[quote=CaptRob1;19347]Have a question I would like to get some feedback on. Really hearing different opinions. Looking for facts.
If a vessel has 2 GPS (or DGPS) are they considered DP2 on that aspect of it. Someone said according to IMCA, that does make them in compliance.
I know GLONASS (Russian Sat system) is ok for one reference, along with a DGPS. GLONASS does not have Differential updates.
But if you have a Mini max and other name brands, does that still make you in compliance with reference?
I know about Taut wire, beacons and so on. Only GPS’s on this question.[/quote]
As long as they are showing on your sensor page on the two DP computer systems as two separate and complete sensor imputs I would think that the answer is yes…
[quote=CaptRob1;19347]Have a question I would like to get some feedback on. Really hearing different opinions. Looking for facts.
If a vessel has 2 GPS (or DGPS) are they considered DP2 on that aspect of it. Someone said according to IMCA, that does make them in compliance.
I know GLONASS (Russian Sat system) is ok for one reference, along with a DGPS. GLONASS does not have Differential updates.
But if you have a Mini max and other name brands, does that still make you in compliance with reference?
I know about Taut wire, beacons and so on. Only GPS’s on this question.[/quote]
I believe you have to have 3 reference systems, and one of the three has to be something other that DGPS…to be in class. I’ll get the info later (Alabama game on). The reference system requirements between class 2 and 3 are the same (minus the extra gyro & wind bird). I have a blank “Proving Trials” format from Noble Denton…that should have everything in black and white.
Anchorman, I argued your point with Rigdon Marine since the day they built their first boat but to no avail. All we had on the first 10 boats was two Leica MX420 DGPS units and the boats were classified as DP2.
We had a Cyscan laser sensor unit but that was useless on the two seismic boats Rigdon had. All the other sensor inputs such as VRUs, Gyros, Windbirds, etc. didn’t count of course as they were not position indicating inputs. The only time we had a third position indicating imput was if we hooked up to the Surveyors’ stuff and that was only on the boats that had Surveyors or Navigators. Rigdon wouldn’t even pay for the DGPS differential signal so we ran our DP System on GPS only for 90 percent of the time…The boat I have been working on has 2 Glonass signals, 2 real DGPS signals, Tautwire, Laser, and the Surveyors’ signals that keep us in position…
[QUOTE=stevefoster;19358]Anchorman, I argued your point with Rigdon Marine since the day they built their first boat but to no avail. All we had on the first 10 boats was two Leica MX420 DGPS units and the boats were classified as DP2.
We had a Cyscan laser sensor unit but that was useless on the two seismic boats Rigdon had. All the other sensor inputs such as VRUs, Gyros, Windbirds, etc. didn’t count of course as they were not position indicating inputs. The only time we had a third position indicating imput was if we hooked up to the Surveyors’ stuff and that was only on the boats that had Surveyors or Navigators. Rigdon wouldn’t even pay for the DGPS differential signal so we ran our DP System on GPS only for 90 percent of the time…The boat I have been working on has 2 Glonass signals, 2 real DGPS signals, Tautwire, Laser, and the Surveyors’ signals that keep us in position…[/QUOTE]
Just because you are classed DP 2, doesn’t mean you are “in class” because the ABS certificate says you are able. If there was no Cyscan, you most likely would not have gotten that class. FEMA should have included losing DGPS (all DGPS) at a structure while using laser. Just because you have two separate DGPS with separate power sources and all of that - that doesn’t mean that corrections received are from separate sources, although that can be set-up through several means.
4.1 - General
Accurate, reliable and continuous position information is essential for dynamic positioning. Some DP operations require better than 3m relative accuracy. A DP control system requires data at a rate of once per second to achieve high accuracy. Reliability is, of course, of vital importance, to operations where life and property may be put at extreme risk through incorrect position data10.
All DP vessels have position reference systems (PRS), (sometimes referred to as position monitoring equipment or PME), independent of the vessel’s normal navigation suite. Five types of PRS are in common use in DP vessels; Hydroacoustic Position Reference (HPR), Taut Wire, DGPS, Laser-based systems (Fanbeam and CyScan) and Artemis. A brief description will be given of each.
DP control systems ‘pool’, or combine, position reference data from two or more position reference systems. If only one position reference system is enabled into the DP then it is simply checked, filtered and used. If two or more are available, then the system needs to use both equally or according to their individual performance.
In all modern DP systems the weighted average option can be selected, whereby individual position references are weighted in inverse proportion to the variance or ‘spread’ of position data; the higher the weighting for an individual position reference system, the greater the influence of that system in the position calculation.
Early DP control systems did not have the capability to learn from the past performance other than by the integral terms of the controller. Modern systems are able to improve station keeping performance by using a Karman filter, which provides a model of recent performance to improve present performance.
For any operations requiring [U]DP redundancy (equipment Class 2 or 3 operations) it is necessary to utilise three position references.[/U] Two PRSs are not adequate, because if one has failed, contradictory reference data provides an impass, whereas three systems provide two-out-of-three voting to identify a rogue sensor.
Where three PRSs are required, the DPO should choose systems that are different. This reduces the probability of common-mode failure, where one event may result in a loss of position.
A brief description will be given of the five commonly used position reference systems.
[quote=CaptRob1;19347]Have a question I would like to get some feedback on. Really hearing different opinions. Looking for facts.
If a vessel has 2 GPS (or DGPS) are they considered DP2 on that aspect of it. Someone said according to IMCA, that does make them in compliance.
I know GLONASS (Russian Sat system) is ok for one reference, along with a DGPS. GLONASS does not have Differential updates.
But if you have a Mini max and other name brands, does that still make you in compliance with reference?
I know about Taut wire, beacons and so on. Only GPS’s on this question.[/quote]
Hey Rob, the interpretation on the II is no; DGPS (whether minimax, CNAV, or from survey) is considered one reference system no matter how many different DGPS sources you utilize. We have to have another reference system in the desk to be operating in class 2.
All gps’s will suffer errors due to the signal passing through the ionosphere. This means that they will all be affected by that single external influence, even if the D corrections are coming from multiple sources.
So the answer is: No way, No how.
S.