Originally Posted by ShinyShoe
I hate it when I get all poly-esq but I think your maths is flawed...
So you need to charge for 7-8 hours to transmit @25W for 1 hour. I'm kind of hoping that when the brown stuff hits the fan I'm not holding the PTT down for an hour...
It takes less than a 10sec to do a DSC mayday transmitting, plus probably a minute of being on flicking through menus etc if you wanted to send some info. 3mins for GPS to settle. Let's call it 6 mins... And you can get a voice call out. So 1/10th of the time you quoted. You quoted 8 hours so 480minutes, so you might get enough charge to power up a VHF + GPS and then transmit a voice call in under an hour. Sure I'd rather it worked the second I turned it on, but if it didn't I might prefer to be putting some juice in knowing in an hour i may be OK (especially as flat batteries often recover a bit after the drain has been isolated - ask any AA man how often they get to a car that wont start that starts after the hour it took them to respond) than remembering that great day out you used the solar panel money on the fuel for...
If there was a recent position known (e.g. you had VHF and GPS working when you arrived at anchor) you probably need less than 1minute of 25W transmit. Provided you genuinely were only going from just too low voltage / amps to just above (incandescent bulb will keep draining, starter motor will. Only electronics will tend to switch off when power low rather than just work less well so depends what drained battery) you might only need 1/60th of what you suggested. So 8mins of charging might get enough to send a DSC message... Granted that's in med conditions but in UK cloudy winter day you would get 40% of that.
But they also were not proposing the panel sat in a locker till the battery was flat. They were saying they would leave it as permenant fixing. So its charging when you anchor up and turn the engine off. At 0.3A/HR going in that's not really compensating for much use. But it probably covers leaving the VHF on *listening* or maybe not switching the plotter off depending on size and screen contrast etc. So when they ho to move off the engine still starts and there is no issue... But that's why I asked about kit and such like...
Please note I did say a flat battery
Maths isn't flawed for the given worst case I used.
However, I understand your point.
If it gives you a warm feeling to have one then that alone is worth the money. Bit like life jackets in a way, just hope never need it.
P.s I'll have a better read later, just taking a break and admiring my suzuki 200 sitting on the hoist ready for going up a hole.