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Mounting Waterlink on a moving boat

(Etienne Demers) #1

Hello,

Has anyone used a waterlink GPS on a boat where the boat follows the ROV underwater?

I take it rigid poles would be required?

Is the position still accurate especially with the boat rocking in all directions?

Thank you,
E.

1 Like
(Jacob) #2

The Water Linked system has a GPS and IMU on board, so it should be able to compensate for both the movement and rocking.

I recommend you contact Water Linked support for more information, or maybe @Torgeir will comment here.

(Bo Koppel) #3

Hi!
I do use Waterlinked on moving ship.
Have mounted plastic pipes on ships, then easy to mount/dismount Waterlinked receivers inside pipes.
I think just hangning recivers overside is not good on moving ship.

Moderate rocking no problem.
Heading sensor inside Waterlinked box is not usable yet (calibration drifting), use other sensor like GPS compass or fluxgate.
Built in GPS is not stable either, use exernal position (ie GPS compass)
Bo

(Etienne Demers) #4

Hi Bo,

Thank you for your feedback, I like your idea.

I was looking at this GPS earlier. https://emlid.com/reach/
Mounting an external antenna as well would be the ideal setup.

I am hesitating a bit due to the range only being 100m. Have you tried testing it deeper, >150msw?

Cheers,
E.

(Bo Koppel) #5

Hi!
Do You get ship heading with emlid stuff?

Waterlinked is limited to 100 m range from the transmitter in their software
Possible solution is to drop the receviers to ie 100 meters depth…
But doing that while moving boat, its a nono

Btw if You have not seen it, the demo on Waterlinkeds wepage show real life:
http://demo.waterlinked.com

(Etienne Demers) #6

Hi Bo,

I do not own one but I think not.

Yeah that is a shame about range its such a neat little kit.

Jobs I am looking at is about 150msw…

Cheers,
E.

(Luis Gamez) #7

Etienne,

Buy the WL receiver with longer cable and you can submerge the receivers up to 50 meters depth then you will get the position up to 150 meters depth perhaps that might work for you? I´ts possible actually the only problem might be the moving boat, moving a 50 meters plastic PVC tube at 1-2 knots might break it.

(Etienne Demers) #8

Hi Luis,

I was wondering if you could lower the receivers that low…

Could be an interesting option to install on a platform but for a boat its not really appropriate.

Cheers,
E.

(Scott Marion) #9

Hi Bo,

Could you possibly quantify the conditions in which you have had success (or not) with the Waterlinked system? I am considering purchasing the system but want to make sure that I will have “reasonably accurate” tracking on a small (~8 m) boat in ~4-5 ft ocean swells, when the vessel is drifting (meaning that it will be sitting in the trough and rocking), with the ROV at 20-40 m depth.

Thanks,
Scott

(Bo Koppel) #10

Hi Scott!
Your boat is about same size as the smallest I use.
Biggest problem if You do not pilot or anchor your boat is piloting problem due to rocking sideways.
Not easy to handle Joystick in that situation.
Of course the waveperiod is a factor, long waves more lifting then rocking is OK.
From Waterlinked point of view you have to put the receivers deep enough so they are not getting to close to surface; that could make disturbing bubbles.
In my experience I would say 3-5 feet waves OK, if not sideways.

Solutions are:
-Competent skipper that can handle the tether and position the boat from Waterlinked info.
-Anchoring, if the situation gives the bow towards waves.
-Drift anchor to hold the bow towards the waves, ROV has to follow boat from Waterlinked info.

Keep in mind that Waterlinked integrated GPS and heading sensor is not reliable.
Use a GPS Compass for ~1 000$ like Hemisphere V104

(Scott Marion) #11

Thanks- very helpful information here.

We have done both piloted and drift transects and generally find more success with drifting (or “partial drifting” with some course corrections) because the tether management is smoother, especially when the wind comes up. For short transects it works to find the boat’s drifting COG and then pilot the ROV at that heading; just dead reckoning. But I would like to use the tracking system to safely conduct much longer transects.

How deep do your PVC pipes go for the receivers go? Do you have to support them very rigidly or is it OK if they wave around a little bit?

(Bo Koppel) #12

Hi!
Depth of pipes/receivers depend on boat.
Must be deeper then splash/bubble zone, in my 9 m boat about 0,5 meters.
On bigger ships to allow working both sides of boat, depth must be deeper then boat keel.
ie free sight from transducer to all receivers.

Only support in 9 m boat is plastic tube, enough, are fastened to hull almost all the way.
On bigger ships I use aluminium L profile around the plastic tube, used to depth up to 4 meters.
If You have small movements on centimeterbase I see no big problem, distance between receivers should be much more, ie ~8 meter lenght and ~3 meter sideway

1 Like
(Steven LE BARS) #13

Hi,

I also did a rigid mounting with 4 aluminium poles @1.5m depth and shrouds. I input an external RTK GPS and furuno GP500 heading sensor (soon replaced by a SBG ellipse). It works fine for shallow water applications in calm seas.

It is too bad the the internal heading sensor does not work in open seas for professional equipment and that I discovered it on my own during demos with a client.

I am still not highly satisfied for deeper and more technical inspections as some bugs remain on the GUI. Furthermore, velocity of sound is not configurable by the user, in tropical areas where I work we have up to 1540m/s VOS compared to the approx 1470m/s configured in the GUI code so we have no way to achieve the 99% accuracy they pretend. I already informed them about that but I am still waiting for a webGUI update.
Last thing is that to my knowledge, there is no possible IMU input for vessel motion correction in the master D1 so it entails a further positionning error in open seas compared to classic USBL systems.

1 Like
#14

Hi Steven,

Glad to hear that you are happy with the shallow water performance.

What bugs in the GUI are you referring to? I don’t have any remaining customer reported issues in the latest 2.3.1 release. Please report any bugs you find on the Water Linked support channel.

Those who have followed the software releases for the Underwater GPS have seen a great improvement in the usability of the system. We have prioritized ease of use over advanced configuration, which means that you have not seen settings like speed of sound yet.

That being said, we see that this is useful for advanced users and we want to offer this in the future. (but first we need to finish the Water Linked Modem M64)

The system does indeed support external IMU input (heading only). We always recommend users to use external GPS and IMU when available. The internal GPS and IMU on the Underwater GPS system is typically less accurate than what you find mounted on vessels and we do see IMU limitations when operating in some combinations of waves and boats.

You are correct that vessel motion correction (pitch/roll) is currently not supported. This is to my knowledge not something Water Linked have claimed to compensate for either. Moving forward, motion compensation might be a feature we want to add if enough customers show an interest in it. This is perhaps especially important as we are moving toward longer range (ooohh… teaser).

1 Like
(Steven LE BARS) #15

Hi,

As I told you, I still got sometimes the heading issue in the past release. I just upgraded to the latest version, I am sure I will not have that anymore. I have seen some improvements on the position display while not in water, the information on each receiver connection (which enabled me to realize one of mine was not working fine).

I had to postpone my inspection planned today because once again I do not get the depth from the BlueRov on the GUI with A1 locator. This may be due to the recent Ardusub update, I will talk to BR directly about it.

I am waiting for the VOS correction then, vessel motion correction is indeed necessary for deep water inspections if we want enough accuracy. Looking forward seeing your new long range products.