I agree fully, it would be foolish to use this for navigational purposes. Where we continue to disagree is in the common sense of the average mariner.
The other point is understanding the limitations of the systems you are using. For example many voyage plans are done using Microsoft Excel or shareware programs like Waypoint for Windows. Both have bugs that can cause serious navigational errors so should these programs both stamp "Not For Navigational Use" on them? Should they be banned from use on the bridge altogether?
The advantage of an iPhone app over a bridge system is speed. On the bridge we are all being overwhelmed by technology and communication but, in fact, it's not the information that's overwhelming us, it's the lost time it takes to organize and process this data that's causing the problem.
Also what about non-critical tasks? Say you want to DSC a nearby ship. It's much more efficient to bring gTrax to the GMDSS console than it is to walk over to the AIS... scroll through the MKD of an AIS display.... try to figure out which ship is the right one (this is easier on ships that have ecdis.... but not all do) write down the MMSI number.... walk over to the GMDSS console and retype it. Using this program you can perform this duty in 30 seconds but without it making this dsc call would take 2-5 minutes (assuming you wrote down the correct numbers).
The extra 1.5-4.5 minutes you saved by using gTrax can now be used on a more important task.
Like anything you need to know the limitations of the system and verify the data. I would not trust an excel voyage plan without verifying the results manually just as I would not use gTrax without verifying the data on a class approved ship systems.
Whenever we get new equipment or software on the bridge I always ignore it during my first few watches and test it when there is free time available on someone else's watch (with their permission, of course). Personally I will certainly be testing the app out on the bridge while I'm off duty.
Last it's simple to use. ECDIS and AIS systems approval does not care about user interface design and it was the complexity of the ecdis system contributed to the Cosco Busan hitting a bridge. Even earlier in the error chain of that incident the complexity led to the pilot's reluctance to learn the system. Now what if the pilot (or an 17 year old cadet!) had gTrax on his iphone (say to monitor his next job from the car)? Within 30 seconds of launching the app it would have been clear he was not lined up on the proper heading.
So while I still agree fully, it would be foolish to use this for navigational purposes, I do not think it should be banned from use on the bridge because, like anything, it has it's uses and limitations and it is up to the watchkeeper to understand these and only use the program for non-critical tasks.... then verify his findings.
Circling around to my initial point... gCaptain was built on trusting our forum members. I don't think we need to provide a big pop-up box saying "The ideas presented in the forum are not verified and should not be used in the navigation of a vessel" just like I'm not going to build a big pop-up in gTrax saying "This app has not been verified by class and, therefore, should not be used for navigational purposes". The members of gCaptain are smart enough to know when a forum poster is giving dangerous advice and they are also smart enough to know not to ignore their class approved ECDIS.