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Trolling motors have been discussed in recent months, but I have a specific question: It is possible to easily set up a system aboard my PC that can solar charge a transom mounted trolling motor? I know almost *nothing* about solar electric systems, but in a perfect world I'd like to have a couple of batteries--one for motoring along, the other for charging. However, I don't know how long I can run a trolling motor or how long it takes to charge a battery with a panel small enough to, say, fit on my cabin roof.

Yes, yes, I know an outboard would be faster and more powerful, but indulge me on this question. If my plan is possible, I would be especially grateful for a shopping list of easy to use products (motors, batteries and panels that are ready to plug in and use). I'm a technophobe at heart.

If this is not a doable plan, it's no big deal. I'm happily sailing without a motor right now.

Paul, I've fielded this question several times and the answer is still the same, you'll have range issues.

The basic problem with all electric propulsion systems, is the amount of storage capacity you have, the time it takes to recover used capacity and the weight and complication this involves. The only way it works (economically) is if your electrical usage is huge, in other then propulsion system needs. A cruise ship can use electric drive pods and it's economical, because they have a 3:1 need for electricity elsewhere on the ship, for hair driers, pumps of every shape and size, heat, air conditioning, etc. This generally means they carry several very large generating systems and only a couple of them are needed for the propulsion system.

On a yacht, even one setup for electric propulsion, you just don't have enough storage capacity (batteries) before weight rivals that of gas or diesel setups. In short, lets say you need 5 HP (3.75 kw motor) to drive your boat. A 5 HP outboard with reverse, fuel tank and starting battery will weigh about 150 pounds full up. It'll self charge it's own starting battery, offer plenty of power and assuming a 5 gallon tank will offer about 8 hours of running time without stopping, with 5 minutes at a gas pump and you're good for another 8 hours..

Now lets look at a 3.75 kw motor, controller, battery bank and charging system. The motor will weight about 50 pounds and cost twice as much as the 5 HP outboard, the controller and charging system will also rival the cost of the 5 HP outboard and to get 8 hours of running time, you need a minimum of 280 to 300 pounds of batteries. Total weight is in the 400 to 500 pound range and when you need to charge, you'll have to wait several hours, if not all night to get them back to 80% of charge!

This is the crux of all small electric propulsion systems. All this said, I use a small trolling motor on my puddle jumpers. I don't have to motor very long to get to sailing areas and often can just sail directly away from the dock, so I don't need much capacity. I use two group 27's, which weigh about 40 pounds each. I can run for about 2 hours on one battery if I keep the speed down, about half of this at WOT, so it's effective at getting me back to shore if the wind dies. This is all I need, so it works, but for most folks, especially if they have currents, chop and contrary winds to contend with, then my little system will leave them stranded in the middle of a lake.

So, if you only need an occasional assist over short distances, then the trolling motor option is viable. If on the other hand you need to motor miles back to the boat ramp after the wind has gone dead, you'll quickly wish you had an outboard to putter your butt back home.

Greetings, Paul B.!

I have a Motorguide 55 lb. trolling motor as the ONLY mechanical propulsion on my (2260 lb.) Catalina 22, and I have been very happy and satisfied with it.  I daysail on inland waters, and on many outings all I need it for is to back out of my slip and motor a couple of hundred yards to the mouth of the harbor, depending on wind speed/direction on a given day.  Most of the time I'm able to sail into, or at least close to the slip when I return.  I mean, these are sailboats, after all.  I have one battery and recharge it with a solar panel connected through a charge controller.  I don't remember the wattage of the panel, but it might be a bit larger physically than would fit on your cabin roof. 

As far as practical recharge rates are concerned, last Summer I sailed almost every day for two weeks, and never had any problems with not having the power when I needed it.  And that was with a battery on it's last legs; I had to replace it at the beginning of this sailing season. 

Putting aside all the technical calculations/considerations, one subjective factor is that it feels good to be completely green!  I don't even have shore power at my slip, and I don't need it.  I don't have to haul to or store aboard my boat heavy, expensive, smelly and potentially explosive gasoline. 

My Weekender, Arwen, will have the same system when she is completed.

Kurt Ayres

Paul, you confirm my suspicions about the power and recharge rate concerns. On the other hand, I'm also on board with Kurt regarding the green aspects of using solar. It just appeals to my sensibilities. That's why I wanted to fully explore this option.

I am pondering my motoring needs as I plan to make the jump from lakes to a possible trip down part of the Intracoastal and/or the Florida Keys. Not the whole route, mind you. I'm toying with a short "cruise" down portions that are scenic, protected, and friendly to small sailboats. Come to think of it, does anyone have any recommendations? I'm looking for sections that allow for sailing (I don't want to simply motor down the ditch) and offer plenty of nature.

Truth is, I'd rather not have to get a motor and I'd like to plan a route that doesn't require a motor. Until recently, my plan for back up propulsion was limited to a sculling oar. But I'm trying to think about all my options.

Most of the ICW requires motoring. There are open, discontinuous sections that will let you hoist sail, but generally most of it is motoring. A weekender isn't well suited for large portions of the ICW, specifically the larger open areas. Again, electric trolling motors are for short hops of an hour or two, with several hours of recovery time on the charging system (what ever that may be). Some gains in speed and efficiency can be had with different props and controllers, but less then 20% in total range can be expected with these options. Solar regeneration requires the most space (measured in sq. yards), the highest cost and slowest recovery values. Faster recovery rates can be had with mechanical systems, such as a small gas or diesel engine (1 HP or less) driving a generator. Some time ago, I hooked up a chain saw motor to an automotive alternator to charge batteries, in hope that I could get recovery times reduced, but batteries only suck up so much at a time. Though I could recharge while underway on the electric motor, it was only a 30% reduction in recharge time and I had a chain saw engine screaming at the top of it's lungs in an insulated box.

I do understand that  most of the ICW is not great for sailing. But I'm thinking of trailering my Pocket Cruiser down to a nice spot and just messing about, anchoring here and there, but not really worrying about making miles or getting from point A to point B. I was reading about the Everglade Challenge on the Duckworks site earlier today and, especially, about the adventure of a couple of guys (regular contributors to that forum) who sailed an 11' SCAMP (without power). Their once mistake was wandering away from the channels between Flamingo and Key Largo. Even with a draft shallower than my boat, they got stuck on a vast expanse of grass when the wind blew the water away. They had to be rescued by friends with canoes. Aside from that misadventure, that's one possible area. Any thoughts on this area or other protected parts of coastal Florida or the Keys? I'm very serious about this idea and want to find a place to go early this winter when it gets too cold in New York.

I also guess that I am backing away from the trolling motor idea. I'd rather stick with sails and oars.

Paul

Greetings Paul Boyer,

Perhaps some very specific numbers might help you understand the limitations of using solar power for moving your boat via a properly re-propped trolling motor. A good rule of thumb for trolling motors (MinnKota factory specs) is that they require about 1 amp at 12 volts (12 watts) to produce 1 pound of thrust. So a smaller 35 lb thrust motor needs 35 amps (420 watts) at full power, and a more capable 55 lb thrust motor needs 55 amps. If you motor for an hour using 35 lbs of thrust, you will use 35 amp hours. Two hours of this will kill a normal 75 amp-hour deep cycle marine battery, so you are going to need multiple batteries.

Current state of the art solar panels that are still affordable provide about 5 watts per square foot (400 milliamps at 12 volts) and will set you back about $30 per sq ft. That means you need at least three square feet of panel (15 watts) to provide the minimum 1 amp of 12 volt power required to re-charge a marine battery. Every three square feet gives you another amp. So if you want to run a 35 lb trolling motor directly from the solar panels, you will need about 100 square feet of panels ($3,000), which pretty much covers every square foot of your entire boat, cockpit included. That's not good. Cover half the boat, and you can motor for 4 hours, and it will take the rest of the day to recharge the batteries. Cover just the entire cabin top, and you will get about 2 hours of motor time with the rest of the day spent for re-charge.

So what is the standard $100, 12 volt, 15 watt, three square foot solar panel good for?  About 7 amp hours per day of recharge. Five days of re-charge (Monday through Friday) will put about 35 amp hours back into your batteries. So if you go sailing on Saturday or Sunday, you get to use your trolling motor for an entire hour, which pretty much limits motor time to puttering around the dock. Two panels ($200) will get you two hours per week of motoring, and so on and so on.

Multiple hours per day, and multiple days during the week is pretty much out of the question, unless you are going all-in and do this ...


http://www.planetsolar.org

Heh, heh.  We've already discussed that rather cool-looking under-performing and poorly designed monstrosity in another thread. But then again, restricted to the ICW, it might be just the ticket for a very slow cruise.  :

But if you are day sailing on the weekends and using the trolling motor to get between the dock and the channel to hoist sail, then a 15 watt solar panel or two will keep your batteries topped off quite nicely.

Hope that helps,

Tom