Very helpful comments.
Smartcraft gauges are a bit small to see at speed for oldies like us??
Similarly the Raymarine 435 with 6" screen would be a problem with simultaneous large numerical display. £660 on jgtech.com
The Garmin 276C is similar, but priced at £500.
I like the proposed solution of
1. the Lowrance 6000C as full GPS colour plotter, and
2. the b/w Lowrance M52i as essentially a graphical depth finder combined with overlay data of Depth, SOG and COG, all three displayed in large letters each .7" high on its 4" diagonal screen. This latter unit has integral GPS aerial, a low res map which we will probably never use, and a low power but perfectly adequate sonar to give us an idea of the bottom structure, and a depth figure. It is only £219.
*The two of them are effectively then stand alone, although I hope the NMEA will enable us to display a large Depth on the 6000C if we need it in very bright conditions in harbour.
*We have a back up GPS in case one fails (as well as real charts and compass)
A few inevitable questions:
a) do we interface both GPS's to the DSC radio?
b) is the 6000C with its 6.5" diagonal screen the correct solution? Or am I going to regret not paying another £290 for the 10.4" 7000C. Would that larger one be cumbersome?
I intend to mount the big GPS on top of the centre of the dual console, with the M25i depth/fish finder on top to its left, and to its right directly in front of the helm the non-electronic ocean compass. The compass will be flush mounted, the other two on their twist and tilt stands.
Cheers and thanks