Most efficient Electric pod type motor/prop

[Mick@itc]

Hi
There are many threads here about the various combinations of deisel, eletric, hybrid, petrol etc motors. Say we know what the most efficeint way of getting electrical power is (bear with me) and that power will be fed to an electric pod slung under the boat with a prop on it (either the turning kind or the fixed kind). Does anyone here know what the most efficient make model is for a mid size (40~50 foot) cat would be? There are versions by various manufacturers like MasterVol, Re-E-Power and others. Does anyone know how to read through all the technobabble and actually be able to compare them. I have tried but quite frankly FAILED.

Hope someone can help.

Regards
Mick

[jehardiman]

"Failed" may be overly hasrh on yourself; as there are plenty of mirrors and lots of smoke on the path you are looking down.

The real problem is that by selecting the generation source and power supply, you by default almost select the motor type and loss. By selecting a "low" voltage DC system, you constrain youself to fairly heavy motors with high amperages but get good low speed torque all the way down zero RPM. By selecting a "high" voltage AC system, you get lighter motors with less amperage loss but much less torque and the requirement for almost fixed speed with precipitious stall. MG sets and variable phase motors sort of mix the two, but come at a weight and price cost.

There really is no single "best" path foward, and certainly no single way to decide what is meant by "most efficient". It all depends on the total powering system design and every decision down that design path will lead you to a small specific niche. And that is what all the manufactures do, they make the best choice for the niche they have decided to fill, and as you probabily have found out, not all those niches are filled.

[Mick@itc]

Thanks Jehardiman. Yes this is where talking the big system picture usually drags the conversation into opinions (usually passionately felt and sometimes poorly phrased) which tends to leave the conversation subject becoming cold. Oh well, lets try it then and see...

OK, for better or worse my propulsion system is going to be an electric generator coupled with a battery set coupled with an electric motor/re-gen propeller set. The Batteries will be divided into two groups...propulsion and service (house). Regarding LV or HV the system will be a combination of both (mostly LV for items with the odd HV for appliences that need HV, eg freezer) so the propulsion side will be able to be LV or HV. My guess is (from what I read) that it will be around 150V. Wheather you hate or love Gideon and the emotion set-up he certainly has provided lots of information and that is where most of this comes from. Whether or not I can afford to buy his system at around $70000aud is yet to be seen but I would like to consider the e-pod type system (fixed rather than retractable). Hence the question I asked should now be viewed as "what is the most efficient Low voltage DC e-pod type drive on the market". Yes, I agree its an answer that must be qualified by lots of overall system info but even giving opinions here on options is good enough for me.

Again thanksfor your reply Jehardiman, all info welcome.

Regards
Mick

[Submarine Tom]

Well, if opinion is good enough then I say buy a sailboat and save yourself $70 000 AUD!

-Tom

[Mick@itc]

Originally Posted by Submarine Tom

Well, if opinion is good enough then I say buy a sailboat and save yourself $70 000 AUD!

-Tom

Thanks Tom...it will be a sailboat but OI would like propulsion to motor out and in to harbour.

Mick

[Submarine Tom]

A reefed jib is great propulsion, for the cost, in a harbour...

Seriously, you're going to spend up to $70 000 AUD to manoeuver in the harbour?

I apologize for raining on your parade but come on.

-Tom

P.S. Welcome to the Lions Den, no, I mean Forum.

[gonzo]

For that kind of money, you can put it at a moderate investment and hire a tug each time you go in and out.

[Mick@itc]

Originally Posted by Submarine Tom

A reefed jib is great propulsion, for the cost, in a harbour...

Seriously, you're going to spend up to $70 000 AUD to manoeuver in the harbour?

I apologize for raining on your parade but come on.

-Tom

P.S. Welcome to the Lions Den, no, I mean Forum.

Hi Tom and Gonzo.

Yes, lions den is a good description. Seems people need to do a lot of dancing around and dodging to get anywhere.

I have decided to put motors on my boat, that won't suit everyone I understand, but thank goodness my boat is not being designed by committee. What I was actually asking in this thread was for opinions on the e-pod type drives that exist in the market. Anyone got some opinions of the actual drives?

Thanks for the feedback.

Regards
Mick

[jehardiman]

Originally Posted by Mick@itc

OK, for better or worse my propulsion system is going to be an electric generator coupled with a battery set coupled with an electric motor/re-gen propeller set.

The Motor-Generator (MG) set is what may be driving costs and efficiency here. If you want the lower unit to be both a motor and a generator in DC, you are limited to commutator dynamo/motor design. These are really not very efficient with speed control and more expensive than a similiar AC brushless motor/alternator. On the other hand, they can work at high load/low speed and don't require a DCtoAC motor controller and rectifier. So you pays your money and you takes your choice. Using a M-G with a PM field would most likely make the DC attractive for a low voltage system, as AC systems have more losses due to field powering, but big (multi-horsepower) PM M-G's are expensive though and pull a lot of amps which means bigger cables, controlers (if you just don't want on/off), etc..

I'm not sure exactly what you are looking for, there are several turnkey systems being offered (http://www.myboatsgear.com/featured_...aPowerlite.asp). For DIY, there are these type of things...http://www.hydrogenappliances.com/manta.html.

Edit to add, I don't think anybody is making a turnkey electric pod drive, especally with generation capability.

[Mick@itc]

Hi
As you can guess, I have been researching this area big time. Luckly in Australia a number of people have gone down this track, some with very unfortunate outcomes, some with good outcomes. The few things I have learned from real world examples from people that have put the dollars into it and are using their choice. My fow learnings were...

• Don't modify anything...if the item you are buying doesn't quite siut...DONT USE IT;
• Be VERY VERY careful of the quality of the items...regardless of price...quality varies big time;
• If there are props in the water there will be drag..fact...and in some cases the prop will spin and make noise...very annoying noise;
• Equivelent horsepower is not equivilent horsepower;
• An on-board generator is a must...if you go electrical and have a good level of comfort (from my viewpoint)

Hope this might help people with e-pod ideas...

Regards
Mick

[Boston]

If your only going in and out of safe harbor then there is no real reason to have an over sized gen set that can supply the entire wattage necessary. What are your chances of getting away with a smaller gen set say no larger than you would normally have and simply running it a bit longer to get those batteries back up to charge.

granted the batteries are less efficient than the fuel for the gen set at charging up the system but you could still only take half the energy from the batteries and half from the genset. Then run the genset a bit longer than you need the motor. Brings everything back up to power and probably costs a lot less. The trade off is that you have a limited time of motor usage before the system cant keep up. IE its a very short term propulsion solution.

here's a cheap efficient gen set that would likely work in conjunction with a few solar panels for a typical yacht of the size you are talking about

http://www.google.com/imgres?imgurl=...MsKcgQeizaW0AQ