electric engine instead of diesel

alanderjakob · Nov 10, 2005

There are many ways to approach this. As an engineer I like to make
some calculations to prove my theory. We asume constant propeller
efficiency no matter what type of engine we are using, this is true
enough. This means we have to apply the same amount of shaft power (kW
or hp) to drive the boat at a certain speed.

The storage of energy is the big problem. In an ordinary car battery,
about 20 kg, we can store about 0.7 kWh wich means the ratio engery
per weight will be 35 Wh/kg. The diesel combustion in MD7a gives
3300 Wh/kg. The energy density is approx 100 times higher in disel
than in batteries! Would you like to carry 1 kg diesel or 100 kg
batteries?

/Jakob Alander

gfloderus · Nov 10, 2005

Interesting discussion!

I was watching the site at ASMO Marine and they had a table who tells us
that you approximately can drive a distance of 9 M with a 48 V battery with
a capacity of 150 Ah in 6 Knots. For me its more like a solution for
emergency situations. As they describe on the homepage its perfect for
navigation in harbours. A diesel tank on 30 litres is enough to take you 10x
the distance. But, as always, it´s depended on the circumstances you are
using the boat.

I like the thought of a silent engine, charged by the nature (windmill or
similar) with no leak or smell of diesel. But I will not be feeling safe
with just an electric engine.

Gustaf Floderus
V 59, Sweden

baviaan69 · Nov 10, 2005

I 've been thinking about a solution like that. Never knew someone
actually made engines like that.
Thanks Rob!
When my present petrol-engine (Vire 7 HP, great little engine btw)
dies, I'll install an Asmo.
After all it's been working great for submarines for decades now.

regards

Wolf

dobermanct_dave · Nov 10, 2005

You hit the nail on the head- The old diesel-electric subs I believe had a combination motor/generator and a diesel on the same shafting. Fine if you need to be able to operate without air, but awfully bulky otherwise.

If you only need power to dock, then the electric would be a great solution. But if you find yourself sailing into prevailing winds and currents, then you might find yourself a little flat if you'll pardon the pun...

Dave V2917

rchrdcoe · Nov 10, 2005

-Wolfgang-
Check out solomontechnologies.com. They make a electric propulsion
unit that tey have installed on yachts. Interesting reading.

Richard, V1812-- In AlbinVega@yahoogroups.com, Wolfgang wolfgangamadeusbach@p...
wrote:

vega2438 · Nov 10, 2005

Hello all vegatarians!

How about this Ozecodrive
http://www.ozecodrive.com/OZecoDrive/Eng/IndexOZecoDriveEng.html .
There is at least one Vega in Sweden with it.
When my md6a die, I think that I choose that one or maybe that
danish Asmo.
And when batteries run out of Amps, I have planned to buy ordinaly
Outboard engine about 6 to 8 hp with electricity outlet. You can
also use it with your dinghy. And couple of solarpanels.

greetings from Finland
Kauko Juvonen, Porcella V2438

stevebirch2002 · Nov 11, 2005

Hi

I always put mine in reverse to stop the prop. Been told by clever people
(Brains the size of Norfolk) that due to some physics law the prop turning
by the speed of the boat actually slows it down, better to lock the prop.
DOnt understand it myself but have been promised it is true. Any Professors
etc care to prove it?

Cheers

STeve B

alanderjakob · Nov 11, 2005

I'm no professor, just a plain engineer, but what you say has been
true for a long time now. Recent tests conducted at Chalmers
University of Technology in Sweden has shown very different results.
These are briefly presented in the boat builder's bible "Principles of
yacht design" by professor Lars Larsson who is head of the
hydrodynamics department at Chalmers. He found by experiments that if
a fixed (ie non folding) propeller were completely free to rotate the
resistance would be about 1/4 of the fixed and locked one. Straight
against the old truth! In reality the propeller is never totaly free
to rotate due to friction in the gearbox and shaft bearings. But the
resistance will anyway be significantly lower with a rotating propeller.

It is very important to check with the manufacturer of the reversing
mechanism whether it is happy with a rotating propeller, not all are!

Jakob Alander

maarten_vanemmerik · Nov 11, 2005

ok, let's give it a try:

if the prop is blocked the velocity of the water running along the blade is more or less the same as the speed of the boat, creating some drag. if it starts rotating the velocity of the water running over the blade increases, depending on rotation speed and distance from axle. this creates more underpressure at the back of the prop blade, which pulls back the boat. think of the prop blades as little wings that obey to the same laws of fluid and aerodymics as sails or airplane wings (bernoulli's law for dynamic pressure due to velocity).

it is the same principle of a helicopter with a stalling engine (or autogiro airplanes): if the rotor is left to rotate freely it will spin and create so much drag that the helicopter can land safely. if you would block the rotation of the rotor while in mid air you would experience a noticable decrease in drag resulting in more speed (albeit not desired in this case). another example is a mapple seed that falls down slowly because it creates drag due to its autorotation.

fotofundi · Nov 11, 2005

Take a look on http://www.electric-boat-association.org.uk/ they have
a lot of knowledge and experience of electric powered boats. I thing
you will find that you still need some sort of shore/petro/diesel
power source to maintain battery charge or to power a suitable
electric motor direct. Wind or solar sources alone would have to be
HUGE to deliver enough amps to keep an electric motor of a size
suitable for the Vega running.

David
V1696

pjacobs55 · Nov 11, 2005

My main concern is to avoid unnecessary wear and tear to the gearbox,
stuffing box, and cutlass bearing. Unless racing, I don't think the
difference in speed (either way) would make a big difference to short
day-sailing trips. I'll check with the Yanmar mechanic, who is
helping with my new exhaust system, and report back.

Peter
"Sin Tacha" #1331

SVFlyAway · Nov 11, 2005

Actually I have seen some studies that state that a freewheeling prop
creates more drag. This is because it creates a ³ball² of water around the
prop which then has to be pulled through the water. Since this ³ball² is
bigger than the prop alone, there is more drag.

Besides I can¹t stand to hear the gearbox whining when I am sailing.

wxt8981 · Nov 11, 2005

I lock my the prop (shift in reverse) to avoid unnecessary
wear and tear. Letting the prop turn will create LESS drag.
By the way- today I've changed the oil and put grease into
the stuffing box and found out I have a (very) small
leakage. Next friday I haul the boat, clean the bottom, and
put a (rebuilt) stuffing box in (I always have one in
reserve, meaning I'm going to put 2 new rings and the bush
into the one I take out)

Wilhelm, V-257

emmajen5 · Nov 11, 2005

Maartin,

The autorotating rotor on a helicopter is producing lift, not drag and that is what is slowing it as it descends. The blades moving through the air act like wings. Secondly, the freewheeling prop of a boat is moving through the water like an inverted helicopter. The prop is designed to produce forward lift (so to speak) therefore the free wheeling prop is actually helping the boat through the water.

Garry
"Raven" V. 2427

wxt8981 · Nov 11, 2005

Hi Maartin;

there's always drag, the most when the prop doesn't rotate.
There's less drag when the prop runs free- and
theoretically when there's no friction, then there wouldn't
be any drag.

Wilhelm, V-257

jvancraaikamp · Nov 12, 2005

Hello Garry,

I have to disagree with your story.
Normaly you put some energy on your prop with a diesel engine.
This energy will be transfered into a forward boatspeed via a prop.
Once you switch off the motor this process will be reversed so the water is
putting energy into
your prop. As a result of this the prop starts to rotate. Theoretically as
long as the prop can rortate without
any resistance it is no problem. But the gearbox does give resistance so the
prop will absorb energy and function as a brake.
The main issue is whether a prop standing still or a freewheeling prop has
the highest yield. This yield is the difference between
the power that you supply to the prop and the thrustpower that the prop will
give on the water.
You mentioned that a rotor of a helicopter does generate more resistance
when it is "autorotating" (slowing the descend)
So once the prop on your Vega should give extra resistance when it is
autorotating.
I think that there is not a simple explanation for all the vega's.
I think that the shape, size, number of blades and the pitch have big
influence on the results.
If you use a 2 blade and turn it straight behind the keel it will give less
resitance than in a horizontal position.
So you cannot compare that with a 3 blade. The best thing is to test it with
your own ship what gives the best result.
For sailing probably the best solution is the old combisystem or a folding
prop.
But for maintenance, reliability and your wallet, a normal prop is the best
solution in exchange for a little speed.

Regards Jan, Lely 973.

garryms82 · Nov 13, 2005

For the lowest of the low drag fixed blade prop check this one:

http://www.westbynorth.com/CampbellSailer/

The Campbell "sailor prop" has been tested and found to have the least
amount of drag of all fixed blade props. (Practical sailor)

regards,|Garry|

At 08:42 AM 12/11/2005, you wrote:

vega1860 · Nov 14, 2005

I looked into an electric power solution several years ago when I re-powered Lealea. At that time I was informed by several people that the weight of the batteries required would make it impractical for a boat of this size and that cost of installation would be more than for the Yanmar 2GM20 that I wound up with. I'm sure that technology has improved since then so it might be worth pursuing now.

Just my 2 cents worth.

Chuck

"R. Kloosterman" rob.kloosterman@... wrote: