Eric's electric propulsion & other electric motor discussion

[s/v Faith]

Windstream Power LLC: Human Power Generator

Here you go;



Less then $500!

The Human Power Generator is small, portable, and dependable - perfect for emergencies, power failures, remote locations, and off-grid applications. It can be pedaled or cranked by hand to charge 12 volt batteries and run small appliances. Incorporate it into your existing 12 volt system or simply plug your 120 volt appliance into the Portable Power Pack outlet and start pedaling.

The typical average continuous power that can be generated by pedaling the Human Power Generator is up to about 125 watts. The maximum power obtainable through hand cranking typically is about 50 watts. The pedals and optional hand-cranks are interchangeable.

http://www.windstreampower.com/humanpower/hpgmk3.html

[Lynx]

Inboard prop gen. First you need to see if your transmission can handle it. Some of them must have the engin running to move fluid inside or else you will burn out the trans. If you have to put the trans in reverse of brake it, you will not be able to use it as a gen.

Solar or wind may be an option to this.

You can get a 1000 W gas gen that may do you better than using the motor.

About $ 800 for Yamaha.

Yamahagen

[olivertwist]

I've swapped my 8 hp Yanmar for an electric motor. I've mounted my re-e-power system 3000 motor to the hull of my boat. She's ready to go in the water this week. The attached picture shows the motor before the final painting with ablative paint. It runs on 4 series 27s @ 48 volts. Cruise range at 5 knots is expected to be 5 to 6 hours. I'll be testing it this weekend and will report back.

[Pappy Jack]

Oliver,

What kind of boat do you have. It might help us know how efficient your system is to know the length, weight, etc. I was also wondering if you have it set up to charge your battery when it is not running.

Fair winds,

Pappy Jack

[olivertwist]

Pappy Jack,

She's a 28' Cape Dory Intrepid. Displacement is 7500 pounds. The engine will recharge under sail given about 4 knots of speed. I'm just getting her in the water now so I can only site the specs. I'll let you know my observations when I've  got some first hand experience using it.

Oliver

[Lynx]

Great, I hope it all works out. I expect to need to replace my moror in 2 to 4 years. It would be GREAT to get an electric instead.

[s/v Faith]

Olivertwist,

  Grog to you for bringing the RE-E-Power system to the table for consideration.  Here is their website in case anyone else is interesting it looking.

  Looks like about 2x the cost of a new outboard, but much less then an inboard re-power (of course you have to add batteries).  Btu then you may be able to remove the fuel you would pay for... unless you run a little honda to charge the thing every once and a while when the winds have been light.......

  The picture you posted does not look like a Cape Dory, maybe that is the picture from their web site?  if so, do you have any pictures of your install?

  I really look forward to hearing more about this system.  Thanks for the post!

[olivertwist]

Faith,

Thanks for the grog. That is a picture of my boat, Credo. The Cape Dory Intrepid is a Chuck Paine design. It's one of the few fin keel designs CD produced. I believe they only made 10.

Oliver

[newt]

I am really interested in the recharging aspect. Did they tell you how many watts you would get at 4 knots. Or maybe you could figure out a watts per knot chart ( I know you'd rather not) but I will if I get the figures! :)
Just feeling rather sparky...
Newt.

[olivertwist]

newt,

I'll see if I can make the knots per Watt chart.  I didn't get launched last week as I'd hoped due to a flaw in my glass job. I hope I've got it fixed now. I'll double check on Friday and try to launch again on Saturday. If there are no leaks I can give her a test drive.

Oliver

[newt]

Fantastic! This stuff is the things dreams are made of. If you could get a decent charge we may never need the generator again! Just think of a boat where you ran the detestablel once a month and in emergencies only. It takes the breath away. ;D

[Captain Smollett]

Newt,

I ran across some data yesterday and I thought of you and this thread.

Data (*):

A three-blade propeller with shaft locked can increase a vessel's resistance through the water by 20%.

Have that same propeller free to spin but NOT able to rotate at the proper speed (the example given is using the shaft to turn a generator) may increase vessel's resistance by an ADDITIONAL 25%.

It is further stated that the maximum drag appears with prop turning around 100 rpm.

Just wanted to share; this may impact the design of the system you envision.

(*) Source:  Hiscock, Eric, Cruising Under Sail, p 193.

[Lynx]

Not know much about props but they are designed to push the boat and are not as good at the same RPM's going backwards. Would it help if the prop was desigend to be used as  a generator?

[newt]

Captain,
I am not sure I understand your stats. What I think you said was that a boat slows down 20% with a fixed propeller and an additional 5% (25% of the 20%) with the propeller  turning. I would agree with that, as the surface area of the prop functionally grows larger. This is all with a fixed prop. I plan on having a variable prop in my system. This will solve two problems- going into reverse, and be able to vary the resistance to the generator to optimize electric generation to the needs of the boat. I also forsee a possible drogue effect when running downwind, although a true drogue has many important actions on the boat which could not be duplicated with a propeller.
I think the main advantage would be simplicity (believe it or not). No wind generator, no solar panels, no electronic cutoffs for the above, and all power needs of the boat located in the engine well- including the batteries. Just a system that I think will and can happen. Even with present technology... :)

[Captain Smollett]

I am not sure I understand your stats. What I think you said was that a boat slows down 20% with a fixed propeller and an additional 5% (25% of the 20%) with the propeller  turning. I would agree with that, as the surface area of the prop functionally grows larger.

The point was that it's not just that the prop is turning, it's that it's not turning at the correct rotational speed for the linear speed through the water.  The internal friction of the generator causes a slower rotational speed for a given water-prop torque generation.  In other words, you are not only fighting prop-drag, but are also transferring generator drag to boat-drag.

I have absolutely no clue how a feathering or folding prop alters this - changing the prop pitch does not effect the internal friction of the generator.  Maybe you can minimize the loss, though?

Rather than saying the boat speed will be reduced by 25%, it is probably a bit more accurate to say the boat is 25% harder to push.  This may or may not equal a 25% speed reduction depending upon wind speed since the power curve for the sails is non-linear.

Just came across it and knew you were thinking about a prop shaft driven generator.  As a potential light air performance issue, I wanted to share it just in case.

Not trying to suggest your approach is not a good one....

[newt]

This discussion is a good one. As I understand resistance to a hull through water, it increases in a log rhythmic fashion till planning speed is reached. So lets say a hull is going 75% of its hull speed, increasing the pull on it 25% shouldn't drop the speed 25%. Since most sailboats already have a prop in the water, The decrease (5%) might be almost unmeasurable.
How would it compare to the pull behind generators? So many questions- I guess we will just have to get a few answers.

[Captain Smollett]

So lets say a hull is going 75% of its hull speed, increasing the pull on it 25% shouldn't drop the speed 25%.   Since most sailboats already have a prop in the water, The decrease (5%) might be almost unmeasurable.

Agreed for that part of the power curve.

On the topic of drag, it's the other end of the spectrum - very light air, slow boat - where a small change in drag makes a relatively large change in boat speed.

If you are in the doldrums (or otherwise light air), a few percent change in drag can mean the difference between moving SOME and not moving at all.  Even 1 kt is still 24 nm per day.  ;)

Since we are in the engineless thread, I'm assuming we don't want to motor through the light stuff.   ;)

How would it compare to the pull behind generators? So many questions- I guess we will just have to get a few answers.

I've no experience with them directly, yet, but definitely plan to have one.  Some folks shun them and I've read the increased drag cited as a reason why.

[newt]

Now Captain, if you have a variable pitch prop, you could turn it to no drag (or very little) in light airs, thus you would have the advantage over a typical sailboat in light air, the only problem I can see is cost. Reduce the cost and we may have a winning system.

[Captain Smollett]

Now Captain, if you have a variable pitch prop, you could turn it to no drag (or very little) in light airs,

:)

Yes, but if it's feathered, it's not turning the generator, right?  Am I missing something? 

[s/v Faith]

Oliver,

I didn't get launched last week as I'd hoped due to a flaw in my glass job. I hope I've got it fixed now. I'll double check on Friday and try to launch again on Saturday. If there are no leaks I can give her a test drive.

Oliver

I can't wait to hear your results and impressions.  I am really hoping you are happy with the system.  How long have you sailed your boat?  If you have a fair amount of experience in different conditions you should be able to give a pretty good evaluation of the real costs of the drag.   

  Even 20% might not be as bad as it sounds.  I bet most boats are losing %20 to poor sailing trim or a less then steady hand on the tiller.