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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