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Author Topic: Electric propultion (ships)  (Read 9336 times)

Posts: 12626

« Reply #15 on: February 09, 2012, 07:52:12 AM »

The main reason of a diesel electric train is the power, controllablity and reliability of electric traction motors. Without this there would be no diesel/electric locomotives and we might still be using steam. Nothing was ever wrong with power of a steam locomotive but maintenance costs were very high. A few are actually studying a modern clean steam designs with fuel prices climbing and us sitting on basically unlimited coal.

Let's hope the next president is coal friendly. The current one has avowed to shut down existing and future coal fueled power plants through draconian regulation and taxation.

The problem with coal is it is not easy to burn cleanly vs natural gas and it needs regulation to make sure it is. Given free reign they would burn dirty. You cannot depend on them to self regulate. Technology exists to burn it cleanly just not as profitable vs no regs. (and it is all about profit) 3 of the nations dirtiest coal plants are are all owned by same company in Georgia. Do you think they would change/upgrade willingly?  Texas has 5 and Pennsylvania 4. Industry would have far more if you let them. There needs to be a balance here.

Ham since 1969....  Old School 20wpm REAL Extra Class..

Posts: 3592

« Reply #16 on: February 09, 2012, 10:41:25 AM »

Navy is experimenting with solar power technology on ships, as an assist and back up to fossil fuel.  Would allow the ships to save fuel, and possibly avoid being stranded.  In the future, some ships might be all solar and batteries, with fossil fuel an emergency back up.

Posts: 9930

« Reply #17 on: February 09, 2012, 11:12:40 AM »

most of the new cruise ships use azi-pods in the rear and side thrusters up front so they can dock with out a tug.  that saves a ton of money, also the steering and propulsion are both done by the azi-pod so you loose the drag from a rudder.  Some azi-pods have variable pitch props which gives even more control.

I have also seen efforts for better fuel economy on ships, everything from a longer nose bubble, to one overseas car carrier has streamed lined the upper part of the ship for less wind resistance and  better fuel economy. some are even trying out rigid sails to assist the  diesel power.  an Azi-pod also gives you more room in the ship because the power generator can be located most anywhere in the ship, and it does not need a very long prop shaft going through a bunch of compartments on the way to the prop. 

any how, I wonder if you can put a large capacitor across the input to the azi-pods to cut down on RF..Smiley

Posts: 531

« Reply #18 on: February 09, 2012, 11:19:11 AM »

Solar flux is around 1kw/m^2 at noon at the equator, and the panels manage at best around 20% efficiency, so under optimum conditions that is 200W per m^2, probably more like 100W in reality.

If you assume that by the time all the conversion and ohmic losses are out the way you need 1kw per horsepower delivered to the shaft, then even a modest Naval vessel running say a pair of 500HP engines (which really is not all that big) needs 10,000 square metres of panel for full power (Plus whatever it needs to recharge the batteries for night operation).
For limp home or low speed cruise, say 10% of that would get you maybe a few knots, but it is not a sane option for serious main marine propulsion.
For reference, the tiny 150 tonne displacement hull ~ 70 ft long on the waterline that I am sitting in now, makes about 5 knots at 100HP out of the main engine, and tops out at about 7 knots at 150HP.

Of course I have worked plenty of gigs that made a big thing out of their solar 'green credentials', there was usually an amazing amount of diesel burned in some very large rotating machines back where the public could not see them....  
I suspect there is a fair bit of that going around these days.

It is mostly the link from the inverters to the drive that tends to radiate, but ships are an RFI nightmare anyway, you would think that all those steel compartments would make them really benign from an RF perspective, but it aint always so.

Regards, Dan.

Posts: 165

« Reply #19 on: February 10, 2012, 06:08:17 AM »

Strong Mediterranean/north African sunshine (presumably Arizona, too) is 1146w/sq.metre, according to DEF - STAN 133. I was at a place in Germany last week: they had over 400 sq metres on their roof top, and a display in reception proudly showing it producing 435 watts!

Not all diesel locomotives are/were diesel electric. The German MAN-Voith hydraulic transmission was used quite widely on the German railways, and also in the 'Hymek',  'Warship' and 'Western' classes on British Railways.

Posts: 1484

« Reply #20 on: February 10, 2012, 09:08:57 AM »

For reference, the tiny 150 tonne displacement hull ~ 70 ft long on the waterline that I am sitting in now, makes about 5 knots at 100HP out of the main engine, and tops out at about 7 knots at 150HP.

Dan, do you mind if I ask what sort of a vessel you're in?  I'm always curious about these things because, 30 years ago when I was an undergrad, one summer I was the World's Worst Deckhand [tm] on a "towboat" on the lower Mississippi river.   :-)
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