Power usage / requirements

[PhillM]

I am starting to think about longer-distance single-handed cruising in Swift (Coribiee MK2 with Seafeather Wind Vane) and would like to have a range of, say a week without needing to plug into a marina to charge the battery.

I think my power needs might be:

SH VHF 0.5A x 24 hours = 12A assuming that I have it on at all times. Of course, I could switch it off from time to time and save some power that way.
Nav lights 0.2 x 12 hours = 2.4
Plotter inc AIS (Onwa perhaps?) 1.5 x 24 = 36A. I don't care that much for the plotter part but I do want to transmit and see AIS and the Onwa unit seems the most parsimonious on power usage even over some of the stand-alone units.
Tiller pilot - 0.5 x 1 as I assume that Windvane will be steering most of the time.

So for every 24 hours, I need 50AH from my battery.

I have a 110 AGM, but of course, I cannot use all of it, so let's work on 50%, which would give me just over 24 hours range.

I am thinking of installing 100W of solar, I would hope it would give me about 4ah into the battery for about 4 or 5 hours a day, on some days.
So let's assume that I can get 20AH into the battery every day. This still only increases my range to 36 hours.

I only have an outboard, so no engine charging capability.

This is leading me to think that I need either more than 100W solar, or add another battery, or both, or compromise on AIS, which being mainly in the channel I don't want to.

What would you do?

 

[mainsail1]

I have been thinking a lot about this subject over the last couple of years. I now have three 180 ah batteries and two 110 watt solar panels. However I can add extra charge by starting the engine if I really need to.
As I have a fridge which uses about 5 amps every hour on top of the items you mention I find that this set up is barely adequate so I switch the fridge off for 8 hours every night. I also turn the VHF off whenever I can.
I might add that the output from the solar panels is disappointing in UK waters but now the boat is in Portugal I do achieve about 50 amps most days which is still below my expectations.
In other words I think you will need another battery and another solar panel!

 

[KevinV]

Handheld vhf to spare the main unit? And keep the plotter off as much as possible - but leaving the AIS running? You don't mention any other instruments? GPS eats power, so if you can share one source across vhf/ais/plotter that would help. Interior lights? Phone charger?
I found that an amp meter showing how much you're drawing by far the best power saving device - instant reward for switching something off
When you've saved what you can, then think about generating /storing more.
I have the same quandary on a smaller boat - I've opted for another battery and charging on the outboard (not very convinced of the cost/benefit of the latter)

 

[AngusMcDoon]

- There's no requirement to have a VHF on at all times.
- AIS transmission is unusual on a boat that size. It's a recent invention. There's no need for it. Switch it on in busy places if you feel the need.
- Chart plotter you switch on when needed otherwise keep it off. You could also install OpenCPN on a phone with cheap o-Charts. You'll probably have a phone on anyway. It will use a lot less.
- Basic instruments don't need much but you need to account for them. GPS is not a heavy consumer of power.
- Interior lights : hurricane lamp or tea lights. Get paraffin from B&Q.
- Anchor light : hurricane lamp.
- Nav lights, you probably won't do much night sailing on your own over a week, it's too tiring. Sail during the day. With that size boat you only need a single tricolour or all round white so will cut consumption when it is on.
- Autopilot and fridge are the biggest consumer, but you have a windvane and no fridge, so no worries there. Bonza.

The sailors of 40' boats with their 90A alternators and 400Ah of battery capacity will probably be horrified by these unseamanlike suggestions, but you need to be realistic. You have a small boat with very limited battery and generating capacity. Compromises need to be made. I sailed nearly 50k miles over 20 years in my outboard engine powered Dragonfly trimaran with similar electrical constraints (60W of solar and 6A charging coil) and didn't come to any harm. The longest I stayed away from shore power was 19 days. With some solar you will be fine. You might even have some Amp hours left over to watch some cat videos on youtube.

 

[PhillM]

Some great suggestions here. To be clear, I would like to be able to go for a week non-stop single handed. Agreed about the vhf and chart plotter not being essential all of the time. SH and tired in the channel I do think AIS is essential.

Am continuing to research and it looks like the Nomad unit will run of USB and takes minimal power. So that might be an option.

 

[AngusMcDoon]

To be clear, I would like to be able to go for a week non-stop single handed.

SH and tired in the channel I do think AIS is essential.

With my feeble body and need for sleep, those 2 statements don't sound compatible, with or without AIS.

 

[mjcoon]

... GPS eats power, so if you can share one source across vhf/ais/plotter that would help.

Is GPS really that bad? Remember they used to be hand-held powered by 2 x AA batteries!

 

[AngusMcDoon]

Is GPS really that bad? Remember they used to be hand-held powered by 2 x AA batteries!

No, only about 25-50 mW for a modern one. That's for the GPS chipset. There will be a bit more for a boat GPS receiver to drive the communications protocol and losses from voltage conversion, but it still won't be a lot. It reduces the battery life of a phone quite a bit, but its use is usually also when the screen is constantly on, and that will chomp much more.

 

[KevinV]

Is GPS really that bad? Remember they used to be hand-held powered by 2 x AA batteries!

I'll admit I based that statement on my phone, which will go all day, or be dead in an hour running navigation - I haven't measured it on the boat, so I could easily be wrong

 

[neilf39]

We have a 914i windgen and 40w solar panel. Just been away for 6 weeks and the only other source of power was the engine when motoring. Main power use was fridge, Instruments, and autopilot and charging phones, tablet, and cameras. Lights are all LEDs. The batteries never went below 12.6 volts. The windgen was putting in 6 to 8 amps as we had winds around 12 - 18 kn for quite a lot of the time. Works 24 hours a day too if there is wind. Sat a week without moving and did not see batteries drop. So a combo approach of panel and windgen may do you.

 

[Blueboatman]

Think I worked on 2-5a/h on a corribee , per day , sailing with windvane and compass /masthead all round light as required. For years and years , offshore, islands.
One 85a/h semi deep cycle ‘ leisure’ battery was sufficient .
4a/h outboard charge
18w solar panel
Small - and irritatingly noisy-windmill

 

[Giblets]

SH and tired in the channel I do think AIS is essential.

Out of main shipping areas is the AIS only being used to let those that need to know where you are? Is so then arrange a specific set of times each day when it will be turned on for a short while to transmit the current position. If a big ship in is the area then turn it on but turn it off when the danger has passed.

 

[steveeasy]

All relative to where you are on the day or night but I’d think paper charts and a hand held gps used when required every hour or 2 would be far better than a plotter on all day.
I’ve a vesper Ais which is stand alone could be on as required. This time of year for 5 hours.
Another battery and perhaps one of those thingys you can drop in the water may work. As for a wind geny they were quite big and noisy.
When I contemplated going to the Azores my chart plotter would have been useless. Paper chart and coordinates far better.
Steveeasy

 

[mjcoon]

Out of main shipping areas is the AIS only being used to let those that need to know where you are? Is so then arrange a specific set of times each day when it will be turned on for a short while to transmit the current position. If a big ship in is the area then turn it on but turn it off when the danger has passed.

I thought AIS sets could be used to receive only, with much lower consumption?

 

[AngusMcDoon]

I thought AIS sets could be used to receive only, with much lower consumption?

They can.

 

[ChromeDome]

The largest consumption in mobile/tablet/gps is by the screen.

Stand by modes preserve a lot of power.

Room for a small genny somewhere just in case..?

 

[Graham376]

Some great suggestions here. To be clear, I would like to be able to go for a week non-stop single handed. Agreed about the vhf and chart plotter not being essential all of the time. SH and tired in the channel I do think AIS is essential.

Am continuing to research and it looks like the Nomad unit will run of USB and takes minimal power. So that might be an option.

I would say nothing is essential, except knowing where you are by whatever means chosen and being able to transmit position if in trouble. Having done many Channel crossings and a few Biscay without AIS or chart plotter, I don't consider them essential items, folks managed well without them in the past and many of us still do.

 

[Black Sheep]

The channel's a tough place for extended non-stop single handed voyaging in a small boat.

And it's an oddity that the smaller the boat, the greater the need for every assistance in making yourself visible.

I use a Vesper Watchmate AIS transmitter/receiver. It doesn't use a lot of juice (afraid I can't remember the consumption; at a guess, a quarter of an amp); it talks over wifi so you can view targets via an app on your phone or tablet.

You could also consider a radar target enhancer - pricey, but takes almost no current.

Handheld VHF and handheld GPS use very little. Most of the time, you just need the VHF to pick up local transmissions, so handheld is fine.

You won't need navlights for 12 hours unless you're sailing on the winter side of the equinoxes.

You will need to recharge GPS (unless you use AA batteries), VHF and phone/tablet. Try to do these in the afternoon when your battery should be full and there's plenty of sun.

I think if you turn the plotter off & just use the AIS with phone app when needed, and only use the fixed VHF occasionally, then you might be OK with what you've got.

But normal caution would suggest that you install as much solar as you can reasonably fit, a decent MPPT charge controller and maybe another battery to give yourself a margin - assuming you can find somewhere to fit it!

Good luck - that's a great little boat to be doing this sort of thing in!

 

[PhillM]

@Black Sheep thank you. I am looking at the Vesper Spec and it says "10-32 VDC, 4W nominal ". With my 12V setup that's 3 ah. Or have I got that wrong and is it only 3A when transmitting and nominal when it is not? Any real-life usage figures would be useful.

Agreed re a phone, app and GPS with AA batteries. I have a Garmin HH and the usual Navionics on a tablet and phone. So a WIFI solution would work for me. I also have a HH VHF that takes rechargeable AA batteries. With a couple of USB power packs I would easily be able to extend the life of these for up to a week.

 

[Black Sheep]

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!