ac versus dc motors

Hey stuff happens on a boat. But I spend alot of time preventing corrosion. Every wire is marine tinned, crimp, heat wrap, dipped in plastic stuff, tape and then electric greas on terminals. Every component that is not marine is taking apart and made marine. True I don't have as much as in smaller boat but give it time and the salt air gets it. I have learn how to ventilate the boat so even thought the windows are open there is positive pressure out of windows so air coming from bow and run through filters, same in engines room. The electric motors are not the problems it is the speed controllers. True, the ones from Siemens for example are sealed and beautiful pieces of work, but most of the people here are trying to do used forklift motors and none marine speed controls. Most of these systems work in the 90 -144 volt system and are very dangerous to someone who is a little clueless.

The Siemens system is the best I have seem, it suffers from one major problem. $$$
To spend that kind of money, to still need a generator and get by boating terms lousy performance , it is just better to have a diesel.

I work on 50 and 100 ton boats all the time, they have anywhere from 600- 4000 hp. It is going to be a long time before you see these guys go away from a simple straight shaft diesel to battery power.

What is really amazing is that people forget the best most reliable solar power there is all the time... The WIND. Have you ever thought of mounting a couple of 800 watt windmills on your cat. They work great on anchor, day and night. That is how you can get 1600 watt to charge your batteries. And you can tell your rich clients, you are green and helping the environment.

Oh the noise... Add more insulation to the deck. Just make sure you mount them high enough that no one gets their head taken out.

 

To use the wind most effectively sails are a pretty good option . I think in the case of a sail electric hybrid Ac would then be preferable for powered propulsion as it is more difficult to regenerate electricity with a dc motor.

 

Um... this isn't my thread. I'm not asking about motors here. The OP asked about AC vs DC and I gave an answer to that question.

I didn't think electric propulsion was viable for my use on a catamaran.

I advised this in my previous post on this thread.

I would have to say I completely disagree about wind. I had wind on my last boat (in addition to sails) and it absolutely sucked. It was never windy enough to generate real power. Solar ran everything. The wind generator made a lot of noise and like 5 amps. Garbage.

 

I think you just had the wrong size propeller. This one works OK.

 

Ha ha ha! Yes, that's wonderful until the wind stops (such as in the picture). Generating zero power all day long.

Interesting to look at though.

 

So am I to take this that you are happy with a range of maybe 50 miles on $40,000 worth of battery power,and have found a place to store the 4.5 tonnes of batteries on your catamaran?

Or $200k worth of Li batteries?

Or have you decided that a 20 to 30% efficiency loss with a DE vs gears is acceptable and are going to run 10 freezers and non stop 15kw worth of air-con?

Siemens may have the sexiest DE "products" but ask Nordhavn how that all worked out.
They spent a fortune,it was too complicated,never worked as promised,so they tore it all out and put in a good old marine transmission and sued Siemens.

This has been beat to death 50 times before in this forum.

http://www.boatdesign.net/forums/hybrid/hybrid-system-sunreef-82-needed-34142-3.html

 

Yes, you are reading that correctly.

All electric motors rely on the attraction between north and south poles of magnets. Because with AC the polarity changes from N to S with every cycle, most of the time only a partial field strength is available. That makes AC motors much larger and heavier than their DC counterparts; theoretical 1.414 times, actually 2-4 times because of magnetic properties of the materials used.

For a given power requirement, the working voltage determines the cable size; doubling the working voltage reduces current by 50%.

 

Thanks mate...appreciated. Yes, the weight of the gennies are crazy in some cases and then the batteries are either heavy and pricy or lighter and crazy priced. You are definately going outboard? Have you got any info on a thread somewhere about which ones and more importantly where they are positioned. There seems to be a bit of deffering opinions about position, cavitation, etc. would love to know your decision details if possible, even pm me would be great with the basics. I am currently trying to finalize the mods to the dh550 design with different propulsion options.

Thanks
Mick

 

When I see the electric motors around the coke ovens or blast furnace area of a steel works I have no doubt that the industrial motors could handle the environment. I checked with the elec ends at work and they just laughed and pointed to some motors in the plant.

 

Ok, that is one of the bits of info I was seeking...there is a difference in size or efficiency between ac and dc. Dc would be smaller or more efficient for a giver output power.
Thanks heaps.
Mick

 

And that maybe why I read 144 volt dc motor systems... Thanks again

 

i think this is only good purpose of 12v motor

 

I'm sorry. I missed this post.

After much debate and wracking my brain, I am going to put the outboards in just like the Seawind catamarans do:



You can see the high thrust prop sticking out below the bridgedeck in the above picture. That's where I'm going to locate mine. I had a big thread on here regarding this stuff and in that thread, Richard Woods suggested that a pointed box for the outboards is better, which makes sense, since if it touches a wave in any way, it becomes a little "hull" in itself - and the better point on a hull, the less drag.

An advantage to this mount over any other is that you can use the engine's built in tilt feature to remove the props from the water for no drag while under sail. That was the goal of my design, so very important. Plus, all that can be controlled from the helm.

Watch out on those lighter generators... they are usually running at 3600RPM or some stupid thing. They won't last very long unless they are at a max 2800RPM or preferably, 1800RPM.

Which outboard is still a thorn in my side. I am seeking a pair of 30HP "high thrust" style outboards, with as close to 3:1 gear ratio as possible. In my dreams, they are diesel. In reality, there is no such thing and I must either get 60HP Yamahas or I may possibly get Evinrudes, if I can get the right props.

Basically, they don't make (or sell) the outboards I need in the States. I have to settle.

 

Outboard locations...

QuoTE=CatBuilder;539283]I'm sorry. I missed this post.

After much debate and wracking my brain, I am going to put the outboards in just like the Seawind catamarans do:



You can see the high thrust prop sticking out below the bridgedeck in the above picture. That's where I'm going to locate mine. I had a big thread on here regarding this stuff and in that thread, Richard Woods suggested that a pointed box for the outboards is better, which makes sense, since if it touches a wave in any way, it becomes a little "hull" in itself - and the better point on a hull, the less drag.

An advantage to this mount over any other is that you can use the engine's built in tilt feature to remove the props from the water for no drag while under sail. That was the goal of my design, so very important. Plus, all that can be controlled from the helm.

Watch out on those lighter generators... they are usually running at 3600RPM or some stupid thing. They won't last very long unless they are at a max 2800RPM or preferably, 1800RPM.

Which outboard is still a thorn in my side. I am seeking a pair of 30HP "high thrust" style outboards, with as close to 3:1 gear ratio as possible. In my dreams, they are diesel. In reality, there is no such thing and I must either get 60HP Yamahas or I may possibly get Evinrudes, if I can get the right props.

Basically, they don't make (or sell) the outboards I need in the States. I have to settle.[/QUOTE]

Hi Catbuilder
The location of the outboards seems to be a bit more complex in terms of the height as well as the hull location. One of the problems I am working on is to get the right height for the length of the drive leg while not putting the head of the motor where it can get swamped from behind as well as from front waves. So even though I have picked the location in plan view I still have to woek out how to get the motors right in the up/down axis.
regards
Mick

 

Slightly obsolete information here. Look:

http://www.electricmotordepot.com/products/Electric-Boat-Conversion-Kit-72V-350Amp.html

PMAC motors, "brushless DC-motors" are actually Permanent Magnet AC-motors. They are the most efficient electric motors on the market.