the boat is training and as a marker indicating that people are in the water. When the boat is used people will be behind it, chasing it and sighting off of it.

I am in northern in Wyoming in the US. At most, there are 10 people ever swimming at a time.

The biggest obstacles are other fishing boats, there will need to be some obstacle avoidance. Generally, people steer clear. Finding hard obstacles on the surface is not as hard.

 

In that case perhaps the autonomous boat should be fitted with active AIS (both transmit and receive) and maybe also a radar transponder. Cost would I think be in the region of £1000, maybe not too much between a group of 10 swimmers.

 

I love swimming in natural water.
I would be more concerned about overall size than self-righting. I swim in both placid and turbulent water. A pace boat is less than useless while body surfing. Two by five feet is way larger that what I'm willing to carry down to the swimming hole.

I would be happy to carry a self-propelled boggie board. Hang all the heavy stuff from it's bottom and it will be sufficiently stable. If it does manage to overturn then it would be easily flipped by the swimmer