Power usage / requirements

[PhillM]

If it's 4W, at 12V that would be a third of an amp (watts equals volts times amps) - that's pretty close to my guessed quarter of an amp! It's certainly nothing like 3A. Over 24 hours that 1/3 amp would be 8 AH. That would include transmitting. I might have real life figures written down, but that would be on the boat.

The Watchmate is a Class B AIS, which means it only transmits one 30 millisecond signal every 30 seconds. The transmitted power of each signal is 2W, which means that the transmitted power, averaged over 30 seconds, is only 0.002 W. So I don't think it makes a lot of difference whether it's transmitting or not.

On my tablet, I have Navionics, and that shows AIS ships on the chart, which is handy. On my phone I use the Vesper Watchmate app which is better for focussing on collision risks (for some reason I never got the phone installation of Navionics showing AIS targets).

It sounds like you might be pretty close to what you need, power wise!

Perfect and thank you for doing the power clacs as I’m rubbish at that. It sounds exactly what I need. I think I shall be writing to Santa and asking for one in my stocking

So with the radio on intermittently and backup with hand held VHF and GPS and the usual paper based chart work, it looks like my battery will give me about 4 days range. Or 8 if I add another battery. Plus whatever I can get from solar which may or may not be enough to give a lot more range.

So yes, thinking frugally and using the Watchmate may well give me the range I want. Thank you

 

[jac]

Some good suggestions here. One point i haven't seen raised is the amount available from the battery. you quite rightly say that discharge below 50% is a nono but that doesn't mean you will have 50% of the nominal battery capacity available.

Maybe after the boat has been left on shore power for a day or so with a good smart charger and no real drain you may get to 100% state of charge, but given the rate at which lead acid batteries start reducing the charge acceptance rate once they get above 80% state of charge it means you will really struggle to get the battery back much beyond 90% State of Charge day in day out . So for practical purposes you're better off planning that the batteries real usable capacity is about 35% - 40% of it's nominal capacity. So your 110 will give you maybe 35 - 45 Ah of useable power after that first day.

More Battery and more charging both needed.I would be looking for 200-250w of panels that might give you 50Ah most days in height of summer. Possibly consider guardrail mounted panels if a gantry is unacceptable

 

[PhillM]

Some good suggestions here. One point i haven't seen raised is the amount available from the battery. you quite rightly say that discharge below 50% is a nono but that doesn't mean you will have 50% of the nominal battery capacity available.

Maybe after the boat has been left on shore power for a day or so with a good smart charger and no real drain you may get to 100% state of charge, but given the rate at which lead acid batteries start reducing the charge acceptance rate once they get above 80% state of charge it means you will really struggle to get the battery back much beyond 90% State of Charge day in day out . So for practical purposes you're better off planning that the batteries real usable capacity is about 35% - 40% of it's nominal capacity. So your 110 will give you maybe 35 - 45 Ah of useable power after that first day.

More Battery and more charging both needed.I would be looking for 200-250w of panels that might give you 50Ah most days in height of summer. Possibly consider guardrail mounted panels if a gantry is unacceptable

Good point re discharge although I don’t think I’ll get more than 2 panels on her - she is only 21 foot and I don’t want any more weight than I must have on the stern. Core wort thinking of one panel on the hatch and one on the lazerrette hatch. Might manage to squeeze 2x 75 or perhaps 100w if I’m lucky.

I recon I can squeeze a second battery in. I’m using sealed AGM so as not to get fumes when charging. Sadly I cannot afford lithium!