Saturday, February 12, 2011

RE: [Electric Boats] Cruising with EP

 

1500 watts is 2 hp. And 60hp is a lot and AC voltage is a pain. Not easily stored nor generated. Are you the houseboat guy?

 

Byron

 

From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of bill garrison
Sent: Saturday, February 12, 2011 2:59 PM
To: electricboats@yahoogroups.com
Subject: RE: [Electric Boats] Cruising with EP

 

 

Hi Byron,
Thanks for the feedback. In one of the other emails someone said about a 25HP or more would be good to start with. Would a 60HP 230/460 volts AC be too much? I also saw a wind turbine that produces 1500 watts with a start up wind speed of 7 mph and can continue producing once start-up is achieved with as little as 2-3 mph wind speeds. The cost is around $800. How does 1500 watts fit into the calculation. I really appreciate your input.

William A. Garrison

--- On Sat, 2/12/11, Byron Evetts <h2ologged@cfl.rr.com> wrote:


From: Byron Evetts <h2ologged@cfl.rr.com>
Subject: RE: [Electric Boats] Cruising with EP
To: electricboats@yahoogroups.com
Date: Saturday, February 12, 2011, 9:43 AM

 

Depending upon where you are, solar may or may not be the answer. Solar ideally produces about 1kW per sq meter but realistically produces about that half that in sunny Florida. If you have the roof top real estate and the money you can generate a lot of wattage with solar. I am staring at a 180W 36v panel that is about 2'x4' and would retail for about $3/watt, say $500-600. So I need 3 per horsepower or 9 in your case to net even, or I charge to a good battery bank with less PV panel and run down what I collected later.

 

As far as what horsepower you need for a BIG FRIGGIN HOUSEBOAT, consider the following:

A light wind easily generates 1-2 psf times the front exposed area of your house boat and can easily be (say 10x14') say over 100 pounds of wind load. That's a tall order for 3 hp. And water is 1000 times denser than air so any current is also kicking your butt.

 

Borrow a friends BIG trolling motor, strap it on and unleash it. You will be underwhelmed at how poorly it does on a non aerodynamic/hydrodynamic houseboat.

 

Not to be nego but a houseboat would be loaded with panels, batteries and a big electric motor to be motivated. Electric subs use about 1/4 of their space for generation and storage and they are very hydrodynamic.

 

Get a copy of Skeene's Elements of Yacht Design and it will help with some speed/horsepower calcs.

 

Byron

 

 

 

From: electricboats@yahoogroups.com [mailto:electricboats@yahoogroups.com] On Behalf Of bill garrison
Sent: Thursday, February 10, 2011 8:36 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

 

 

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