Scott,
I believe that Myles covered quite a bit of good information. But I would like to throw in a few other considerations.
As to the accuracy of fuel gauges, I can drive my 2007 Honda Fit for almost 100 miles before the gas gauge moves off of full after a fillup. This means that "full" means anywhere 70 to 100% of my total range or capacity. Should I return the car for that? When the low fuel light comes on, how much range is left? The manual says 20 to 30 miles but I've gone more than 50 on occasion. Does it make the car unsafe? My wife's Honda Insight has a "miles remaining" display. It will often change dramatically while driving, leaving the house it might read 100 miles, 5 miles later it indicates 130 miles and 5 miles later it reads 75 miles. But it's not broken, even for a gas vehicle, predicting range is difficult because it is very dependant on how the vehicle will be operated. As another example, my 1989 Suburban goes dry when the guage reads about 1/8 of a tank left. I could fix it, but since the truck is out of warranty, it's my problem, not GM's. Relating this to your client, has he ever experienced a time where the gauge indicated that he had "fuel" left but the boat was actually out of energy (dead in the water)? That is the only "dangerous" situation that I can see that would be a problem, if the gauge consistantly reads low, then your client has a definate margin of safety built into his meter.
Discussing the idea of "going out to sea", every Duffy that I am aware of is definately not a seagoing vessel. These boats are designed for protected, calm waters. They are typically harbor launches, so any time that the drive fails, either through operation or failure (just like a gas engine), the occupants should not be in a life threatening or dangerous situation.
As many people have already said, battery capacity prediction is a wiley beast and most battery gauges are spotty at best. More examples include cordless tools, toothbrushes and cell phones. Most of these displays are more accurate when the batteries are new, but if the batteries have many cycles on them, they have lost capacity. Weirdly, batteries that have almost no cycles on them but were not kept fully charged, will have lost capacity too. The techinical question is "how would the gauge know?" Many battery capacity gauges rely on simple resting voltages, and they are only vaguely accurate. Most people consider them to be accurate enough. More sophisticated meters, as described by Miles, are more accurate, but they need to configured for the specific batteries in use. And like Myles stated, these meters would need to be re-configured to compensate as the batteries age to retain a high level of accuracy. Changing the batteries could also justify re-configuring the gauge, but in all of these cases, the original set-up will be as accurate as the fuel gauge in my Honda.
So far, you've described your client's impressions, concerns and anecdotal evidence. He would need to collect some specific data concerning the meter readings, actual measured usage and independantly measured battery voltages before I would be convinced that the meter is not precise (consistant). In my ealier examples, my Honda Fit and Suburban gas gauges are both precise if not accurate. They are still useful for using the vehicles and planning trips. Once precision has been determined, then accuracy can be discussed. The Insight "miles remaining" display is not precise, but generally accurate. I depend more on the trip odometer than miles remaining display or the fuel gauge if I am concerned about running the car to it's limits. The objective data to suport your clients claim could be collected right at the dock. Charge the boat, note the data, run the boat and check the meter and voltage readings at various elapsed times. He may find that his gauge is precise (if not accurate) and perfectly usable for it's designed use case.
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, barristerla <no_reply@...> wrote:
>
> Myles,
>
> Thanks for your response. I disagree with your assessment about my car. If the fuel gauge is not working properly it is absolutely dangerous, as I could get stranded somewhere dangerous. I've had quite a few manufacturers buy back vehicles like that.
>
> As for other Duffy owners complaining, that is the main thrust of what I've been looking for. Seems like not even a scant few are doing so, which makes me wonder what is up. Perhaps many of them view this issue as most of you do, that is, sure, it may be defective, but, so what? Apparently it's inherent in an electric boat and one should just live with it.
>
> Thanks again.
>
> Scott K.
>
> --- In electricboats@yahoogroups.com, "Myles Twete" <matwete@> wrote:
> >
> > >That all said, it seems like you are saying one can never rely on their
> > gauges? If that's true, these craft seem quite dangerous by design.
> >
> > "quite dangerous by design".hmm.does your car include a fuel gauge that
> > tells you reliably how much time you have left to drive?
> >
> > No? Yet you still drive the car anyway. Would you say that the car is also
> > "quite dangerous by design" then?
> >
> > A bit of info for you: First, your client's boat likely has lead acid
> > batteries. Depending on how your client and the previous owner of his boat
> > treated those batteries, the fully charged capacity they actually have could
> > be anywhere from 30 - 100% of the rated capacity. That's a wide range.
> > Further, your client may not know how to properly operate the charger or
> > perhaps has the impression that charging for 1hr is enough---I have a friend
> > that never trusted his charger to leave it plugged in overnight, so I know
> > this happens. Further still, of the 6 or 12 batteries that are in the boat,
> > there may be some real losers that severely limit the discharge time and
> > range. And it only gets worse with time.
> >
> > The meters themselves vary and I haven't a clue whether the boat in question
> > uses a Link10 style meter or some in-house design or what. In the case of a
> > Xantrex Link-10, the only way to depend at all on the "time remaining"
> > readout is if you have manually set the battery capacity parameter
> > appropriately for your pack. So if, as in my case, you have some seriously
> > old batteries which are rated for 225ah, yet probably are only good for
> > 80ah, to at all believe the "time remaining" readout, you'd need to select
> > 80ah or so for the capacity parameter in the meter. Failing to do that, the
> > 'time remaining' readout on the boat is largely meaningless as it hasn't a
> > real clue how much capacity the pack has. It could infer it by reading how
> > much charge was brought in at the last few charge cycles and noting the
> > depth of charge in each case prior, but I doubt it does that.
> >
> > Now, does this meter make the boat unsafe? Of course not! For one thing,
> > any such meter that includes a 'time remaining' display likely also allows
> > the user to view Battery Voltage, Battery Current and most important,
> > Charge/Discharge in Amp-Hours. That last one is your best gauge to know how
> > far or how long you can run---i.e. if your last outing ended up with the
> > gauge reading -140ah and you still had a voltage that wasn't near the
> > 1.75v/cell level, then after a full recharge, you'd expect that the next
> > outing could similarly deliver 140ah. And at a steady 40amps of cruise
> > current, you'd have some level of confidence that you're good for at least
> > 3hrs of such cruising. I don't think you'll find many people on this list
> > who leave their meters on the 'time remaining' readout---to do so trusts
> > that the SW in the meter that predicts this has the right parameters and
> > data to figure this out.
> >
> > Sure, your client may have a defective gauge. But having been on this forum
> > now for some 8yrs, I don't think I've ever heard of Duffy owners chiming in
> > about defective gauges or "dangerous duffies" and so I don't think you'll
> > develop a case from this list. I can tell you this: If your client's meter
> > is a Link-10 and if they monkeyed around with the battery pack wiring,
> > there's a good chance they could have fried the current sense inputs on the
> > gauge. The result is that such a gauge delivers no meaningful current
> > information and without that, no meaningful AH or Time info. This has
> > happened to a lot of owners of these meters and there are more unsafe ways
> > to wire up and power up these gauges than safe ways. In my case, I have a
> > single connector for all the connections to my meter---I don't take chances
> > as it is a known defective and unforgiving design. Any time I contemplate
> > removing battery cables or rerouting wires, I pull the plug to the meter to
> > keep it safe.
> >
> > Anyway, we know too little about your situation to help really. But if you
> > and your client think that his boat is unsafe because of an inaccurate
> > depletion predictor gauge, I'd suggest taking some boater's safety and basic
> > electricity courses instead.
> >
> > -mt
> >
> >
> > From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com]
> > On Behalf Of barristerla
> > Sent: Thursday, December 16, 2010 8:51 PM
> > To: electricboats@yahoogroups.com
> > Subject: Re: [Electric Boats] New member, Q re: Duffy Boat
> >
> > Dear Rick and Mark,
> >
> > Thank you for your insight.
> >
> > I think the main issue with this gentleman is that the gauge always seems to
> > be inaccurate, even when fully powered, so, when it says it has 2.5 hours
> > remaining, he is never sure what he's got. The representation from Duffy as
> > to the efficacy of the gauge was quite different.
> >
> > That all said, it seems like you are saying one can never rely on their
> > gauges? If that's true, these craft seem quite dangerous by design....
> >
> >
> > Regards,
> >
> > Scott Kaufman
> >
> > > On Fri, Dec 17, 2010 at 7:16 AM, barristerla <no_reply@yahoogroups.com
> > <mailto:no_reply%40yahoogroups.com> >wrote:
> > >
> > > >
> > > >
> > > > Hi folks:
> > > >
> > > > I'm new to the group. As you may have guessed by my "handle" I am an
> > > > attorney. I am NOT, repeat, am NOT looking for business here.
> > > > I could use some input from you folks though.
> > > >
> > > > I currently have a client who claims to have issues with his2008 Duffy
> > 18
> > > > Snug Harbor craft. More specifically, he claims that he has issues with
> > the
> > > > readout on his Digital Energy Gauge. It does not appear to show the
> > proper
> > > > time remaining even when initially charged and going forward, during
> > use. He
> > > > feels he cannot depend on it and if he did he may end up stranded at
> > sea.
> > > >
> > > > I have searched the net and not really seen any other folks having these
> > > > problems. Are any of you experiencing this issue or do you know anyone
> > who
> > > > is? Usually I expect at least some smoke before I believe there is a
> > fire...
> > > >
> > > > Thanks in advance for your thoughtful responses.
> > > >
> > > > Regards,
> > > >
> > > > Scott Kaufman
> > > >
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