Electrical draw of autopilots?

[peteris]

I am looking for a selfsteer solution for a 26' sailboat. I am leaning towards an autopilot instead of a windvane, but am concerned about running out of juice powering it.

The Simrad TP20 which I am looking at states that it draws 500mah, but in past experience, you cannot accurately calculate exactly how long a battery will last based on just that.

I am thinking I will have to install 4-6 deep cycle marine batteries, and a small generator. But even then, will I have to run the generator every day?

What's your experience? Thanks!

[Zanshin]

The real drain is when the autopilot needs to do work. If the boat is not balanced, the autpilot set to maximum sensitivity and the seas uneven you will drain more power. the 500mAh is just the minimum drain when turned on, but that is only 12Ah for a 24 hour period and a typical boat battery will have 100Ah. Does your boat have any means of charging batteries (perhaps an alternator on the outboard/inboard)? When the Simrad has to control the boat the drain will go up to several amps while the motor is turning.

[nickmerc]

I have an old Autohelm 1000 for my Pearson 30. I can sail about 10 hours (80% under autohelm) anchor overnight with my 12 VDC cold plate running, cabin lights and anchor light all night (incadecent bulbs) and make the return trip the next day and have plenty of juice left over. I have 2 group 24 wet cell batteries for my house bank. The only time my engine runs is leaving the dock, dropping and hauling the anchor, and returning to dock. In total about 45 minutes for the trip. I do start off with a full charge.
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[sailingdog]

As Zanshin has pointed out, the draw of the typical autopilot will vary with the balance of the sailplan. To minimize the draw, try and balance the sailplan as much as possible when using the autopilot.

As to whether you'll need to run the generator every day, it really depends on how large your battery bank is, what your typical daily electrical usage is, and what passive charging systems you have aboard. On my boat, I can run my refrigerator, the VHF, autopilot and such and still have the three solar panels keep the batteries fairly well topped off... never have to run the engine to charge the batteries, which is a good thing, given the low amperage output it has.

[mitiempo]

I'd do anything I could to avoid running the generator - solar first choice as it's the least annoying with no moving parts. Windvane is a good choice and most wouldn't use the autopilot unless under power. Are you going offshore or daysailing?
Brian

[peteris]

Going offshore, looking to do Panama -> French Polynesia -> Australia. I know a windvane is probably what I should be looking at, but I'm wondering if some of you rely only on autopilots even for offshore.

I'm the barebones type and would be running strictly the autopilot on batteries. No radar, stero, fridge, etc... I don't mind burning a little bit of petrol for a few hours here and there, just don't feel like running my engine or the generator 24/7. I've heard solar panels only really produce about 20% of their rated output, and that just doesn't cut it.

[mitiempo]

The better solar panels will do better than that, of course only when the sun is shining. See this link for good solar advice.Solar Power on Boats | Adrift at Sea
As sailingdog says, he really never has to run the engine to charge his batteries - solar takes care of it. And I bet he runs more electrical items than you will. You should be able to get all your amps from a solar panel of a reasonable size taking into account your planned electrical items.
For the distance you're going to travel I'd certainly take a good wind vane which will take care of 98% of your steering as you're not going to power long with the fuel you could carry on a 26' boat. I'd probably throw the generator overboard out of annoyance. Besides you can't easily fill the fuel tank in rough weather, when you need the self steering the most. As well the tillerpilot will not use the miniscule power the specs say when it has to work hard.
Here's a link to what I think is a good fairly affordable wind vane.NORVANE Self-Steering Wind Vane. Stainless steel, servo-pendulum. Powerful, sturdy and reliable for sailboats 20’ to 60’
If you already have the tillerpilot I think it will be of some use when powering in calmer conditions but I don't think it's up to steering offshore in all conditions as a good vane is.
Brian

[sailingdog]

LOL... Mitiempo, did you know that is my blog???

Peteris—

I'd second getting a windvane instead of an autopilot. The main reason for this is that a windvane will work in heavier conditions than an autopilot, and not use any amp-hours. In heavier winds, the tiller pilot will use a lot more amps than the minimum and there's much more chance of it failing than a windvane, since the windvane works with more force as the wind strength increases, which is not the case with an autopilot. Also, minimizing electrical usage on longer voyages is a necessity, especially if you're going to be relying on a generator for charging—since fuel is a scarce resource on the open ocean.

[marujosortudo]

Some wind vanes also function as emergency rudders, which hopefully you'll never have to use....

[mitiempo]

Yes dog, I knew it was your blog - full of good info.
To expand on your post though, sailors in Ostar and other singlehanded races with smaller boats with tillerpilots usually take several to allow for breakages. And I just can't see filling a tank and running a generator on a 26' boat not when you want to but when you have to charge the batteries - rough or calm.
Brian