The Electric Hobbit

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  • 09 Jun 2020 04:29
    Reply # 9024355 on 8732915

    Hello Jim & All,

    I don't think this has been mentioned here:

    If the boat's battery charger is one which can operate as a power supply (not all can) then the generator can be run while motoring under way.

    A 600W charger, for instance, would have my 6.3m 'minim,' for instance, going about 3 knots in a calm (or we'd be sailing.) Going slower than that, the excess power would charge the batteries. Done routinely -> less generator noise in anchorages.

    Your 2kW generator could handle a 1kW+ charger for your bigger boat, so I'd consider your situation in the same practicality ballpark. 

    'minim' and 'mehitabel' do without generators, requiring compromises many people wouldn't like. I got rid of the 1.3kW DC generator I put together for 'mehitabel' and I haven't missed it.

    Darren Bos's words describe it well: "Without a generator I think you'd need to sail like you didn't have a motor, and then use the electric at low power levels for extremely pleasant motor-sailing, or for the convenience of getting in and out of anchorages." 

    [... or up and down canals & rivers, or anywhere - slowly...]

    Cheers, Kurt

  • 06 Jun 2020 00:13
    Reply # 9018220 on 8732915

    Thanks for that factful reply. I'll study it carefully. I'm better informed than I was yesterday. Now I have more questions for my technician.

    I had wondered about a floating ground. My system is pretty simple. It may be a good way to go.

    I'll get back with more detail to match with your information.

  • 04 Jun 2020 17:57
    Reply # 9015346 on 8732915

    I'll take a shot at this with the disclaimer that I'm not a trained professional and that some of the decisions involved here could lead to life threatening circumstances that anyone reading this needs to take personal responsibility for.  Also, criticism and comments are welcome, I've written this to try and help, but it is just as true that writing something out and having it criticised  makes plain any gaps in ones knowledge.

    Looking at how long this post turned out, I've come back to the beginning to add that if your boat had no corrosion problems before, the simplest solution is to choose a new single point to "ground" your negative bus.  This might be easiest done by using a metal through-hull, but in that case I would also use the motor disconnect mentioned at the end of the post.

    The word ground is a bit abused in recreational marine quarters.  It tends to be used to describe both electrically connecting the negative bus to seawater (which should only be done at one point, usually the engine), and it is also used to describe the AC ground which is usually necessary if you have shorepower.  Although both of these are often the same physical connection (a single point on the engine), they actually serve different purposes.  The  AC ground is as you would normally expect in a house, it provides a safe path to ground for dangerous AC current should a fault arise in a live conductor.  The DC "ground" can also serve this purpose, should a live AC wire come into contact with a DC wire, but it also has the purpose of providing a low resistance path that a DC fault can travel so as to minimize corrosion.  Without it, if you had two faults in your DC ground wire, lets say one to a seacock near the bow and another to the engine shaft, they are unlikely to be at the exact same voltage because or resistance in the wiring.  This voltage difference is very much like you took a very low voltage battery, perhaps a fraction of a volt to a volt, attached the positive to the motor and the negative to the forward seacock.  The result will be electrolysis, and can lead to erosion of metal.  If you look at a galvanic table, zinc has a value of about -1, while 316 stainless is about 0.  So, you can actually make the stainless dissolve rather than the zinc if you apply a voltage of greater than one volt and overcome the protection provided by the zinc.

    As for solutions, lets start with safety first.  If you have an AC shorepower connection, you really need an AC ground or an isolation transformer.  The main reason for this is if you have AC and don't connect the ground, then a fault means you could leak current into the surrounding water.  Particularly in freshwater, if a swimmer (or hull cleaner) is in the water they can offer a path of less resistance than the water and die of electrocution.  Even in "saltwater" the places where we moor our boats are often brackish or even have a freshwater lens floating on the surface so that it could be dangerous for swimmers.  An isolation transformer gets around this by breaking the connection with the shore, in it there are two parallel but isolated coils of wire, the magnetic field from one coil creates electric current in the second coil and there is no physical connection with the shore.  Thus if a fault exist, it doesn't try to go back to the shore ground because there is now no connection to it.  Swimmers are safe.  Follow the instructions that come with the isolation transformer to keep people on the boat safe from AC faults.

    There may be a third solution, perhaps some of the European members could comment on.  I think the use of ground fault interrupts are more common there on dock pedestals and in boats.  This could also provide protection, but I don't know enough to say any more. 

    For the DC side, you can have a completely floating (no connection to "ground") negative bus if you like.  However, this requires a great deal of care.  You must have no faults in your wiring.  Neither positive nor negative wires may contact any metallic bits of the boat.  This may be harder than you think, lots of electronics ground the negative to the case, a mast-top antenna might have its mount connected to DC neg, etc....  Because we have an aluminum hull we've gone to the trouble of installing a floating DC ground.  However, the first thing I installed was a tester that can be used with a push of a button to check that there is no connection at all to the hull.  Every time new equipment goes in, I have to check that we've maintained isolation.  Even something like corrosion on a connector might lead to a high resistance fault.  Chasing these faults is really difficult if you have typical DC breakers that only break the positive lead in the circuit.  We went to the trouble to install double pole breakers that interrupt both the positive and negative branch of every circuit.  This makes hunting down faults much easier.  With a metal hull, our case is more difficult to isolate completely then if you have a wood or fiberglass hull.

    If your boat has a simple wiring system, a floating DC system might be possible.  I would disconnect the battery and all the known grounds and then use a multimeter set to the resistance or continuity setting to test to see if any unknown leaks exist.  Test between the Negative bus and every bit of metal on the hull, same for the positive bus.  If there are no leaks a floating DC system is possible.  Because internal combustion motors are so difficult to fully isolate (due to using the block as a DC negative ground) and keep isolated, we have an isolation switch for the motor.  The one we chose is double pole again, so that when it is off both the negative and positive are disconnected from the motor.  You could do the same if you like and then the path for corrosion to the shaft is disconnected except for the relatively small percent of time you run the motor.  This is also nice to have if you want to work on the motor and make sure it is not energized, and if placed discretely is a pretty good anti-theft mechanism.  In this case, you should have a zinc on the prop or the shaft, especially if you have something like a stainless shaft and a bronze prop.


  • 04 Jun 2020 15:32
    Reply # 9014804 on 8732915

    Attached is a simple sketch of Hobbit's wiring system.

    (No solar panels of wind generators yet.)

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  • 04 Jun 2020 15:23
    Reply # 9014788 on 8732915

    I have a conundrum. 

    I am nearly ready to connect my batteries and motor. The wiring diagram shows a negative bus to which all negative leads are connected. It reads: SINGLE POINT GROUND CONNECTED TO BOAT SYSTEM.

    At present, I have no boat grounding system when at sea. It is grounded when the boat is connected to shore power. Before, the diesel motor was my ground. I asked the manufacturer to clarify. Could I use the new motor, which is connected to seawater as my ground? They replied that there are so many theories about this subject that they cannot advise me. I have a friend who installed one of this manufacturer's motors years ago and he remembers the same discussion but he can't remember what they did in the end.

    One of our members who seems to have a sound knowledge of electricity warned me that if I use the motor, current will pass from motor shaft-bearing to shaft causing pitting of both. (See what I mean?)

    There are objections to hull grounding plates. I don't know what they are.

    The two mast lightning conductors are attached to the steel fin keel via two keel bolts. One doesn't use those locations.

    Any suggestions? 

  • 07 Apr 2020 20:35
    Reply # 8884325 on 8883693
    Jim wrote:

    Meanwhile, its an opportunity to tidy up one's life and find other doable projects, including things necessary for the boat. New seats for the Porta-Bote, for example. I'm sharing a workshop with some friends, one user at a time, so I have a place to go.


    It seems Jim that everyone's lives are being turned upside down at present, which includes some disappointments such as cancelled holidays, (me!), and deferred projects such as yours. But something has got to be done to bring this pandemic under control and minimise the tragic loss of life. I really hope you get a chance to complete your project and try it out during your coming summer. But as you say a good chance to tidy up ones life. I am relishing my forced month at home. There is massive progress on my catamaran build, and I am finally getting around to various property maintenance items which I just never had time for previously. 

    Here in NZ we are only halfway through the one month lock down, but at this stage the country seems to have control of the virus with cases diminishing by the day. We are not sure what happens at the end of the month, the Government is still working on that. Hopefully there will be a gradual return to the new 'normal'.

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    Last modified: 07 Apr 2020 23:12 | Anonymous member
  • 07 Apr 2020 16:13
    Reply # 8883693 on 8732915

    I am just about ready to install my new batteries and wire up the new system. But yesterday, it was announced that only members with boats are allowed on the yacht club's grounds. And they are only allowed to stay a short while and it has to be essential. Winter covers are not to be removed. Only the liveaboards are allowed to stay. No boats will be launched until further notice. That could be for many months. So much for sailing this year. That puts a damper on things.

    Meanwhile, its an opportunity to tidy up one's life and find other doable projects, including things necessary for the boat. New seats for the Porta-Bote, for example. I'm sharing a workshop with some friends, one user at a time, so I have a place to go.

    On April 17, our club is having its first-ever video meeting. It will be a learning experience! 

  • 24 Mar 2020 14:22
    Reply # 8853651 on 8732915

    I took delivery of my 8 batteries last week. They weigh 76 lb/34.5 Kg apiece, for a total of 608 lbs./275.8 kg. I ignored the advice of two drive-by sidewalk superintendents to use a forklift. I hired a young man to carry them, one by one, up the stairs and locate them near their new homes down below. 20 minutes and a few dollars. Each battery weighs about as much as the motor.

    They will be put into three double-battery boxes and two single-battery boxes. I made sure I had the right size boxes. The will be strapped to pieces of 3/4" plywood which are lag-screwed to the boat. There has been a lot of fiddling and re-discovering that in many cases, putting new equipment into this boat, there is just enough room.

    I will do as much of the installation as I can, before bringing in my marine electrical technician to wire it all up. He will connect the batteries together in series using AWG 2/0 cable and the banks to the motor with AWG 4/0 cable.

    The city is as quiet as Boxing Day with the not quite complete lockdown. I continue to go to my boat because I make no close encounter with people. When I'm done, I'll clean up and disinfect any surface areas likely to be contaminated around this job, Then, I'll get my techy in, but separately. We can communicate with Skype or something.

    By the way, by the time I got the old diesel motor out, we were well into winter. This winter has proved to be fairly benign so I elected not to put on my custom made cover. We have the most freeze-thaw cycle winters in North America. I did a little shoveling but melting took care of the rest. Annie, you will be pleased to know that not a single seam has opened this year. Another revelation was the serendipitous discovery of two leaks. One between the after deck and the cabin bulkhead and another at the top of the rudder.


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  • 07 Mar 2020 13:20
    Reply # 8807507 on 8800681
    Anonymous wrote:

    Here is a link to a recent demonstration of a similar, electrically powered propulsion system called DeepSpeed.  Like something out of Star Trek. When you look into it, you see only an empty passageway, no blades.

    FYI, the previous discussion was based on:  https://plugboats.com/amazing-new-electric-boat-motor-based-on-fish-fins/


    I should explain the previous motor was called FinX, made by a French company. They provide some good drawings that explain how it works.

    The second motor, called DeepSpeed, is a hydrojet built by an Italian firm. Their video is quite impressive.

    It will be interesting to follow these developments.

    Last modified: 07 Mar 2020 13:21 | Anonymous member
  • 06 Mar 2020 11:51
    Reply # 8800681 on 8732915

    Here is a link to a recent demonstration of a previously discussed, electrically powered propulsion system called DeepSpeed.  Like something out of Star Trek. When you look into it, you see only an empty passageway, no blades.

    FYI, the previous discussion was based on this:  https://plugboats.com/amazing-new-electric-boat-motor-based-on-fish-fins/



    Last modified: 06 Mar 2020 12:19 | Anonymous member
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