Trolling motor adaption for hydrogeneration

[rowlock]

Is there practical knowledge, experience and advice that may be drawn on within the community before proceeding with a project to exploit the potential of both power and generation from one of these devices. The notion is a dinghy motor that when stored on the mother craft can generate power either for its own battery or the main service bank.

 

[Arcady]

Good question! I too would be most interested to know whether this is practical ...

 

[AngusMcDoon]

Propellors designed to be optimum for propulsion are poor at extracting power from a moving fluid, i.e. they are designed to be good one way but will be poor the other.

 

[Rappey]

what a great idea.. 72 amps though ???

 

[Neeves]

I've raised the opportunity a number of times.

If the only impediment is that a different propeller is needed then the unit needs 2 props, one for the propulsion and one for power generation and the development of a way to quickly remove and replace. The propellors are available, WattnSea and Torqueedo, what is needed is an easy way to switch them round.

There is another issue and that is that in their opposing formats they produce different stresses on their method of securement - and I would have thought on the bearings - but neither seem insurmountable.

Jonathan

 

[Arcady]

Propellors designed to be optimum for propulsion are poor at extracting power from a moving fluid, i.e. they are designed to be good one way but will be poor the other.

Just a quick thought, but what about turning the motor through 180 deg so the propeller faces forward for generating? There might be some implications regarding the electrical aspects...

 

[duncan99210]

At first glance, the biggest problem is the mechanical strength of the motor. Best speed for the motor pushing a dinghy is perhaps a couple of knots or so, whereas sailing will be up to 7 or 8 knots. I’m not at all sure that the relatively flimsy motor stem would be up to those sort of forces. If you look at the Watt and Sea arrangement, it is robustly engineered with little distance between the mount and the generator, whereas trolling motors have a simple tube with a long gap between mount and motor.
Ive got an Aquair, the propeller that sits at the end of the rope has a relatively small diameter and only 2 blades. Trying to pull that in against more than a knot or so of boat speed is difficult: I’d have thought putting the same strain on a trolling motor would bend or break the stem in fairly short order.

 

[TLouth7]

Modern battery powered motors are really AC motors. They have drivers which take the DC from the battery and convert it to multiple phase AC, in the process allowing you to vary the speed. It is perfectly possible to design these drivers to be bidirectional, that is, to allow electricity to flow from the motor (acting as a generator) to the battery. This is not the default though, so you would have to check the specification of the particular device you plan to use.

 

[pcatterall]

At first glance, the biggest problem is the mechanical strength of the motor. Best speed for the motor pushing a dinghy is perhaps a couple of knots or so, whereas sailing will be up to 7 or 8 knots. I’m not at all sure that the relatively flimsy motor stem would be up to those sort of forces. If you look at the Watt and Sea arrangement, it is robustly engineered with little distance between the mount and the generator, whereas trolling motors have a simple tube with a long gap between mount and motor.
Ive got an Aquair, the propeller that sits at the end of the rope has a relatively small diameter and only 2 blades. Trying to pull that in against more than a knot or so of boat speed is difficult: I’d have thought putting the same strain on a trolling motor would bend or break the stem in fairly short order.

So when my batteries are pumped up and there is still excess solar power can my Watt and Sea 600 hydro genny ( on my xmas list!) be used to help propel the boat?!

 

[duncan99210]

So when my batteries are pumped up and there is still excess solar power can my Watt and Sea 600 hydro genny ( on my xmas list!) be used to help propel the boat?!

Could be!

 

[Hallberg-Rassy]

At first glance, the biggest problem is the mechanical strength of the motor. Best speed for the motor pushing a dinghy is perhaps a couple of knots or so, whereas sailing will be up to 7 or 8 knots.

If to face forward, then it would be easy to construct its mount, so that it held and reinforced its head as well. I'd imagine a swinging device that could be lifted out of the water when required.

As to 7 or 8 knots, I'd guess a lot of people on this forum would reply, "you wish". 4 to 5 being a healthy norm.

 

[duncan99210]

As to 7 or 8 knots, I'd guess a lot of people on this forum would reply, "you wish". 4 to 5 being a healthy norm.

I agree that 4 to 5 is a good working average but seeing above that speed for short periods is not all that exceptional, hence my remark.

 

[Slowboat35]

I too have raised a similar question in the past but it seems the preoblem is likely to be identifying a suitabale spec of the propellor that is to be repurposed in a job it was not designed to do - act as a turbine.
To date I have found zero expertise or even theoretical knowledge in this critical matter of 'reversing' a propellor. Pitch and diameter would be dramatically different from a thrust-producing prop.

I suspect that specialist things like trolling motors have a very limited range of props available to fit them as there is so little variation in power output across the motor range so it'll be a fortunate chance if one worked well as a turbine.

I suspect you'd do better to re-engineer an outboard leg (stronger, more durable) with a small alternator on top as the range of props available for outboard ranges are likely to be larger than for electric motors.
Even so the challenges like getting to gearing right to spin the alternator at the right speed are going to be substantial.

 

[Neeves]

There must be enough dud small outboards around and alternators from car yards must be as cheap as chips. Trying something would not be perfect, at all, but would indicate if the concept has merit, which could then enjoy a lot of polishing.

Jonathan

 

[Rappey]

Isn't it more about adapting something that's fairly easy to do?
Fitting an alternator to an outboard leg is a much more complex task.
Looking at an aerogen towable propellor it is quite basic . The blades look like they have been cut out from the wind turbine blades complete with square ends.

 

[Neeves]

Having broken a blade (I assume because we hit something like a piece of wood, there were no teeth marks on the shaft ) on our aerogen towable propellor I made 2 new ones, a matching pair, from stainless steel plate. The seem to work well enough.

When I look at the work Rainman did to get their de-salinator unit to work I don't see that adding an alternator to an O/B is beyond the skills of some people here, but accept its beyond my skills. If someone did it and provided the cheat list it would be an interesting project (considering the cost of the WattnSea).

Jonathan

 

[CaptinHaddock]

E-Gull

 

[Hallberg-Rassy]

E-Gull

Clearly has additional gyroscopic benefits stabilizing any dinghy it is fitted too.

It's a bicycle wheel motor?

What about looking out for an old Dynastarter to play with?

 

[rotrax]

Having broken a blade (I assume because we hit something like a piece of wood, there were no teeth marks on the shaft ) on our aerogen towable propellor I made 2 new ones, a matching pair, from stainless steel plate. The seem to work well enough.

When I look at the work Rainman did to get their de-salinator unit to work I don't see that adding an alternator to an O/B is beyond the skills of some people here, but accept its beyond my skills. If someone did it and provided the cheat list it would be an interesting project (considering the cost of the WattnSea).

Jonathan

I have tought about it. Driving through a toothed belt to get a suitable gear ratio - alternators need to spin fast - would not be difficult, making a bearing and shaft extension would be a bit trickier though. If an aluminium prop, welding and trial and error would no doubt improve the turning moment.

If you chose the right alternator the OE engine cover might even fit which would make it look good.

The final thing to get is a round tuit......................................

 

[CaptinHaddock]

The motor there looks like one of those hoverboard wheels, stripped of its tyre and mounted vertically.