Presence Detection for Sailing Boats

[neoandrewson]

Hi all,

A friend of mine owns a small dock place which he is planning to rent out in summer. I donot have the exact picture, but looks very similar to this [1]. Perhaps, the best representation of the space he owns is this [2]

We are planning to build a motion sensor to detect the presence of a boat and log it, while he is away. I can confidently interface GSM/GPRS sensor with an arduino to send data to my server at home. But I am not sure which sensor to use. I am planning to place the entire module in a PVC casing between corners of [2], under wooden floor, diagonally facing the boat. As it will be in close contact with water, I guess waterproofing is necessary. I guess the module will be atleast 1-2 m away from the boat, when boat is docked.

I have read about waterproof ultrasonic sensors, but they are very expensive. Magnetic proximity sensor has too less range to be any use. I was thinking of using PIR sensors as they have good range and are relatively cheap. But my questions to all experts out here is that can it detect metallic objects like boats? And can I waterproof PIR sensor without hurting its range? (say a plastic cover or resin gel)

Thanks a lot for your patience folks & please don't hesitate to ask any thing for clarification!

 

[MikeMl]

PIR sensors respond to the body heat put off by a living thing. They do not work reliably where the object they are trying to detect is at the same temperature as the background.

Look at post 10 in this thread.

 

[neoandrewson]

Hmm. So what are my options? Magnetic sensors? But I could only find sensors with range limited to 10 - 15 cm.

 

[MikeMl]

Hmm. So what are my options? Magnetic sensors? But I could only find sensors with range limited to 10 - 15 cm.

Look at post 10 in this thread.

 

[Mr RB]

The Sharp IR sensor GP2Y0A700 - 5.5M is good for sensing any colour object reliably up to 5.5 metres away. Unlike ultrasonics it can go in a completely sealed case with a glass window;

https://www.emartee.com/product/41985/Sharp%20IR%20Range%20Measurement%20GP2Y0A700%20%20%205.5M

 

[neoandrewson]

Thanks for the info!! I have few questions though. I am curious as to how it works. Infrared? or Laser? But important question is does presence of water droplets on the casing affect the beam (like rain drops on casing)? But I will give it a shot. Thanks again.

 

[neoandrewson]

The Sharp IR sensor GP2Y0A700 - 5.5M is good for sensing any colour object reliably up to 5.5 metres away. Unlike ultrasonics it can go in a completely sealed case with a glass window;

https://www.emartee.com/product/41985...%20%205.5M

@Mr RB, Thanks a lot for info. This comes very close to what I need. I need few clarifications though. Is it same as this? I mean specs read the same, its just the trailing PCB board and difference in cost I am concerned with. Amplifier + UART?

Thanks again!!

Any different ideas are also welcome

 

[Mr RB]

Yes it's the same part. Water droplets on the glass or dirty glass will affect the operation.

Actually when rain is happening it will probably fail to work too, but so will ultrasonics generally.

You will need some other decoding hardware to check for rain, and/or dirty glass.

The sensor will produce a voltage that represents the distance, so if you put it on a post and point downward 45' to the boat, it will pick up the movement of the boat. That small voltage change should let your processor know that it is seeing the boat, and not just a fouled glass (which will probably just make the same constant voltage).

The sensor datasheet is downloadable, it runs from 5v 30mA and produces a voltage readable by a PIC ADC input.

 

[languer]

Are you detecting just your friend's boat or any boats (or many boats throughout the dock)? I ask, because IR is really not optimal for those situations unless you protect it against the environment; in particular dirt, scaly deposits, and of course water. IR is no more or less than a light beam, the detector is really not more than detecting the absence or presence of light. So if you were going to use IR, then you should somehow encode your signal. That will not eliminate the fact that the complete absence of light (say because the lens is cover with grime) will obscure any detection capability of the sensor, but will go a very long way in avoiding false detections (which I see as your number 1 problem).

If you are only detecting one boat in one location on the dock, I would think of a "transponder-like" setup. You could do this with IR, where the transmitter is on the boat. I would have about three (transmitters) in the boat, with wide beams, sort of aimed at the general location of the receiver, and taking turns at sending the "I'm here" signal. The receiver would also be a wide beam (angle) device which is looking for this "I'm here" signal (encoded, of course - or more correctly stated, modulated). As long as the receiver keeps receiving this "I'm here" signal (say every hour (or 2, or 3, or whatever you think it's best), the boat is considered at dock. This of course is good for monitoring 1 boat; because both the boat and dock are match to each other. A better option for this scenario would be an RF "transponder-like" system. Same idea, but as opposed of three IR transmitters and one IR receiver, just one RF transmitter and one RF receiver. This has the distinct advantage that the RF eliminates (for the most part) the effect of the environment.

I'm not sure how you could optimally detect the presence of any boat in the dock, arriving at any designated location. That is a more general problem and I will assume denies the option of having any sort of electronics on the boat; and would entirely rely on the dock-side for detection. An IR system (like the one you were discussing) maybe better for such a case (but still with the same caveat as before). That I would attempt to pair with some good encoding of the signal such that I'm not relying on just the return signal, but the "signature" of the return signal (e.g. you send a pulse train of "1001101" and expect the return to look just like that - think RADAR - in much lower scale). And I would not completely rule out ultrasonic either, encoded of course (a sound wave has better tolerance to blocking, under such environment, than a light wave).
I've never done what you're doing before, but it sounds extremely interesting.

 

[dougy83]

You can get sealed ultrasonic transducers; you don't want to gum up unsealed ones with resin.

Here's an example product: **broken link removed** datasheet is available on that page also. The device can be used for both transmit and receive; so you can use two in the configuration you normally see (e.g. SRF-04) or just a single device with a multiplexed driver and receiver.

Or have a look on ebay - **broken link removed** -- I'm not sure, but these may be sealed, or they may just be splash resistant.

 

[Externet]

If you are able to send wireless data from the dock to home; I would use a very low resolution camera properly aimed to the docking areas of interest and see/save the time stamped image at home. Even a picture an hour or as often as needed, will register activity. I do not know enough about computing resources, but even the owner could check happenings via the net while vacationing in Timbuktu.

If you go this way, I would like to learn the details on how to do it.

 

[Mr RB]

Are you detecting just your friend's boat or any boats (or many boats throughout the dock)? I ask, because IR is really not optimal for those situations unless you protect it against the environment; in particular dirt, scaly deposits, and of course water. IR is no more or less than a light beam, the detector is really not more than detecting the absence or presence of light.
...

Hi Languer, sorry to argue but the Sharp IR sensor we are discussing is already quite sophisticated.

It send out a modulated beam, has auto gain control (so reflecting surface colours do not matter) and uses triangulation to detect the distance to the reflected object. Then the analog voltage output represents the distance to the object (1m to 5.5m range).

It's designed for industrial distance sensing. The only thing needed would be a sealed box with a glass window.

 

[languer]

Hi Languer, sorry to argue but the Sharp IR sensor we are discussing is already quite sophisticated

I stand corrected then. That system does include some sophistication. I would still rate IR measurements third for such an environment; mainly because light waves are more heaviliy influenced under that environment (due to wavelength). But the Sharp device is definitely robust.

 

[Mr RB]

Yeah that boat detection is a tricky thing to design a sensor setup for, for sure.

The best system might be a high pole with a weatherproof camera overlooking the whole area (multiple boats). Then send the images to a secure internet page or something. Then the docks owner could check the web page to see the stored photos and see if someone is using the dock without paying.

 

[neoandrewson]

Wow, thanks a lot for the interesting discussion!!

The project sure seems challenging. I am planning to scale this implementation to multiple dock spots in the area, so that others can also use it. Now, the problem with video camera would be that if a person owns multiple dock spots in a marina, then she has to go through a pile of videos. Placing a camera on a high pole to cover a large area also doesn't seem to work that well, because it might raise security/privacy issues

On the other hand, IR sensor seem plausible.

Yes it's the same part. Water droplets on the glass or dirty glass will affect the operation.

Actually when rain is happening it will probably fail to work too, but so will ultrasonics generally.

You will need some other decoding hardware to check for rain, and/or dirty glass.

What do you mean by decoding hardware? You mean a "electronic hardware" or a "material"?

I am planning to use something like **broken link removed** or this for water & snow. I am sure excited about it and I can use the paint for other stuff as well . Anybody with experience with similar product?

Here's an example product: **broken link removed** datasheet is available on that page also. The device can be used for both transmit and receive; so you can use two in the configuration you normally see (e.g. SRF-04) or just a single device with a multiplexed driver and receiver.

If ultrasonic sensors are indeed so cheap, then I will use it. I am concerned about their operation and their survivability at low temperatures. An exposed sensor is my concern. I wonder how well do they work with a coating of paint or spray mentioned above.

Yeah that boat detection is a tricky thing to design a sensor setup for, for sure

Looks like it!! As I reckon, its not only the sensor, but also the factor environment resistance adds to the difficulty of the setup. The sensor should be fine during summer, but in winter temperatures can drop to as low as -30 degree celsius. Though sensor & electronics can be turned off, it sure needs to withstand the temperature.

Btw, how about magnetic sensors? Can we boost its range? I have seen one application for smart parking **broken link removed**. Wondering if I can use it for boats as well. After all entire boat hull is metallic and they work in tough outdoor conditions.

 

[misterT]

I was wondering if it would be possible to make a metal detector, or "inductive loop", on the side of the dock. They use that method to detect cars when they arrive to traffic lights. That could be extremely reliable in that weather etc. You can keep the electronics in a box on dry land.
https://diamondtraffic.com/technicaldescription/124
https://en.wikipedia.org/wiki/Induction_loop
I found many circuits for car detectors with google.

 

[ericgibbs]

If ultrasonic sensors are indeed so cheap, then I will use it. I am concerned about their operation and their survivability at low temperatures. An exposed sensor is my concern. I wonder how well do they work with a coating of paint or spray mentioned above.

hi,
A common yacht ultrasonic frequency transducer is 150KHz, its about 5cms in diameter with a threaded shaft.

They are often mounted inside the boats fibre glass hull, in contact with the bottom surface of the hull. So they transmit and receive thru the fibre glass hull

To improve performance and range thru they can be mounted inside a short tube filled will a light oil, they do work well.
http://yachtvalhalla.net/articles/transducer/transducer.html

They are also designed to mount thru the boats hull.


Go to your local yacht chandlers store and you should be able to buy a complete system, transducer and acoustic transceiver unit or simple fish finder sounder.

EDIT:
I would suggest you determine the tidal range at the berth if its open to the sea, before you mount a side ways looking transducer below the water line on the pontoon, also the draft of boats using the berth.

 

[dougy83]

If ultrasonic sensors are indeed so cheap, then I will use it. I am concerned about their operation and their survivability at low temperatures. An exposed sensor is my concern. I wonder how well do they work with a coating of paint or spray mentioned above.

Yes, the transducers are very cheap. You do need a circuit to drive the transducer and to listen for the echo. The datasheet brief of the Jaycar device is available at the above link (another version here http://www.quartz1.ru/images/T_R40-16B.pdf); it states the operating range is -40° to 80°C. Those units are sealed and waterproof, so you shouldn't need to paint them. Painting may decrease the sensitivity. Possibly anodising it would affect it less.

How many moorings do you need to monitor?

 

[neoandrewson]

Thanks a lot for your feedback!

To improve performance and range thru they can be mounted inside a short tube filled will a light oil, they do work well.
http://yachtvalhalla.net/articles/tr...ransducer.html

Yes, the transducers are very cheap. You do need a circuit to drive the transducer and to listen for the echo. The datasheet brief of the Jaycar device is available at the above link (another version here http://www.quartz1.ru/images/T_R40-16B.pdf); it states the operating range is -40° to 80°C. Those units are sealed and waterproof, so you shouldn't need to paint them. Painting may decrease the sensitivity. Possibly anodising it would affect it less.

Thanks, I will look into it. I guess for time being, I will work on Infrared and then move to ultrasonic if need be. Right now, its only one mooring.

I will keep you updated anyways.. Have a nice summer!