Julian,
This should help you sleep like a baby.
The Arc is a 20 ton monohull that draws 3 feet. I put a motocycle sprocket in my diesel driveline that has 3 bearings, two universals, a V-drive and I'm spinning my Borg-warner tranny in neutral to boot. I hung a 48V, 7 kw golf cart motor alongside it and ran a #40 chain. I have 5 kW of solar panels and a sundeck on the stern that creates a substantial wind signature. I can make way in calm water and winds at 5 mph at 140 amps, (the full 7 kw) and with a nice little tailwind I've made 6 mph at 75 amps. On the flip side, I was heading up into a gail on Lake Okeechobee with an angry 2 foot washing machine chop and was able to maintain control of the boat and keep it off a menacing jetty to my lee making way at 1.5 mph. I almost peed my pants and as soon as I cleared the jetty after leaving the decievingly calm lock I immediate switched to my diesel which is a moderately involved process that requires removal of the #40 chain and can't be done on the fly.
I don't have any specs on my prop other than to say it's somewhere between 15-20" with 3 blades at reasonably aggressive pitch. I wish I knew more myself but it seems to work well so I left it alone.
Wind, even with my large wind signature, does not have nearly the detrimental effect you would think. But even the slightest wave action kills me and strong currents are a big problem as well. Admittedly, at .35kW/ton I am grossly undersized and I would not recommend this extreme to others. Budgetary consideration forced me down this trail and it was all for experimentation and fun anyway. But turns out, I can get the boat around pretty good just off my 5 kW of solar, which is a good thing because my lame bank of lead acid golf cart batteries only lasts about 45 min at full trottle. I'm not in any particular hurry these days, most of the time, and I can crank up my 50 yo, 38hp diesel when I am however I like to just let Grampa rest, take my time, and run for free off the sun. (He's a thirsty old guy that likes to guzzle diesel)
If my case is not extreme enough for you, I talked to a guy the other day that is trying to push something like 8-10 tons (I think he said)with a surplus 3 hp motor in a similar configuration and says he getting good results. His goal is to simply troll electrically at 3-4mph. Maybe he'll chime in later with his specs.
So if you're anywhere near the recommended nominal 1 kW/ton, you'll be fine and don't worry about the nay sayers.
My plan is to save my sheckles while I cruise the familiar coastal waters of Florida for while on solar while I learn more about the boat and how the solar rig performs in the marine environment, then when the diesel finally does die, to scrap my entire diesel driveline, install something like a 15 kW motor straight to my propshaft with two synchronous pulleys and a belt, fork out the cash for about 40 kWhrs of LiIon batteries,(which hopefully will be a bit cheaper by then) and add a 10kW diesel genset to run as a serial hybrid in emergencies.
Then head out and try to be the first person to do the great loop without burning a drop of diesel. (If no one beats me to it in the mean time.)
Carter
From: Julian Webb <julian.proto@gmail.com>
To: electricboats@yahoogroups.com
Sent: Sunday, March 24, 2013 9:48 AM
Subject: [Electric Boats] does anyone have current real world performance figures please
To: electricboats@yahoogroups.com
Sent: Sunday, March 24, 2013 9:48 AM
Subject: [Electric Boats] does anyone have current real world performance figures please
Hi All
--
- Does anyone have actual real-world speed figures for an electric drive vessel they have built or been on please?
- Just simple overall "she's 6 ton, 38', and my 10KW electric pod pushes her along at 4 knots comfortably" will be great thanks.
- That's the short story/request on how you make me sleep better tonight with some examples of figures, and you don't have to know the whole gory story to help me feel better, but if you want to know the logic/story behind my plea, read on:
- I am just finishing a Diesel/Electric canal cruiser and it has gotten down to the props.
Her specs are: Built 1964 - 32' w/l - 35' o/a - 11' beam - 4' draft - displacement hull - 9 ton.
She had 2 x 45 HP Fordson Diesels, original and never overhauled, running through 2:1 V drives that pushed her along at 8 knots cruising and 11 knots top speed spinning 2 x 23" props, borrowed, mismatched and both LH!
- I thought I had it all figured, read Lynch and others on rule of thumb "electric drive can be 1/3 the HP/KW of an ICE and still be close to the same performance" but now I'm meeting doubt and silence at every turn!
- I have installed 2 x 11KW/15HP 6 pole 1000RPM @ 110Nm and of course can use 2:1 reduction and get 500RPM @200Nm (including losses) which I would have thought would be enough to push the old girl down a quiet canal at 6 knots?
1) I emailed 8 prop "makers" (from Italy to the USA) and when they saw the words "electric drive" most ran for cover.
2) 4 bothered to answer and in the end only 1 would guesstimate any thrust but even he has steadfastly refused to estimate boat speed, despite the fact that I have given him (and them all) figures, displacement etc and even a primitive hull plot.
- After MUCH pushing (although I couldn't do it too hard or maybe scare him off completely) I found out that although they say the software they use has provision for calculating props for an electric motor, they work on HP or KW and the torque is "included in the power figures" as it were an IC engine.
- When I said to them I can reduce speed 2:1 and double the torque they say they can't take that into consideration and it's based on HP/KW so the whole thing is looking shakey to me! HELP - HELP - HELP!
All input kindly received, Cheers, Julian
--
unit 9 Somerton Industrial Estate, Belfast, BT3 9JP, U.K.
Phone; (+44) 02895 811251 - Mobile; (+44) 07427 696 796 - Fax; (+44) 0871 9898296
Company number; NI067673 VAT number; GB975375474
Company number; NI067673 VAT number; GB975375474
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