matthewA750 12:05pm, 3 November 2013
I'm trying to work out my power requirements (to be self sufficient at sea) and the solar panels needed to satisfy them. Whether, for example, I can use a Garmin gps with ais - and whether I can transmit ais as well as receive (seems to use many more nimble amps...).

The solar panels themselves. Any experience of using them for real - how much of the stated charge do they really give? Where did you mount them? How many watts did you go for?
Any thoughts gratefully received....
Skykomish1 5 years ago
I think that you are possibly seeking the "Holy Grail" as most systems available will only produce limited output. For example the stated output of many solar panels is based on them being mounted in an optimum position to get maximum light and no shadows... even the shadow cast by a halyard can dramatically reduce output.
Obviously with the advent of LED lighting being totally self sufficient has come a step further, but when you start bringing in relatively high consumption items like autohelms you really do need a serious charging system, those of us with inboard engines have the luxury of an alternator to boost the batteries but from experience of ownership of an A24 with an outboard engine in the well the brain was always running through calculations trying to work out power consumption and relatively low input from my solar panel. (I did manage to run a fish finder from a relatively small solar panel (about the size of 2 x A4 sheets) but this would not charge the battery, just keep it topped up through winter.
Remember also that you do not want to drain your battery to below half of it's stated amp hour rating or you risk damaging it and certainly shorten it's life, so for example a 70 amp hour battery will only give you 35 amp hours of realistic use....
We used to look at options to charge the boat , but ended up taking a shore power hook up and battery charger to give the battery an overnight charge whilst in a marina and rely on our small solar panel just to take the edge off our consumption.
An A24 doesn't normally require a lot of power for general sailing, it is only when you start adding the "toys" that you run into problems. I would look at keeping the use of high consumption items to a minimum, you don't need the depth sounder when out at sea only inshore, keep the AIS use only for busy shipping lanes in poor vis, convert to LED nav lights, and use Autohelm very sparingly.
NormanKlipspringer 5 years ago
All boats will be different. Factors which affect the charge required include:
Type and usage of navigation lights.
Instruments type and usage.
Tiller pilot type and usage
Engine starter (if fitted) and usage
Fridge( if installed) usage
Charging capabilities of engine (outboards are not very high)
Solar panel performance is affected by position and amount of sunshine.
There have been many articles in the magazines about estimating requirements. Basically add up your estimated consumption over a 24hr period, subtract your estimated generation capability and double the result. This will give a minimum starting battery size.
As Malcolm says above the solar panels are useful for keeping batteries charged but not much else.
I use 2 batteries which are completely interchangeable. While sailing I keep one in reserve and use a voltage alarm on the second to avoid too much drain on the battery in use. Once alarmed I then have to make a decision about charging, use of second battery, switch of fridge and forego the cold beer etc depending on how near to shore power, use of engine etc.
Voltage alarms are incorporated into most fishfinders and chartplotters.
My solar panel is flexible and can be walked or sat on. It is installed on the garage roof (I do not have a sprayhood). I do not know the output since it came with the boat but the flexible panels do not output as much as the rigid type. Installing anything bigger on an A24 would be very difficult and probably very ugly (gantry on stern??). To be self sufficient you will have to be prepared to use the engine or carry a generator.
Red Marlin 5 years ago
OK I have a 9 metre so that gives me more options, especially with engine charging, but I am pretty self sufficient. Batteries have been mentioned and they are important as what you are using is stored energy. No point in having loads of charging options if you have nowhere to put it. Big batteries, a gantry and large solar panels weigh a hell of a lot and on a 24 would be a disadvantage.
AIS. Think I may get one for next year as I plan to do some singlehanded stuff possibly at night. But I will look at receive only. Big ships will switch small ships off to reduce clutter. Anyway what I need to know is where they are so I can avoid them. I do not rely on them knowing where I am so they can avoid me, even if there is someone on watch they might not change course.
rothwell_neil 5 years ago
I have one 10W panel that I mount at about 50 degrees to horizontal in cockpit facing due south. This keeps a 130Amphr battery fully topped up all through the summer, I start on this and then charge the back up 65Ahr battery off the motor only.. I take the batteries out in winter. Panel is only in use when in marina and put away when sailing. I do have a charger off the inboard which tops the standby battery but other than in and out of the marina try not to use that. Malcolm is right that LEDs are the biggest single saving. Nav lights, anchor and interior lights save massively on power. As for the VHF I use a hand held more and more for in and out of the marina and that last ages between charges, fixed VHF probably about 0.3A on standby and that equates to 3Ahr on a 10 hour sail or 8 a day if left on, that is significant.

GPS drain is very low as my little garmin geko uses 60mA on continuous and as I use this for navigation and also as the feed for the VHF DSC in case I ever need it. I haven't gone back to a fixed chart plotter as use Navionics on the phone/tablet and also the geko for SOG/COG when sailing. Find the geko is more than adequate for navigation and as water proof and can be set up with all the waypoints you need. You can also power these devices from a 12v lighter socket with a cable that also drives the NMEA for the DSC. Fixed plotters use about 0.5A so need thinking about.
SHAMAL411 Posted 5 years ago. Edited by SHAMAL411 (member) 5 years ago
On Shamal we use Yuasa deep-discharge gel batteries (as used on golf caddies). These have several benefits which could reduce the need for solar topping-up .They tolerate greater than 50% discharge (though we keep to the 50% rule generally). They also have a very low self-discharge rate if left unattended (months even) which is reassuring if you can't get to your boat for long spells.
We have three 20Ah units ,they are comparatively small and weigh about 15lbs each so are easy to take home and charge between trips .
1.Runs Nav lights (led),cabin lights(led),Log and Depth sounder.
2.Runs the Vhf radio.
3.Runs two handheld gps- one for the dsc the other for speed, direction and to feed the lap-top plotter.
We also have two 7Ah gels as back-up .
I reckon we can easily run for 10 days without recharging.Our trips in the Bristol Channel take in a Marina now and then for top-ups.
As others have said, leds and low energy devices are key ,If I were going for longer episodes on the water I would get more of these batteries !
PS beware of fridges - luxury on an A24 - whatever next !
matthewA750 5 years ago
Thanks guys. Very useful info'.
The actual proposed 'toys' are - assuming I can power them - one nasa led tricolour nav light 200 ma; one Garmin 4" chartplotter 1 amp; and one ais receive only .21 amps. If I've got my calculations right.....
Echo sounder on it's own battery. VHF very rarely on. Internal lights on own batteries.
The ais transmit/receive (which would be far preferable for poor viz or sleeping with less fear!) uses 2 amps.
I imagine the chartplotter and ais will be largely switched off and only on when needed. Inevitably, they will be wanted more when visibility is poor, and therefore charging is worse.
Nav light (summer) say 8 hours per day.

I can see the benefit of the Garmin geko - although there is something very satisfying about a chartplotter (and it has all the charts you might want).
Shamal411 - My understanding is that using a lap top plotter would use a lot of power?
Any more thoughts and experience very welcome - I'll keep reworking my assumptions in the light of your comments and perhaps come up with a solution over the winter.
Thanks again, Matthew
Skykomish1 5 years ago
We used a laptop chart plotter on our A24 for an entire 8 hour trip with no ill effect powered by a small inverter too (laptop is 19volts) We had no other charging system at the time other than the solar panel which was mounted out on the pushpit to maximise charging.... so not sure if they are that power hungry, but the advantage with a laptop is that it does have it's own power source as a backup.
As the others have said I am not sure that I would like to rely on the AIS transmitter. The receiver option is good for poor vis. But a lot of times there is not anybody keeping a watch on ships and this may give you a false sense of they are really quite expensive....
spearhead_027 5 years ago
People have written books on this! If I can give a few pointers:-
1. You will be lucky if you can get the equivalent of 4 hours full charge per day - clouds, sail positions, other fixtures and fittings all knock the output back, often totally.
2. You need the biggest battery capacity you can fit in to the boat - at the very least 200 amp hrs. If that is lead/acid, bear in mind that if the voltage drops below 10 you will soon have to buy another battery. And that level is reached at only 30% discharge.....
3. GPS uses very little current if all you want is your position to plot on a chart - it's the displays that run away with your current.
4. Class B AIS (which I haven't used) uses a lot of current as it transmits, but fortunately only does so once in is it 3 or 6 minutes? and for a fraction of a second. It's probably more important to receive the ship's data well - you can then call him up if need be on VHF and sooner than waiting for your own automatic transmission. It all uses linked-up electronics which gets expensive in both cash and current!
5. On my A24 I did my best to cover the lazarette locker lids with solar panels. In port and very calm conditions at sea you can take them off and angle them about to catch the sun at the best possible angles (but don't rely on it). Other boats I have seen with rigid panels slung on brackets just outside the lifelines abreast the cockpit - these could be raised to catch some sun, or lowered to act as dodgers. Much ingenuity can be exercised here.
6. Use LED's for lighting, but be aware that when it comes to nav lights they are currently very poor at separation of colour sectors and no way match the 0ne-and-a-half-degrees criticality that big-ship deck officers are accustomed to (and used to expect - perhaps still do in a court of enquiry!).
7. I almost always ended longer passages with a flat battery and no lights - if you have an engine, make sure you can still start it somehow. And beware fishing boats heading out!
Think hard on't.
SHAMAL411 Posted 5 years ago. Edited by SHAMAL411 (member) 5 years ago
Yes lap-tops can be power hungry. Ours (an elderly rugged Itronix) is mostly run on its own batteries ; I keep it in standby mode and wake it up for the occasional fix or close quarters work. Most of the navigation is with paper chart ,observation and gps coordinates.
On this machine the biggest power draw by far is using it for internet weather forecasts.I would expect a more up to date 3g phone/pad to be much more efficient but getting forecasts one way or another I think should be factored in to your energy budget.
OK - I'm curious now as to the kind of trip you have in mind ,distances , hours , seas ?
rothwell_neil 5 years ago
Navionics on phone or tablet is great way of seeing where you are or where to park in a bay but use little power in sleep. So I use the geko for sailing and the phone/tablet for occasional fixes or when parking in bay to confirm depths with depth gauge on chart. Use the cheap water proof bags cases off ebay and can still use screen through them so perfect.
AchillesHeeled 5 years ago
I have two NASA 10W panels installed on the lazarette covers plus a moveable 20W panel I can plug in when not sailing. These gave me enough puff over the summer for all-day use of plotter and depth sounder, and a few hours a day of autohelm. The maximum charge current I've seen is 2.6A at 14V (36W) on a hot sunny day. The key to getting a decent charge is angling towards the sun and having no shadows over any part of the panel - even the shade from a guard wire will decimate the charge. I'd recommend getting a digital battery monitor (I have a NASA one) which assists battery management enormously and gets very addictive. LED nav lights are a must. Personally I'd be tempted to get an AIS receiver if the fog comes down but not sure I'd go as far as a transmitter... If I were doing lots of night passages I'd go for a small wind generator as well.
matthewA750 5 years ago
Lots of really useful information here. I'll carefully digest it. Many thanks everyone.
rothwell_neil 5 years ago
For AIS the Marine Traffic app is excellent. This in the free version is updated every 15 minutes with location, track, direction and speed, plus pretty pictures of the vessel. The paid for one at a massive £2.99 gives real time position of all vessels. MAIS is an app that will report your phone position with your vessel details to the Marine Traffic database. This is not the same as sending it to the AIS on board other ships so less useful.

Both rely on internet connection! However the Marine Traffic has been excellent for me in the Irish Sea when visibility drops. Nice to see where things are and which way they are heading. Never used the MAIS.
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