Monday, April 11, 2011

the buzz and the box

This is to detail the installation of the electric drive after a very satisfactory first trial. The pic above shows the battery box, which is simply held captive by slotting over the keelson, and held fast when the lid is slid over the box and the catches engaged. The grey plug is an 'Anderson plug' and is an easy way to disconnect the battery. Behind that is a black plug (with waterproof cap) into which the battery charger is plugged. In our case, that battery charger is powered by homegrown solar electricity from our ten year old household power plant. There are various additions and refinements possible here, but I'm keen to keep things as simple as possible.

Incidentally, the wooden thing there is the boomkin in repose after its first outing.
This complicated pic shows the control for the motor. When the knob faces forward the system is off. Turning it to the right gives a range of forward speeds, and turning to the left makes you go backwards. This is so much more fun than an outboard, and so incredibly easy to control.

What this system won't do is completely replace an outboard because battery range will always be a limiting factor without considerable weight and expense. But if you often launch from a marina, or simply want to explore a non-sailable stretch of creek or river, then this will be easier, quieter and much more fun than a stinky thing.

Now a small confession. The system as shown does not use the electronic components discussed in the previous post called 'power resistor versus mamba max'- it uses the resistor supplied with the motor, under that knob. The reasons are that I was quite concerned about the small scale electronic wires and connections in a wet, corrosive and hostile environment (managed by an incompetent with big hands and less than perfect eyesight). The consequences are that I won't get the efficiency that I had hoped for, but that simply translates into running time, and if that becomes an issue I can simply carry a second battery.

The major surprise in using this system was the positivity felt in controlling the boat. Because you don't need to 'start' the motor, or reach back to change from forward to reverse, and because the drive is in front of the rudder (and not going to cut great chunks out of it) the rudder is very effective under power; I can place the boat accurately and confidently. I've never felt that before with an outboard. I also felt more confident in approaching the marina because I knew that reverse was so easy to go to from the forward position.

As I expected, the motor compartment carries about 20mm of water, but this is easily drained, and it just requires that the motor wires are well (triple in my case) insulated. The waterline will be a little lower when the outboard isn't pulling down the stern too- particularly since mine is overpowered and weighted at 5hp.


  1. Rob, with regard to the mamba max, could a consideration be the use of a water tight box with the unit inside. A shaft extension and gland could provide access to the control inside the box.

    As an aside you "could" use a bluetooth interface for your iPhone. Voice control to the engine room!

  2. Spot on Dale, I did set up a water-tight box in the side compartment, but even so, there were so many connections of such tiny wires, and the controls were so 'dinky' I put it into the 'to be considered later if I get around to it basket', because everything else was ready, and the month was marching on, and I really wanted to have a sail in sunshine if possible!
    Also, the whole gig was a big stretch for me, investing so much time in something that could have been no more than an embarrassment....How was I to know that it would work?
    In the hands of someone competent, the bluetooth idea would be brilliant!
    As it is, I messed around in the boat all afternoon, in and out of the marina a couple of times and a bit of cheeky 'motor-sailing' and scarcely used 1/4 of the battery, so I'm not too fussed.

  3. I should have mentioned that the mamba has heat sink castings that needed quite a bit of air and space too, and all those complications aren't good when something goes wrong

  4. Excellent Robert. I always wonder why more people don't go this route. Small sailboats so seldom need reserve power that any kind of gasoline engine, no matter how small, seems way overkill. Not to mention way too much maintenance headaches, noise, and smell. I hate small gasoline engines anyway, but on a sailboat seems it completely ruins the whole esthetic without much added benefit. Maybe a just sense of security.

    I didn't read back far enough to see the details on your motor. I have a 24volt saltwater version that's now 6 years old. It has never needed a tune up or winterizing or cleaning of fuel tank or carburator. With two 12v batteries it has pushed two people and all our gear all day long at 4.5 knots, hull speed, and still had charge left at sundown. If you only need yours to get to and from the launch, and to run for shore to duck into a sheltered cove in a pinch, you'll never have to worry, certainly not with two batteries anyway.

    Great job.

  5. Cheers Barry, I really value your perspective.

  6. Would love to go down the electric path. Have concerns about longevity (and reliability) of batteries that are rarely used. Petrol, for all its faults, is just so darned reliable & convenient for the occasional user. Thoughts? Experiences?

  7. G'day AJ, in my case I hope that hooking up the charger from time to time will be less irksome than flushing the outboard after each sail, and making sure the fuel is topped up, and the machine is serviced. Although as I've said, there will be times when I do use the outboard.
    The right battery charger should make it easy. I've bought a small multi-stage job which lets me know what's going on...
    But it all does take some extra work to make an easily dismountable inboard.
    We had a rechargeable rotary mower for years to do a little lawn, and it was a similar battery, and it just lived near a powerpoint, and was never any trouble even after months of not being used. The battery outlasted the switching components- I guess we had it for ten years.

  8. The only real advantage I find to gas engines is the quick "recharge". You can get fuel almost anywhere, and it only takes a minute to refill the tank. The batteries currently available take hours to recharge. In practice, this is only a problem if you spend several days away from civilization and/or use auxiliary power enough to drain them, unless you plan occasional overnight stops at marina slips to recharge. If you take weeklong trips in remote areas with only brief stops to resupply, and use a motor frequently, a gas engine has a clear advantage.

    Aside from esthetics, where electric systems shine is reliability. If you're like me - mechanically challenged, rarely take trips longer than a couple of days, and rarely use a motor - an electric motor is a more practical choice. You never have to wonder how many pulls it will take to start (or if it will start at all), and it never needs any maintenance. You just flip a switch and it goes, every time. That can be really critical when you suddenly find yourself in a tight spot and need instant power.

    Gas engines are so complex, vulnerable to so many problems, needing regular care and maintenance to stay reliable, I often wonder if we don't feel safer with them simply because they're so familiar. "The devil you know . . . "

    Robert, I'll be interested to hear your thoughts after this season or the next, since it sounds like you'll be using both for a while.

  9. Barry that is nicely expressed, but for me until now it has been about having 'belt and braces' until I felt confident in my work! So if I have a chance to sail this week, it will be without the outboard hanging off the back. Last time I hardly used any measurable power at all....and my 5hp is overkill in the weight department.
    Incidentally, I took the time to explore your blog more thoroughly to-day, and find myself much the better for it. You have a breadth of perspective that I engage very happily with.
    For my other reader, Barry's 'Melonseed' (and thoughtful other things) blog is now on my blog list and i do most heartily recommend it.