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Discussion Starter #1
Hello, I'm wondering how much power an autopilot uses?

On a monohull a windvane seems a better idea, but on a catamaran the only option for self-steering is an autopilot (if I understand correctly). So I'm trying to determine how my power requirements will be affected by an autopilot. I presume it would be on continuously more or less.

Thanks
Jim
 

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What size boat? Which auto pilot? So many variables. I would think the manufacture would have the power consumption specified.
 

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That would depend on how much work the AP is doing. Motoring in flat seas the rudder hardly moves and power consumption is quite low. Sailing in sloppy seas the AP works much harder... especially if it doing a lot of corrections.
 

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The autopilot is intermittently on and off. So just looking at the power draw when on will grossly overestimate the average Ahr usage. As SanderO said above, when motoring in calm seas, it will be off most of the time. When sailing it will be on more, but how much more depends on the boat, how well the sails are trimmed, how strong the winds are, how big the waves are, etc.
 

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Discussion Starter #5
Thank you. I don't know anything about autopilots. I just was wondering how much of a larger power system a boat would need if it has an autopilot and is selling in oceans, on average, in general. For example, would one extra solar panel provide the power an autopilot needs if you sail back and forth across the Atlantic 10 times? I say that so that it averages out all kinds of conditions. That sort of naive, beginner level info is what I was looking for. Thanks again
 

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More than anything, it really depends on how well you have trimmed the sails to maintain the course you want. A heavy lee or weather helm will of course make the AP work much harder (much more than most seas), so your most important job is to trim her up properly.
I can't think of any reason why a good vane gear wouldn't steer a cat. If you know of one, I'd be interested.
 

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Discussion Starter #7
More than anything, it really depends on how well you have trimmed the sails to maintain the course you want. A heavy lee or weather helm will of course make the AP work much harder (much more than most seas), so your most important job is to trim her up properly.
I can't think of any reason why a good vane gear wouldn't steer a cat. If you know of one, I'd be interested.
Well I'm not in a position to judge them, but when I searched I found at least six or seven different kinds in YouTube videos and I bookmarked them for later watching . The one I see mentioned most is the hydrovane and I think it's pretty well respected. Kevin in how to sell oceans and the guy in sailing wave Rover YouTube channels both designed and made their own. My favorite two YouTube channels.
 

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I don't understand why a windvane is not an option on a catamaran. I know at least two that have them. Granted I'm not a catamaran sailor, so, grain of salt and all that.
 

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I noted that my 110 watts of solar panels supplied all the power the AP needed.... ie there was no net drain on the batts sailing offshore in bright sun, Alpha AP, Contest 36s
 

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Unfortunately a windvane or equivalent is not an option for our boat so we went with L&S linear drives on a Furuno AP. We found that the draw on a 12 volt system when the AP is actuating is about 30 Amps. In challenging seas and overnight, we use about 200 Ah through the 12 hours (1800-0600) which we cover with a hydrogenerator. In easier conditions, it is nearer 100 Ah

I would be surprised if a 110W panel will cover an autopilot except maybe during bright sunshine for 3 hours either side of noon in gentle seas and consistent winds...

However for a cat, a windvane system may well be a better option.
 

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Unfortunately a windvane or equivalent is not an option for our boat so we went with L&S linear drives on a Furuno AP. We found that the draw on a 12 volt system when the AP is actuating is about 30 Amps. In challenging seas and overnight, we use about 200 Ah through the 12 hours (1800-0600) which we cover with a hydrogenerator. In easier conditions, it is nearer 100 Ah

I would be surprised if a 110W panel will cover an autopilot except maybe during bright sunshine for 3 hours either side of noon in gentle seas and consistent winds...

However for a cat, a windvane system may well be a better option.
I reported what I found with my boat... once when I checked. I used the AP for 95% of steering and I never saw draws at the levels you mention.
 

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Unfortunately a windvane or equivalent is not an option for our boat so we went with L&S linear drives on a Furuno AP. We found that the draw on a 12 volt system when the AP is actuating is about 30 Amps. In challenging seas and overnight, we use about 200 Ah through the 12 hours (1800-0600) which we cover with a hydrogenerator. In easier conditions, it is nearer 100 Ah

I would be surprised if a 110W panel will cover an autopilot except maybe during bright sunshine for 3 hours either side of noon in gentle seas and consistent winds...

However for a cat, a windvane system may well be a better option.
WOW, Thats certainly gobbling up your power,
Running my Raymarine AP 100% and every thing else, Nav lights Etc Etc, 24/7 I never used any thing like that,
380 Watts Solar, I never even came close to running out of power, No sun at Night,
 

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I noted that my 110 watts of solar panels supplied all the power the AP needed.... ie there was no net drain on the batts sailing offshore in bright sun, Alpha AP, Contest 36s
My apologies Sandero. I just reread my post and realised the danger of late night posting. I was not intending to question your figure for an Alpha AP and your boat setup. The 30A pull in heavy seas is similarly just what I observe. It's about 2x your unit which seems about in line other the specs that I see on line.

My 100-200 Ah draw is for the boat systems as a whole including the AP and I was trying to say that I would be very surprised if I could run the whole boat on a 110W panel outside the middle of the day... It sounds like my draw is high.
 

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My apologies Sandero. I just reread my post and realised the danger of late night posting. I was not intending to question your figure for an Alpha AP and your boat setup. The 30A pull in heavy seas is similarly just what I observe. It's about 2x your unit which seems about in line other the specs that I see on line.

My 100-200 Ah draw is for the boat systems as a whole including the AP and I was trying to say that I would be very surprised if I could run the whole boat on a 110W panel outside the middle of the day... It sounds like my draw is high.
Sailing I use little electricity... especially when the radar in not on... it's just the AP and a few instruments.
 

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The autopilot is intermittently on and off. So just looking at the power draw when on will grossly overestimate the average Ahr usage. As SanderO said above, when motoring in calm seas, it will be off most of the time. When sailing it will be on more, but how much more depends on the boat, how well the sails are trimmed, how strong the winds are, how big the waves are, etc.
My experience is more in line with Sanders and JimsCAL. When you are motoring, it's not an issue at all because your alternator will be putting out plenty of power. As Jim mentioned just above, sail trim is a too often ignored factor while on autopilot that can cause your autopilot to work much harder than necessary and that means lots of extra amps. So when sailing on autopilot, be sure to take a look at your rudder position indicator and make sure it's very close to centered and if you don't have one of those on your boat, just disconnect the autopilot momentarily and note whether the boat immediately starts to turn. If so, then you are asking the autopilot to constantly fight that tendency and if you trim your sails properly your autopilot will be much happier and use much less energy. Probably no need to modify your electrical system to accommodate your autopilot because it's not a really big load item, especially if used properly. On my boat I have a rather modest 375W solar and a KISS wind generator. If not motoring we usually run the genset for about an hour a day, mostly to power the water heater and watermaker, and during this time the battery charger is also turned on. I try to do it early in the day when batteries are at their lowest ( evening usage and refrig/freezer running all night) to get the max amps out of the charger, and let the solar/wind gen top them off during the day. Almost all our lights are LED's but we have both refrig and freezer operating constantly and this regimen is plenty to keep our batteries topped up unless we have several cloudy days with little wind. My 5.5kw genset only uses about 1/3 gallon per hour so energy costs are not a big deal because for us as this equates to about a dollar a day.
 

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Hello, I'm wondering how much power an autopilot uses?
Ours uses less than I think it would, and much less than its rated power usage. Like others said, sail trim is important. I have an ammeter on ours and it uses 3-5A when operating the drive, but there is a duty cycle so the average draw is probably 2-3A. I doubt the electronics themselves draw more than 0.5A, so perhaps a maximum draw for planning usage during most conditions might be an average of 4A - leading to ~100Ah/24hrs. An unbalanced boat or rougher conditions may be higher.

I can't think of any reason why a good vane gear wouldn't steer a cat. If you know of one, I'd be interested.
Most modern catamarans have so much cabin freeboard, arches, flying bridges, etc that a windvane simply can't be placed in free air to allow it to work. Even with a vane on each hull, the disturbed air can be a challenge. The bridgedeck saloon on most catamarans actually pull a suction from the stern, and if you mount it high enough to clear all of that, the flow off the mainsail can be a problem. Performance designs usually have less of this issue, but their problem with a vane is how much they accelerate and respond to changes. A vane can't react fast enough to accommodate the rapid 20-30* shifts in apparent wind as the boat accelerates/decelerates, and it ends up hunting around. A technical issue for many catamarans is just how to connect the steering system for a vane. An independent rudder is the only workable design for many.

Mark
 

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If i have my sails adjusted properly my autopilot uses around 3 amps and i sail with it on a setting of 2-3 out of 10 to reduce steering. My boat balances well and 5 degrees of rudder is a lot normally.
 

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Unfortunately a windvane or equivalent is not an option for our boat so we went with L&S linear drives on a Furuno AP. We found that the draw on a 12 volt system when the AP is actuating is about 30 Amps. In challenging seas and overnight, we use about 200 Ah through the 12 hours (1800-0600) which we cover with a hydrogenerator. In easier conditions, it is nearer 100 Ah

I would be surprised if a 110W panel will cover an autopilot except maybe during bright sunshine for 3 hours either side of noon in gentle seas and consistent winds...

However for a cat, a windvane system may well be a better option.
I thought you had a tri?
 
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