[Rhodes22-list] Bill Effros - Another Alternative For Electric Drive

Sat Sep 25 13:46:08 EDT 2004

Bill,

You might want to take a look at the following web page:

http://www.abcpm.co.uk/pages/vetus_pages/thrusters.html

This web page will give you some data on Vetus bow thrusters.  Vetus makes
12 VDC thrusters rated at up to 209 lbs thrust & 5.4 kw.  Vetus also makes a
couple of 24 VDC models rated at 352 lbs thrust & 7 kw and a whopping 484
lbs thrust & 12 kw!  Thus, you can get sufficiently big off-the-shelf
electric thrusters to get your boat's performance to be roughly equivalent
to a 9.9 hp outboard if you wish.  These are continuous duty ratings & the
motors are variable speed & reversible.  Another advantage is that Vetus
also offers all the control hardware & these units are designed for marine
use.

Note: These thrust vs. kw relationships are in same range as my earlier
calculation & gives a little more confidence in my estimate.

Note: The price for these bow thrusters will suddenly make your outboard
look like a really good deal!  That's even before you've purchased the
genset.

Roger Pihlaja
S/V Dynamic Equilibrium

----- Original Message -----
From: "Roger Pihlaja" <cen09402 at centurytel.net>
To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
Sent: Saturday, September 25, 2004 10:17 AM
Subject: Re: [Rhodes22-list] Bill Effros - Electric Drive

> Bill,
>
> I looked in the 2004 issue of the West Marine Master Catalog on pp. 223.
> The most powerful transom-mount electric trolling motor listed is a Minn
> Kota M/N RT101/S-3X.  This trolling motor is rated to deliver 101 lbs of
> thrust at 36 VDC and 37 amps.  To power this load, you would need:
>
> P = V * A = 36 VDC * 37 amps * 1 watt/VDC-amp / 1000 watts/kw =  1.33 kw
>
> However, most portable generators are designed to deliver only 120 VAC or
12
> VDC & this trolling motor requires 36 VDC.  For you, as an aftermarket
> application, the simplest way to generate this DC voltage would be to use
> the 120 VAC power output to drive a 36 VDC power supply.  This power
supply
> can be built with off-the-shelf solid state components, will be very
> reliable, & about 95% efficient:
>
> 1.33 kw / 0.95 =  1.42 kw continuous
>
> You don't want to run your generator at its maximum rated output for very
> long because the advertised maximum load on generators is usually for an
> intermittent load.   Typically, the maximum continuous load rating of a
> generator is about 75% of the maximum intermittent load rating:
>
> 1.42 kw / 0.75 =  1.87 kw or 1870 watts max intermittent
>
> A Coleman Powermate Model Pulse 1850 has a 4-cycle 3.5 hp Briggs &
Stratton
> engine & is rated at 1850 watts intermittent load & 1500 watts continuous
> load at 12 VDC or 120 VAC.  So, this genset is sized about right.  This
> genset looks like a rectangular box with a handle on top with dimensions:
> 8.3" Length X 11.8" Width X 16.4" High.  I don't know the weight.  The 36
> VDC power supply would easily fit into a box of similar or slightly
smaller
> dimensions & could be permanently mounted inside the lazarette
compartment.
>
> The horsepower ratings of outboard motors are on the basis of power output
> at the crankshaft.  The above Minn Kota trolling motor power can also be
> expressed in terms of horsepower:
>
> 1.33 kw / 0.746 kw/hp = 1.78 hp
>
> This horsepower is at the output of the electric motor, which is
underwater
> & directly coupled to the propeller.  So, the trolling motor has no
> mechanical losses due to a transmission or lower unit.  Assuming the
> outboard will have a full F-N-R transmission, a right angle spur gear in
the
> lower unit, & roller or needle bearings throughout (in other words - a
high
> quality, state-of-the-art unit), the mechanical efficiency will be about
72%
> at the 5500 RPM transmission input speeds typical of a gasoline engine.
> Note: The details of where that 72% efficiency came from are from my ME451
> Machine Design class & are beyond the scope of this discussion.  Assuming
> you are willing to trust my estimated power transmission efficiency, you
> would need an outboard rated at:
>
> 1.33 kw / (0.746 kw/hp * 0.72) =  2.48 hp
>
> So, in big round number, this 101 lb thrust trolling motor would be
roughly
> equivalent to a 2-1/2 hp gasoline powered outboard.  All of this stuff
> scales up pretty linearly.  To get an electric trolling motor that
performed
> something like the 9.9 hp outboards that everybody seems to favor on our
> Rhodes 22's, you would need one rated at about:
>
> 101 lbs thrust * [9.9 hp / 2.48 hp] = 403 lbs thrust
>
> Assuming the voltage stays constant at 36 VDC, the current would be:
>
> 37 amps * [9.9 hp / 2.48 hp] = 148 amps
>
> The genset required to run this bad boy would need to be rated about:
>
> 36 VDC * 148 amps * 1 watt/VDC-amp / (1000 watts/kw * 0.95 * 0.75) = 7.46
kw
> or 7460 watts max intermittent
>
> Bill, hopefully, this answers some of your questions.
>
> Roger Pihlaja
> S/V Dynamic Equilbrium
>
> ----- Original Message -----
> From: "Bill Effros" <bill at effros.com>
> To: "The Rhodes 22 mail list" <rhodes22-list at rhodes22.org>
> Sent: Friday, September 24, 2004 11:39 PM
> Subject: Re: [Rhodes22-list] Bill Effros - Electric Drive
>
>
> > No, Bob,
> >
> > I just took a look at what others had been talking about, lifted it,
> noticed that it was seriously quiet, and went back to the experts on the
> list.
> >
> > Roger, Michael, anyone
> >
> > These electric motors are rated at up to 105 lbs. of thrust.  What does
> that mean?  How does it relate to...anything.
> >
> > I bought a $100 electric motor several years ago, clamped it along side
my
> Tohatsu, and sure enough, it would move the boat.  But it was not what I
> would call robust.  Is this an idea that has any possibility of working?
> >
> > Bill
> >
> >
> > ----- Original Message -----
> > From: Robert Skinner
> > To: The Rhodes 22 mail list
> > Sent: Friday, September 24, 2004 8:38 PM
> > Subject: Re: [Rhodes22-list] Bill Effros - Electric Drive
> >
> >
> > Bill -
> >
> > Are you using an hybrid electric drive too?
> >
> > Brad -
> >
> > Would you send me the pix of the Beijing boats.
> >
> > /Bob Skinner
> > ------------------------------------------------
> > brad haslett wrote:
> > >
> > > Bill,
> > >
> > > Your idea of combining an electric drive with a small
> > > generator is quite good!  Yamaha now makes a competing
> > > model to my Honda which is cheaper and lighter.  The
> > > noise level is about the same and is certainly less
> > > than the quietest outboard.  It is nice to have around
> > > the house as well.
> > >
> > > Attached are a couple of photos from the Summer Palace
> > > in Beijing.  The lake is full of electric boats.  We
> > > rented an 8 passenger boat and I was suprised at how
> > > fast it moved.  The other photo is of a solar powered
> > > cruise boat on the same lake.  If I ever get the time
> > > to build a "houseboat" this is what it would look
> > > like.
> > >
> > > Brad Haslett
> > > "CoraShen"
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> > __________________________________________________
> > Use Rhodes22-list at rhodes22.org, Help? www.rhodes22.org/list
> >
> >
> >
>