I've found recently that there's a 3-blade ALUMINUM prop available for the Motorguide... whether it can be adapted to fit a Minn Kota I don't know, but being aluminum the blades can be bent for more pitch.
--- In electricboats@yahoogroups.com, Chris Moss <moschris@...> wrote:
>
> Thanks very much John,
>
> Your comments tie in with what I've learned in the week since I posted
> the request. (I don't know whether this post will be moderated too.)
>
> It seems perverse that they only supply these 'trolling motors' with
> propellors with 4" pitch. The UK Minn Kota agents confirm that but can't
> discover whether there are any propellers available with 6" pitch or
> more. The 4" is the same as the cheapo I bought as an "outboard" not a
> trolling motor.
>
> Clearly one couldn't drive nearly such a large boat without danger of
> overheating, but the 1.3kW should be enough. I've measured my current
> outboard's thrust at zero speed and it's only about 50lbs. And I've
> calculated the power used by a 50lb thrust at 5 mph to be a mere 270
> watts. So there should be something there for all the inefficiencies of
> the various stages.
>
> It's hard to calculate the required pitch without knowing the speed of
> rotation of the prop and I'd need a working motor for that (and
> something to measure it with).
>
> Basically 3.8 mph just isn't good enough.
>
> Chris
>
> On 09/08/13 20:31, oak wrote:
> > Chris,
> >
> > I have a Catalina 22, which is probably a bit bigger than your boat,
> > and likely heavier. I recently went through what you discussed, and
> > can offer my observations, based on comparing the Traxxis 80 to the
> > Torqeedo 2T:
> >
> > TRAXXIS 80:
> > This is a MUCH less expensive solution ($529US at Cabelas.com vs.
> > $3300 for the Torqeedo 2T at WestMarine.com)
> > Traxxis web page:
> > http://www.cabelas.com/product/Minn-Kota-Traxxis-Transom-Mount-Trolling-Motor/701484.uts
> > 24V system
> > Top speed on my C-22 going down wind at 100% throttle with a modest
> > breeze (no sails up) was about 3.8mph
> >
> > TORQEEDO 2T:
> > http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?productId=1043184&catalogId=10001&langId=-1&storeId=11151&storeNum=50596&subdeptNum=50616&classNum=50619#.UgU2H5Kkq-8
> > Note: The Torqeedo is also available in a "remote steer" option, if
> > you have a wheel-steered arrangement.
> > 24V system
> > Max power at about 2000W
> >
> > I can EASILY run the C-22 at 4mph in light wind at about 1000W. At
> > 1500-2000W, I can run at 4.5-5mph, but it will drain my batteries
> > pretty quickly (less than an hour). If I run at 3-3.5mph with the
> > Torqeedo in light wind, my batteries will last several hours.
> >
> > I currently have two banks of two each Flooded Lead Acid batteries,
> > both Group 27, one rated at "160 reserve minutes" (160 min. at 25A
> > load), the other rated at "182 reserve minutes" (182 min. at 25A
> > load). That is, there are two battery banks, with each bank having
> > two 12V batteries in series to give the 24V. The battery switch
> > allows me to select bank 1, bank 2, both, or off. I have a SHUNT
> > wired in the negative side of the load to monitor current out of the
> > batteries (though it sounds like I can measure the voltage drop across
> > the battery cable itself, and use that as a shunt instead! I will be
> > experimenting with that soon!).
> >
> > The Traxxis is a good motor. I have no complaints. However - it's a
> > TROLLING motor. Because of the pitch of the prop, top speed on a
> > small dingy probably still wouldn't exceed 4mph. It compromises for
> > thrust, not speed. And thus, you probably won't be happy with the top
> > speed (unless you're fishing).
> >
> > Also, when I ran the Traxxis at high power for 45 min. constant, the
> > power head got VERY HOT. It would appear the Traxxis is not meant to
> > be run at full power continuously (though I didn't notice any warnings
> > about that in the documentation...).
> >
> > The Torqeedo is designed to be an OUTBOARD. The prop is pitched to
> > drive significantly sized boats. I'd be REALLY curious to see how
> > fast it would drive my 15' plywood runabout! But so far, all I have
> > is data for the Catalina 22 which is a full displacement swing keel
> > sailboat.
> >
> > My experiences have verified what has been suggested in this forum on
> > several points:
> >
> > * The Torqeedo will drive your boat substantially faster than a
> > trolling motor, for much less power.
> > * Running faster takes exponentially more power - more power from the
> > motor, and in turn more power from the batteries.
> > * At full speed, I can deplete my batteries in an hour. At slow
> > speed, I can run for many hours....
> > * Tying the battery banks in parallel to reduce the power drained out
> > of each battery DOES allow the batteries to run longer.
> > * There is definitely a "battery recovery". If I run my batteries
> > down to the point that the motor drops out, I can turn the motor off,
> > and the voltage will almost immediately come back up a substantial
> > amount. I can't run at FULL speed, but I can run at LOW speed for a
> > lot longer.
> >
> > It's unfortunate that the Torqeedo is SOO expensive (not any more
> > expensive than any of the other options in that power range, but MUCH
> > more expensive than a simple trolling motor!).
> >
> > I can buy a bank of 2 deep cycle marine batteries for about $200.
> > I have no doubt that a single Li battery would be MUCH better - but at
> > $2500 for the battery and another $600 for the charger, I'll have to
> > let someone else try THOSE experiments...
> >
> > Please feel free to email me any questions you might have.
> >
> > John
> >
> >
> >
> >
> >
> > ----------------------------------------------------------
> > *From:* watergeus55 <moschris@...>
> > *To:* electricboats@yahoogroups.com
> > *Sent:* Friday, August 2, 2013 10:13 AM
> > *Subject:* [Electric Boats] Outboard for caddy cabin boat
> >
> > Hi, I've just joined the list. I live next to the River Thames in
> > England and my main project is to be a solar powered river boat. But I
> > have an immediate issue: we live on the other side of the river from
> > the road and use a 15' caddy cabin boat with a 10HP Mariner outboard
> > to get across daily.
> >
> > The engine is giving out and I've been thinking about replacing it
> > with an electric outboard. I did buy a cheapo on ebay a couple of
> > years back (around £130). Rated "55lb thrust" it was just about usable
> > when the river is as slow as it is at the moment, but no use at all
> > when it's flowing fast, so we never did use it on a regular basis. For
> > one thing only the top speed setting was bearable and that ran down
> > the battery fast.
> >
> > None of the outboards on the market here seem to deliver much over
> > 80-85 thrust and I'm certainly not going to try another cheapo. It's
> > stopped working and I took it apart this morning. Immediately I
> > withdrew the main restraining bolts, which were stained with rust I
> > knew these things were not made properly.
> >
> > The Minn Kota Traxxis 80 seems a little more reasonable. It uses
> > 1.34kW max and costs about £650 in the UK. But I'm doubtful it'll give
> > the 4-5mph we need when the river's really running.
> >
> > Anyone got an opinion on that. Are there other better outboards available?
> >
> > Chris
> >
> >
> >
> >
>
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