Going electric?

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Going electric?

Postby PromptCritical » Thu May 18, 2006 1:09 am

Currently I have a 1.5 HP Johnson Colt outboard, but since I put in the deep cycle for the lights, I was thinking of possibly going to electric. With the solar panel I plan on getting, my boat will truly be a "green machine". (not that I buy into that global warming/peak-oil stuff) but I still think it would be neat.

Considering that the 1.5 horse is great for simple maneuvering and beats the heck out of a paddle if the wind dies, what size electric would I need? I was thinking a Minn Kota "Endura" 30 lb thrust motor should be about the same...

I see Roger has replaced his 5 HP suzuki with a 55 lb thrust electric. How does the power compare? How much run-time will a full size battery get? (I'm running a wheelchair battery which is about half the size)
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Postby jmy9366 » Thu May 18, 2006 6:12 pm

I'm running a 40lb thrust Minn Kota, seems to be fine for getting off the ramp, dock, dousing sails when in bound, or getting across the lake if the wind dies. I don't think I'd trust electric to push against a decent current in salt water, but fine for lake use. I'm using a standard size marine battery, and charge life depends on speed of the motor. The Minn Kota's have a graphic on the body that gives you a general guide for hours of use at the different speeds.
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hours of power

Postby Roger » Thu May 18, 2006 10:41 pm

Based on trial runs I made last year with a group 24 deep cycle marine battery and my 55# thrust Minkota Endura, I was able to determine the following:

Setting/ Speed(kts)/Batt(hrs)/ Distance (nm calculated as TSD*)
1/ 0.75/ 12/ 9
2/ 1/ 9/ 9
3 / 1.35/ 6/ 8.1
4 / 1.8/ 4/ 7.2
5 / 2.65/ 1.5/ 3.97

*time speed distance calculation

Sorry, I can't seem to get the table to show properly. As an example the best speed/time ratio according to my calculation is setting 4 which drives the boat at 1.8 knots for four hours for a distance of 7.2 nautical miles.
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Re: Going electric?

Postby GreenLake » Tue Aug 12, 2014 1:06 pm

A comment on an older thread:

I took some GPS data for speed settings 4 and 5 on a 40# Minn Kota with a Kipawa propeller fitted and got the same speeds as Roger reported. (Sails down).

However, in my experience, the battery hours are about 1/2 of what Roger reports. I also use group 24 batteries and would normally switch to the second one after 45 min, not 1.5 hrs.

I find it interesting that the 15# difference in thrust does not translate to different speeds. I wonder whether that means the combination of propeller pitch and revolutions is the limiting factor ?
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Re: Going electric?

Postby curifin » Tue Aug 26, 2014 11:02 am

A great link to a really good discussion about using trolling motors on boats:

http://www.boatdesign.net/forums/boat-d ... 96-17.html

I have used electric exclusively with a 105 amp hour deep cycle. It's all wired in place and charged with solar and/or AC. 40lbs works okay for lake or dock work if the is not too much wind. I can sail much faster than I can motor which is what I really like about the setup. I get about 1 hour on setting 4 (about 2.5 mph) for 50% battery. I don't run past 50% battery intentionally. Ultimately I will pair this setup with a Honda EU2000 and multi bank high amp charger for a true hybrid boat.

Make sure to get the higher end motor with the PWM controller built in, this greatly increases efficiency. Also, I recommend very heavy gauge wiring if you are running from the Cuddy/mast area to the roller. I used AWG 6 and would go with 4 if I did it again.
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Re: Going electric?

Postby GreenLake » Tue Aug 26, 2014 3:46 pm

If you get 2.5mph, your setting 4 would seem to be in between my settings 4 and 5 (in mph, I get 2mph for setting 4 and 3.2mph for setting 5). That scales roughly with the run-time you are getting on a battery of your size. Perhaps we also have different controllers.

On wire gauges I entirely agree. I don't instal my motor permanently because I use the boat for (beer can) races and don't want to drag the extra weight when I do. I did make an "extension" cord" to allow the batteries to be stored in front of the seats (on a DS1). I simply bought the heaviest gauge wire that I could a) afford and b) wouldn't sink the boat. The proper thing to do would have been to get a longer length and replace most of the original wiring as well, but you can't have everything.
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Re: Going electric?

Postby talbot » Fri Aug 29, 2014 2:06 pm

I am running a 30-lb Minn Kota. I was interested to see that the speed with the larger Minn Kota is not much greater. I get about 1.9-2.0 kt under full power (#5). It makes me question whether a larger motor is worth the extra weight. For any situation where we might have to buck tides or current, we use a 2hp Honda (short shaft, 4-stroke). The gas outboard pushes the boat at about 4kt at 50% throttle.

I use a keelson-installed battery under the cuddy floor between the mast and CB trunk. AWG#6 wiring back to a receptacle near the stern. The battery also runs the navigation sidelights and the compass light. The solar-charger receptacle has a bypass circuit around the charge controller so it can function as an outlet for charging cell phones, VHF, and GPS. I have been using a little series 20 battery, but the battery compartment would accommodate series 24.
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Re: Going electric?

Postby GreenLake » Fri Aug 29, 2014 2:25 pm

There are two issues here.

One is that at some point the power/speed curve becomes steep, so that even double the power will not add near double the speed, but just few percent or tens of percent.

The other is that these motors may be limited by the combination pitch x revs. Once the helix described by the moving propeller tips does not go faster than the boat, you could add as much power as you wanted without adding speed.

The first issue gets much worse at speeds around 5 knots and higher, but there are indications that the curve is already a bit non-linear at 3knots. So that could be a factor. I never tried to work out the math for the second issue, but I have a hunch that this is also a factor.

Hence the small differences that are reported for #30 vs #40 or stronger trolling motors. The difference is not zero, as you point out, but about the difference between my two settings (4 and 5). Psychologically, I do notice that extra 3/4 of a knot and usually don't use setting 4 unless I need the extended range it provides. (This 3/4 of a knot comes at nearly double the power consumption, so that tells you something about the non-linearity of the power/speed curve).

Something like a Torqeedo is different in that it's intended to reach somewhat higher speeds (so probably fixes the second issue) and with the advanced battery technology etc. is able to produce more power than the smaller trolling motors, with overall result of higher speeds. I would expect the DS to be slower with a Torqeedo than the inflatable that they show in their ads or that show up in reviews.... (Also the speed/dollar ratio is unfavorable compared to regular outboards, by the time you shell out for one of them).

The nice thing about the trolling motor setup is indeed that you can run some electric system connected to it, which works well for cruising applications where there are some electrical consumer that would be more conveniently handled by having a "main" battery and charger system. If you add this to an outboard you have the weight penalty for both.
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Re: Going electric?

Postby talbot » Fri Aug 29, 2014 5:04 pm

Yes. The weight penalty is substantial, with the weight of the gas motor (30-40lbs), electric motor (20-25lbs), and battery (40-50 lbs) comging to about as much as one additional person. We are about to leave on a saltwater excursion where we need the gas motor. Once we come back, I will rethink the whole issue. We don't sail at the coast often, which argues for keeping the fixed battery. On the other hand, the battery weighs a lot more than the gas engine, which argues for pulling the electrical system and going back to temporary lights. We're thinking what we really need is a second boat.
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Re: Going electric?

Postby GreenLake » Fri Aug 29, 2014 6:09 pm

For some occasions a bit more ballast can be a good thing. Certainly when I use the DS in the local races, I don't want to be carrying batteries (except on days where there's a good chance that I won't make it to/from the starting line because of lack of wind before/after the race -- it's too far to paddle the DS).
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Re: Going electric?

Postby curifin » Sat Aug 30, 2014 7:58 pm

I reached the same conclusion and bought a keelboat, but honestly, the DS is way easier to deal with. If there was some way to assure self rescure it would be a no brainer. It's not the flipping that bugs me.... its the hosed without help that plauges me.
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Re: Going electric?

Postby GreenLake » Sat Aug 30, 2014 11:11 pm

One interesting aspect about electric vs. outboard is whether either of these technologies is more reliable when used purely as standby.

The way I use my trolling motor, it mostly sits in the car and gets mounted only when I expect I might need it, but even then, it may not get used, depending on conditions. Over many years I've had two failures. Once, a battery died without warning. Another time, the contacts had a bit of corrosion and overheated enough to melt the isolation.

Given that I don't test the motor, or service it (other than topping off the batteries every month - or every other month), I'm quite satisfied that the system will work. I take two batteries, so it would mean reduced range, not being without all power, if one of them quits suddenly.

What about outboards? Do you find them reliable in "standby" applications? Or do they benefit from being run everytime you use the boat?
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Re: Going electric?

Postby talbot » Sun Aug 31, 2014 4:55 pm

Because gas motors are so heavy, I tend to keep mine mounted if I use it at all. Which in turn means I tend to use it more. So mine does get tested, maybe not every trip, but perhaps once every week or two.
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Re: Going electric?

Postby GreenLake » Sun Aug 31, 2014 5:08 pm

@talbot, that pretty much describes how I see outboards typically used. It's a use pattern that's sporadic, but it's not "standby" in the sense I'm using that term here.
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Re: Going electric?

Postby K.C. Walker » Sun Aug 31, 2014 8:46 pm

I don't use my 1974 twin cylinder 4 hp Johnson as a standby but as an auxiliary. I use it pretty much every time I go out. I prefer to dock and leave the dock under power rather than sail. At the beginning of the season I put 2 gallons in the tank and I just put in another gallon. I tuned it up about four years ago and last year put a carb kit in it. I sometimes don't use it for two weeks. Also, the summer season is short here so I don't use it for nine months. This summer it's been pretty much starting on the first pull, maybe second. If I'm not going to use it for a week or two, I always disconnect the gas hose and run all of the fuel out of the carburetor. I've had no problems with pump gas and stabilized two cycle oil. Even with stabilizer I don't use gas that's older than a month or two, though. I had a Johnson brand plastic gas tank which was pretty junky and the new price is about $110. I replaced it this year because the old one had a cracked part which would've cost more than buying a third-party tank. I got a Moeller for about half that price and it's a much nicer tank. I have pretty much have zero gas smell on board now. So, there is some maintenance but I do find it plenty reliable.

Of course, I'd rather be sailing than motoring (either gas or electric). However, having an auxiliary I find very liberating. I really enjoy light air sailing early in the morning when the lake is flat. I have no hesitation going out even if I think the wind may die. If it does, and the morning boat traffic on the lake has started I don't hesitate to start the motor and head home. For me, five or 10 minutes of motoring is not bad compared to waiting for the wind to come back. And besides, if I'm sitting there with no wind, I start thinking about breakfast and another coffee. :-)
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