I'm looking for a 'tank' to test the performance of a small electric
outboard, (PWM speed controllers, batteries, hydrodynamic
slipstreaming mods etc) so am thinking of a circular tank, possibly
about 3' / 90cm in diameter so that I can set the outboard off to one
side and get the water circulating around the tank, rather than just
turbulating in it (as when in a dustbin etc). It would also need at
least around 18" deep sides to stop the water climbing / splashing
So, after a bit of Googling I came across the IBC water containers and
1) wondered if anyone knows where there might be one that still holds
water (at least over the lower half) near Nth London that someone
might like to see the back of and 2) if you think it might be suitable
for my needs please (or if not, why not etc). If not there seem to be
plenty on eBay cheap enough.
Would it being nearly square (all be it with round corners) with maybe
something in the middle to ensure water actually flows 'round' the
container be free moving enough or do you think I'd need to fit a
round liner inside it?
If the bottom (inside) isn't flat or couldn't easily be made flattish
(from a water flow POV) could I use the top half upturned instead (I
could fit my own drain cock etc).
Any other ideas around the above welcome of course. ;-)
Cheers, T i m
On Wed, 23 Aug 2017 17:19:05 -0000 (UTC), Nige Danton
Nice 'outside of the box' thinking Nige, thanks. ;-)
An octagonal or even hexagonal box would probably be close enough for
my water-flow needs and could be screwed or (cable-tie?) hinged
together if it had a waterproof lining (I don't think there would be
that much pressure at 18" deep and if there were, nothing a couple of
ratchet straps wouldn't hold)?
It might be easier to make something rectangular (and if I was making
it myself I could of course) with angled inner corners and a central
baffle to create a 'circular' water path?
Cheers, T i m
A concern may how much strength there will be left once to top is cut
off though the one I have seems fairly heavy gauge material and you
still have the reinforcing cage to help with that, but you may have to
cut that down as well.
The bottom is fairly flat apart from a section a bit lower for the
To satisfy the above concerns it would seem like a lot of kerfuffle to
do rather than but a round tank in the first place from a suppler like
an agricultural merchant.
How much depth do you need? I've seen an instant garden water feature
made by using a section of concrete pipe lined with an off cut of pond
liner , the latter can often be found as remnants at water garden
supplies but for intermittent use a bit of DPC membrane should
suffice. As would doing the same with a large truck or tractor tyre
but that could lead to disposal problems later.
If you go down the IBC route what it originally had in it may have a
bearing, mine had contained a detergent that was for washing
supermarket food crates so rinsed clean easily, some that tend be at
the cheaper end of prices asked have had things like fibre glass resin
in which is harder to deal with for some applications.
You can also get half size 500l ones but being rarer and sough after
tend to actually cost more.
On 8/23/2017 9:22 PM, email@example.com wrote:
If you leave it in the metal frame, that will still support the
container adequately. I have a couple which I use to store spring water
and/or harvest rainwater at a stables and these have large (600 mm
square) holes in the top to allow for periodic cleaning with a pressure
washer. (As an aside, standard paddling pool / swimming pool floats
containing a chlorine tablet more or less eliminate algae).
My question is what sort of power are you talking about here? Unless it
is pretty small, it could get exciting. Even a small one will need a
pretty strong and secure support.
It is very small. ;-)
It is a Yamaha M12 (re badged Minn Kota) electric outboard or
'trolling motor' as they call them in The States and gives about 30lb
thrust on full.
'Full' is about 30A and at 12V that would make 360 watts (~0.5 hp).
However, on speed 3 (of 5) pushes our 3m folding dinghy along (3 +
dog) at the rivers speed limit of around 5 mph but silently. ;-)
However, these smaller outboards often use what they call 'speed
coils' (load resistors) to lower the current for the speeds 1-4 and so
I've got a PWM speed controller from China that I can plug in series
and see what speed increases (hopefully) I get for the speeds 1-4. It
may be slightly less efficient on speed 5 as that would normally be
the battery connected directly to the motor. However, whilst it's nice
to have that extra 'oomph (relatively speaking etc), the current draw
is disproportionately high for the increase in hull speed so we
generally don't both and just enjoy the range instead. ;-)
I also recently picked up 6 x 16000 mAh LiPo packs with the though of
making a lighter and higher power replacement for the 60Ah traction
lead acid battery we currently use but the complexity (charging,
storage charging and transporting), cost and risks outweighed the
short term (it's only an issue when carrying the batteries from the
car to the boat) advantages. So I'm probably going to get two (or more
) new lighter traction batteries, mainly to make it easier for the
Mrs to handle.
So the goal is to try to get a days cruising with a combination of
individually weight manageable LA batteries and efficiency
improvements on the outboard (PWM power control, hydrodynamic fairing
on the tubular shaft and a spinner on the prop).
That's why I need a suitable test tank to be able to reasonably
accurately measure or at least compare pre / post 'improvement'
values. ;-) 
Cheers, T i m
 Basically we are only limited to the weight of battery we would
want to carry in the car as the boat is rated for '4 Persons' and
there would typically be only 2 of us. ;-)
 Whilst some of it is academic on the folding boat(s) we intend to
mainly use, I also have a 16' Canadian canoe that would probably give
a higher speed through the water for a given battery load, plus I like
the saying, 'You can manage what you can measure'. ;-)
Please let me know how you get on.
I have an electric outboard ("John Azur"), and a PWM controller from China,
presently awaiting tuits...
I've also looked at this and its brothers:
"Digital LCD DC combo Meter Watt Power Volt Amp RC Battery dis charging
which does current times voltage over time, and could work as a "fuel gauge"...
If you want to see what's possible -- look for "Torqueedo" outboards. They have
an accurate range estimate in miles in their system, using a GPS. (Note: for the
price, you will be ble to hire someone to paddle you upstream for a week).
As to the tank -- Dunno about round, and the water moving in a circle: the
watter current would speed up, dropping the electric current, and the water
would start to climb up the sides of a circular container, and the outboard
might start to move to the side and the propeller hit the container wall.
Turbulent flow would provide a more constant load.
Other than that: rainwater butt? Inflatable pool? a "Fast set pool", 8 ft diam
for 30 quid (which would required external support for the motor)?
Or, here, I'd be looking at mortar pans, like here: bit small, but very cheap
I bought something similar recently (supposedly 130A rated) and as it
was from China, probably the same inside. ;-)
Yup. I was going to use mine for both the testing / modification and
general running stage, at least to start with.
Yup, already looked at those but are way outside my price range and
comfort zone (if something goes wrong outside warranty etc). They also
seem to be a bit noisier than the typical trolling motors?
Whilst I'm sure you are right to a degree, this is why the container
needed to be reasonably big to increase the water volume and reduce
the speed. That plus I'm only talking about ~5mph so that shouldn't
become an issue (but I'll keep the thought in my mind of course).
Not if I've fitted it it won't <weg>, plus if the container is
plastic, that won't be as bad as the prop hitting some rocks on the
bottom of the river. ;-(
But wouldn't help with my hydrodynamic fairing and prop spinner tests?
Yes, I've considered all those as well but don't feel they would be
robust enough to last if left out etc. That said, it's possible that
once I have done my initial tests I won't need it so something I can
fold away might be a good idea. The '4 ring' inflatable paddling pools
look cheap / deep / large enough. I already had a 3 legged design for
a frame that would stand over the pool, support the outboard and any
cylinder that was going to create the 'core' in the middle (an
upturned cylindrical water container or large diameter drain pipe
etc). It would have to be suspended from such a frame if used on an
inflatable pool as it won't be so easy to hold such in place on the
bottom without risk of damaging it etc (but not impossible with care
Yeah, that was the sort of style but as you say, probably a bit small.
Nige's idea about making something from say OSB and lining it with
some DPM or pond liner could be a good compromise as it could be made
fairly cheaply and fairly easily (it could be stitched together using
cable ties) and then flat-packed or reused for other roles if / when
the project was over.
Square (or rectangular) would be the easiest and possibly the most
self supporting (square corners), the top edges could be stiffened
with a bit of batten (and / or the outboard supporting frame) and a
circular inner wall could be formed inside the liner, to manage the
water flow if required.
1 x 11 x 1220 x 2440mm (£15) for the base and two sides and another
for the remaining two sides and maybe some inner corners to make an
octagon plus 20 quid for 3 x m of DPM? A bag of cable ties to stitch
it all together or some lightish line?
I was thinking on that if I wanted to slow the water circulation speed
/ apply some (more) load to the motor I could just build a weir under
the water (engineering bricks?) maybe 90 degrees behind the position
of the outboard around the tank?
Cheers, T i m
They have a system I'd love to have: flexible roughly folding-boat-shaped solar
panels, Li-ion batteries and a small motor. If going slowly enough in enough
sun, the panels give enough power to keep on going all day, and end up with full
Several (many) thousands, though.
not at all...
Or truly round, using cooper techniques: tongue-and-groove boards, i.e. decking,
cheap paneling? Plain boards, and ratchet straps around the outside?
Ratchet straps, which are also useful in other ways, afterwards.
Maybe in California Thomas <g>, but I agree, they seem to be a very
clever and well thought out package.
Quite. My point was I can buy several Minn Kota outboards and traction
batteries for the same money *and* could use easily use a car battery
if I had to or try LiPo or LiIon if I wanted to. The Torquedo is a bit
too propitiatory for my wallet and needs.
Wow, that would be a project and probably require more patience than
I've got! When you say that a hot tub comes to mind ...
True and I already have plenty of them. I still think the corners
might appreciate being held together, at least initially, along with
the sides being held to the bottom, till it's filled with water? Easy
to do with some cord stitching. Just lay each section against it's
partner and drill though both with say a 10mm bit. Then you just run a
line (or releasable cable ties) though each hole to 'stitch it
together into the basic shape. Add liner and water and you are away
and nothing is going anywhere. Add the 45 degree corner sections to
make the octagon and you wouldn't need the liner to make it circular
and it would brace the sides so you don't need the straps. ;-)
Cheers, T i m
p.s. I Googled your 'John Azur' outboard and they look like they might
be quite old? I do like the design of the underwater unit though,
especially how they return the diameter of the motor housing down to
that of the prop and then get close to the diameter of the prop (so
not having a central hub etc).
I note it also has the tubular pole connecting the underwater head to
the rest and I think I understand that a tubular section has 5 times
the drag of an aero/hydro-foil of the same diameter. Now, I know these
outboards don't go though the water at the same speed as many IC
outboard but at the same time we would be looking to maximise the
efficiency of what little power we have available. The lower leg of
most IC outboards are have a hydro dynamically efficient shape.
So, because I have a 3 printer and like to play, I was going to design
and print some clamshell type 'trims' to add to the lower leg to both
help with the hydrodynamics and with the steering (it acting like a
small rudder when the motor is off).
Coming back in again , if you are going to line it with pond liner
would a collapsible compost bin make a good start and save a lot of
something like this
I've seen square ones as well.
On Thu, 24 Aug 2017 10:59:48 +0100, firstname.lastname@example.org wrote:
Welcome back. ;-)
Well, I can, if the structure isn't waterproof etc ...
Oooh, now that looks interesting, unless I could find a second hand
one they don't look cheap though:
I think the hex one would be the best option but after Googling around
I saw a round composter made from a wire mesh. Given that I could line
something with DPM to make it waterproof, maybe a wire ring with a
semi rigid sheet and then the liner might be ok?
Cheers, T i m
Yes, old. Cheap used:-) Goes with the "Faltboot", a used one cheap from the
early 70's. The motor is mostly metal, the switch bakelite, and pretty basic and
There's only about 3" or so of the pole in the water. The motor in mounted on a
wooden bar across the transom, off to the side of the boat. This is similar to
the sail and leeboard holder, only sticks out more on one side.
Have look at <http://www.faltbootbasteln.de/fbb-tuemmler.html , which describes
an East German sideboard two-stroke motor, popular back then.
And on ebay there was a wonderful sideboard motor from 1920 or so, more than
complete, original box, original tools, extra spares. Same model some guy had
used in Arctic waters in a folding fabric boat. And I would have bought it, damn
the expense, but combustion engines on water a heavily regualted here, and
two-strokes a nono...
Or this, another diy/East German thing:
Combined rudder and motor...
Have a look at this propeller guard for the John Azur:
As long as it was also 'loved', old and used can be fine. ;-)
Do you have a link to what you have as there may be different
It looks it. ;-)
Understood, however, I understand that if you were to put foil section
over it would reduce the effective diameter to 1/5th.
On my Seahopper Kondor I think there is more of the pole in the water
but some of it may be masked by the square transom.
I have an ally version of the same thing.
Neat. It reminds me of the ex car engined powered longboats you see in
the Far East and Africa etc.
I love the whole 'folding' concept (we also have a 12' Porta-Bote
(American) and a Rapido Confortmatic folding caravan (French)). ;-)
We are seeing some of that here.
That was the sort of side effect I was envisaging when adding a foil
section to the bottom of the Minn Kota. That one looks like the
steering might be quite 'heavy' with the pivot so far away from the
Yeah, I saw those on some motors when I first Googled for the 'John
Azur'. I assume it might not only protect the prop but make the
steering more direct and possibly the drive more efficient (less water
spilled off the side of the prop)?
I ran my 40A PWM controller against a 60W headlamp for a while this
afternoon, just to check that it worked and see how warm the
controller got. It did warm up a bit so I might need to consider some
form of fan cooling if I'm running it at 15-30A for prolonged periods.
This one was a reversing model and I assumed (incorrectly) it would
use an output bridge. So I also bought a pair of HD C/U relays to make
my own reversing solution on a straight Fwd only controller (that
would only pull in when reverse was selected). However, I found the
one I bought also used relays for the reverse but it seems one pulls
in when Fwd is selected and then the other when in Rev?
Because the amount of time it would be in reverse would be tiny, I
would have thought only pulling the relays in when required would be
more efficient? Have I overlooked something with this one for each
I was also wondering if simple prop revs (in the same water tank)
would be sufficient to measure the straight / PWM comparison (no good
for the prop / leg mods etc).
Cheers, T i m
Possibly hundreds of versions. It was a big thing in Germany, starting about
That's why I would guess that reducing the drag of the pole is irrelevant --
because it is a small part of the total.
But two-three airfoil-shaped plates, and a bit of flexible plastic to wrap it
around, and a large tank to test it would put some facts up against my guess!
Possibly. I think I saw a DIY version with the motor closer to the rudder shaft,
on ebay, but it went for lot more than I was prepared to pay for it.
And these rudders are at the back, and moved by two cables and foot pedals, so
it's easy to put a lot of force on the rudder.
It should, but it would also increase the drag. OTOH, weeds wrapped around the
prop increase the drag, too!
Avoid fans if you can, and just use large heatsinks instead. Plenty for free if
you can get at skipped computers. Or unsolder the hot components, and wire them
to the inside of a metal housing. Fans clog, make noise, and provide hole for
water to get in.
The relay won't use much power, not compared to the draw of the motor.
Maybe use the spare relay to disconnect the PWM when off, and to connect the
motor directly to the battery for "full speed ahead". My PWM says it draws power
even when off, and while the few mA are irrelevant during use, they will
needlessly drain the battery during storage -- some sort of "true off" that
can't be forgotten is nice. Though I was planning to use fat clips attached to
the battery terminals, and unclipping would happen when lifting the battery out.
You'll probably end up with some sort of force measuring arrangement anyway.
Scale, or measuring the torsion of some sort of mounting bar...
But still part of the total and may be a more relevant improvement if
I use it with say my 16' Canadian canoe?
Easier for me to 3D print it Thomas <g> and as I said, may give me a
better rudder effect when the motor is off (especially).
Understood. However, I still think it looks like it would try to
'flop' to one side or the other, rather than being balances around the
centre of effort?
As do plastic bags etc. ;-(
I already have plenty of salvaged heatsinks. ;-)
The only problem with that is checking that the tags are either
isolated or making sure they are isolated from any heatsink and the
resistance of the cables joining the output devices back to the PCB.
Where you see output devices heatsinked away from the PCB they are
normally soldered to the edge of the board so they can just be bent
over without adding extra cables. That's not to say 'remoting' the
output devices wouldn't be worth doing, just that we are back down to
Agreed, but less so when used in a dinghy (clog), it would be a larger
fan speed controlled to be quiet and I would make it rain proof. If it
ever got immersed I would probably have more pressing issues than an
£8 PWM controller getting wet! ;-(
Agreed, I think I measured it (on my Wattmeter) as 50ma.
Funnily enough, that's what we did on the electronic 'speedo' we
designed for electric RC car racing some 40+ years ago. The supplied
speed controller used 5 micro switches on a cam, 3 to progressively
short out series resistors (in series with the motor) and the last two
to give reverse (plus the others still). Our electro-mechanical one
used a 2N3055 as the output transistor and a relay to short it out at
full speed. ;-)
I get similar results on my existing (60Ah) battery. I have a couple
of m of *very* heavy (but flexible) cable merging into some thinner
(16^2mm) at the end going into an Anderson SB50 connector. I cut the
end of the lead with the terminals off the outboard when I first got
it and fitted an SB50 to that, and to the original end as a backup. I
have a 50A resettable fuse on the +12 at the battery end. Now I'm
going to replace (or supplement) the single 60Ah battery with 2 or 3
smaller (~40Ah) batteries I will probably just fit the new batteries
with a resettable fuse and a short 16^2mm 'tail' to a SB50 and have a
~2m extension lead of a similar size so I can keep the batteries in
the bow. The PWM controller / Wattmeter can then be inserted in the
SB50 connection at the outboard end.
I wasn't sure if there was enough of a direct relationship between
outboard force versus hull speed but it might be an easier way of
taking an output effort measurement so I can compare pre / post PWM
control (at least). Thanks. ;-)
Cheers, T i m
I doubt it... The East Germans couldn't travel much (at least to places they
wanted to go) and did a lot of diy and furtling and making-do, and some of that
was amazingly ingenious. (Some of it was complete crap, often reinventing the
wheel poorly, mostly because something wasn't available, i.e. electronic
circuits...) And something like that is easily furtled.
Have a look at these, both East German, both still available on ebay:
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