Thanks Howard for another interesting viewpoint on the question of DV voltage. I think I can understand most of that. The take-away for me is that higher voltages may have some advantages, maybe OK for tech-savvy people - and may well be the way of the future for off-the-shelf marine propulsion systems. However, us ordinary folk should probably stay with what seems to be mainstream at the moment – no more than 48V in the marine environment. Evidently, apart from safety, there is also the question of easier availability and perhaps lower cost of the various pieces of other equipment needed (transformers, controllers etc.) which starts to become an issue with higher voltage.

Thanks to all those knowledgeable folk who chimed in – its good to be able to learn things the easy way.

“Regen” or hydrogeneration from outboards.

I'd like to start another thread for this.

What excites me far more about the idea of an electrical propulsion system and the way it harmonises with sail power is the possibility of quietly motor-sailing sometimes. That is, adding just a tiny little bit of engine power while sailing to windward in light conditions – maybe not much more than needed to overcome the drag of the propeller – just enough to keep moving between the puffs, and on a fine sunny day, perhaps at the flick of a switch, being able to do this on not much more than solar panels alone.  

Since the wind is only another manifestation of solar energy, that’s not really cheating is it?

Graeme wrote:

Thanks Len (and you others). All good stuff.

As a matter of fact, I have been turning around in my mind for a few weeks now, the question of whether a clapped-out outboard motor can be re-engined with an electric motor - I mean, whether or not it is actually a practical proposition. (Smaller sizes I know can be done (here's an example)

b

Almost everything I have read of regeneration suggests to me that at speeds of under 5 knots its just not going to happen. There do appear a few exceptions. Of course, with variable pitch and intelligent controller systems, wonderful things can be achieved (eg OceanBlue) but even then I suspect we are looking at 6 knots plus and a large wallet. For KISS my conclusion is: forget it. It needs a different type of propeller. Perhaps a retractable dedicated unit for regen would make more sense for the DIY messer-about.

Howard: I would like to know the details of an outboard motor with regen capability.

Graeme you and I have been talking about outboards and my experiences with the 9.9hp motor on Footprints. Oddly enough throughout my many years of owning Footprints and with the outboard in the well I had thoughts of some sort of alternative drive through the well using the lower part of an outboard leg. This was driven first by some friends who had retractable hydraulic drive units in a catamaran, but I quickly gave up that idea because of the weight and the need to have a motor of some sort to drive the hydraulics. Then after I met Kurt on Mehetibel I tried to think of various ideas using electric drive. In the end I did not bother to do anything because the Yamaha worked so well, and on a annual basis I used so little petrol that there was to be no saving to make an alternative worth the trouble. Yes, there were perhaps some environmental arguments for going electric, but not sufficient a driver in my situation. I also looked at an electric outboard set up for my new catamaran but The cost of a proper setup in New Zealand, ($5000 plus), did not warrant the expense over any possible savings.

This is not to say I am disinterested in environment saving alternative fuel and propulsion systems and I follow with interest the hybrid technologies in high level motor racing because those technologies will eventually filter down to everyday transportation for all of us.

One outboard which does offer hydrogeneration is the Spirit EVO 1.0. I read an article about these in a glossy yachting magazine, I expect there is information on the internet. 

Anonymous wrote:

"Efficiency".............  What does that actually mean?    Do you get more mechanical power per watt?  1 horsepower is approximately equal to 750 watts

The question should be where do you measure that "power"? The proper place to do this is how far forward does a boat with a certain mass move in a certain amount of time. Motor input power, motor shaft power (after electrical losses) and propeller shaft power (after bearings, reduction, etc.) do not even start to tell the story. All of these things have a long history of being the best compromise for an IC engine which has 0 torque at 0 rpm and has to be running at some speed to have any torque at all. An electric motor has maximum torque at 0rpm and that torque remains constant to a set speed after which it starts to decline at a rate that gives constant hp. It has more in common with a steam engine.

So an IC powered setup will look for the rpm within it's best range of torque and power which is too high for a propeller to run efficiently. So a gearbox is added to reduce the prop rpm but that gearbox looses efficiency as the reduction ratio goes up so the propeller runs faster than best efficiency to counter this. So it is a smaller radius and smaller pitch too. So when installing an electric conversion, the boat owner is stuck with the size of the propeller aperture the boat is designed with and the companies who make these units in general use the same running gear and a gearbox (often with belts) to make the best use of the stock propeller.

Getting the best efficiency out of an electric motor would mean redesigning the boat with a bigger aperture for a bigger propeller with a larger pitch probably. Though an adjustable pitch propeller would be best and, in the same way an mppt charge controller maximizes solar charging, the motor controller should do the controlling of the pitch for best efficiency. There is another use for variable pitch:

     To me the beauties of electric on a boat are regeneration.... The ability to store and use solar.

The best regeneration will happen at a different pitch than the best motive force.

So the best electric motor for a boat is one that gets it's power at the best propeller speed which is slow. That is, torque rather than power is the best measure. A higher torque at the same input power at a lower speed will move the boat faster or farther, maybe both (remembering that boat movement over time is the true measure of power). The problem with this (time for another compromise), is that high torque motors that run at slow speed are big. Bigger in diameter and bigger costs more and weighs more too. There are a lot of 10kw motors around that are (relatively) cheap, small (easy to fit in various places), light enough for a person to lift, etc. Torque is not great, but pretty good and with a speed conversion, they work well with currently installed shaft and prop.

      The other HUGE benefit IMHO is the ability to entirely eliminate through hulls and motor shaft by using an outboard, which also means you can lift the prop entirely out of the water gaining a huge efficiency advantage over a folding prop with their abysmal efficiency.   In an ideal situation there would be zero through hulls below the WL.

An electric outboard can be done in two ways, slap a motor on an outboard leg or put the motor in the water to direct drive the prop.

Most small drives put the motor in the water (most really big cargo ship size drives too). It is simple, there is no transmission loss, cooling is all around, the unit can be designed with no preconceived IC constraints. However, the motor does present more frontal area to the water flow which is a loss. The higher the torque, the more frontal area there is.

electric sail-drives, put the motor inside the boat and a gearbox in the water. Because the motor shaft is vertical, the width can be larger and more torque applied. Also, the whole unit, being of one design, can have a larger prop with adjustable pitch. (see some of the "Uma" videos over the years)

Outboards using a lower gearbox are more constrained by overall motor size (so it can tilt up or be put in a motor well) and so will have a less efficient torque to play with. Also, they are all (that I know of) based on IC legs which add frontal area for things like exhaust and water pump stuff as well an exhaust hole either in the middle of the prop or elsewhere that while adding to forward movement with exhaust flowing, create drag otherwise. Some custom solution would be best.

Probably way more than you wanted to know... sorry.

The part you wanted, higher voltage vs. lower voltage all has to do with wire size. Not just in the wiring outside the motor but inside as well. It allows windings to be closer spaced for smoother running at low speed to make the best use of torque. (the quick version)

     Engines and their cooling systems, transmissions, control systems, prop shafts & glands and cutlass bearings fall in with standing rigging and complex steering mechanisms as maintenance intensive trouble spots to be eliminated.   Outboards with regeneration are available.

This is all true. The truth is that even though electric motors for boats are in their infancy, they still do quite well. I would say that says something about IC drives.

"Efficiency".............  What does that actually mean?    Do you get more mechanical power per watt?  1 horsepower is approximately equal to 750 watts.   "Efficiency" could mean that batteries and motors can be more compact and lighter.  That conductors can be smaller and lighter.  Conductors are sized by amps and distance.   1000 watts at 40 volts is 25 amps.    1000 watts at 400 volts is 2.5 amps.  That adds up to a huge difference in weight throughout the system.  Batteries themselves make no difference....it's just a series / parallel connection difference.  Most monohulls have a lot of payload capacity.  With a car there is the issue of weight and size that effect efficiency significantly.  That is not so much of a consideration on a boat where the primary propulsion is sail.   Though larger displacement boats require larger everything, and overall operating costs are considerably greater.

     To me the beauties of electric on a boat are regeneration.... The ability to store and use solar.  Slow and steady wins the race they say.  When you have strong winds you are limited by hull speed, and you can generate more drive than you can use.  That drive can go into regeneration to charge the batteries for when the winds are light.  You could even adjust course to maximize regeneration in such conditions, and in lighter winds motorsail a more desirable course to compensate...... depending on the circumstances. 

      The other HUGE benefit IMHO is the ability to entirely eliminate through hulls and motor shaft by using an outboard, which also means you can lift the prop entirely out of the water gaining a huge efficiency advantage over a folding prop with their abysmal efficiency.   In an ideal situation there would be zero through hulls below the WL.

     Engines and their cooling systems, transmissions, control systems, prop shafts & glands and cutlass bearings fall in with standing rigging and complex steering mechanisms as maintenance intensive trouble spots to be eliminated.   Outboards with regeneration are available.

The big difference between below and above 50 volt is that you and I can install DC-systems below 50V in our boats and homes without buying professional help. If we do that in a 220V-240V system, we will be fined, at least in my country.

As for ‘48V system’; yes, the charger delivers about 50-52VDC, just as the generator of a car delivers 13-14VDC to the 12V battery.

Arne