There’s no need to become hostile. Comments were not (and neither were they intended to be) patronising.
Many here that seek help do not, perhaps, have the level of understanding or experience that you yourself have outlined. Some are genuinely of the uninformed belief that GPS is a panacea of unbroken reliability - that will work flawlessly in all situations.
Thank you for providing additional detail as to your situation and application. For those of us that are knowledgeable in this field, a greater understanding of your application offers opportunity to provide specific and informed comment.
From your description, I assume that your are operating in UK waters - and as such, hopefully, will be monitoring either Notices to Mariners and/or Notices to Airmen. If so, you will hopefully be aware that there are many jamming trials being conducted throughout the UK that regularly interfere with civilian GNSS and ISM systems over wide areas.
You are correct in that there have been some reports of issues with Navionics Apps when used with iPad. Of those that have encountered difficulties, issues have often been resolved by installing a GPS repeater above/below deck - and/or by utilising an external GPS receiver (e.g., BadElf) coupled to the iPad using either a cabled connection or Bluetooth.
