Hi Kirk,
These guys are not alone. There are few electric boat vendors that spell out their range/performance numbers in explicit terms, even our preferred vendors in this group. None of the flashy new products that get listed in publications like Gizmag have any of this described accurately. I've done the same kind of analysis when people here have posted about the all electric ski boat last year, the all electric "jet ski" from 2 years ago (hmmm, I haven't heard anything about that for a while) and all of the other "coming soon" (or not) products that come along.
But realistically, mainstream products rarely do this either. The latest Ford truck can get 22mpg and it can tow 7500lbs, but it doesn't get 22mpg WHILE towing 7500lbs. A ZR1 Corvette get up to 21mpg and can hit 190mph, but it doesn't get 21mpg at 190mph or while knocking down a 12 second 1/4 mile.
The advertisers just give the highlights, and you, as a consumer, have to figure out what's reasonable. The promoters prefer ambiguity. They love it when a customer thinks a product is better than it is. That's their job. And of course, the makers of this new hydrofoil never claimed that they have a 100km range at 40km/h. If one thinks that they did after reading the article, it's really the reader's mistake. But I saw no lies in that article.
Everything that I said about the hydrofoil's performance is based on the assumption that everything in the article is correct, that they were not telling any out and out lies. I just paid attention to what they actually said and figured out what it probably means.
This next part is not meant to be condescending, but I think that this is a good place to bring it up. This type of analysis is all part of the critical thinking process. Here's an excerpt from Wikipedia that covers what I'm talking about:
"Critical thinking examines assumptions, discerns hidden values, evaluates evidence... and assesses conclusions.
"Critical" as used in the expression "critical thinking" connotes the importance or centrality of the thinking to an issue, question or problem of concern. "Critical" in this context does not mean "disapproval" or "negative." There are many positive and useful uses of critical thinking.... Critical thinking can occur whenever one judges, decides, or solves a problem; in general, whenever one must figure out what to believe.... and do so in a reasonable and reflective way. Reading, writing, speaking, and listening can all be done critically or uncritically.... Expressed in most general terms, critical thinking is "a way of taking up the problems of life."
http://en.wikipedia.org/wiki/Critical_thinking
Fair winds,
Eric
Marina del Rey, CA
--- In electricboats@yahoogroups.com, Kirk McLoren <kirkmcloren@...> wrote:
>
> Dont they think a buyer expecting 60 kilometers would be miffed?
> Referrals are the best advertising and if they lie they wont get them.
> They should go into politics if that is their attitude.
> Â
> ... How beautiful it is to do nothing, then rest afterwards
> Â Â Â Â
>
>
> ________________________________
> From: Eric <ewdysar@...>
> To: electricboats@yahoogroups.com
> Sent: Thursday, May 17, 2012 1:59 PM
> Subject: Re: [Electric Boats] hydrofoil 100 km range at 4kts (or 7.4kmh)
>
>
> Â
> Hi Kirk,
>
> And this is another example of somewhat misleading promotional information. One has to read between the lines. The 100km range is not at 40kmh. The motor pulls 3.7kW and the battery pack is only rated for 4.5kWh. If we assume a safe discharge to 80% DoD, the battery has 3.6Kwh usable, which works out to 54 minutes (using Peukert's exponent of 1.03 for the Li-Ion batteries) from full to empty at full speed. This pegs the range at 36km or just under 20nm at 40kmh/22kts.
>
> To get to 100km using 100% of 4.5kWh, one needs to drop the discharge amps to 6.5A, which should deliver about 4kts (according to specs derived from Torqeedo's published data) and in almost 14 hours, one will have travelled 55nm which is roughly 100km.
>
> That just doesn't sound as exciting as the original headline.
>
> That said, it does look like a fun toy, and certainly much cheaper than the all electric ski boat discussed a few months ago.
>
> Fair winds,
> Eric
> Marina del Rey, CA
>
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