What can cause a sudden jump in a speed (speed set-point of 0.03 m/s jumped to a 0.2 m/s) just before reaching a set-point and therefore resulting in an overshoot? DP system is IHC
What exactly were the circumstances of how you moved the boat? >10m pre-set move? Or series of 5m bumps? Has anyone looked at maintainer settings? Gains, etc.? You saying this is a one time event (never happened before) resulting in DP incident?
As a side note, DP incident reports can be found here:
Filter by Division = Marine
Filter by Type = Station Keeping Incidents
Incident has such a negative connotation to it. Let’s go with undesired totally random occurrence instead.
Dood dont be mashing dem buttons wrong and dere won’t be none of dem incidents
I’ve seen it happen on boats that had the gains up too high combined with the need to scale the boat.
[QUOTE=Fraqrat;189053]Incident has such a negative connotation to it. Let’s go with undesired totally random occurrence instead.[/QUOTE]
Not as negative as; “the vessel sunk”.
I much prefer the legal term; “the vessel took an attitude of negative buoyancy”. Much more lawyerly, don’t you think?
[QUOTE=Flyer69;189054]Dood dont be mashing dem buttons wrong and dere won’t be none of dem incidents[/QUOTE]
“Don’t be mashing buttons wrong”?? Seriously???
[QUOTE=Quimby;189051]What exactly were the circumstances of how you moved the boat? >10m pre-set move? Or series of 5m bumps? Has anyone looked at maintainer settings? Gains, etc.? You saying this is a one time event (never happened before) resulting in DP incident?
15m step, high gain. Just before reaching a set-point (~2m) upsurge in the thrust demand up to 80% => went down to medium gain, switched off the bias => speed 0.2 m/s from 0.03 m/s => overshoot of 3m => vessel stabilized => station keeping regained
https://www.uscg.mil/hq/cg5/ocsncoe/docs/Lessons%20Learned/DP%20Ergonomics%20Lessons%20Learned.pdf
He mashed de wrong button dood
[QUOTE=Flyer69;189054]Dood dont be mashing dem buttons wrong and dere won’t be none of dem incidents[/QUOTE]
“Don’t be mashing buttons wrong”? Seriously mate???
[QUOTE=Flash_Royal;189071]15m step, high gain. Just before reaching a set-point (~2m) upsurge in the thrust demand up to 80% => went down to medium gain, switched off the bias => speed 0.2 m/s from 0.03 m/s => overshoot of 3m => vessel stabilized => station keeping regained[/QUOTE]
Assuming the DP system is tuned properly…the only time I’ve seen thrusters ramp up like that near the end of a move is if the operator was adding distance in a direction off the original course such that the boat had to change its vector against the current. The fact that you are using high gains might have something to do with it. I don’t know the IHC system, but if I had the gains maxed out I would probably be running weather patterns/hove to. The system I use if you are in calm weather with gains maxed out the boat tends to overcompensate and ramp up. Possibly double check your Kalman filter, bias multiplier if you have one. Otherwise, if you’re bored and have the time try to replicate the scenario.
Dood is dere an echo in here? “Mate”?
[QUOTE=Flyer69;189072]https://www.uscg.mil/hq/cg5/ocsncoe/docs/Lessons%20Learned/DP%20Ergonomics%20Lessons%20Learned.pdf
He mashed de wrong button dood[/QUOTE]
What is that have to do with my case? Had your read the file you have posted yourself? You are not helping here!
I am gonna go out on a limb here and guess you are British, “Mate”?
[QUOTE=Quimby;189089]Assuming the DP system is tuned properly…the only time I’ve seen thrusters ramp up like that near the end of a move is if the operator was adding distance in a direction off the original course such that the boat had to change its vector against the current. The fact that you are using high gains might have something to do with it. I don’t know the IHC system, but if I had the gains maxed out I would probably be running weather patterns/hove to. The system I use if you are in calm weather with gains maxed out the boat tends to overcompensate and ramp up. Possibly double check your Kalman filter, bias multiplier if you have one. Otherwise, if you’re bored and have the time try to replicate the scenario.[/QUOTE]
Indeed, adding distance in a direction off the original course does ramp up (depending on the speed) but it was not the case.
I did not mention that it was only a stern thrusters ramp up, bow thrusters were ok as the vessel was moving ahead. Other thing I haven’t mentioned is that the vessel was laying a cable at 10m depth and DP system doesn’t have a tension sensor.
So what is your gut feeling about how the DP system is modeling the forces on the ship without a tension sensor? Is it possible the model was corrupted by an unexpected and unmeasured spike in tension causing it to ramp up?
Generally tension inputs are “feed-forward”, and without a sensor this external force is likely to be accounted for as calculated current. Possibly your model is not handling this scenario well.
[QUOTE=Flyer69;189162]So what is your gut feeling about how the DP system is modeling the forces on the ship without a tension sensor? Is it possible the model was corrupted by an unexpected and unmeasured spike in tension causing it to ramp up? Generally tension inputs are “feed-forward”, and without a sensor this external force is likely to be accounted for as calculated current. Possibly your model is not handling this scenario well.[/QUOTE]
The tension wasn’t that big on a cable, so I don’t feel that this could cause such a ramp up. And like you say unknown forces are likely to be accounted for as calculated DP current. Plus the vessel have been laying a cable using the same set up for already a month or so.
This is my first experience with IHC DP System and I must say that it is not user friendly. I’m not saying it’s bad, just not comfortable/easy to work with.
Was hoping that someone had a similar issue.
So what is the Master on your ship saying is the reason/theory for the issue. I’m assuming he/she is more familiar with the system.
Crap PID controller in the software, this is one of the differences in different DP brands due to the complexity time and expense of doing it right.
Unless it was a position jump and most DP systems will move at 100% thrust to get there, thats something many dont know, its a big surprise when it happens.
AFAIK only 2 vendors have added fixes/warnings for it in the last couple of years on some versions.