Giving serious consideration to....

[Genesis]

I should be careful here not to put words into FEYS' mouth but I believe their new approach involves a direct (coaxial) connection of the motor to the prop shaft, eliminating the gearbox. Of course this moves the engineering compromises over to the motor design which is no longer "off the shelf". I believe the earlier earlier approach used a gangable gearbox from Siemens, and that wa$ an expen$ive component.

I don't think I like that change one bit.

One of the attractions of the FEYS design was the relatively small size of the individual motors due to the gangable nature of the drive. This made removing a failed motor feasable, allowing you to run on the remaining units (with less total power of course)

A single motor removes this capability.

 

[MikeP]

The one thing I don't understand about the concept is that it seems to me it goes through several energy conversion processes. A diesel engine converts fuel to power to spin a generator whcih then generates power to run the motor. But there are inherent losses in every process. I realize it must work or it wouldn't be done but I don't see how it's more efficient to do this than to just turn a prop with the diesel engine. It seems like free power and that isn't possible. So how does it actually provide more power for less fuel?

 

[Genesis]

The one thing I don't understand about the concept is that it seems to me it goes through several energy conversion processes. A diesel engine converts fuel to power to spin a generator whcih then generates power to run the motor. But there are inherent losses in every process. I realize it must work or it wouldn't be done but I don't see how it's more efficient to do this than to just turn a prop with the diesel engine. It seems like free power and that isn't possible. So how does it actually provide more power for less fuel?

Hehehehe.... yep.

Damn pesky laws of thermodynamics.

That was what I nailed the FEYS guys with as well. They were claiming that I could remove my 1000 HP (two 500HP engines) and replace it with one 700HP motor, and get the same performance with better fuel economy.

That perked my ears - and the hair on the back of my neck - right up!

They kept coming back to "more efficient torque curve" as their explanation. My counter is "torque accelerates you, but horsepower moves the boat." They ALSO said they'd be approximately the same price to repower with their system as with a conventional pair of diesels.

We hashed this out with them unable to satisfy me that they were right. So I told 'em that I might be interested in their system BUT I wanted both a fixed-price quote AND a written guarantee backed by both their company and corporate officers (personally) that should the system NOT provide the same performance (they were welcome to come verify the speed of the vessel prior to the repower, in person, on deck) that they'd replace the FEYS system with two new conventional diesels, to be agreed upon in advance of the job (e.g. QSM11s + gears) at their expense.

Things got REAL quiet after that.

It should have been easy, to be honest, if they're anywhere near right. They'd be removing two thirsty Detroits and replacing them with one common-rail engine. That alone (going from the old tech to new tech engines) typically results in a 20-30% fuel economy improvement! As such meeting the conditions of that should have been a no-brainer - unless they were concerned they'd not hit the speed numbers....

A few months ago I emailed them for an update on the status of their system and its installations (their web page hadn't been updated in a loooong time.)

That drew NO response.

I think they remember me.

 

[Avenger]

Geez Karl, you're a tough guy when it comes to guarantees. You want your rebuilt engines warranted for life and a repower and upgrade on the failure of your diesel-electric installation. No wonder you do all of your work yourself!

I love these mental excercises in engineering. Are you thinking AC or DC? Have you considered belt drive instead of gearboxes? I know, not as neat, but much simpler to make. If I were doing it with gears I think I'd try to do a ring gear and pinion type gearbox for multiple motors instead of that bevel-gear design. Keeps everything in a straight line, and preserves the ability to use multiple motors and swap them out independently. As far as direct-coupled, why would the motor be non-standard? You'd put a coupling on the shaft of a standard motor, or did you have something different in mind.

What kind of layout are you considering? Single engine on centerline? Most of the time when I see these things it's twins or more multiples of the same size so generating capacity can be brought on as needed.

As one of my co-workers keeps telling me "You're as limited as your imagination." And I keep replying "and your bank account." So what's your plan?

 

[Genesis]

I'm not sure yet on AC .vs. DC, but am leaning towards DC. Both have advantages. DC used with PWM controllers can be small for their output and very efficiently cooled, since the windings are against the case and they're inherently brushless.

The problem with a single big motor is the size and weight of the motor! Not trivial to work with at all. Of course gearboxes have their problems too....

I'm still in the "thinking about how I want to approach this" stage.... but my gut says one big engine on one side, with the other holding the smaller (house/genset) engine and the dive gear, which is likely to be as heavy as one of the engines (gas storage bottles, etc)......

This is very much a "thinking project" right now as opposed to one reduced down to an operational plan (yet)

 

[labrador]

Karl, It's not just you they ignore! I emailed them at least 3 times with no response. I think it's a great concept and really wanted to explore more however as stated above never rec'd any response at all.

 

[Avenger]

This is very much a "thinking project" right now as opposed to one reduced down to an operational plan (yet)

That's why I use the term "mental exercises." Please keep us posted, it sounds interesting.

 

[tomrealest]

Back to the Yachtfish
I don't dive but a previous owner of mine had a compressor under the cockpit and holders for tanks.
Some do have 14 ft ribs with 40 or 50hp 4 strokes.
We take our YF over to the Bahamas and do snorkeling and love it.

 

[jim rosenthal]

Is the FEYS system the one that was recently written up in Passagemaker Magazine? Someone has a lot of hours on a boat with that system, which seems to be working well. However, it is not a planing boat, and doesn't weigh what a Hatteras 45C weighs....
I think the reason that a D/E system is more efficient is that electric motors convert electricity to rotational motion more efficiently than diesels convert fuel to rotational motion. Also, the use of a diesel engine to generate electrical power is probably more efficient than using it to turn a propeller. With that said, I don't think the D/E system is orders of magnitude more efficient than diesel inboards, especially since you are turning an old-fashioned propeller which limits efficiency. Now, if you were talking about a system that included adjustable-pitch propellers, that might make more sense. But all of these things add complexity and will break sooner or later, not to mention costing more to begin with.
A few years back, someone in PMM did the math and found that a trawler yacht was actually cheaper to run than a sailboat, if you looked at the cost of sail replacement etc etc. Plus if you value your time getting someplace at any vallue above zero. However, I wonder at what point in the rise of diesel fuel prices the comparison breaks down. We must be close.
I took my boat out this afternoon to get some time on the water, watch the cooling system (no rise in temp!) and just generally decompress. I was out for about an hour or two. That was probably a seventy dollar trip. I better not do this kind of math too often....

 

[Genesis]

I don't get PMM, so I don't know...

Problem is Jim you can't get away from turning energy into rotation with the diesel - you have to turn the generator end!

There are REAL advantages though if you have a system which has two engines with one matched to low-speed running and one matched for high, with "maximum" allowing the use of both. An engine running around 70-80% of capacity is more thermodynamically efficient than one running at 5-10%, because the parasitic losses are minimized as a percentage of output. So there are pretty significant gains to be had there over just throttling back on a big engine.....

 

[SKYCHENEY]

In 1996, I replaced our old limestone crushing and screening plant. The old plant had diesel engines on all of the crushers and the new plant was all electric. I will say that the new plant is much more efficient and cheaper to operate. There are no oil changes or engine rebuilds and an electric motor will last much longer before rebuild (and the rebuild is cheaper than a diesel). The difference here is that I buy power from an electric company, I don't generate it myself. If I had to generate the electric, I don't think I would see any benefit.

Question--how do you control the motor speeds? My plant has up to 350hp electric motors, but they are constant speed motors. I have a 40hp with a VF drive, but even on a motor that small, a variable frequency drive is very, very expensive.

 

[Genesis]

Question--how do you control the motor speeds? My plant has up to 350hp electric motors, but they are constant speed motors. I have a 40hp with a VF drive, but even on a motor that small, a variable frequency drive is very, very expensive.

The general scheme works something like this....

When a generator engine is running, it is running at either idle or a constant speed (e.g. idle or 1800 RPM.) A controller chooses between those two, and the governor on the engine provides the proper fuel for the load.

With a brushless DC motor, the amount of power the motor consumes is directly controlled by the electronics. The exact position of the rotor is known via (usually) an optical encoder. This allows the electronics to feed the windings very precisely so as to produce very little torque, maximum torque, or anything in between irrespective of the rotor's speed. The windings are all on the outside (stator) and thus are easy to cool since they're up against the case.

The usual scheme is to use high-power FETs to drive the motor windings. These are driven in a PWM mode, so they're either "on" or "off", keeping dissipation within the semiconductors reasonable and cooling achievable. Protective circuitry is put in place that senses the in and out current to the motor; if there is an imbalance (e.g. any path for current other than through the motor windings) the system trips and turns itself off. These circuits are fast enough to prevent you from getting shocked if you were to bridge the output across your body.

So as the power demand increases, the governor of the engine draws more fuel. If you are dealing with a multiple-generator setup the control system is programmed to bring additional generator(s) online as required as one engine approaches maximum capacity.

You can do the same sort of thing with a VF drive, but the circuitry is actually more complicated than a brushless DC motor controller, and you run into serious cooling problems with AC motors due to the requirement for a wound rotor. Ideally you want to avoid rejecting heat into the engine room in a boat for obvious reasons.....

 

[SKYCHENEY]

okay, so in a DC motor setup then the generator is a DC generator?

 

[Genesis]

Not necessarily; there are multiple ways to skin that cat too. One of them is to use what amounts to one of the brushless DC motors as a generator (but larger of course) and use electronics once again to take the power off (since what you will get out of the stator is a not "clean" DC by any means!)

The trick is all in the electronics.....

 

[chris]

Hello
Just curious as to how all of the electronics would hold up in a marine or salt air environment. Seems like more chance for something to go wrong.
Chris

 

[Walter P]

Karl, Some years ago I toyed with the idea of playing with a Diesel/Hydro set up on a scaled down stern wheel river boat. We had various designs done up by a marine eng. and naval architect.. It was to have a single diesel (65 hp) engine running a hyd. pump which supplied the power to two small hyd. motors on each end of a common shaft with a split paddle so that each side ( Port and Stb) could be controlled by a flow valve independently of one another. The problems were many but most were resolved and the system is actually being used on many current stern wheeler dinner cruisers today. For a small (42 ft) boat it lost efficiency. Perhaps a new look with electric motors instead of the hyd. units would work better and with less hyd. pump whine. (one of many problems). Do you think hyd motors instead of electric for your proposed project might be viable? Your thoughts please..

Walt

 

[MarioG]

Karl,

you would like reading this:

"Now Pacific Asian Enterprises has taken the lead in adopting an advanced Siemens-developed version of this proven propulsion system to large yachts in the form of a proof-of-concept diesel-electric Nordhavn 72."

http://www.nordhavn.com/constr_con/diesel_electric.php4

 

[MikeP]

Pretty good article! It echos Karl's comments about having two motors, a low and a high speed which keeps the genny in the best RPM range for efficiency. considering that, it starts to make some sense to me. Nordhavn noted the same issues with something for nothing so it's well done. Neat stuff and possbly something we can take advantage of in the future.

Hey interesting things are happening! I mean, whoever thought you could (or would want to) run Windows on a Mac?

 

[Genesis]

Yep - that's basically the sort of thing I'm talking about

 

[Maynard Rupp]

I still have to reflect on Karl's original comment. My thoughts are simple. If you take a bucket of diesel fuel with a known # of BTU, run it through a diesel engine and a transmission, you convert that fuel and its BTU directly to the prop. If, after you throw it through the engine, you convert it several times, there is always,(always is a bad word), percentage losses along the way. An example is when our gen sets make AC, charge batteries, which makes DC, then someone runs something from an inverter which has converted the DC to AC, etc., the whole mess wastes alot of energy. Now if that electric moter would turn the prop shaft at a constant speed all the time and you adjusted the prop pitch to get the desired motion , or lack of it, that may svae energy and make a smooth operation. Turbo prop airplanes do that.