Outboard Motor conversion

Technical discussion on converting internal combustion to electric
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mr_grumble
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Outboard Motor conversion

Post by mr_grumble » Tue, 01 Feb 2011, 11:35

Hello all, my first post so I'll keep my query general.

I've been looking into the possibility of partially navigating the Darling / Murray River systems in an aluminium 'tinnie' much like the John Doyle / Tim Flannery ABC documentary 'Two men and a Tinnie' and as a first timer, I'd like to know what I propose is actually feasible on a budget.

Initially the assumption was that we'd utilise that of a 10-15hp outboard engine, but considering the actual range of one of these 2-stroke engines, the constant supply of fuel will be the issue.

Thinking of alternatives, we considered converting a conventional outboard motor to electric and rigging a platform above the tinnie to mount panels to (and provide shade).

Now, I've never converted anything substantial to use electricity before, so I don't pretend to have a clue ;)

The tinnie will typically be 4.0m in length, which when converted to allow installation of solar panels, should allow up to three 125w panels giving me a maximum of aprox 21A utilise throughout full sun..

As for the conversion, I plan on taking an existing 2-stroke motor, removing the combustion engine, engineering an adaptor plate and coupling to an electric motor.

This creates a couple of initial questions......

1). With a desired constant engine speed of 2000rpm, I don't know what capacity / type of electric motor to consider. Ideally I would like to only have to rely on the instantaneous power output of the solar panels and not so much on stored energy which would create excessive weight.
We'd like the average cruising speed to be around the 10 knot (19km/h) zone, be able to run for the majority of the day and preferably, be able to run direct from energy created via solar panels. Any suggestions regarding the fundamental equipment, ie motors / battery / panels / regulators etc ?

2). I imagine an electric motor, continually running under load at 2000rpm will generate some heat. Will most electric motors run under these conditions with just the ambient airflow surrounding the motor ?

3). What assumptions could be made regarding the longevity of a motor configured to operate under these conditions, given the coupling to the outboard leg is adequate ?

Steve

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lithbattboss
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Outboard Motor conversion

Post by lithbattboss » Tue, 01 Feb 2011, 15:24

mr_grumble, I am sorry to disappoint you but you will need to continue to grumble since what you propose (and the performance you require) is not possible and aint going to happen).

If you want an electric outboard why not just buy an off the shelf professionally made electric outboard?
A total of only 375W of solar panels will push your tinnie along at a crawl of only about 1 knot.
You say you want a speed of about 10 knots. I can tell you that a 4kW (10hp) electric outboard ie, 10 times the power you propose pushes a tinnie along at about 4-6 knots.

Sorry to disappoint you but those are the facts.
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rhills
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Outboard Motor conversion

Post by rhills » Tue, 01 Feb 2011, 20:44

I agree that unless you're keen to spend more money building something that probably won't work as well as an off-the-shelf unit, I'd not go down that path. WRT cooling, most OTS units are direct drive, with the motor under water which makes cooling a non-issue.

Lithbattboss, are you referring to a specific Off-the-shelf unit with your specs about a 4kw electric outboard? If so, which one?

I've been close to buying a Torqeedo unit, but want to try one out behind my Plaka Boat to make sure it performs well enough before shelling out the cash. Unfortunately, no-one stocks them here in WA and I've not yet come across anyone that's bought one here.
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Electrocycle
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Outboard Motor conversion

Post by Electrocycle » Tue, 01 Feb 2011, 22:22

the sustained power requirement for a boat doing ~10knots is very high.

It is possible to get pretty good cruising speed with very little power if you use something like the hulls from a small sailing catamaran.
They're pretty cheap if the sails, etc are missing or damaged.

Something like a Hobie 18 would be good - and you could fit plenty of solar panels above it.

The cheapest motor option would be a large electric trolling motor, with a modified prop for more speed (the standard props will only do about 3 knots)

I have put an electric motor on an old outboard leg and it worked pretty well, but I still only got about 6 knots top speed using about 4kw of power.
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bga
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Outboard Motor conversion

Post by bga » Wed, 02 Feb 2011, 01:48

This may help: Electric Boat Association of Australia

More gutsy electric outboards here, up to 30HP - batteries beware.
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lithbattboss
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Outboard Motor conversion

Post by lithbattboss » Wed, 02 Feb 2011, 01:57

rhills wrote:
Lithbattboss, are you referring to a specific Off-the-shelf unit with your specs about a 4kw electric outboard? If so, which one?

I've been close to buying a Torqeedo unit, but want to try one out behind my Plaka Boat to make sure it performs well enough before shelling out the cash. Unfortunately, no-one stocks them here in WA and I've not yet come across anyone that's bought one here.
Yes the Torqeedo Cruise 4 is rated at 4kW and is equivalent in power to a 10hp petrol outboard. In addition to Torqeedo some other manufacturers of electric outboards are Parsun and Aquawatt.
Several of my electric boat customers use LiFeTech lithium batteries with the Torqeedo motors so I am very familar with their relative power and performance.
I attend quite a few lectures and information nights at universities, yachting clubs, etc. as well as at boating trade shows educating the petrol guzzling outboard motor loving boating enthusiasts of the benefits of silent, emission free electric boating. Most of these lectures and informational evenings I attend with Steven Mullie who is the secretary of the Australian Electric Boat Association and a major Australian distributor of Torqeedo electric outboards and Bellman/Mastervolt inboard electric boat motors. If you are after a Torqueedo motor Steven would be happy to ship one over to Perth for you. He is a really great guy and very helpful. You can contact Steven on either the EBAA or Eco-boat websites-
http://www.electricboats.org.au/

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bga
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Outboard Motor conversion

Post by bga » Wed, 02 Feb 2011, 02:14

Another thought: Propeller matching is really important.

It's a compromise against the coupling (mass-thrust) efficiency and drag on the propeller. Water being dense and viscous produces a lot of friction drag, reducing the optimum size of the propeller.

An optimal low power propeller will have considerably thinner and longer blades than would a typical marine propeller. This allows greater coupling efficiency and lower drag.

Most 10HP outboards are designed to push a small tinnie along at 10 or 15 knots. The propeller diameter and blade section are set for this task. Also, weed clearing is a factor in the shape of the propeller.

Some years ago, I had a small crusing boat (cole 26) that weighed about 2.5 tonnes. We found that pushing on the boat with the 10HP dinghy at full throttle resulted in about 1/2 knot of boat speed, but the 8HP Yanmar inboard diesel could push the boat along at about 3-4 knots.
The Yanmar's 2-blade prop was about twice the size of the outboard's.
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Outboard Motor conversion

Post by bga » Wed, 02 Feb 2011, 02:32

Electrocycle wrote:I have put an electric motor on an old outboard leg and it worked pretty well, but I still only got about 6 knots top speed using about 4kw of power.
I have seen a bunch of commercial products that are exactly this.
here's one ... about 6 kts

Your 6 kts from 4kW sounds sounds like a good effort!
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Richo
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Outboard Motor conversion

Post by Richo » Wed, 02 Feb 2011, 20:58

I would have thought an Etek-RT would be enough.

I guess if you are sitting in the boat for the day fishing etc
Then 375W x 6hrs=2.25kWh from solar.
Which would be about an extra 1/2 hour running time at 4kW.
How long you want to run the boat for will determine the total battery capacity.

An extra couple of hours at 4kW would be 8kWh pack.
At 72V this would be ~110Ah cells.
Or 2 strings of 60Ah lithium cells. 46 cells in total.
So the short answer is NO but the long answer is YES.
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Mesuge
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Outboard Motor conversion

Post by Mesuge » Sat, 05 Mar 2011, 14:52

Richo is right, Etek should be enough (plus it has been done before w. retrofiting old outboards). The energy needed to power the boat also varies wildly, from light cat to a barge or ponton boat and other contraptions..

There have been a number of successfull e-boat applications lately, incl. outboards and solar power. Perhaps you may start the inquiry with the Electric Mundoo project to get real data on solar power, obviously you will have to scale it down accordingly to your ideas.

Her designer/project was completely australian made, although the basis for these fine boats had been established by the famous american boat desinger Phil Bolger decades earlier. Using solar to power recreational boats in Australia/ClubMed countries or whatever sunny place is absolutely fitting idea..
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Last edited by Mesuge on Sat, 05 Mar 2011, 04:02, edited 1 time in total.
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