T-Pain Is On A Boat: RE: [Electric Boats] Cruising with EP

Thursday, February 10, 2011

RE: [Electric Boats] Cruising with EP

Hello again Myles,
Did I already mention how much I appreciate your contribution? I really do. From what I have read so far from all of the feedback is that short of docking at a marina to hook up to their 110 outlet, there is nothing that will fully charge the battery bank regardless of the size. With that in mind, for the size boat I have in mind, what size electric motor (HP) should I use, what size bank, and at a cruising speed of 5-10 mph, how long should the bank last before I have to use either a back-up motor (diesel) or dock and plug in at a marina? This is the kind of info I can't seem to find through a search engine. My best results have come from you all. Thanks again.

William A. Garrison

--- On Thu, 2/10/11, Myles Twete <matwete@comcast.net> wrote:

From: Myles Twete <matwete@comcast.net>
Subject: RE: [Electric Boats] Cruising with EP
To: electricboats@yahoogroups.com
Date: Thursday, February 10, 2011, 6:06 PM

Regarding motor requirements for your needs, I defer to the experts who know the Great Loop.
As for recharging with wind or solar, it comes down to doing an energy analysis and knowing what your operational environment will be. Having a 48v battery bank doesn't tell us anything really as regards solar and wind recharging.
I have a 36v system. I have hooked up from three - 50watt solar panels and a 400watt wind turbine at the same time.
Was that enough to recharge my 36v bank? No.
Was that my goal? No.
What was my goal? To take advantage of some of the free energy available to "extend" my range (and here's the key for me) while cruising.
How well did it do? Not well really---with solar, I saw but 1-2amps delivered into the 36v bank---i.e. 36-72watts for 150watts of panels. With the wind, with a following wind of about 12-kts, I was able to deliver between 1 to 1.5amps into the battery bank---about 36-54watts.
Now, you might say, "hey, that's great!" Well, not really. Collectively, this was just over 100watts. But to put this in perspective, the motor was drawing some 50amps from the batteries---i.e. about 1800watts and cruising at a bit over 4kts. So I saved 100watts, or 1/18^th of the power the motor was using. The thing is, I could have instead reduced the throttle to reduce the motor power by 100watts and would not have noticed any significant speed difference. Saving energy is much easier and more efficient than generating it!

Anyway, yes indeed---if the wind is blowing towards you and you deploy the wind generator, you will be generating electric power at the expense of drag. And drag wins---don't do this! It will again be a net-negative---not a net-zero gain, a net-negative. On the other hand, with a following wind, a wind generator would not only generate power but will also present drag that helps push the boat a tad.

-mt

From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of bill garrison
Sent: Thursday, February 10, 2011 5:36 PM
To: electricboats@yahoogroups.com
Subject: RE: [Electric Boats] Cruising with EP

Hi Myles,
You seem to know the concepts and numbers pretty well. So, my next question is about solar vs wind. How many panels would I need to recharge a 48 volt battery bank? Does a wind turbine create drag against what your propeller is doing. Also, since my 3.1HP motor is too small to push a 40' x 14' houseboat around the Great Loop, what size electric motor would be appropriate for the taskSpeed is not a major concern. I am more interested in range. I have been spending hours on the web searching for answers only to find sales info rather than answers. I appreciate having people like you who are willing and patient with helping newbies like me? Please forgive my ignorance.

William A. Garrison

--- On Thu, 2/10/11, Myles Twete <matwete@comcast.net> wrote:

From: Myles Twete <matwete@comcast.net>
Subject: RE: [Electric Boats] Cruising with EP
To: electricboats@yahoogroups.com
Date: Thursday, February 10, 2011, 8:51 AM

GNH offered: "You're last question about recharging the battery is the best one."
And then also: "http://www.pkys.com/alternator_installation.htm Contact Peter Kennedy, he'll be able to explain the In's & Outs."

I don't think these comments help.
Let's look back at what Mr. Garrison asked: "Will I be able to produce enough DC from the alternator to charge the bank?"
Now let's look at what he wanted to do with his houseboat:
"I would like to attach one axle to a propeller via a pulley configuration. I think running a generator off of the other axle could turn a generator, which is turning anyway. The generator could then be recharging the battery bank as we are cruising."

SURE, you could attach an alternator to the drive train of an electrically-driven boat. But what's the point?
If your intent is to generate power at some other voltage (e.g. 12v) to power boat accessories, that might be jusitified.
But the way this was worded, it reads to me as if the expectation is that somehow an alternator or other generator can deliver more power back to the battery bank than the motor used to power the drive train. As someone else noted, that is expecting perpetual motion and that violates some serious laws of physics. But hey, give it a try and let us know how that works out for ya'! But first consider a hypothetical on the power losses in the process: 100% power IN * 0.96 (controller) * 0.85 (motor) * 0.95 (tranny) * 0.7 (generator, at best) = 0.54 or 54% efficiency
So, say you're "cruising" and using 3.5kw of power just to drive the boat.
Now you think "hey, why not engage the generator to put that 3.5kw back into the batteries?"
So you do that.
Here's what happens if you actually delivered 3.5kw back to the batteries:
1)      The motor needs 6.48kw EXTRA power in order for the generator to deliver 3.5kw to the batteries
2)      The total motor power is now 10.0kw
3)      Net power from the batteries: 10-3.5 = 6.5kw
In other words, all your hard work to add a generator has been worthless.

Now, what CAN you do with the other leg of the axle if you choose to go that way?
Maybe you could optionally "drive" that axle with a small gas or diesel motor, making your boat a plug-in-hybrid and now having the ability to indeed "generate" power to the battery bank, only now it would be power derived from burning fossil fuels and using the motor as a generator. Conceivably, you could be generating power while underway if the ICE engine were delivering enough power and speed.

In case this makes sense-

-Myles Twete, Portland