I can provide some real feedback from my experiences of the HemisphereGPS Vector OEM unit using two standard GPS
mushrooms. I have no direct experience of other units.
View of the sky is not a big issue , no more then any GPS
unit. The HemisphereGPS unit has an integrated flux gate plus accelerometer which provides heading if you loose lock. In practice you don't and mine was stern rail mounted. Placed on a radar
can or similar construction above the Bimini
etc would be fine. ( beside your antenna
farm ) , my mates used to slag me that my boat actually was really a Russian spy trawler
Separation distance , ie between the two antennas has a major impact on accuracy, processor performance and first fix time to solution. Further apart requires much more tuning and in certain circumstances can lead to long ( > several minutes) time to first solution. This is why most commercial
units use about .3-.4 metre separation. ( I trialled up to 0.8 )
Really sat compasses are the best heading units you can buy. Until you used them, you'd never go back to flux gate units. The main reason you haven't seen them on small yachts is purely price
. But I expect with the increasing penetration of overlay radar, MARPA , AIS
overlays and the reliance on good auto pilots, well see much more of these.
You are right Dockhead they are capable of incredible position accuracy , well beyond what's useful on a boat.
Yes we are only scratching the surface of GNSS systems. When we have 2-4 competing system and we can aggregate between them..........!!!!
If you can get one for 2k , run out and buy it. Certainly better then wasting money
on so called high performance flux gate units.