Electric Motors

[bflosail]

Hopefully I'll have my DS I in the water by late summer, would a 30 lb thrust electric trolling motor work as an auxiliary ? The boat would spend most of its time on a mooring in a bay on the Canadian side of Lake Erie although I have thought of taking her to the Finger Lakes or one of the Lakes in the Adirondack at some point probably not his year but maybe next.

[Alan]

That's big water for any trolling motor. I've been less than impressed with my 80-pound motor, and there's at least one other person here who hasn't been happy with a 55 and two batteries.

Unless you're just planning to use the motor for maneuvering around a marina, I'd get something bigger. A gas motor is probably a good idea.

[GreenLake]

I have used a 40 lbs trolling motor what seems like "forever" and it's served reasonably well.

Here are some observations:

I can get to / from the race on the lake if the wind isn't/is not longer there
I can tow a 5o5 or a Laser in and out of the channel, if I have to
I will not get over 3kn, so with any wind at all, sailing is faster
I sometimes wish it would go a little faster under the bridge so I can get out of the traffic sooner
I find the motor handy for docking (but rarely required)
I get about 40 mins out of an 80 Ah battery, meaning 2nm at full power (subst. more at lower power settings, incidentally)
I cannot win against the tide, so in that event, I wait
I cannot power against the wind, in that event I sail, or wait
I wait for wind on longer cruises, rather than powering home
I learned to carry a second battery, because when they die, there's no warning (and to double the range).
I leave the motor at home when the wind looks good, esp. for races.

Overall, I like that there's no gasoline or oil involved, and that it's quiet. I like the fact that the motor needs no maintenance. I put up with all the limitations, because I really want an "auxiliary", not something that is designed to drive the boat better than under sails. (Paddles are the solution for any short distance maneuvering for docking, unless the motor is already rigged).

If I had the money, I would have bought a Torqeedo ...

[Alan]

http://forum.daysailer.org/forum/viewtopi ... ling+motor

Here's a thread where Roger Conrad posted time and distance specifications for a 55-pound thrust motor. It demonstrates GreenLake's point, that range increases greatly at lower throttle settings.

So, with that in mind, here's a thought: What if you used two trolling motors, each with its own battery, and ran them at low throttle settings? Seems to me that you'd have long range and good power, with the advantages of an electric, at well under the cost of a Torqeedo.

If you used one of the trolling motors that have a built-in battery indicator, you'd have some warning that the charge was running low.

There's gotta be a flaw here someplace, I just can't think what it might be.

[GreenLake]

The speeds that Roger reports for a 55lbs trolling motor seem totally comparable to what I think I'm getting with a 40lbs motor.

Now, I'm the first to admit that I never measured things in a dead calm on a lake free of currents using a GPS, but more a combination of seat of the pants and occasionally timing the arrival at the stern of a bit of of floating stuff thrown off the bow.

(As an aside, I once "calibrated" my speed estimates against a GPS and was surprised how close I could judge things from the appearance of the wake).

Anyway, this stuff is sure not linear, because there doesn't seem to be a nearly 50% difference between the 40lbs and the 55lbs motor...

You are dealing with not only the non-linear resistance curve of the hull but also with the non-linear response of the motor and propeller which gives different efficiencies at different speeds.

So, don't know what your dual-engine trolling motor setup would give you, but I bet I can predict one effect: if there's opposing wind, you should be able to make progress at slightly higher wind speeds (about 40% higher, given that wind resistance goes as the square of the wind velocity)

But, I admit, the thought had occurred.

[Peterw11]

If I were you, I'd consider a second hand, 3 or 4 hp, outboard.

My 2 stroke/2 cyl 4 hp Evinrude cost me 300 bucks (average for used small outboards, I've found) and will run for an hour on a gallon or two of gas. Even though it's old (1978 model), it's simple, dead reliable, and only weighs about 30 lbs. Four horses are plenty to power a DS under most conditions.

Predicting the conditions under which you might need an auxiliary and for how long, especially when sailing on big water, is a tough thing to do. I'm guessing your overall costs would be close to what an electric would run.

[K.C. Walker]

I've got the Johnson version of the old 4 hp 2 cylinder 2 cycle that Peter has. I almost never run at full throttle and it has plenty of power.

I would guess that Peter is being a little conservative about fuel usage. I put 2 gallons in at the beginning of the season and maybe another gallon later. I sail on pretty big water and I end up using the motor quite a bit. I'm a lot more adventurous about sailing in one direction for a number of hours if I know I can get back if the conditions change.

I went out recently with the wind blowing 15-20 kn. The wind was blowing right in on the boat ramp and docks with no protection. There's no way I could've left or returned to the dock under sail. The channel isn't that wide and there are rocks on both sides. It was nice to have an auxiliary with some reserve power in those conditions.

[GreenLake]

Yep, under those conditions, I would prefer something more powerful as well. The two sites I launch from most often are nicely protected in all the prevalent conditions so that I never need a motor at those launches, except if it is totally calm inshore and I can motor out to a patch of wind, for example. Because of the way conditions differ, what works for one person is not going to work for everyone.

[bflosail]

Thank you for the good advice

[Marv Irwin]

I have used a trolling motor for three years and am now on my second $150 deep cycle battery. The first deep cycle battery left me high and dry (becalmed) earlier this year when I had fully (I thought) recharged it at the start of the season. This led me on a google excursion to learn all I could about deep cycle/low or no maintenance marine batteries. My conclusion: The battery is the serious weak link. At their best, they will last three or four years. They need to be regularly used and recharged (for long periods) at low amperage. When you purchase a new battery, make sure that it was manufactured no less than 6 months previously. If you don't use a fully charged battery it deteriorates and may be useless within the year because of some mysterious process called sulphonication. A slow trickle charge from a small solar panel may keep things in good working order when the boat is moored, but can really trust that the $30 solar panel charger will not "overcharge" the battery and render it useless.
At this stage I have now invested enough $$$ that I could almost have purchased a new 4 stroke 2 1/2 hp Honda or Yamaha.

For what its worth...

Marv

[GreenLake]

You are absolutely right about batteries being the weak link. You left out weight as another serious drawback.

There are chargers for deep-cycle batteries that change voltage and current based on where in the charging cycle the battery is.

I've been able to get more like 6-7 years out of my batteries. And I usually use two, because at the end of their lifetime they are unpredictable.

In addition to keeping them charged (monthly or so, as well as after each use) you want to not discharge them to more than 50% of rated capacity.

That's totally unlike NiCd batteries and many people getting started with lead-acid batteries will need to train different habits.

There's a device that claims to restore sulfated batteries by using extremely short pulses of high voltage. You can actually connect it to the battery while in storage. I've read many reports and descriptions of this on other forums, so these do seem to work.

Some people are selling LiIon packs that can be used in place of 12V batteries. $$$. Otherwise could be very interesting - they are so light, and you can use more of the rated capacity. That's what the Torqeedo people use. There's a US outfit making a smaller electric outboard and they use NiMH batteries. Those are also interesting, but getting those charged requires temperature monitoring...

I wish there was a cheap, reliable, robust, and much lighter alternative to the lead-acid battery. With that, electric propulsion for boats like the DS would be competitive.

As it stands, you have to be willing to live with substantial limitations. For me, on balance, the electric solution works and in the bargain provides a few things I value - silent operation, and no oil changes

[Alan]

I can tell you from experience that AGM lead-acid batteries, manufactured in 2007 and kept on a smart charger, still deliver more than 13 volts. And yeah, they are heavy. Hoisting 62.5 pounds in and out of the cuddy is a definite chore.

I hadn't heard about lithium-ion substitutes for 12-volt batteries. Sounds like something whose cost will come down over time (I hope).

[scbobk11]

I like the reliability and power of my 2 stroke, 3.5 hp Nissan, especially when needing to outrun a pop-up thunderstorm that's common in the SE USA. I've used an electric trolling motor in the past on my DS (sorry, don't remember the lb thrust) but found that it couldn't deal with windy conditions.

Gas might be louder and less environmentally friendly but how much are you going to use it? I only use the motor to get in and out of crowded boat ramps and when I need to run away from heavy weather.

For safety reasons I'll stick with gas for now. If I ever need to replace my Nissan I'll consider electric motors if the price, power and reliability are competitive.

[Jett]

Though I no longer sail a Daysailer, I do use an electric motor on my ComPac 16. Can't ski behind it, but it does push the boat around enough get in and out of tight quarters around the docks, or get to some wind. I used this same motor on my DS1, and it worked well enough.

I, too, don't like moving a heavy battery in and out of the boat, so I've opted for a lighter model I'd recommend for consideration. It's sold at Batteries Plus and is made, naturally, in China. It's called a Werker, model # WKDC12-35J. A deep cycle, AGM. Don't know the weight but think it's about 30-35 lbs. Rated at 35 amp hours, so it won't run as far around the lake as larger models (my Optima blue top is 55 ah), but so far it has not failed to get me where I want to go when I needed to use it. Costs about 80 bucks.

My electric motor has 45lbs of thrust, and it pushes the ComPac (1100 lbs) pretty well in moderate (or less) conditions, oddly just about as well as it did for the lighter Daysailer.

[GreenLake]

At the speeds that these small motors obtain, the drag components that are independent of the displacement could appear to be dominant. Or, the drag curves are so steep, that a small reduction in speed (not noticeable to the casual observer) easily makes up the difference between boats.