My Experience with EV – Part 8 Sea Trials

I can now say that we have extensively sea trialed the Manta Drive. We started with a little trip around Lake Union then stepped it up to a few overnight cruises.

First Trial – Cruise on Lake Union

Ava and I motored off the dock one faithful summer night here on Lake Union to test her out. I completed tightening the bolts holding the belt tension and said, “Alright! let’s take her out!” Ava looked down at me skeptically from the cockpit. The sun had set, so it was going to be a nice night time trial cruise, maybe 30 minutes or so.

The first thing I noticed was how responsive the boat was, I can now turn the propeller at 1 rpm if I so choose. This is a very nice perk for backing Cinderella out of the slip. I could use quick bursts to overcome wind drift and keep the bow under control, yet go back to a very cautious slow speed in an instant. This was not the case with the Yanmar, the Yanmar did not like shifting from neutral to reverse, and would die occasionally during the shift. This kept me on high alert in close quarters, and I tended to over throttle to compensate making close quarters tricky. (To enter and leave the slip I have to slide Cinderella between two boats with about a foot on either side, and the same goes for reversing out of the slip)

We then proceeded to motor around the lake and I let Ava take the helm so I could go below and look at the gauges, I could not believe that under full throttle, not only were we hitting 5 kts (the same max speed as the Yanmar), but we were only drawing 25 amps! I was expecting closer to 100, so this was huge. Backing her down to 10 amps Cindy would hover right around 3 kts. I was taken aback by how little energy this was taking (though I shouldn’t be too shocked, I managed to row the boat to 1kt when we were out of wind Sailing around Canada). Let me tell you, the motor sure beats rowing!

At full throttle, the belt was slipping and smoking. There was no trouble motoring around at 3kts, but if we pushed it, the belt would slip and smoke. I first wrote it off as bad tension, but on further inspection I was sold a A type drive pulley and a B type driven pulley from the bearing house. The B type belt was not getting enough purchase on the A type pulley and slipping under load. I called McGuire Bearing here in Seattle, and they remedied the situation by swapping my pulley at no charge. The belt no longer slips under a load, and all is well.

Next Trial – Afternoon of crabbing, and a day sail to Poulsbo

The first decent cruise with the Manta Drive was to Poulsbo, WA with 5 friends aboard. 3 of us had the afternoon free, so we headed out the lock early to do some crabbing until the rest of the group could get free. At this point I was completely unsure of the range of my battery bank. To get through the locks out of the lake and into the Puget Sound its about an hour trip, and I bought the cheapest batteries you can find, they aren’t even full deep cycle batteries, but the plan is to test inexpensively and upgrade prior to departure.


We sailed most of the way to the locks, only motoring under the two bridges and through the locks themselves. It was a beautiful summer day, and we were tacking like crazy to get up the canals and across the bays. The wind was perfect 15 kts or so, so we played around setting the crab traps and retrieving them while under sail. (This was actually good practice for a MOB drill, knowing how to heave to where you want to, and how the boat reacts). After a delicious crab lunch, we headed to Shilshole Marina to pick up the rest of the crew for the trip. I still had only motored the boat for a grand total of maybe 30- 40 minutes and had 67% of my battery bank remaining.

After picking up the crew, we sailed on towards Poulsbo (approx a 17nm trip), but the wind decided to stop just as the sun was setting with about 4 miles remaining to the destination. We were out of the strongest current area of Agate Pass, but we were going to fight a slight current most of the way there. Based on my rough calculations, we did not have enough battery remaining to make it…. We motored slowly for about an hour until the battery was toast. Unfortunately, I did not really pay attention to the amps or the time, so I am not entirely sure of the capacity of the bank. We drifted close enough to shore to drop anchor and everyone crashed out for the night.

I spent the night in the cockpit fearful of the anchor. I was not able to set it adrift, so as soon as the wind picked up I was going to weigh anchor and set sail. Sure enough, I awoke around 6am to a very slow dragging of the anchor, and I hoisted the sails and headed out before the crew woke up. The wind was gentile, and I sailed under main alone back out Agate pass. My plan was to sail slowly and arrive at the pass just as the current started build into an ebb. After we got out the pass I again dropped anchor, this time along with crab pots and went back to sleep for a few more hours.

When we all woke up, I told everyone of the new plan to sail to Kingston due to my fear of losing wind in Poulsbo again and not getting back to Seattle on time. We continued on and the wind was perfect, 15kts and Cinderella was charging along at 6kts to windward, the perfect time to test out the regeneration from the propeller. I gave the motor a quick burst in reverse to open up my folding prop, and put the motor back in “neutral”. The prop was now spinning and recharging my battery bank. We sailed on for about an hour alongside a half dozen orcas playing all the way to Kingston.

Upon arrival, I was unsure how much battery I had to dock. I decided to come in under sail, and use the motor only minimally to stop us neatly at the dock. (It’s also fun to engage a bunch of non-sailors in the group challenge of dropping sails on command while coming into a marina). The motor performed admirably stopping our forward motion at the dock. I again didn’t have the for-thought to check the charge level of the bank when we arrived, this was the first time using regen on the motor, and my regen amp gauge wasn’t hooked up yet, so I couldn’t get a good feel for how much power was going back into the batteries.

I paid for a few hours at the marina in Kingston and plugged into shore power to recharge the bank. We wandered around, had lunch and set sail again to Seattle. After dropping everyone off, I motored back through the locks, all the way back to my slip, about an hour and a half of motoring, and there was still plenty left, at this point, I was pretty happy with the motor. I could get out of the locks from my slip, and the regen seemed to work enough to handle docking in a marina. I called it a win even though I drained the batteries to dead on the trip.

Remaining Trials – A couple cruises and a few races

Over the course of the late summer, fall, and so far this winter I have taken a handful of trips to further my understanding of this new electric motor drive. We entered a Duck Dodge race last minute, I participated in the Race Your House, and attempted to first of the Snowbird Series. The latter two showed me that I have right about 3 hrs worth of usable motoring on my battery bank at about 3-4kts, just enough to get out of the locks and back into my slip. We also cruised a bit further to Port Ludlow (again anchoring when the wind died to sleep for a few hours) and later to Port Townsend over Thanksgiving (through a gale on the way there, and navigating micro wind bursts on the way back)

Manta Drive Overall

I am happy with the manta drive, it serves the purpose I wanted when I came up with the idea. I have a simple, clean drive system with no maintenance, and very minimal points of failure. I can motor into the Sound and back from my slip, and I have opened up my cabin allowing for me to build a better layout for our living space.

1 – I can drive the boat the the same max speed as I could with the yanmar (I believe this can be bettered by modifying the propeller)

2 – I have a bout 3 hours of motoring available or approx a 9 mile range as a slow cruise with the cheapest batteries on the market (after upgrading to Oasis Firefly’s we should have about 4x the range) 12 hrs is going to be plenty for what we plan to do with Cinderella

3 – Regen seems to work well, I was able to charge my battery from 57 to 75% over the course of a couple of hrs worth of sailing. I still have an issue where the controller stops the motor if we sail too fast which is kind of annoying, but I am sure there is an easy solution.

4 – I was able to repurpose the seacock for the engine water inlet for my sink drain along with regain lots of room in the boat.

5 – NO MAINTENANCE!! Being a permanent magnet DC brushed motor, the only maintenance I may have to worry about are changing a belt if it wears out, changing brushes if they ever wear out, or changing the motor bearings if the wear out. 3 simple parts that I can carry in about 1 L of space. I won’t need spare alternators, starters, exhaust fittings, fuel filters, gaskets, pump impellers, and so on. The best part is that the components I may need can be easily be found anywhere in the world as they are standard parts used in many different applications.

39 Replies to “My Experience with EV – Part 8 Sea Trials”

  1. Hi,
    I’m in the middle of conversion of 25 ft sailboat 4000 lbs displacement.
    There is no inboard motor before, I’m making a stern tube for shaft. My motor is goldenmotor 3000w brushless and my battery is 7000 w*h li-ion, at 48v. I don’t know what speed I can achive with this configuration and how long I can go using batteries. Your experience is very interesting and useful for me. Good luck for your and 7 feet under keel

    1. Hey Artem,
      Sounds like quite the project! Assuming you have a displacement hull like Cinderella, your max speed should be based on your length at the waterline. Consider building your system around the propeller rather than the other way around.

      It sounds like you have lots of power in that battery bank, we only have 5500w on Cinderella.

      Consider setting up that motor to run as a hydro generator while sailing. It is probably the biggest benefit to going electric on a sailboat.


      1. Hi,
        thanks for tips!
        I’m decided to install a high-pitch 3-blade propeller to get the hull speed at low rpm (less 600). I believe that slow revolving propeller with high pitch is more effective. I’m planning to finish conversion go down to the water at June and than I can check it.

    2. i would love to know more about your conversion. I too am looking at installing electric power. and my 20 ft boat 3000lbs also has no sterntube. anxious to know all about your conversion

      1. Sounds like the perfect opportunity for an electric conversion! I would suggest snagging yourself a copy of My Electric Boats He does the same process you are describing on a similar boat.

        Our system is working pretty well so far, but we are also kind of sailing purists and have become very… patient. After this I wouldn’t consider putting an engine on a day sailor, electric is the way to go on smaller boats.

        You might be the perfect candidate for a Torqueedo. It would make the conversion much quicker and simpler.

    3. Artem, same here 2500 displacement. no stern gear before. this is my biggest obstacle. installing a stern tube and choosing a prop and shaft. very limited room to work.need hint as to what to base decisions on ,prop? shaft size? where to find tube?fiberglass or bronze tube?..etc; thanks

    4. @artem: I’m planning a similar conversion, maybe you could share your experience and performance data with me ?

  2. Thank you so much for sharing your story with us. I have yanked my 2GM20F out of my 1966 Morgan 34. Been working on figuring out my plan to install an electric motor. Your story & all you info has been very helpful. I have 12,500 lbs displacement do you think a 10hp will do the job? Going to have 100 watts solar & a 400 watt wind gen to keep me powered. Did you use a D.C. To D.C. Converter to keep your 12v house system running? I just can not make a decision in which motor to buy. Any advice would be greatly appreciated. Thanks.

    1. Hey Paulina, Congrats on getting ready to go electric! I believe A 10kw electric motor should handle your boat just fine assuming you gear it properly and match it well to your prop. Those numbers look really low for charging though.

      One thing to consider is using the motor as a generator, it will produce substantially more power than a wind generator while under sail.

      We will have 760watts of solar onboard Cinderella and 2 charge controllers, one for 48v and one for 12v that way we can simply select what we would like to charge.

      DC to DC converters are still pretty “dumb” and you would run the risk of boiling your batteries. Solar charge controllers are very advanced and can determine how much juice to send to your batteries based on type/temperature.

      All of the cruisers I have met have told me to only consider a wind generator only after you have filled every square inch of your boat with solar. I don’t have any experience with them, do I can’t really comment.

      Hope that helps!

      As for the motor, you might consider a brushed DC motor for simplicity. We have used ours for over a year now and it still works flawlessly.

      1. Thanks for the reply. I have to think on the gearing & matching it. I had not thought of that. Will have to ask lots of questions when ordering my motor. How do I now what my prop is geared for?

        1. Prop pitch is out of my realm of knowledge, I’d start by scouring google and asking someone with experience if possible.

      2. Hi Pajo,
        What do you think in account of remove 12V batteries and use DC-DC 48V -> 12V for navigation, light, etc.?
        This will allow to remove one solar controller (for 12V).

        1. It depends on your situation, but it isn’t prudent for us. For a day sailor, I’d say go for it. If you are extended cruising, you don’t want all your eggs in one basket. It is very nice to have isolated systems (think engine starting vs house bank) if you are out cruising.

          If you run down your motor bank, do you really want the fridge to stop working?

  3. Hi Pajo,
    I read your electric motor story out of breath while beginning to end..
    Nowadays electric propulsion excited my attention.
    I want to ask you some questions, first of all did you make for regen button or something ? I mean while sailing how would you turned on regen ?
    Secondly, where did you put the controller and batteries on Cindy.. ? wiring seems too complicated do you have any tips for .. ?
    I have to be say that you made a great work and your experiences light comes overseas.. 🙂
    Thanks for your answers
    Good Luck

    1. Hola Cagri, Ask away!

      Regen is 100% controlled by your motor controller. Our Kelly 4qpm controller allows for regen…but it was designed for golf carts going down a hill. It wasn’t designed to be used as a charge controller, which is what we really need.

      Think Hydro-generator. I believe midnight solar is in the process of testing a hydro charge controller they are gonna bring to market soon, that should be interesting.

      Our motor controller has a wire that is designed to be used as a brake switch that controls how much regen you are putting into the batteries. I wired that to a on/off type switch that we can use to turn on/off regen.

      The issue is that the controller can’t handle more than 60 amps and the motor produces more than that when we are under sail (after about 5.5kts it shuts down). We haven’t been using it while underway very much unless we don’t have much wind and have to sail slow. It also works much better when sailing to windward.

      The most important thing to consider with the location of the batteries/controller is water intrusion. Keep them in a dry place! After that, the closer you can put them to the motor, the smaller diameter wires required. I initially installed everything in the lazaret under the cockpit, but moved everything forward under the starboard settee when I rebuilt the interior. I am very glad I did, we have taken several waves over the stern and water has found it’s way into the lazaret on occasion.

      Draw yourself a nice wiring diagram and follow that. That should help simplify everything. If you can, keep the wires color-coded. If not, a label maker will do wonders. I used a termination block to keep everything inline and make the connections easier.

      1. Are you saying that when you sail at around 6 knots you get 60amps at 48v of regen? That seems like an amazing amount of regen.

        Veryhelpful articles. Thanks for documenting and sharing yourexperience.

        1. Hey Dave, I wish we could get 60amps back! I have a feeling its more like 6a @48V. Unfortunately, we took a wave over our stern the first night in the ocean and some saltwater fried our gauges. So I have no long term data…

  4. I also plan to go electric. MyrO’day had an inboard which was removed by previous owner along with shaft and propeller. Any suggestions on how to install a shaft?; drilling hole, packings, angle, etc. Thanks.

    1. Hey Victor, sorry for the late response. We have been sailing and learning how to manage a life cruising, its very different.

      That is quite a project! You are looking at serious boatbuilding. Definitely beyond my knowledge, but if it was me:

      Two options, sail pod or inboard. Then, do you want to use prop walk as a poor man’s bow thruster, or is your boat responsive. I have never sailed an O’day so I’m not sure. I know full keelers don’t turn so well, so the prop walk helps. Cindy turns on a dime, so the prop shaft can be inline and well ahead of the rudder (like it is) and no prop walk is felt (makes backing easier). I would imagine on a less maneuverable boat you would want it offset and closer to the rudder (to utilize prop walk).

      If you go inboard, starting with a fiberglass tube is probably the place to start. The hole wouldn’t need to be too perfect, as you will be building up glass around the tube to make it an integral part of the boat. The more horizontal the shaft, the more efficient, but you need some angle so the propeller will fit. Picking and pitching a propeller are a special science of their own. I would start there and go backwards if I was starting from scratch (what’s available and max efficiency). Some type of strut will be needed and a cutless barring installed. On the interior of the boat, I would also glass a support for a thrust bearing of some sort so that you could belt drive the prop and it would be plenty reinforced. I have dripless packing and I would definitely go that route, its so simple and no leaks.

      There are pods available (I think) that skip all of those steps and you just bolt on a drive pod to your keel/rudder.

      Lots to think about. How big is the boat, and what are your intentions with it? Distance cruising? Day sailing? Racing? Lake sailing?

      Hopefully that gives you some ideas of where to start.

  5. Well presented, very much enjoyed. Thanks. One question, do you have propane on board and if so, are you concerned about using a brushed motor? Sorry, that was two questions.


    Ron (Sailing Infidels)

    1. Hey Ron,

      Thanks! We do have propane on board for our stove/oven. In short, one electric motor is far less spark/explosion hazard than the engine was. The engine had two motor bolted onto it! They also handles far more amps than this one draws.

  6. Great project. I plan to do the same thing on my boat (29 LOA, 6700 lbs displacement). I am also reading about manta motors and I wonder if you had any luck using it as generator when under sail?

    1. We did, but we found that the charge controller we have does not do well for regeneration. When I have a chance to redo that system, I will diode block out the input and output of the motor. I would like to have the motor generation run through a separate diversion load controller.

      Maybe in New Zealand I will tackle that one.

    1. So we have heard! We were planning on staying a bit in NZ to make some $$$ again. Looks like that may be on hold for a bit.

  7. absolutely fantastic read. Very interesting project and something I’m quite interesting in pursuing in the future.

  8. Pajo

    Finally got around to reading the nitty gritty about the manta. Your detailed explanation was fantastic. I hope to use it as a guide someday. Super great to see that the system has treated you kids well thus far. Just curious, have you found an elegant (or not-so-elegant) solution to not-being able to regen while generating > 60A? What a tragedy that you’re actually generating so much energy that you don’t get to keep any of it. Maybe a different controller? Maybe the solar you’re getting is plenty enough? Maybe some fancy electrical trick that is over my head? (charge some big capacitors?, I have no ****** clue) Continue to inspire!

    -Fellow Serbian Dan

    1. Hey Dan! Great to hear from ya. We may be back in the PNW for a bit. To answer your questin, yes, I believe I have found a controller that can make our regen work all the time. We may be picking one up while we are stateside. I am also working on a custom controller that can handle a bunch of stuff. More to come on that when its starts to materialize.

  9. Great blog.
    As a fellow E35-2 owner strongly considering going electric, I love your blog. We are in Maine and on a mooring, any thoughts on the feasibility of battery charging in less solar intense regions? Also, any insight on longer term cruising with electric only; specifically have you had any safety issues due to lack of range?



  10. thanks for the write-up I’ve been looking at electric motors for sailboats for a while now my findings pretty much match what you’ve described I have worked with DC brushed motors in the past one tip for you if the motor ever stalls carry a small hammer to tap on the housing brushes can get stuck and a little tap will allow the springs to push them back into contact with the rotor.

  11. Thank you so much for sharing this. When we bought our boat the intention was always to go electric, we’re not there yet as the cost seemed prohibitive. Though I’ve just spent two weeks trying to figure out what is wrong with our yanmar (it seems to be getting air into the system after old goopy diesel clogged it up) still haven’t got it sorted and am at my whits end. Though I figure I could probably sell the engine for a good amount and with your setup it makes it affordable to go electric if I can get the parts in Greece.

    Out of interest, what size is your battery bank in AH? I don’t recall seeing this in the posts. Also you mention going with fireflys in the future, have you thought of Lithium? Reasons for not going other than cost?

    1. Our bank is 110Ah. If money wasn’t an issue, there are some quality LiFePO4 batteries on the market. I’m happy with the new firefly batteries we have for the motor bank. We are a sailboat after all, not a motorboat.

  12. I did’t read all the posts so this may be redundant.

    I too am fascinated by electric propulsion. I drive a Chevy Volt, which charges to the full capacity of 8 kilowatts (4 hours on 220, and 8 hours on 110). Prior to the Volt, I purchased a non-working Toyota Prius which I managed to repair using parts purchased from a nearby salvage yard, and with no knowledge of electric cars or their respective charging systems. After driving the Prius, which mainly uses electric to propel the vehicle from a dead stop to about 20 mph (the zone of highest fuel to to speed ratio), I decided electric was the way to go.

    I searched for what I’ve discovered to be the best automobile ever produced, the Chevy Volt. It runs on pure electric, and only uses gasoline in its 3 cylinder turbo generator when battery level is depleted.

    I only buy about $50 worth of gasoline for the Volt per year. The Volt serves as my commuter to and from work, which is a total round trip of about 30 minutes at 65 MPH. I discovered that distance in electric vehicles varies depending on several factors such as topography, wind, driving speed, and ambient temperature.

    I say all that to say that (if) a sailboat could be designed in such a way that the entire ballast was comprised of some sort of battery system such as that of the water cooled version in the volt, and vented of course, for safety, then your idea of regeneration coupled with solar and wind power could be produce extraordinary results.

    I understand that some vehicles utilize planetary gears to overcome the need to shift gears. As I understand it, it simply an infinite gear ratio, so to speak.

    last but not least, and this gets totally away from the electric side of the conversation, it the drive belt. Another of my vehicles is a 2012 Harley Davidson Ultra Limited that utilizes a belt as apposed to a chain to drive the rear wheel. This is a drive belt with teeth or grooves, that so far, have proved indisputable. The only belts that have failed were on Bikes during “burnouts”, which at age 62, don’t feel is a factor.

    It would be interesting to know what it would take to maintain a full charge on battery ballast under sail, and just how far one could travel under power with a variable pitch prop such as used on aircraft (i’m also a private pilot), but never sailed a boat in my life.

    In summary, you’re on to something big. I’m sure there are countless commercial options out there but I like your hands on, pioneering approach. Like the Prius I fixed, it only takes some time and research to DIY.

    Thanks for the great article

  13. Hi,
    A very well documented project overview which helps me in my endeavour to convert a 1957 British built aluminium inboard Runabout, the Albatross. I very much liked the can-do “how hard can this be” approach which gathers essential learning which you’ve shared with other like-minded craftsmen, many thanks.

    In my application I’m adopting the following specification:
    Displacement 720lbs.
    Length 13’
    Width 5’
    Motor Motenergy 15-30kW Water cooled Permanent Magnet Brushless AC.
    Volts 48v.
    Controller Zapi BLE4 550-750Amp max 1000rpm.

    Any advice or any glaring issues spotted from your growing community greatly appreciated.

    Many thanks,

    1. You won’t get her planing, but that motor should suit you very well. I’d recommend a set of quality batteries. We went with the Firefly Oasis and are happy, but there are lots of other great options out there. Just find something that can sit happily with a partial state of charge and recharges fairly quickly.

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