Bud, If I might interject a few points(OK, more than a few) regarding the solar panels and the Autohelm (aka 'Tiller Pilots'). I have both a Tiller Pilot and solar panel on my Flicka, and a small panel on my M15. In addition, I have (as a builder of passive solar homes) installed several large stand-alone and grid-intertie PV (photovoltaic) systems. I posted a piece on the use of smaller panels on M-Boats last year (which, I might add, brought on some grumbling). Here are a few derived points from that posting that might prove helpful to your question: 1) Calculate your total battery capacity at no more than 50% discharge. Even the best batteries will be very short lived if you repeatedly discharge them deeper than 50%. The best batteries for really deep discharge are Gel Cells, but you MUST limit the charging voltage according to manufacturer's specs (usually less than 14.1 volts), or you will ruin them in short order. AGM batteries will also tolerate relatively deep discharges, and some are more tolerant to higher (14.6v) charging voltages. Both Gel and AGM batteries have extremely low self-discharge rates, and can be left for long periods without consequence. (addendum: I now use AGM batteries exclusively, and regulate the charge voltage if panel output is high enough to warrant doing so). 2) Not all so-called 'Deep Cycle' batteries are. Most sold under this appellation (especially at car parts stores and discount chain stores) are merely slightly better car-type batteries. If you are serious about real capacity and longevity, buy one of the better brands that truly have different plate thickness and composition suited to long, deep discharges. I have found that the cheaper batteries are a false economy when compared to a properly maintained and charged true deep cycle or industrial battery. (addendum: again, I suggest AGM over Gel or Lead Acid--also, I do not favor traditional motorcycle batteries, as they are not intended for deep cycle use). 3) Most panels that are/would be appropriate for use on an M-15 are low-output units primarily designed to maintain batteries, or at best, replace small discharges. 4) Your ability to support/sustain an Autohelm/Tiller Pilot by solar panel will depend on several factors as follow: a) The make, model, and average continuos draw of the Tiller-Pilot (Raymarine ST-1000 is 0.5-1.5 amps--use 1.0 amps for calculations). b) The intended durations of use (how many hours per day/week will you actually have unit ON, not standby). c) Durations between access to AC or other non-solar charging. e) The size and type of battery banks. f) The size and type of solar panel(s). g) Solar radiation gain by region h) Panel/system efficiency loss. Let's do a sample analysis. I will use the Unisolar USF-11 (I have on both my M15 and my Flicka--fits perfectly on the sliding hatch of the M15) coupled to two West Marine AGM (Absorbed Glass Mat) PWC batteries (these are basically small AGM batteries that are close in size to the motorcycle batteries you mentioned. First, let's look at the potential of your battery bank. Each of these batteries is rated at 18 AH (amp. hours). Two of these have a total rating of 36 AH, but that is the rating for 100% discharge. Because we want these batteries to last a while, we will only discharge them a maximum of 50%. That leaves us with a total two-bank capacity of 18 AH. If you want to hold one battery in reserve for lighting, electronics, etc., you would need to adjust this accordingly, but for purposes of our analysis, let's say that both batteries are dedicated to autopilot use. Second, let's look at the potential of your solar panel. The USF-11 is rated is rated for a *maximum* output of 0.62 amps. This is the output at optimal panel angle, maximum solar irradiance, and everything in perfect condition. We adjust this downward by a typical 25% (as stated in the Uni-Solar manual) for system efficiency loss (basically, it takes more than 0.62 amps of power from the panel to replace 0.62 amps of battery used--it's an oversimplification, but it works here) . This brings us to a best-case realized output of 0.465 AH. Third, let's assume that you live mid-country, and according to the solar irradiation charts by region, let's say you net about 18 AH/week (or about 2.5 AH/day--a typical solar day for such analysis is 5 hours). Again, this is an optimistic situation, but let's assume you sail when it is nice and sunny.

From this, we know that a 50% discharge of our two batteries (18 AH) would take a bit more than 7 days to replace under ideal conditions (18 AH/2.5 AH), and this with no additional draw during that charging duration.

What does this equate to in terms of Tiller-Pilot usage? Well, we know that the ST-1000 draws an average of 1AH. We can calculate from there. If you used it intermittently, and then only for short periods (going to the head, preparing food, reefing, reading chart--you know, short breaks from the helm) then this system might be self-sustaining indefinitely. We can see that anything more than 2.5 hours of use in one day is getting you into a deficit situation, but maybe that's OK if you are at anchor the following (sunny) day, or you are only out for a few days. Cloudy day? Adjust total downward from 10-80% depending on cloud cover/sun angle. Changing to a higher output panel, more panels, or a larger battery bank would all increase potential maximum capacity, but we need to be careful here. A larger battery bank will result in more time until 50% depth of discharge, but remember that you have to replace those amps at the same 0.465 AH rate unless you also go to a larger panel. This might be the way to go if you don't anticipate being out for more than a few days at a time and keep usage appropriately low. You could then (and probably should) hook the batteries up to a GOOD AC charger when you get back anyway. The larger group U-1 AGM batteries have a 32 AH rating, and might prove better for your purposes if this is your pattern. Similarly, you can add more panels, or go with a high-output panel, but again, this is no guarantee of adequate capacity or recovery time if the conditions don't cooperate. So, in summary, you need to determine all of your variables prior to setting up a system. Change the above numbers to fit the specifications of the equipment you are considering, and the climate where you sail. Unfortunately, there are no small (less than 4hp) outboards with charging systems available for the M15. That would be an ideal augmentation to this solar system. My guess is that the way most M-sailors use their boats (daysailing, and the occasional overnight), the above sample system would work well. The usual disclaimer applies: 'Actual mileage may vary' Note: if you are thinking about electric trolling motors and solar panels, read my earlier post! Scott M15#478 PSC Flicka #392 In a message dated 2/9/05 1:42:32 PM, montgomery_boats-request@mailman.xmission.com writes:

Hi Connie,

Thank you for you reply to my question re self steering. When I first bought my M15 I wanted to put an Auto helm 1000 tiller auto pilot on it with 2 motorcycle batteries with a switch to select one or the other battery or both batteries at the same time. I thought I would keep the batteries charged with a solar panel on the cabin top. When I was told it wouldn't work I didn't look into it any further. I'm still not sure how large of a solar panel I would have needed to charge the batteries.