I'm wondering if the limitation is simply on the strength of the plastic: you need to go to a stronger material for a bigger pitch and the companies supplying them don't do this for some reason.
I'm also reluctant to go for the extra cost of the Torqueeda unless it's absolutely necessary. For my purposes, lithium batteries are a waste.
Chris
On 12/08/13 03:31, stmbtwle wrote:
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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