Sailboats can get away with a smaller motor because they have the luxury of the additional thrust provided by the sails. Let's assume an electric only boat needs one KW input per ton for a displacement hull for adequate speed. You can divide this into two components referencing the hockey stick curve. The handle is the resistance due to the friction of the hull and the blade is the drag due to the wave-making resistance. Assuming a 50% split for the two components then you need 500 watts for the friction of the hull and 500 watts for the wave-making. If you let the sails do the heavy lifting - compensate for the wave drag - then your motor would only have to be half the power of an electric only boat. Thanks. Steve S.
--- In electricboats@yahoogroups.com, John Green <v_2jgree@...> wrote:
>
>
> Hi, John,
>
> There are a few low power fans in the group, that's for sure. Bear in
> mind that lower power setups are by nature less critical and so are
> probably less discussed due to that.
>
>
>
> In answer to your first question, that of why, the answer is probably
> the same as the one I got after asking why the garage moron had his
> wheel impact gun torque set to 100 ft-pound instead of the correct 70
> ft lb for that sized wheel nut, and that is that it is generally safer
> to have more power than less, and it is likely the same for customer
> complaints re the commercially available setups.
>
> (BTW, I was ultimately able to oxy-acetylene torch off the
> wheel-shrouded 2 rounded nuts that I had, and believe me it was
> 'safer', as the wheel indeed had no chance of working loose while
> driving!)
>
>
>
> I would be interested in reading more re your description of 'adequate
> propulsion'.
>
> I also have a few easy questions, if that is OK with you, as I have a
> similar sized boat and am interested only in lower powered electric.
>
>
>
> How far do you have to motor each trip?
>
> What size of batteries do you use?
>
> Does the currently used 70 lb thrust make the old 35 pounder seem
> inadvisable even allowing for boat size?
>
> Finally, do you ever get totally stranded/badly inconvenienced due to
> headwinds/currents?
>
>
>
> Thanks in anticipation,
>
> John
>
>
>
>
>
> 1b. Re: Planning Cal 2-27 conversion, advice needed Posted by: "John
> Francis" [1]surv69@... surv1895 Date: Fri Nov 16, 2012 6:32 am
> ((PST)) WOW! We are talking about sailboats . . . aren't we?
> Personally, I don't know why anyone would even consider $5000+ to put
> an electric motor in a sailboat and still have to concern themselves
> with whether or not it might not be enough engine for the boat. I have
> a 70-pound thrust motor on my 28' Newport . . . adequate propulsion for
> a boat that generally doesn't need an engine. Years ago(about 15), I
> adequately operated my MacGregor 25 with a 37-pound thrust motor. I
> have made many, many thousand mile trips on a 250cc Yamaha. My 400cc
> Yamaha was always more than enough engine to make trips. BUT still
> virually E-V-E-R-Y-O-N-E claims that 1100cc is the absolute minimum
> engine needed and a lot of posters on the internet say something around
> 1500cc. Even if a discussion includes a utilizing a 650cc motorcycle,
> it seems everyone jumps in to virtually berate the very idea of using
> 650cc for trips. Why is everyone so doggone power crazy . . .
> especially in an endeavor that's not about "*POWER*", such as sailing.
> Seriously . . . this leads me to wonder if this is a real discussion
> about green energy, which generally requires some degree of
> compromise(on the side of conservation), on the part of participants,
> or is this really just another conversation of one-upmanship and
> full-speed ahead in what's new for the moment? If everyone so
> desperately needs the speed and power they've always enjoyed in the
> past(and over utilized), then why not just keep the old boiler-plate
> engines in place, keep the speed as high as possible and leave the
> smell behind . . . in your oily wake. argh
>
> References
>
> 1. mailto:surv69@...
>
> --
> http://www.fastmail.fm - One of many happy users:
> http://www.fastmail.fm/help/overview_quotes.html
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