Good luck with that Jim.
It takes 5.5kw to drive my boat 6kts and I assume my efficiency to do so is, at best, 65%, battery electrons to boat motion.
In doing that, the prop is spinning around 1000RPM, with what, 30% slip?
IF I reversed the process and were driven by the wind at 6kts, the PROP would likely only be spinning, what 500RPM? Probably much less.
At less than ½ the speed as in propulsion, and at 100% efficiency, it couldn’t capture more than 1/8th the power that it did at 2x that speed---ie 440watt.
Ignoring inefficiencies, you’re already at 12% return----hard to believe you’ll be able to get to a 10% number when you consider inefficiencies.
The data mentioned so far shows that e-sailboats are only delivering about 100-130watts for a boat that requires about 5kw to go 6kts by electric. Analysis will probably show that it’ll be difficult and costly to boost this much more than 3x. And even if you could hit 500watts, Eric’s ratio of 40:1 would be reduced only to 10:1, meaning it’d take you 10hrs of regen sailing to make up for just 1hr of propulsion at 1-kt less in speed.
-MT
From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of jim_ranger_26
Sent: Thursday, July 14, 2011 3:00 PM
To: electricboats@yahoogroups.com
Subject: [Electric Boats] Re: Direct Drive Motors and Regeneration
Hi Eric,
I wound up conflating my response to this post in my reply to Mike, but, the bottom line on the prop is that "analysis continues" - or at least it will continue after I'm able to get into/out of my slip at all.
A geared system is obviously the most efficient (and expensive, I'm guessing, but, maybe not by much, except perhaps lifecycle costs over decades/centuries - e.g., belt life vs. your 100,000 hour warranty) and should have no problem running in regen mode. There are asymmetrical-toothed gear systems that are only supposed to be run under load in one direction, but, those are exotic even for well-heeled boaters (yachters, really), and would have no use in our application (let alone budget).
All the Best as I descend back under the rock,
Jim
--- In electricboats@yahoogroups.com, "Eric" <ewdysar@...> wrote:
>
> Hi Jim,
>
> My sampling includes boats with 3 and 4 blade props that have swept areas exceeding 85-90%. My boat with a 4 blade 13x15.5 prop is one of those boats.
>
> The commercial hydro-generator for boats people have been working on this for ages and still seem to be limited to less than 100W at 5-6kts. But maybe you'll figure out something that they haven't been able to. There is a $10k dedicated hydrogenerator on the market that uses a hydraulic variable pitch prop to optimize power to drag ratios while generating power. The system does the adjustments on its own, but the price has limited the user base to global racers for now.
>
> On the reduction conversation, if you think about it, the prop isn't ever going to push more power into the system than the motor does, so I don't see where the issue come up. But if the vendor is concerned, I would heed their advice. I know that it is not an issue for the Propulsion Marine systems.
>
> Fair winds,
> Eric
> Marina del Rey
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