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Old 06-19-2004, 08:50 AM   #1
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Default why no diesel electric in small boats?

I was just thinking about something. Most large non-nuclear powered ships use diesel engines to run generators that actually drive the ship. Locomotives do this too. It saves wear on the engines and gives you more control.

So why don't we see this on smaller boats? I figure boats that are at least 50 feet LOA would be good candidates for this. There would be some weight penalty but boats of this size should be able to absorb that. It's also possible that you could fit smaller diesel engines and get weight back that way. We have generators on boats all the time, so they can't be that hard to fit.

Any ideas?
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Old 06-19-2004, 09:24 AM   #2
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Default Probably cost, weight and space.

I bet having mini azipods would be neat when they figure out how to get the power-to-size problem licked. You could ditch your trolling motor(s) and just use your batteries.
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Old 06-19-2004, 09:31 AM   #3
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Default RE: why no diesel electric in small boats?

Just thinking on the surface, and comparing it to some big generator systems I've designed for power plants (using marine and rail grade engines,) I would think that there are a number of reasons. Cost, space, type of engines required, efficiency, weight, capability of on-board personnel to maintain them, etc.

Cost: The switchgear and gen set will cost more than twice what a smaller engine does. Remember that the engine must now drive a generator. That generator must in turn drive an electric motor that in turn drives the screws. There are also a number of transformers and other electric equipment involved. All that extra equipment cost big $$$$.

Space: Space is at a premium and cost big$$$. Consider that you'll need somewhere in the area of an additional 5 to 10 feet in length. That's about 10 to 20% more length on a 50' vessel (or an additional 25% cost on the hull.) I'd rather have the conventional power set up and another berth, head or bar......actually, a bar sounds nice. LOL

Types of engines: Why did they go to an extra step in the process anyway? Think about...why add all that extra weight, gear, expense, and maintenance requirements? Bigger vessels with diesel-electric have much different diesel engines than the ones you may be thinking of. They needed a LOT of power so the engines got BIG. (Many of those I used in designs had catwalks for the maintenance personnel to reach the upper parts.) These larger and beefier engines are designed to run as long as 20,000 hours (or more) without shutting down. (The thermal cyclic fatigue of starting and stopping on engines that big with that much mass isn't good for them). Also, they are BIG (think standing in the cylinder big) and generally have relatively low RPM's (600 to 900) to reduce wear. They are also designed to run at one RPM, and not designed to vary their speed. (think about your engine driving the prop at idle (say 900 rpm) and then at WOT (say 5,200 RPM). These BIG engines don't do that much of a spread. They like to get up to speed, then stay there, it's not good to try and vary that much mass up and down the RPM scale. So to deal with all these issues, they let the engines run gen-sets and have electric motors spin the screws.

Efficiency: Going from fuel to diesel to screw is bad enough. But think about going from fuel to diesel engine to generator, to switch gear, to transformers, back to switch gear, to complicated controls to motor, to screws. There are a lot of places to loose a few percentage points of efficiency each along the way. You need a pretty big vessel and large power needs before you hit the point where the efficiency curve for these items exceed that of the conventional set up we see in smaller vessels.

Weight: All that stuff is HEAVY. So now you have to haul around a LOT more weight. That takes energy and energy is expensive. Also, the vessel must be built much beefier and stronger to carry that extra weight.

Maintenance: This stuff can be rather maintenance intensive. Most vessels in that size range don't have a full time maintenance staff at the call (industrial electricians, mechanics, ships/maritime engineers, etc. to keep things in operation.

I may be off on some of my assumptions, but I'm probably pretty close overall.
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Old 06-19-2004, 09:38 AM   #4
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Default RE: why no diesel electric in small boats?

There was an article in Passage Maker about a trawler in the Tampa area that was just converted from twin diesels to diesel electric. The boat sat higher in the water and used MUCH less fuel. The boat was around 45 feet in length. I would say that you will start to see more boats with this power combination in the future. The great thing was that the full amount of torque was avaliable at idle. With combustion engines you don't get that until you get into the mid to upper RPMs.
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Old 06-19-2004, 09:39 AM   #5
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Default RE: why no diesel electric in small boats?

So what about the new electric hybrid setup we're seeing in cars now? Would something like that not work in a marine application? Seems like that might be worth trying simply for the increase in range you could potentially see...
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Old 06-19-2004, 09:46 AM   #6
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Default RE: why no diesel electric in small boats?

Batteries weigh more than fuel and engine. Cars can coast downhill (not heavy engine loads compared to boats) and have the ground to hold them up, boats need more displacement. Also the equipment costs more. I don't see a break-even point on a large hybrid boat any time soon.

If two worn engines are removed and replaced with a newer high efficiency DG set there may be some associated savings regarding efficiency, maybe enough to cover the added costs if the vessel is used a lot. There are a lot of variables and such when comparing an older worn system with a newer one. But looking at the two alternatives side by side for new planing hulls on say, a 50 foot battle wagon, I'm seriously doubt that you'd gain any efficiency and certainly not enough to warrant the expense and the space you'd give up. If one were to compare the equivalent net present value of the two systems side by side, I'd still think a conventional set up would be the overall winner for non-displacement hulls.
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Old 06-19-2004, 10:03 AM   #7
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Default RE: why no diesel electric in small boats?

This is the guy/firm that was discussed in the Passagemaker article.

If anyone has seen the yellow water taxis in Fort Lauderdale, they're diesle electric.

The military is also developing diesel-electric all terrain vehicles.
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Old 06-19-2004, 11:35 AM   #8
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Default RE: why no diesel electric in small boats?


Ta daaaahh

Now this systems not to be confused with the Fractored Amplitude Reactive Thermistor (FART) drive....OK?

Far from just sounding the part - my system has the guts to leave skid marks in your undies for real..

See if you can get this down in one go... (Coz theres a 20 question test at the end OK?)

Powered Obtuse Overunity Plasmoidal Induction Scalar Electromagnetic Hydrodynamic Caterpillar Drive. (Poop for short )

Heres a little schematic and notes to help you all get the hang of this.

Internal wave structure of the scalar potential

Internal wave structure of the scalar potential (end)

The overunity principle, the secret of extracting and using free energy from the TIME domain using spatial circuits!

This is what it looks like when you build a working model!

Too simple really - just hook up the scalar electromagnetic collection overunity device to my hydrodynamic, plasmoidal induction drive system, and jacks your aunty, (at least she would be if she had balls) - free energy drive system from the TIME domain!

Just remember M = Δ T

Ohh yeah - and always earth the alloy hull and no insulators on dissimilar metal above waterline hardware, especially n a thunderstorm / lightning hazzard area!

You too could end up looking like this!

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Old 06-19-2004, 12:38 PM   #9
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Default RE: why no diesel electric in small boats?

Hmmm...good points. Let me argue the other side (just for fun):
*complexity: boats have so much electrical stuff these days that I'd be surprised if diesel electric was too much worse. Yeah, there's some more complexity because there's no physical connection from the engine to the propeller. Then again, you don't have a transmission. Or, the motors could be considered the transmission.

*weight/size: small, high-torque electric motors are becoming pretty common. The torque advantage is the big reason for using diesels, right? AFAIK, nothing beats electric motors for torque, which is the reason they're used on locomotives. So you should be able to get the torque (power) you need by leveraging the capability of an electric motor and keep the diesel engine smaller. I figure efficiency would be greater since you wouldn't have all the friction losses from the transmission. The smaller engine and lack of a transmission means the weight and size could be a wash. You could also get rid of your genset. You might need a couple more batteries so there's a weight penalty. I don't figure it would be huge though. It would work like a big capacitor for the motors in order to even out the spikes

*control: you can change motion from forward to reverse really easily. You could also do everything through fly-by-wire systems. You wouldn't have the worry about running control cables.

*maintenance: Would the maintenance be any worse than on a boat with a diesel and a separate genset? The fact that the motor is turning in a narrower speed range
should reduce wear. Right? So that reduces the need for maintenance.

Here's an interesting article on the FEYS site:
...and a few more:
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Old 06-19-2004, 03:06 PM   #10
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Default RE: why no diesel electric in small boats?

There was a long thread in BoatDiesel,com last year concerning a company in Texas that was installing diesel electrics in big convertible boats. They made all kinds of claims. The arguments went round and round about maximizing efficiency by using the diesel at its most efficient RPM, using one diesel and both screws to troll, ect, ect. Finally someone from the company chimed in and the argument continued. The most frightening aspect to me was the system was 440 Volts. You better hope the bilge stays dry.

I let my membership in expire and can not go back that far in the archives. It is a great forum but with only a half dozen postings on the Yanmar LHA a year there is rarely anything new. Hopefully that is because they are holding up so well.
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