Hi All,
Yes, the subject of regen does come up on a regular basis. I would like to share some real world experience.
First of all, I won't dispute Chris' claim of losing 1kt of speed and only getting 200W. However, I would suggest this is an unusual case. Unless, you are using a folding prop, you will have a certain amount of propeller drag regardless of whether it is stopped, regenerating or free wheeling. I am not a propeller expert and won't attempt to predict the difference in drag under various conditions. I will suggest that there is some difference, but there is going to be some drag, regardless of the condition.
One thing we must accept is that the propeller is essentially operating in reverse and isn't at its best. I did some limited experementation a few years ago and got about a 2X improvement from an outboard arrangement that could be rotated so the prop was facing the right way when regenerating. Unfortunately, we can't do this with our inboard auxiliaries.
In my experience, there isn't much of a change in boat speed between full stop, regenerating or free wheeling. This is with a three blade prop and a fin and spade rudder boat. I need to put it in reverse and add significant power to slow down by 1kt when sailing at 5 - 6kt boat speed.
On my boat, the prop will start to turn slowly at about 3.5kts. At 4kts, there is a small amount of power going into the batteries. At 5kts it is in the 100-150watt range. At 6kts it is in the 200-300W range. I don't think the prop ever turns at more than 200-300RPM, but have not measured it.
Bottom line, it isn't going to provide all of your power needs, but it is something and it is more or less free. If you are racing or performance oriented, use a folding prop and forget about regen.
I haven't gotten a great deal of quantified feedback from customers, but results seem to be consistent with my observations.
One issue is the need to adjust the throttle on many systems. This does seem rather inconvenient and isn't really the "right" way to do it. Our Electric Yacht controllers regen automatically when in neutral. The Sevcon controllers can also be programmed to regenerate automaticlly. If you are designing your own system and want to do this, I would strongly suggest using a controller that has this functionality built in.
Scott McMillan
Electric Yacht
--- In electricboats@
>
> Regen is an interesting recurring topic on this forum.
>
> And there are various ways to look at it---find the way that suits your
> needs and go with it.
>
> Just be sure to respect the laws of physics and known applicable equations
> and curves.
>
> As mentioned by Chris, the return is not great and if the regen is to be had
> while under sail (rather than anchored in current), there's a penalty to be
> paid: Speed of boat in water.
>
> Where the regen tradeoff is not worthwhile for sailing is if you need to
> keep the speed up to reach the destination by a certain tide or time and if
> you will have power available at your destination anyway. If it costs 1knot
> on your speed to capture a mere 200watts of electricity, while it requires a
> doubing of power for the boat to increase speed by 1knot, the cost of regen
> can be steep if the primary need is to cover distance quickly and you expect
> good wind the entire way.
>
> Where it would certainly be worthwhile is if you're sailing and really don't
> need the speed, but could or will need the electricity later.
>
> And there's a million other circumstances between these that could swing
> either way. Be conservative and have backup plans---having regen can be
> part of that backup plan. But you might best add a wind generator instead.
>
>
>
> Of course the no-brainer free-energy case is where you expect to be
> anchoring in a high current zone----but how often do you really want to do
> that?
>
>
>
> -Myles
>
>
>
>
>
> From: electricboats@
> On Behalf Of Chris Baker
> Sent: Sunday, March 07, 2010 6:43 PM
> To: electricboats@
> Subject: Re: [Electric Boats] propellers
>
>
>
>
>
> Hi Larry,
>
>
>
> For while I had an Epod on my boat and experimented with regen. There were
> too many design faults with the motor to continue with it, and I eventually
> abandoned it in favour of a Torqeedo 4.
>
>
>
> But I did actually see some regen in the limited opportunities I had to test
> the Epod. I needed around 7 knots or more of boat speed to get some useful
> amps - around 2 -3 amps I recall, and at around 10 or 11 knots I've seen up
> to 6 amps going to the batteries (thats a 48v bank).
>
>
>
> These results are from a fast trimaran and it seemed that on days with a
> nice wind of say 10 to 15 knots and quite a few hours sailing, you could
> recover the amps from typical motor usage to get on and off the anchor or
> mooring. The cost was around 1 knot - that is, the prop drag when
> regenerating slowed the boat by about 1 knot.
>
>
>
> From this limited experience practical regen for a keeler of less than 40 ft
> seems out of reach for every day sailing. The boat speeds are just not high
> enough on a regular basis. Especially keep in mind that regen slows the
> boat, so even when the boat is doing 7 knots under sail, just adding the
> drag of regen could slow it by one knot, and that reduction in speed reduces
> the regen to a barely measurable level.
>
>
>
> As to Kevin P's idea of electro-sailing - I suspect its pie in the sky. I
> never saw it despite trying for it a few times. I'd set the throttle so
> she'd do a few knots under power - for those moments when the wind died
> completely, hoping that when the wind picked up, I'd see regen to top up the
> batteries... Well, it never happened. And she'd easily accelerate to 10 to
> 12 knots, and at these speeds there was no regen. To get the regen back I'd
> have to reset the throttle to chase the sweet spot that showed some amps
> flowing back to the batteries.
>
>
>
> To answer your question about how much power should be generated with time,
> I would be content if I could have about a 10:1 factor for regen. That is,
> if 10 hours sailing could give me 1 hour cruise speed motoring, I'd be happy
> with that rate of return. For me, 20 amps under power gives a useful speed,
> and that would mean regen would need to average 2 amps. To be useful for a
> broad range of boats, I think regen would need to kick in around 4 to 5
> knots of boatspeed. Would this be practical?
>
>
>
> I suspect that a prop that is designed with regen in mind may have different
> properties to the props we have to choose from - all designed for
> propulsion. Perhaps in future we'll have props that are good for regen, and
> the price we'd have to pay is a reduction in efficiency on the propulsion
> side. With your expertise, maybe you can come up with prop thats good for
> both?
>
>
>
> In the meantime, I'll press on with setting up a towing generator - with
> that I can optimise the pitch for generating. I have a variable pitch
> pro-pulse prop available for experiments with that.
>
>
>
> Cheers
>
>
>
> Chris
>
>
>
>
>
> On 07/03/2010, at 5:16 AM, gramplarry wrote:
>
>
>
>
>
>
>
> this discussion sounds to me that regeneration has been discussed and even
> tried but seems to have been less successful than everyone would like. by
> this i mean pure regeneration not just matching the prop to sailing speed.
> what happened and what are the reasons for not being successful.
> how much drag for regeneration would be acceptable?
> how much power needs to be supplied by the propeller to the motor to have
> regeneration?
> what propeller rpm and torque would start and maintain regeneration.
> How much power should be regenerated with time.
> what usage? house batteries and power batteries of both etc.
>
> --- In electricboats@
> <mailto:electricboa
> <aweekdaysailor@
> >
> > I believe, but can't yet prove, that the one area where "regeneration"
> might actually be practical is in what Kevin P calls "electrosailing" -
> matching the prop rotation to the boat speed so that it's regenerating about
> 50% of the time (very low wattage mind you) The point of this is not really
> regen, but rather nullifying the prop drag and getting the extra 1/2 to 3/4
> knot of speed. Over a sufficient distance, this extra speed is the practical
> equivalent of a feathering prop (without the drawbacks) and nearly net zero
> energy use.
> >
> > I currently have a 3-blade, so the above is more necessity than choice.
> >
> > -K
> >_,___
>
No comments:
Post a Comment