Hi Arby,
Thanks for that very useful and detailed reply.
I haven't looked at the prop shaft in my boat, yet (there seems to be this rather large Infernal Combustion Engine in the way :) If the prop shaft setup is typical, the only function that the through-hull bearing provides is lateral support, along with the packing gland to keep water out (more or less, usually less, in most boats ): So, a thrust bearing, if used for a direct drive, should go between the prop shaft and the motor to eliminate the axial load on the motor, for which I'm sure they're not designed, as well as the through-hull bearing.
I assume the primary desirable characteristic of a direct-drive motor is useful power up through relatively low RPM (~100 RPM?) - all electric motors have max torque at stall, obviously. So, that suggests as many poles/windings as possible, which is going to be more expensive. I'm wading through the pros and cons of brush/brushless, DC vs. AC, the various magnet and winding configurations and technologies, etc. It appears that the lower maintenance and reduced exposure to saltwater condensation (which can pit, corrode, and actually vastly reduce magnet strength) of brushless motors are well worth the higher acquisition cost and potential troubleshooting effort due to there being circuitry beyond giant inductors (aka windings) on the brushless motors. It would sure be nice to see some failure rate numbers on the various choices, particularly the in-motor, non-winding circuitry. If the cabling is kept large-diameter and as short as possible with solid connections, it appears that DC is the way to go, as AC would require yet-more power-consuming and increased-complexity DC-AC conversion components, reducing efficiency, increasing cost, and increasing overall system failure probabilities.
I did see mention somewhere of the high advisability of using fully-potted components in the marine environment and, given my experience, I can't imagine not doing that. I hadn't drilled down to determine whether each of Steinberger's components was suitable from the headroom perspective but, even though he appears to be a lawyer, he did have enough sense to go with a potted controller, although you have to read between the lines by looking at what he paid, vs. the starting price for the non-potted version. Although he doesn't say so, it appears that he also went with high-speed firmware - I haven't looked to see what that means. He's got a direct drive, so, it's not motor speed - is that the data transmission speed at which the firmware loads when reprogrammed?
I'm definitely looking at portable generators as a long-term desirable addition, but, for now, the few minutes of power that I'll need to get in and out of the channel and do some local sailing around SF Bay can be very adequately recharged via shore power (which I'm paying for anyway), and I'll still have a ton of reserve power for emergencies. I have to sink a bunch of money into replacing the standing and running rigging, replacing fittings, and acquiring some decent sails, first (it _is_, after all, supposed to be a sailboat! :) I can't complain, though, as I got the boat for a song, and it's fundamentally structurally sound all around, modulo the rigging.
I'll be making the rounds to every e-boat owner who's willing to put up with my inane questions. Even as a computing weenie, it's still amazing what I've been able to find out in just a few days, and making contact with Those With The Tall Shoulders On Which We Can Stand. The last few days' worth of info would have taken months to compile before the Net became commonplace (if I could have found some of it at all), and I've only scratched the surface. I can't wait to get down into the nitty-gritty, and finally feel like I really know what I'm doing, despite my technical background. Frankly, I can't believe that there haven't been a lot more horror stories involving fires, explosions, and other similar sources of excitement and insurance rate increases!
Thanks again for the encouragement and pointers - it's been a while since I've been around folks with common interests whom are willing to share what they know without a meter running on their foreheads. I hope that I can be as helpful with things on which I may be the resident expert, or I can at least play one on TV!
All the Best,
Jim
--- In electricboats@yahoogroups.com, Arby bernt <arbybernt@...> wrote:
>
> Hi Jim,
> Thrust bearings are overkill, since the side loading is well within normal bearing specs. I use axial thrust bearings anyway. I'm aiming for 10,000 hours service-free, about 70 years of use in an average boat. I doubt a set of regular single row bearings would ever wear out in under 10 years. The Mars motor you listed is not an effective direct drive choice.
> The Kelly controllers I'm using (KBL series) do not like continuous rated output. I usually set mine at 50%, They can be run all day at "full throttle" to produce the rated 5kw output (KBL48301) of the motor. A fan cooled heatsink also helps. Overbuilding gives you headroom. Skimp, and you'd better have ground tackle handy. Sevcon provides one minute, five minute, and one hour ratings for their controllers. Again, the KBL48101 listed below would be hard pressed to deliver reliable performance with a stiff breeze on the nose. Choose the marine option to get the controller fully potted. Any air volume in the controller will cause the marine atmosphere to be pulled into contact with the electronics within.
> Battery technology is still hovering around poor to pricey. Most conversions AMeP has been involved in use enough storage for three hours run at full throttle. That seems to close to the original engine mass in 25 to 30 foot boats, keeping the original waterline. Go easy on the same bank, and you can run the boat for 6 hours without hitting a deep discharge. A portable gas generator, stored above deck, can provide power for extended cruising, provided you have decent power conversion technology. Iota makes marine-rated units, WFCO makes RV-types. Pure battery chargers aren't designed for continuous output, but I still use one on my boat anyway, as does Myles and many others. I use WFCO power converters for lab work on the dyno.
> Spending some time talking with a few people and going for a ride can provide the visceral sensation reading emails and visiting websites cannot. If you're in the Bay Area, come by for some quality time. Please contact Kevin from our website, or any of the many local e-boats on the Bay. James at Propulsion Marine is just down the coast in Santa Cruz.Â
> Be Well,Arby Bernt, AMeP
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