In an ideal world you would want displays for both radar and plotter at both stations but there could be problems with this such as limited budget, limited space for mounting, particularly at the upper helm, and waterproofing (whatever the suppliers say, these units will not stand regular soaking for long). It also depends where you prefer to helm from, how easy it is to move between each helm and how good the visibility is from the lower helm at speed. Some people prefer to helm from the flybridge even in the foulest weather whilst some wont venture upstairs unless the weather is perfect. Personally,assuming the visibility from the lower helm is OK, I would have both plotter and radar displays at the lower helm with a plotter repeater or at least Course to Steer/Distance/Cross Track Error display (maybe available on autopilot display if interfaced) up top. This is because you're more likely to be helming from the flybridge when you're in confined waters and thats when you need the plotter/GPS info the most. You're going to need the radar most when it's foggy and, personally, I ask a responsible crew member to helm whilst I concentrate on the radar. I think working all the various controls on the radar needs maximum attention so it's best to be dry and warm below - that's my excuse, anyway!
For what it's worth I ran Raytheon Pathfinder radar/plotters at both helm stations on the Round Britain. Invaluable being able to have all the info in both places provided that you regularly use the interior helm, as we increasingly did, as well as the flybridge.
Upper helm (LCD) unit survived many soakings, salt and fresh and is now in service on Calm Voyager. Unless the manufacturer of your boat has been brave enough to put a steep angle on the fascia use the trunnion mount for any unit, avoids the sun going direct onto the screen and blacking it out (mono) or completely ruining the colour image (colour)...that is unless your budget stretches to the new generation of daylight viewable colour screen which is much better (wish my computer laptop had one).
Radar in a solo installation downstairs only really works if you are prepared to helm the boat from there at night and in poor visibility (many owners hate that) or have a competent crew prepared to monitor the screen. Even then you are not using it to its maximum effect by keeping it on during good vis to bone up on your skills for moments when you really need it.
Pre-departure checklist on my boat always includes radar on and it is always used on passage, whatever the conditions. Call me lazy but it is the easiest way to monitor collision avoidance with ships on cross-Channels, for instance.
Kim, I had a trunnion mounted Autohelm Navcentre repeater on the flybridge of a previous boat, supposedly designed for exterior use, which kept going blank at inconvenient moments. It went back to Autohelm twice and was replaced once completely in 2 years use. Mercifully, some thieving b.....d stole it.
Agree with you on radar use. Being a complete wuss these days, I tend to helm from downstairs, particularly on long passages, and have whiled away many a long hour playing with the radar in good visibility. A bit disturbing, though, when you see that 40' yacht passing half a mile abeam barely registering a speck on the screen
Perhaps we can start the wuss club together? Increasingly have become an inner helm couch potato over the years, these wet summers are a great encouragement.
Can promise the RL70-series was a much better piece of kit; suspect a lot of lessons taken on board with the earlier units. Certainly we threw some pretty serious weather at it, although I must admist we took advantage of the trunnion mount and demounted it on those rare occasions when we were holed up for a day. Ditto if we were tied up to public quays.
It has been said (there was a long thread on this ages ago) that radars fry your brain, therefore you need to be down below when the radar's on in most modern flybridge boats (where the radar arch is head height). Hence no point in upstairs repeater. Not sure if it's true. Kim did you run the radar on the round-Britain while people were on the flybridge? Any probs? (If I racall the Sealine radar mast would put the radar at roughly head height)