Hi Mike,
Thanks for the data points. If it wasn't clear before, since I'm leaving the prop until the very last improvement, regen is at the same priority level - last. I just didn't want to paint myself into a corner by choosing a motor (and associated reduction, if any) that would be sub-optimal if/when I ever did crack the prop issue (I was going to say "nut", but some of us have undoubtedly cracked nuts and other prop-associated parts ): 40:1 means 2.5%, and that just seems lower than it could be. 10% at the high end seems to ring a bell, but, that might only apply to much larger-diameter and higher plan-area props with dynamically-variable-pitch blades, running at our low speeds.
In addition to my ocean engineering background (hence, my familiarity with undersea power systems, along with marine engineering - ship/sub power plants; naval architecture - hull design; hydrodynamics - tow tank fun; nuclear engineering, etc.), I'm also a fixed-wing aircraft and helicopter/autogyro pilot, and I'm more than a bit familiar with some of the tricks aeronautical engineers have come up with over the last century (until the Wright Brothers, aircraft props were essentially large-diameter, fat-bladed ships' props that looked more like an air circulation fan than a typical modern aircraft prop). Dynamically-variable-pitch prop blades made their way back from aircraft to ships' props, and more technology can make the transfer (one of the problems with our ever-more specialized world is that there's ever-less cross-pollenization between disciplines happening).
I happen to have access to massively-parallel research computing resources for running simulations for applications like this (my day job) and should be able to justify some resources on something like this, as there are people who would be very interested in any improvements (see the Navy Secretary's recent statements and interviews about how the military is getting deadly serious about energy efficiency improvements of even a few percentage points - that's billions of dollars of savings in some energy applications).
I'm not at all surprised at a price tag of $10,000 for a prop like you described - that's a bargain in naval and merchant marine markets, and even for higher-end power boats. If/when I have the time, I'm pretty sure I could come up with something useful with better than a 40:1 ratio for less than $10,000 - order the 39.999:1 unit now at the bargain-basement price of only $9,999.99 - quantities are extremely limited (currently zero ;) Seriously (who, me?), I have put off this phase until last since it's the pit with the highest probability of being more bottomless than the others, and ~40:1 may be Nirvana at these low speeds and prop diameters. It will be months before I get to seriously look at the problem and potential solutions, but, I am very interested in the answer, positive or negative.
For example, there are composite (e.g., carbon-fiber) dynamically-variable-pitch aircraft prop blades that can change blade geometry via embedded metal spines that are tensioned/relaxed in-flight, and they start at $1,000 retail for a complete three-bladed prop assembly (for experimental aircraft - certified parts required for commercially-built aircraft cost, as they say, "somewhat more" ): Fortunately, we don't have that certification constraint (not sure about commercial boats/ships - there might be, above a certain tonnage/passenger count), so, we should be able to achieve similar costs - warranted parts would increase the cost somewhat, though.
The concern about running a drive system in regen mode seemed to be more like "we don't really know" due to lack of design and testing, than actual experience. I can definitely see where the inevitable slop in a belt/chain system could cause trouble if the torque is coming from the opposite direction than that in the originally-intended design. This could become especially problematic for belts at the higher speeds where, even for those with large amounts of steel reinforcement, some stretching could occur, especially with age. Indeed, there are toothed belts that can only be tensioned in one direction due to the way the reinforcing material is aligned (I doubt any of the systems offered for our application have that limitation, but, sometimes, not-so-funny stuff like that happens, just when you're least expecting it - like when you're being driven toward the rocks ):
As a former Navy Officer of the Deck (at Sea), a victim of two semesters of celestial and electronic nautical navigation at the Chesapeake University of Naval Technology (note the acronym, then adjust for political incorrectness to get the actual institution's name in that geographic region), and a certificated pilot in visual and instrument aeronautical navigation (airplanes and rotorcraft), I think I recall something called "set and drift" due to some unfathomable forces with names like "wind" and "current". In other words, yes, I know how to cheat with a GPS using one-way runs that take advantage of the aforementioned phenomena ;) If only there were a thousands-of-years-old technique of trailing a small-diameter line with knots tied in it at regular intervals, that might be fed over the transom to estimate speed through the water (and ruining the day/prop of the guy under power behind you :) OK, now I'm just being a complete jackass - I do appreciate the pointers!
Well, Myles is probably ready to electronically terminate me with extreme prejudice for such a long post, but, I've been a good little boy for a few weeks, so my average post length per unit time is fairly small, and it seemed ridiculous to break this up into as many posts as there are sentences.
Truly, thanks for the response, and All the Best,
Jim
--- In electricboats@yahoogroups.com, "Mike Gunning" <mike@...> wrote:
>
> Jim,
> My experience with regen is almost identical to Eric. His rule of thumb of 40 to 1 is just about right, although you might be able to adjust it with a more efficient prop. Small boat = limited regen. I suspect that we are getting limited regen starting at 4.5 in my Newport 30 only because we have a three bladed prop. If I can get better than 30 to 1 I will be very pleased. Also remember that it is speed through the water and not over ground that is important, your GPS is not the best indicator for regen.
>
> I would not focus on regen as the most important element of the decision making or selection criteria.
>
> Please be advised that I am a dealer for Electric Yachts. I believe that the negative of the direct drive motor is that you are constrained in customizing the motor for the boat or your ability to modify the system like you can with a pulley or reduction gear system. We just experienced this with a system in which the original information on the prop was not complete and when the performance was not what was expected, we were able to swap out a pulley and the performance increased dramatically, both speed and efficiency.
> Mike
> Electric Yachts So Cal
>
> --- In electricboats@yahoogroups.com, "Eric" <ewdysar@> wrote:
> >
> > Hi Jim,
> >
> > I'm not sure why you believe that a reduction setup (gears or belts) has any effect on regen capabilities. The problem with regen in boats our size the the limited speed potential (when was the last time you sailed faster than 6.5kts?) and the inefficiencies of propellers to collect energy at these speeds.
> >
> > Just like all of the wind generators or towed hydro-generators, which are optimized for energy collection (not propulsion), slow speeds just won't develop any significant output.
> >
> > All of the regen capable electric boat conversions that I have heard of, with either direct drive or reduction drives, generate about the same amount of juice through regen, somewhat less than 100W at 5-6kts. The only regen that I have heard of on a sailing vessel that sounds successful to me occurs around 8tks or faster. These boats are basically multihulls or fast monohulls in the 50' range.
> >
> > All of the drive systems (direct drive or not) from the regular vendors here can develop about the same amount of power via regen.
> >
> > The real question is how long does really good regen take to replace the power used while motoring out. Here's my answer, followed by a copy of my post that explains how I came up with the numbers:
> >
> > "Ignoring house loads, the ratio of drive distance (at 4kts) to regen distance (at 5kts) is about 1 to 40. Motor one mile at 4kts (15 minutes) and you need to sail 40 miles at 5kts (8 hours) to get the charge back. If you use a radio, autopilot or lights, the ratio gets worse."
> >
> > I've been using these estimates for years now, and I have never had anyone dispute them. I really wish that someone could prove me wrong.
> >
> > ----- Start post -------
> > Message # 16453 - Nov 29, 2010 - [Electric Boats] Re: more regen conversation
> >
> > Larry,
> >
> > As the most visible "regen naysayer" here, the link that you provided completely supports my previous premise.
> >
> > According to the Whoosh site "... And since we average 5-6 kts, that's over 100 amp/hrs/day – for us quite possibly 150 amp/hrs/day – that is available for running the radar at night, making water with offshore water quality, feeding the SSB radio, and keeping the iPod charged..." So what does this mean? They get 100-150Ah at 12V in 24 hours, that's 1200-1800Wh in 24 hours or 50-75W at 5-6kts. They do say that the harvested water power is sufficicient for house loads, a statement that I wholeheartedly agree with.
> >
> > My statement is (and always has been) that regen at speeds around 5kts is not a viable source of charging for a traction battery bank. The speed is important because most displacement auxilliary sailboats between 27-32 feet (optimal for a 5kW electric drive) have a hard time hitting sustained runs above 6 kts. For this size boat, average sailing speeds of about 5.5kts is more realistic.
> >
> > So let's say that you use 4kWh of energy out of your 10kWh battery bank, that's about 10-12nm at 4kts in most of our boats. How far would you have to sail using the system described by Whoosh to bring your batteries back to full charge, assuming that you are using no electrical power in the mean time? Generating 75W at 6kts, that's 12.5Wh/nm. So 4kWh will take 320nm of sailing at 6kts and will take over 53 hours. Slow down to 5kts under sail and the recharge distance is up to 400nm and will take 80 hours. If you have a 12V house load of
> > only 2A, the recharge times and distances double.
> >
> > Ignoring house loads, the ratio of drive distance (at 4kts) to regen distance (at 5kts) is about 1 to 40. Motor one mile at 4kts (15 minutes) and you need to sail 40 miles at 5kts (8 hours) to get the charge back. If you use a radio, autopilot or lights, the ratio gets worse.
> >
> > So regen works, but is not as effective at recharging your traction batteries as some drive vendors would like you to believe.
> >
> > Fair winds,
> > Eric
> > Marina del Rey
> >
> > --- In electricboats@yahoogroups.com, "Larry Doyle" <ldoyle@> wrote:
> > >
> > > Here's to those NaySayers that say regen doesn't work. Here's some boats that are doing it using towed gens as well as the free wheeling the prop/dc motor in regen mode.
> > >
> > > www.svsarah.com/Whoosh/WhooshPacificPrepTowGenerator.html
> > >
> > ----- End post ------
> >
> > As far as reliability or wear is concerned, my Browning reduction gear box is 97% efficient and has a MTBF of around 100,000 hours of use. So I don't think that there is any reason to be worried about that.
> >
> > Fair winds,
> > Eric
> > Marina del Rey, CA
> >
> > --- In electricboats@yahoogroups.com, "jim_ranger_26" <jim_manley@> wrote:
> > >
> > > Hi everyone,
> > >
> > > So, I've been continuing my research and it looks like the final decision point is the motor, which will be the most expensive single component in my system. The gist I've gotten is that, in order to support regeneration, a direct-drive motor has to be used for efficiency, as well as wear-and-tear on belts, pulleys, etc., associated with power/torque transfer/conversion components used in indirect-drive systems.
> > >
> > > It's not clear to me whom here is using a direct drive motor and/or regeneration, and I would greatly appreciate any thoughts and opinions on the current (double entendre fully intended) motors available in the 2 ~ 5 KW range. I'm repowering a Ranger Yachts 29 foot sloop that weighs about 5,000 pounds, and will only need to motor for a few minutes in/out of the slip, with most capacity held in reserve for no-wind cruising and emergencies.
> > >
> > > Thanks,
> > > Jim
> > >
> >
>
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