Is solar electric propulsion practical for a medium sized cruising boat for river and lake use and how does it compare to outboard propulsion?
Mundoo 3 Solar Electric – A Duck Flat Plan
11 metres x 2.5 metres
12hp Permanent magnet electric power
Top Speed 8-9knots
or 10/15hp 4 stroke outboard
Top Speed 10-12knots
Please contact Duck Flat for plan information. I was drafting for the project.I have just been burning the midnight oil on a huge job for Duck Flat Wooden Boats – drafting out all the details of their Mundoo 3 hybrid solar liveaboard.
It is their design drawn out on the shop floor. I’m operating in Draftsman mode taking measurements and transferring them to a full set of detailed drawings.
Happily (and with a great sigh of relief) I have just (December 1, 2005) handed them 22 detail drawings plus documentation on the building procedures for their Solar Electric Mundoo III riverboat.
| See our Riverboat Plans for Simple Outboard powered boats with accommodation. |  |
The boat was featured in Woodenboat magazine and they have faced a growing demand for plans, so have been cracking the whip (in the kindest possible way) in my direction. The magazine featured the Mundoo on the front cover. A PDF file of the issue is available here – Article stars on page 74.
The original boat’s hullshape was based on the existing 4 stroke outboard powered Mundoo 3, but in a sense, grew organically out of the collaboration between the Ducks and the owners John and Gabby – with just about every aspect of the boat changed apart from the main hullshape.
The main hull remained the same shape, but gained a raised foredeck for much more volume in the forward cabin, a nacelle beneath the main hull was added to carry the batteries, motor and prop shaft (other major changes were – a bow thruster was fitted, the cabin extended aft, the galley enlarged and much shifting of interior spaces – not one bulkhead from the original design remains in the same position).
As almost every detail of the boat was revised from the original the Ducks asked me initially to document the boat during the building process so they had the information to build further boats.
Original High Thrust Outboard Version of Mundoo 3 Riverboat
Original Mundoo 3
The more liveable layout of the Solar version of the Riverboat
Original Mundoo 3 GA
Are Solar or Electric Boats Ready for Prime Time?
This boat is a great success for matching John and Gabby’s requirements in every sense – it far exceeded the technical expectations of the hybrid electric power with a higher cruising speed and a higher yield from the solar panels than expected. On a reasonable summers day the “break even point” where the solar panel output equals the motor’s consumption is at about 4.5 knots.
The original brief was for the solar power to be heavily augmented by hooking up to shore power most evenings of a cruise, but in actual use has proved to be much more independent of outside power sources than expected.
There is a portable generator aboard if things get really desperate, but it hasn’t been used a great deal so far.
The above statements have serious caveats if a wider range of use is intended
The electric version has a break even speed of 4.5knots in sunny Australian conditions. It is not a lot less in moderate cloudy conditions. Take note of this figure.
It also has 10 hours of battery power for motoring. However a significant amount of power is needed in reserve for “home amenities” when the boat is tied up at the end of the day when cruising which cuts into the 10 hours. Providing a more realistic 5 or 6 hours of motoring
The boat truly suits John and Gabby’s use patterns. They like to cruise for several hours or a day on the Murray River, which is narrow and protected for the most part. Then they pull over and stop for a day or two. DThere are large lakes near the coast which take several hours to cross. Just like a sailboat they will choose the right weather for crossing as the lakes can be dangerous – long fetch and shallow water means big square waves.
The Solar electric Mundoo is constrained by both range and the degree of power.
A quick comparison is with the dual high thrust outboard version. It hits 10 knots and can happily cruise at 7 or 8. It has enough power, more than double the Solar Electric version and range that can be augmented with cheap plastic fuel tanks to punch against serious headwinds or rough water on the large South Australian lakes that are part of the Murray Darling River system.
On the Murray River John ahd Gabby will seldom meet much more than small waves where the river is aligned with the wind direction.
Even moderate sized waves on a lake, say a foot tall can increase hull resistance by 50 to 70 percent. This means that the break even speed will come down by 25 percent, as will range. So break even point becomes 3.5 knots. The powering time moves from 6 hours to 4.5
Pushing speed up to a more common 6 knots will halve the range providing only 3 hours of electric power. Resistance increases with the square of the speed at these modest speeds.
Bring in more serious head winds and waves and the tonne of batteries starts to peak out at 1.5 hours of running or a bit over 2 hours with nothing left for amenities when the boat gets in.
However the low overall power of the boat provides a potential for the motor just not being able to supply enough power. 12hp is not a lot for a 30 plus foot boat in adverse conditions.
So after that, lets recap.
This boat was a stunning success because it fitted the owner’s needs. They wanted to cruise quietly a few hours a day, then tie up somewhere pleasant and hang out. Swimming, bushwalking, reading, canoeing and talking for a couple of day. Or maybe some short trips.
The Murray river is a relatively narrow by standards of other continents, usually slow moving and meandering.
This means no significant waves and a lot of protection from wind as well. Perfect for a Solar Electric boat.
But the size and amount of resistance requires the boat be matched to use patterns
We also have a design for an Electric Canoe using a trolling motor. Intially dreamed up by Dana Stovell who adapted the plan for one of my Quick Canoes to have a flat transom.
In a sense the smaller boat is a greater success. The power plant and batteries can be relatively cheap compared to an outboard. The boat moves at 5 to 7mph with a 34lb thrust trolling motor.
| The Quick Canoe Electric plan |  |
| Article on typical use – Joe’s family picnic |  |
There are identical caveats if wind and wave get up. But again it is to be aware of the boat’s limitations and choose the right days. Just like canoeing in general.
Plus if the power runs out it is kindof paddleable.
Again .. fitness for use patterns.
But it is an interesting comparison. The Mundoo 3 solar electric will only meet the requirement of few people who want a cruiser or live aboard.
But the Quick Canoe Electric ticks the boxes for a lot of use patterns for the type of boat
This leads to the observation that electric power will become more useful in smaller boats before it is truly useful for a broad range of larger boats.
Interior Layout of Mundoo 3 solar electric hybrid riverboat
Solar Mundoo 3 GA
Then when the founder of Duck Flat, Robert Ayliffe, got the opportunity to submit a major article on the solar version for “Woodenboat” magazine it quickly became clear that there was a large demand for plans.
Enter Storer (er, me) and his trusty* computer to turn the documentation of the hull into a full plan that a first time builder could follow as well as providing preliminary drawings of all the variants.
(*or not so trusty – as it turned out – it died halfway through the building process, but no data was lost!). A note on computers – I do all my design on a three year old laptop – when the old one died I was able to pick up another for about $320. Probably little more than getting a tech person to look at repairing a newer model.
It really goes to show how the hardware has sped ahead of the software. In other words – if you have great design ideas but someone tells you that you need a squillion dollar computer and squillions of dollars of software – ignore them and get stuck into it. It’s all about the ideas – the purpose of the computer is simply to transform them for distribution.)
It is some time since I have done a plan of this complexity, so I had forgotten how the complexity somewhat overwhelms one; the effort of holding the interrelationships of dozens of parts in my mind’s eye is rather intense – eg, just how the parts attaching to one bulkhead relate to the adjacent bulkheads, or when finding that some crucial part like the cabinside is wider than normal plywood dimensions and then having to go through and change just about every drawing.
The advantage of designing on computer is considerable, allowing a huge amount of extra detail to be incorporated in the plans. Comparing the original Mundoo drawings (developed the old way – on paper) with this new batch is like chalk and cheese – it makes it infinitely easier (OK I am exaggerating … much easier!) for a builder to make an accurate boat with huge labour savings as the builder can see EXACTLY where that next bit of wood goes. It is all left a bit up to the skill and imagination of the builder with conventional drawings.
Such is life.
Anyway . . . a truly great boat – I had a good look on the net a few weeks ago and I think this is the most fully developed electric boat plan available. It is a real boat for real use (and IS being used as I speak (write) cruising the Murray River and its extensive backwaters) and must be one of the largest commercially available solar boats (or plans) available.
It was great to be involved! Thanks Duck Flat! Thanks John and Gabby!
Now it’s time to catch up on some sleep!!!
The smaller and simpler Mundoo 2 Riverboat for single high thrust outboard.
Please contact Duck Flat Wooden Boats for details.
Also see the EPOXY and Boatbuilding FAQ for more detailed info about the methods a.nd troubleshooting and preventing problems
For more information about the Mundoo 3 Solar Electric, the smaller Mundoo 2 and conventionally powered versions contact Duck Flat Wooden Boats
