It was fine when the head unit was plugged in this morning (it, and the sounder head unit, is kept in the house when not in use), right through until I had finished bottom fishing and was trolling lures (thankfully didn't really need GPS for trolling, but having speed indication would have been nice) - unit had been running without issue at that stage for approx. 5 1/2 hours, not an unusual duration as often go out much longer than that.

Has anyone else experienced issues with a similar Navman unit, and if so was there a straightforward solution?

In the past when I have received the "no fix" message it has been a short duration loss of signal and seemed to sort itself with no intervention at all. Very 

I just searched trademe and can't find any $5 aerials, would you have a link to the one you are referring to?

I found a similar antenna and got that sent down only to find that didn't work either - turned out that the issue was with the SMA connector on the back of the GPS unit - seems to have spread the contact surface of the female socket. As the unit is now obsolete and (even though a sparky!) didn't feel confident that I would be able to successfully replace the faulty part my creative streak/#8 wire mentality took over and I figured that I could stuff a few strands of copper into the socket to enable the plug to make contact - SUCCESS, had the satellites up immediately. Only problem was that I had already cut off the suspected dodgy plug so had to replace that, but all's well for now at least, and the new antenna bought also fired up so I now have a back-up stashed on the boat.