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

Eric,

Thanks for adding this clear explanation concerning regen. I've found the
people who are asking us about regen under sail seem to think of this as
"free power" and that it will solve all of the charging problems. What we
know is that it's a trade off and you really need to make some choices if
you want to have regen work for you at all. Most folks want to be able to
motor as fast as possible so they make sure the gearing on their electric
systems is such that they can get optimum propulsion. If this is 5 knots on
a boat that can only sail (because of displacement ratios) 6.5 knots, then
the window for regen is that 1.5 knots of speed. The regen does not kick in
until you get past the point where your motor is set to motor at top speed.
I'm a sailor and I know that being able to sail at my boats hull speed for
any length of time is dependent on many factors and usually doesn't happen -
especially if I am only out sailing for the day and tacking a lot. To be
able to make regen work, the top motoring speed needs to be set lower, and
you need to be able to sail for a sustained period of time at that higher,
constant speed to get anything back into the system. Even then, as you
pointed out, the numbers are not huge. I don't understand the math involved
- I'm the artist and idea person, but I do understand the basic theory as I
explained it above. Regen is a fantastic idea, it's just not the solution
to our charging problems we would love to have.

Sally

On Mon, Nov 29, 2010 at 6:52 PM, Eric <ewdysar@...> wrote:

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@... <electricboats%40yahoogroups.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

?

?

?

?

Probably the best you could do is get the same prop and conversion
efficiency as your system does in delivering electrical energy into boat
kinetic energy. So if you happen to have a damn good prop that gets 65-70%
propulsion efficiency and assuming the other electric-mechanical efficiency
is a decent 80%, we see perhaps 50% energy loss in the electric-to-kinetic
energy conversion.

Reversing this, you'd similarly expect AT BEST, a 50% return energy
efficiency of water energy delivered to the propeller in a generation mode
to your battery bank. Now, as a drive, the prop sends out a water stream
that is significantly faster than the free flow under the boat. Therefore,
cruising at say, 5knots, the water flowing thru the prop might be 8knots.
Since the power is proportional to the speed cubed, the prop driving 10knots
of current will transfer substantially less power than if it is "driven" by
the water with the 5knots of water stream current in regen (assuming
efficiencies were the same both ways, which they aren't).



So say that it takes 2kw from your batteries to cruise at 5kts.

And say that the water shoots out thru the prop at nom. 10kts to do this.

It's arguable that the best you could get in regen at 5kts with the same
prop is about 2kw*(5/10)^1/3, or 125watts.

This is optimistic depending on the prop and the boat.

But with regen we can take the boat largely out of the equation because it's
just a matter of stream flow and prop and prop loading. Someone might want
to explore this for a few typical props used on your sailboats.


-Myles Twete

OOPS.I meant to say: Since the power is proportional to the speed cubed, the
prop driving 10knots of current will transfer substantially MORE power than
if it is "driven" by the water with the 5knots of water stream current in
regen (assuming efficiencies were the same both ways, which they aren't).

-mt





From: electricboats@... [mailto:electricboats@...]
On Behalf Of Myles Twete
Sent: Wednesday, December 01, 2010 11:07 AM
To: electricboats@...
Subject: RE: [Electric Boats] Re: more regen conversation





Probably the best you could do is get the same prop and conversion
efficiency as your system does in delivering electrical energy into boat
kinetic energy. So if you happen to have a damn good prop that gets 65-70%
propulsion efficiency and assuming the other electric-mechanical efficiency
is a decent 80%, we see perhaps 50% energy loss in the electric-to-kinetic
energy conversion.

Reversing this, you'd similarly expect AT BEST, a 50% return energy
efficiency of water energy delivered to the propeller in a generation mode
to your battery bank. Now, as a drive, the prop sends out a water stream
that is significantly faster than the free flow under the boat. Therefore,
cruising at say, 5knots, the water flowing thru the prop might be 8knots.
Since the power is proportional to the speed cubed, the prop driving 10knots
of current will transfer substantially less power than if it is "driven" by
the water with the 5knots of water stream current in regen (assuming
efficiencies were the same both ways, which they aren't).



So say that it takes 2kw from your batteries to cruise at 5kts.

And say that the water shoots out thru the prop at nom. 10kts to do this.

It's arguable that the best you could get in regen at 5kts with the same
prop is about 2kw*(5/10)^1/3, or 125watts.

This is optimistic depending on the prop and the boat.

But with regen we can take the boat largely out of the equation because it's
just a matter of stream flow and prop and prop loading. Someone might want
to explore this for a few typical props used on your sailboats.





-Myles Twete



From: electricboats@... [mailto:electricboats@...]
On Behalf Of Glenn Dennis
Sent: Wednesday, December 01, 2010 10:31 AM
To: electricboats@...
Subject: [Electric Boats] Re: more regen conversation





All

I was disappointed to learn that regen would not "completely solve all
problems" ;-) But as I read the last post I wondered, has anyone tried a
different ratio for regen sort of a two speed trans, one for propulsion and
one for regeneration. Wouldn't be that hard to fab up, but would it work?
I'm inclined to think not, in that there is only so much force being exerted
against the prop by the water flow.

You could get the motor to turn faster with a small resistance or the motor
to turn slower with large resistance, which would produce more power?

Thoughts?

Glenn
--- In electricboats@...
<mailto:electricboats%40yahoogroups.com> , Sally Reuther <smreuther@>
wrote:

Eric,

Thanks for adding this clear explanation concerning regen. I've found the
people who are asking us about regen under sail seem to think of this as
"free power" and that it will solve all of the charging problems. What we
know is that it's a trade off and you really need to make some choices if
you want to have regen work for you at all. Most folks want to be able to
motor as fast as possible so they make sure the gearing on their electric
systems is such that they can get optimum propulsion. If this is 5 knots

on

a boat that can only sail (because of displacement ratios) 6.5 knots, then
the window for regen is that 1.5 knots of speed. The regen does not kick

in

until you get past the point where your motor is set to motor at top

speed.

I'm a sailor and I know that being able to sail at my boats hull speed for
any length of time is dependent on many factors and usually doesn't happen

-

especially if I am only out sailing for the day and tacking a lot. To be
able to make regen work, the top motoring speed needs to be set lower, and
you need to be able to sail for a sustained period of time at that higher,
constant speed to get anything back into the system. Even then, as you
pointed out, the numbers are not huge. I don't understand the math

involved

- I'm the artist and idea person, but I do understand the basic theory as

I

explained it above. Regen is a fantastic idea, it's just not the solution
to our charging problems we would love to have.

Sally

On Mon, Nov 29, 2010 at 6:52 PM, Eric <ewdysar@> wrote:

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@...

<mailto:electricboats%40yahoogroups.com> <electricboats%40yahoogroups.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

Myles

Thanks for the explanation.

But which would be more efficient, turning the motor faster or slower with more resistance?

Glenn

From: electricboats@... [mailto:electricboats@...]
On Behalf Of Glenn Dennis
Sent: Wednesday, December 01, 2010 10:31 AM
To: electricboats@...
Subject: [Electric Boats] Re: more regen conversation

All

I was disappointed to learn that regen would not "completely solve all
problems" ;-) But as I read the last post I wondered, has anyone tried a
different ratio for regen sort of a two speed trans, one for propulsion and
one for regeneration. Wouldn't be that hard to fab up, but would it work?
I'm inclined to think not, in that there is only so much force being exerted
against the prop by the water flow.

You could get the motor to turn faster with a small resistance or the motor
to turn slower with large resistance, which would produce more power?

Thoughts?

Glenn

From: Dave Kellogg
Subject: Re: [Electric Boats] Re: more regen conversation
To: electricboats@...
Date: Wednesday, December 1, 2010, 9:10 PM

?

Regen has always been a controversial subject here on this forum and will continue depending on which position you take.. ?I personally can't give you exact percentages on what would be acceptable for all of us, it depends on what we need in our own application. ? We work with trade offs in each case and as we all experiment within our own budgets and expertise we will find the groove we can accept.. ?and the tradeoff's we can live with, so, we keep plodding along and sharing what we learn, that's what is the most exciting about this group.. ?Dave K

---

From: Eric
To: electricboats@...
Sent: Wed, December 1, 2010 3:03:43 PM
Subject: [Electric Boats] Re: more regen conversation

Myles, your numbers look good.? I have noticed that most prop manufacturers use a 50-55% "slip" factor in determining the proper pitch for displacement auxilliary sailboats, so your 65-70% prop efficiency may be a bit optimistic for many of our conversions.

One problem in tuning a prop to maximize regen will decrease it's drive efficiency.? Since I'm personally more interested in drive efficiency to maximize my powered range, then I'm will to accept less regen.? You have clearly demonstrated why regen is limited due to the different water and prop speeds, so adding 20% to regen efficiency could make a small difference, but if came at the cost of 20% drive efficiency, it looks like a losing proposition to me.? Others may think differently...

Fair winds,
Eric
Marina del Rey, CA

Eric,
Your slip factor seems unnecessarily pessimistic, at least for driving forward. I have no experience with regen. Perhaps you are using slip factor for reverse which may simulate regen. See for estimates and formula. They suggest 6-10 percent which agrees with my experience with my Torqeedo 801 on an easily driven very light hull at nearly hull speed.
Ned

On Dec 1, 2010, at 3:03 PM, Eric wrote:

Myles, your numbers look good. I have noticed that most prop manufacturers use a 50-55% "slip" factor in determining the proper pitch for displacement auxilliary sailboats, so your 65-70% prop efficiency may be a bit optimistic for many of our conversions....


Fair winds,
Eric
Marina del Rey, CA