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Added 02/27/04

As my A-4 ages more and more, I am really thinking about switching to electrics.  I
have found an electric motor that will push the boat at hull speed, however the
manufacture suggested 8-10 standard batteries would give me about a 4 hour
running time.  As I am often having to motor for longer periods, I need to up this
amount of time.  For starters could I get more juice out of golf cart or rollsroyce
batteries?  Since I do not have a generator and am trying to avoid getting one, I need
something to recharge the batteries while underway.  I am thinking that a wind
generator is the answer but have no idea on what I could expect as far as generator
output and how long it would take to charge batteries.  I guess I should tell you I have
an 8.7.  BTW the motor I found will recharge the batteries while undersail but I do not
know to what degree.

Sam, the one to ask about electric propulsion for a Columbia is Chris McKesson. He´s done it for his C_36. Maybe you can find his posts back in the archives
 john

First the good news:  I have electric drive in my C-36 and it works fine.  We have sailed boat the length of the west coast from Canada to Mexico and this system has been fine.

Now for the bad news:

To push an 8.7 at hull speed you are going to need about a 4kW motor, like the ADC A89 or K91 or the new E-Tek.  You will probably wnat to run at 48VDC.  At hull speed you will be pulling somewhere between 75 and 100 Amps out of the batteries. Assuming a steady load of 3kW for propulsion, you can quickly see how much battery capacity it will take to steam for a given length of time.  FOr example, if you want to have 8 hours of range at that speed, you will need 24Kw-h of battery capacity.  A standard golf cart battery holds about 1 kW-h of stored energy at the 20-hour rate.  To get 1 kW-h at an 8-hour rate you;d probably need two golf cart batteries.  To get 24 kW-h you are going to need 48 golf cart batteries.  Wow!

 Onward to the solutions:

(1) Slow down.  We normaly run our C-36 at about 1 kW total power, versus the 3 or 4 kW we were just talking about.  At 1 kW we make about 3 knots through the water.  Half the speed, but only a third of the power, so as you can see the "mileage" will get better.

(2) Go hybrid.  We only have about 10 miles of range on batteries on our boat - or less.  But if we need to motor for a long time we fire up a quiet Honda generator and plug the shore power cord into it. The generator will steam us at the same 3 knots all day.  We carry 5 gallons of gasoline for the generator, which is about 24h of motoring.

Chris McKesson

Chris,

I am following this discussion from afar. I hope my Atomic-4 will be with me for many years (just converted it to fresh-water cooling so you see I am serious about this) but at some point I will have to look for alternatives.

I really like the hybrid idea. Two questions:

1) did you think about a diesel generator instead of the Honda? I know it is noisier, heavier and more expensive but how much of each of these?

2) are there situations where you need more power than 3KW (or whatever your absolute max is now)? And by 'need' I mean 'need critically'? I remember last year when we steamed head on into what we later learned was a Beaufort 9  gale. I wouldn't have wanted to have one half horse power less than our diesel provided (this was not my boat but a charter). I doubt that we could have made headway with 3kW (how much is that, 5hp or so, right?). And we HAD to  make headway, to get into the protected anchorage, and to skirt some nasty  rocks on the way.

-Ernst


 

Good questions Ernst:

I would love to have a diesel rather than the Honda.  Were I rich, or were I designing this system for a client, it would definitely include a below-decks diesel generator.  The issue for me was entirely financial:  Honda at $800 for 2.5kW, versus diesel for about 5x that.
 Power level:  Yes our system is a calm-water system.  Our greatest crisis regarding power was one time landing at the San Diego Harbor Police transient dock.  We had an unexpected breeze up to about, oh maybe 20-25 knots from dead astern.  We also had, unbeknownst to us, kelp around the prop.  On entering the slip I was unable to stop the boat.  She kept sailing forward under just the windage of the dodger, despite my being in reverse gear and throttle to a full 125 amps.  We T-Boned the main dock pretty good that time!  Oh well!

 We do not steam into gales.  We do not have the power to stem a 5 knot tidal stream.  We do not have the power to motor against a 25 knot headwind.  Any of those situations would require us to either (a) sail (b) anchor or (c) wait.  And we have indeed done all of a, b, and c.

To understand why we are ssatisfied with the 3kW plant you have to understand that we come from a background of engine-free sailing.  So the electric drive is like an amazing gift:  We don't have to paddle the boat into the marina anymore - wow!  By contrast, if you come from a foundation of 5hp/ton, and your sailing skills and habits are based on reliance upon mechanical propulsion, then the 4kW motor wil be certainly insufficient.

That said, let me also hasten to state that most boats use only a tiny fraction of their installed power.  I have a lengthy essay on this somewhere, but I won't burden this message with it.  Let me simply state that a typical C-36 is very rarely taking more than about 10 hp, even in adverse conditions.  Here's the test for a diesel boat:  Can you Black Smoke the engine?  If, even in a gale at full throttle, or tied into the slip at full throttle, the engine still doesn't put out black smoke, then odds are that you are not getting 100% power out of that engine.

So a Rich Man's hybrid drive for a C-36 would involve something like a 5 to 7 kW diesel generator, a slightly larger battery bank, and of course a slightly larger motor.  The price of such a system would then rise to approach the price of a conventional disel drive.

Best regards,

Chris McKesson, PE
Naval Architect

Thanks, Chris, for your clarification.

I admire the sail-only approach but I don't think it is practical for me. I definitely do not have the skill level required to sail into my slip (which is a tricky one but, honestly, I wouldn't trust my sailing skills to dock under sail routinely  even into a simple slip).
Anyway, what piqued my interest even further is your last statement, that a n 'ideal' diesel-electric setup (with diesel generator and sufficient horsepower) 'approaches' the cost of a standard diesel propulsion. To me, it seems that such a system is far superior  to a standard installation. In no particular order;

1) For instance, placement of heavy/large components (genset, batteries) ca n be basically anywhere, with the only exception of the propulsion motor itself which is relatively small.

2) Things like engine alignment should become essentially a trivial task.

3) There is redundancy built into the system: if the diesel fails, there should still be a couple hours of propulsion in the batteries. (OK, if the electric motor or controller fails, this is not true but I would imagine that this is less likely than for a combustion motor).

4) The advantages of having a genset on board (for running an A/C if desird etc). Whether you want to use it or not is a different question but it comes for free...

5) You _can_ use the genset but you don't have to. So, if you want to glide  out of your slip silently, using just the power in the batteries that has been put in there by a charger (or even wind/solar power) you can. For my typical daysailling outings, this would apply in 95% of all cases.

6) Possibility of using regeneration (plus solar/wind power as mentioned). If the cost of such a system is comparable (or even less, as you seem to sa=y), then it seems the only disadvantages would be

1) the added level of complexity

2) additional weight and need for space for the batteries (assuming the diesel genset is comparable in weight to a diesel propulsion engine).

Am I correct so far?

Ernst
   

Jay you might look at inverter/chargers.  They are often found in 24, 36 and 48v models.  They are expensive, but if you have a use for an inverter anyway, then the combined unit may price out as competitive versus buying two separate items. 

I am planning to upgrade SUNDANCE to a 48V drive system, so I have been looking at the Xantrex SW4048, or the much less expensive unit from Tripp.  Tripp also makes a 24V version which is about the sameprice as a charger alone.

Chris McKesson

PS:  Thanks for that link to Cruisenews.  I was surprised to find SUNDANCE listed!

John,
many years ago I used the same idea ( small drive components, remote placings, etc) when I used a Wankel power unit with a Vickers hydraulic pump to run a small seven ( or 5) cylinder hydraulic motor which was deep in the keel of my T/4. It allowed a nearly horizontal drive line, and thus a smaller, more efficient
prop set-up. the Wankel was remote, with just two hoses to be run, letting me keep the little monster on it's original lines.  it raised my IOR rating slightly, but the prop allowance more than compensated. Too bad no- one had at that time solved the seal problem
 inherent with the Wankel design.  Mine was built by Fichtel und Sachs, the original Wankel producers, I think. had to replace the center section every twenty or so hours.
of course, on that Lapworth design, a conventional diesel  (or gas) or outboard installation would have been a true disaster, both in terms of weight and drag. I'm staring at a trophy on my wall  it reads "PMYC hors d'ouevre race  sept 5 1976 first place"
We had to sail a twenty mile triangle race, while preparing, simultaneously ,specialty "horse doovers" which were judged by the race committee at the clubhouse after the race NO cheating, we had to hand them over at the finish line committee boat! Try crouching below in a T/4 on a roaring spinnaker reach whilst
trying to handle a frosting bag and retain your composure while deckhands dump wet sails on you and drag highly flammable nylon over the alky stove!
Our ladies had TRUE GRIT!
Cheers
Dr Dave
 

Ernst, even the propulsion motor could be placed anywhere if you used hydraulics to power the electric motor... Soome boats have been designed with the diesel engine situated at the boatg´s center of gravioty, with a hydraulic pump driving the prop shaft (slight loss inb efficiency compared to direct drive, tho)
 john
 pampero iv

 Very interesting concept with the electrical engine reconfiguration.  I am wondering the same as probably most of you are.  What are the long-term costs and disadvantages of the electric?  As a cruiser, again the ability to use my generator and not generator and diesel saves room but I think I would loose it in battery space.   I am going to look into this with a critical eye and calculator and see what the advantages are: for a 41-45' going out
on the weekends and a few weeks a year on extended cruising, will be.  It appears on the surface to be that the extra battery capacity will drive my electric needs better than the standard 1 motor-2 house system.  Bonus, when under electric sail, the wife can take her nap down below and not be angry from the engine noise.  But how long the batteries last will be an issue before they need recharging.

Jay, thank you once again for your wonderful references.

How is bio-diesel keeping your engine going? Where do you get fuel? I have an old but (so far) reliable Westerbeke, and like you am thinking of the time when it gives up the ghost.

Caspar

Caspar,

biodiesel has greater lubricity than regular diesel.It creates and leaves significantly less carbon deposits, even when used as a 10% blend.

My valves can no longer be ground and the valve stems "slop" a little, the lower carbon will make the last valve job last until the death of the engine, probably 3 times longer than
on straight diesel. (I could get the head machined and new seats and valves "made" for the engine but,...) The greater lubricity is helping out the marginal rings and scored cylinder walls, My injector which would occasionally stick, now runs free and my fuel pumps which used to bounce all over the place with pressure readings are much more consistent.

The head gasket which used to "blow" a little oil under heavy load doesn't anywhere near as much. (the head gasket is only available as part of a rebuild kit)

I bought 5 gallons in Seattle and trucked it north for use as a 20% additive. It's available from two places, the manufacturer and one Chevron.

Dr. Dan's Alternative Fuelwerks:  912 NW 50th St.
(206) 783-5728

 Bellevue Chevron:  1607  145th PL SE
(425) 641-1531   5AM-11PM
Immediately, the engine became quieter, smoother and made more power, (5.5 knots vs. 5.1 knots at full throttle,no other changes).

It also seriously reduces the "diesel" smell from raw fuel and the exhaust. The exhaust no has a "popcorn smell"and the raw fuel smell is faint.

I do have to use starter fluid to start the diesel, ( no glow plug) so the fuel is a little harder to start than straight diesel. The fuel mix is much more prone to "gelling", but here it's not so much of a problem.

In my case, the cost for parts to rebuild my engine are the same price as a new 9hp Bukh with Saildrive.

Da plan is to limp the engine along long enough to replace it with an electric/regenerative on a saildrive, recharging from solar and shorepower. I only use the engine to get out of the marina, the occasional pass, power through lulls on a day sail or schedule and set the anchor.

Between the regen, the solar and shorepower, I figure I'll have more than enough power for my use, and as I'm looking at replacing a 9hp diesel with a 10 "hp" electric, I should have more than enough power for my needs.

Chris is constrained in power output by his prop, and his motor/voltage combo. At even "full" electric power he is "underpowered" when compared to the typical auxiliary,
where I will actually be "overpowered", but have no plans to use that power.

Just to clarify:  I am not constrained by my prop, but only by my choice of motor and voltage.

That choice, in turn, was constrained by financial considerations.

Chris

PS:  I do wish that the E-Tek motor had been on the market when I did
SUNDANCE's system.

Chris,

could you not swing a bigger prop at the same rpm/amp use for more speed and power?

This electric stuff is all new to me, but fascinating. Would an E-tek power a  C-36? To what extent? What size generator are you using/would you use for an E-tek?

Caspar Davis
C-36 Bon Aire
Victoria, B.C.

Probably true in a theoretical sense, but not practically, for a
variety of reasons:

First, peculiar to the C-36 is that there is practically no limit on prop size due to the underwater arrrangement.  So this means that we are able to swing a pretty big prop anyway, since there's no reason not to.  I am swinging a 16inch three blade right now.  I removed the 17 inch two blade which we have used for the last several years.  I
removed it only for a most bizarre reason:  I needed to clean it, and it was easier to remove it and replace it with one that was already clean, rather than just clean the one aleady installed.

In general a larger diameter propeller will be a more efficient propeller, but this is only a general rule of thumb.  A similar rule of thumb is that the minimum total blade area results in the most efficient propeller, but this "rule" is even more limited in application than the diameter rule.

[[Since I know that you like to understand the physics of the thing, the issue with blade area is that blade area equals friction which equals "wasted" torque on the shaft.  But if the blade area is too low the water can't absorb the thrust.  I always like to think of a bowl of Jell-O:  If I put the spoon in it and move it gently I can use the spoon to push the bowl all around the table.  But if I push real hard the Jell-O will tear apart, and I will end up with a
spoonful of dessert.  The same situation applies with water, but the 'tearing apart' phenomenon is called 'cavitation.'  So the goal is to minimize the propeller's drag due to blade friction, but keep the thrust loading low enough that we don't induce cavitation.  In
commercial ship design we normally design for about 2% back cavitation.

The next major parameter is the RPM.  See, that blade friction that I spoke of will increase as the square of the blade's speed through the water.  And, ingoring the boat speed, the blade speed through the water is directly dependent upon the RPM.  So double the RPM will
produce double the blade speed and this will produce 4x the blade
friction.  Better to "slow that baby down" to reduce the torque.  But....If I slowed it down but kept the diameter the same, then I'd have to take the pitch way up, and by taking the pitch so high I'd run into that cavitation limit again.]]

But the reality of the matter for small boat props is, that as long as you are not squeezed by something like a too-small prop aperture, and as long as you are not running at a non-optimal angle of attack (i.e. RPM/HP match point) all small-boat props are pretty close in
total efficiency.  Probably something around 60% I'd say.

So why am I saying that this is so much simpler, when most diesel guys know about the hoops they have had to jump through to find the right wheel for their Kubota?  Because of the unique HP/RPM curve of a shunt-wound DC motor.  See, for most diesels we can pretend that the HP of the engine at full throttle will vary linearly as RPM-cubed. 
So if we are trying to run at, say, 5 knots at 10 hp at 2000 rpm, we
have to find a prop such that at 2000 RPM, the angle of attack corresponding to 5 knots of boat speed also corresponds to 10 hp of input power.  And this is quite a sensitive issue.  I think the aviators will chime in to tell us how improtant 5 or 10 degrees of angle of attack can be for a wing's overall performance...or for a
prop's.

Once you match them it's ok, because a screw propeller also has a cubic speed/power relationship, indeed the engine manufacturers even call this the "prop law curve."

But the Shunt-wound DC motor will produce, at full throttle, its full rated HP at any RPM.  So a shunt-wound motor will match to any prop.  In effect, the shunt-wound motor will deliver the power regardless of RPM, and will not "force" the prop to run at a non-optimum RPM.

Cuation:  Be advised that your E-Tek motor, being a permanent maagnet type, does not have this characteristic.  (It has many other highly desirable characteristics - this is not any sort of slam on the motor!)  This means that you will have to do the normal propeller
selection process. 

Well...whew...I didn't intend to write so much and really ought to go back to work (writing about fuel cells for possible application in naval combatants...)  I hope this was helpful - I suspect I've muddied as much as I have clarified!

Chris

In haste, since I oughtta be at work...

Sure it would.  I'd have to look at the specs but I think we want to run at 48V.

I'm running a Honda EU2500i 2.5kW gas engine generator, and it will drive my 36VDC charger at about 40 amps, which is to say it will drive my boat at about 40A, which is about 2.5 knots in calm water (in heavily overloaded liveaboard configuration.)

I keep getting sucked into the "More Power" camp, so my wish listincludes moving up to 48 VDC, and I even daydream about moving to the 3500 Watt Honda...

Chris

I'm sorry Jay, I made a hash out of that discussion of propellers. I'm sorry.

You are correct:  A larger-diameter slower-turning propeller will always be more efficient than a smaller/faster prop.

There were no errors of fact in my message, just a hash of presentation.  I think my point was that I'm already turning a pretty big prop for a 5hp input.

But gee, it might be fun to try to find a 28-inch skinny two-blade (looking like an airplane propeller) to play with!

So:  You're right:  Bigger is always better.

Chris

PS:  There was one error of fact:  What I said about electric motor torque characteristics applies to Series Wound motors, not Shunt Wound motors.  I got my S's mixed up.

 
I also was interested in electrical propulsion for my boat, a C-28.  It's pretty pricy though if you want to go with full propulsion. Chris's answer is the most practical for most of us on this list who don't have a ton of money to spend.

I read an article on a larger boat with exclusive electric propulsion.  It provided for regeneration so that when the boat went down a wave while motoring it would charge for those few seconds and also charge when sailing on wind power.  The author of the article
stated that they returned to port with a bigger charge than when they left.  If I remember right the price tag was upwards of 20,000 for the system installed.

I believe that Lynch was the company.  You can search the weve for it.  They called one "Supermotor"  I just searched for "Lynsh Supermotor" and got a hit with pictures and diagrams.

I believe that you could have your motor generate and recharge batteries while wind sailing by using a permanent magnet DC motor.  I even thought about mounting one with a v-belt connection to the shaft to allow both electric and combustion engine propulsion.  I assume
that the electric motor would act as a generator in such an arrangement.  I have no idea if the practicalities would allow such an arrangement, but it was just a thought.

I have saved some info from Lynch about the topic, but it is in digital format and I wouldn't be able to put it on this sight.  I just looked breifly at this stuff and lynch has an electric outboard which might interest some.

Art Albertson