Mike,
We finally have a nice day today and are in fact moving along quite well for a change. Got the first mate at the helm for a while and came below to check email and get out of the wind for a break.
Comment on my earlier post to Steve on this thread: I actually misrread his post and thought he was extrapolating that he could cut his power in half because he had half the displacement. After reading it again when I was reviewing some of Erics data I noticed he was just extrapolating that he could get by with what Eric had because his waterline was the same and his displacement was half. So my lecture on hydrodynamics was unnecessary because obviously that's a good call.
I agree, more data is better. I wish I knew the specs on my prop and will check it the next time I haul. Although I'm hoping to get the worn out auto prop rebuilt by then and put it back on because it did run a little better with that prop, it just made an aweful grinding noise because it was 20 yo. and getting worn out. For the record we're pushing 20 tons, 45' lwl, 13.5'beam, 3' draft at an average 3.5 mph at 55amps at 48V right now as we speak. The 4 kW solar array is collecting about 65 amps but I'm holding back on the trottle to get the batteries charge up since we left out at 7:45am this morning before they had time to juice up.
Hope to break my all electric record of 32 miles that we set in the Gulf on the way up to Alabama but we're bucking a brisk headwind today and that day we had a nice favorable current.so we'll see. But today should be an all solar record though, I think we were running in hybrid mode when we were testing that day in the Gulf with an extra 20 amp boost from Quickcharger on the EU2000. We should be able to shatter our first day all solar run of 18 miles from Pirate's Cove Alabama to Pensacola no problem.
Carter
From: Mike <biankablog@verizon.net>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Saturday, April 6, 2013 11:02 AM
Subject: Re: [Electric Boats] Re: Measured performance - even more data
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Saturday, April 6, 2013 11:02 AM
Subject: Re: [Electric Boats] Re: Measured performance - even more data
Carter glad to see you moving around just using the help of Ol Sol. Thanks for reporting on your progress and findings as well as others like Eric's detailed report. I'm hoping to do some more testing after my boat is splashed later this spring. I think when reporting on tests we should also provide some basic boat specs too like:
weight, boat length, beam, prop size, prop pitch, # of blades when reporting on tests.
I think it might help others looking at electric propulsion compare their boats with those of us who have made the conversion. Our real life numbers when compared with their boats based on size would be very helpful for them. Over time as more and more boats become electric maybe we can develop a nice database of specs and the results of different parameters. Especially when it comes to prop size and pitch. Which seems to be the biggest X factor in optimizing our EP systems.
Capt. Mike
http://biankablog.blogspot.com
From: Carter Quillen <twowheelinguy@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Friday, April 5, 2013 7:51 PM
Subject: Re: [Electric Boats] Re: Measured performance - even more data
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Friday, April 5, 2013 7:51 PM
Subject: Re: [Electric Boats] Re: Measured performance - even more data
Steve,
Yes, slower is better, but that is not modern way.
We made 8 miles at 2 mph today in totally overcast skies today. I mean you couldn't tell where the sun was at but I was getting 25 amps off the solar array and that will push the Arc at 2 mph. The rain finally stopped and we where tired of bouncing off the hook waiting for the sun to come out so when the batteries hit full charge about noon I figured the hell with, lets make way til they're dead. I was surprised to get as far as we did, even in a choppy Pensacola bay with a blistering oblique headwind.
For the Arc, I'm learning that amps and speed are pretty much a flat out exponential relationship.
Although my data collection is very informal, I'm finding that for the Arc gets about 2 mph at 20 amps, 3 mph at 40 amps, and it takes a full 80 amps to get 4 mph. Of course actual performance is all over the map depending on winds and current but it pretty much averages out to that. I don't know much about what happens after 80 amps since that's about all I can get off my 4 kW solar array and I try to keep the batteries full and track the solar input. I've separated one kiloWatt for house power and don't use it for propulsion.
However when I do put the hammer down, I can just barely make 5 mph with my full on 145 amps at full throttle on my 7 kW shunt motor. Although I don't like to stress that little golf cart motor at that rate for too long and it kills the batteries in about an hour anyway.
One time I made 5 mph at 20 amps with a 30mph tailwind though, that was interesting and I often hit the 4+ mark at 50-60 amps with favorable winds and current.
I starting to think we can get this 20 ton barge around Florida on nothing but sunshine!
Carter
From: Steve <sstuller@netzero.com>
To: electricboats@yahoogroups.com
Sent: Friday, April 5, 2013 5:34 PM
Subject: [Electric Boats] Re: Measured performance - even more data
To: electricboats@yahoogroups.com
Sent: Friday, April 5, 2013 5:34 PM
Subject: [Electric Boats] Re: Measured performance - even more data
Thanks for your reply. It is interesting that Eric's boat's input power at six knots is 1000 watts per ton which correlates with the one KW/ton rule of thumb. Increasing his boat's speed from three knots to six knots increased the input power by ten times. That thought will temper your use of the throttle if you want your batteries to last for more than a few minutes. I'm more interested in staying at the lower end of the speed range if I expect my batteries to take me any distance. Steve S.
--- In electricboats@yahoogroups.com, Carter Quillen <twowheelinguy@...> wrote:
>
> Steve,
>
> I would be careful making this extrapolation. Your ultimate top speed, (velocity), is more a function of the hyro and aero dynamics of your vessel, and not necesarily it's mass, or displacement. With the same waterline length and similar hull configuration your boat might require pretty similar power requirements to reach the same velocities even with quite a bit less mass,(displacement). What will be effected is your accelation. You' might get to that speed a lot faster if you are lighter, but it could take almost just as much power to maintain it. You will also have a lot more control over your boat in heavy seas with less power if you have less weight with a similar hull. But just because you have half the mass, you will not necessary be able to get away with half the power and achieve the same terminal velocity results. Maybe. Maybe not.
>
> Although displacement does indirectly take into account the wetted surface area of your boat which has a large determining factor on your hydrodynamics, hydrodynamic charactistics can vary considerably from one vessel to another with the same displacement or be quite similar from one vessel to another with wildly different displacements. Consider that you can add a significant amount of mass to many boats and have very little effect on their terminal velocity in calm conditions. Your top speed will primarily be affected by the additional hull surface area that is coming in contact with the water which could be a quite minimal percentage for a considerable increases in mass. It will take you longer to get to your terminal velocity with the additional mass and you'll be a lot slower in heavy seas, but in calm water and wind, you will often see very little change in your terminal velocity per unit power input.
>
> A comparison of your boat's wetted surface area and streamline characteristic to Eric's boat is also very important in accurately predicting your power requirements. What is your draft, beam, and projected surface areas compared to his and what are the specs on your prop. These parameters will be more important in determining your ultimate power needs than a simple comparison of length on the waterline and mass. Although mass is very important parameter, particularly when considering performance against wave action, unless you want to apply some really nasty mathmatical modeling to the problem, just take into account as many things as you can and stick with some of the rules of thumb as a guide for sizing.
>
> I don't agree with the old adage, "use your thumb if your dumb" because your thumb is a very useful tool. Just don't let it get in the way of good design. The rule of thumb of 1 kW/ton is an excellent generalized guideline but there are many other factors if you want to split hairs to achieve the most cost effective results. Always try to consider as many of these factors as you can, then use your best judgement and you'll usually get good results.
>
> Carter Quillen, P.E.
> www.shipofimagination.com
>
>
>
> From: Steve <sstuller@...>
> To: electricboats@yahoogroups.com
> Sent: Friday, April 5, 2013 4:48 AM
> Subject: [Electric Boats] Re: Measured performance - even more data
>
>
>
>
> An interesting correlation between displacement, speed and KW input for your boat: at 3 knots, KW input is 100 watts per ton of displacement; at 4 knots, 200 watts per ton; at 4.5 knots, 300 watts per ton; at 5 knots, 500 watts per ton. My boat is half the displacement of yours on the same waterline length so I think I can extrapolate from this data that the power requirements will be the same per ton of displacement. Thanks. Steve S.
>
> --- In electricboats@yahoogroups.com, "Eric" <ewdysar@> wrote:
> >
> > Last weekend I realized that it had been about 2 years since my last performance test, and I wondered if anything had changed over time. I was at the marina on Easter morning and the conditions appeared to be ideal for another performance test. I ran through the same process listed below in about 100 minutes, covering a little over 7nm in total.
> >
> > Here's this weeks results:
> > 497W = 3.1kts
> > 1000W = 4.0kts
> > 1500W = 4.5kts
> > 2500W = 5.2kts
> > 3975W = 5.7kts
> > 5000W = 5.9kts
> >
>
>
>
> ------------------------------------
>
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>
>
>
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>
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