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Discussion Starter #1 (Edited)
I would like to find a boat from 25’ to 28’ with at least 5’ 8” headroom. A separate head would be great. I’m looking at a 28’ S2 or Catalina 27. Usage will be Long Island Sound maximum five day trips. Overnight trips will be common but two nights or more will be rare. For one or two people most of the time possibly up to four for a day sail. No cooking.
The eventual goal will be to re-power with electric drive. I’ve read this thread http://www.sailnet.com/forums/gear-maintenance/42593-electric-propulsion-solidnav-com.html and read “Electric Propulsion for Boats”.

This is what I think I know and perhaps I can get some forum member to recommend appropriate boats and vet the following thinking.
<O:p></O:p>
But first some expectations:
I’ll be at a dock with shore power with at most 30 minutes motoring to get to sailing. I’m willing to wait 6 hours if I have to wait for a favorable current. I expect that a range of 8 hours will be sufficient. I figure that one of these inexpensive motors should do the job. Thunderstruck Motors - Electric Sailboat motor Kit. Mars Brusless motor with Sevcon PMAC millipak regen controller.
I’m hoping the electric parts and the batteries will cost under $5,000.
<O:p
Here are the proposed facts:
  • It will take about 30 to 50 amps to move the boat from 3 to 5 knots.
  • I can find room for 8 series 31 AGM’s for a total capacity of 800 Amps
  • At 50 amps usage this gives me about 8 hours at 50% discharge.
  • I’ll need a Link monitor so I’ll know how dead my batteries are.
  • I’ll need a 3 stage charger.
What I would like to know is:
  • If I deplete the batteries 400 amps how long will it take to charge them with a shore power 3 stage and what model should I use?
  • If I deplete the batteries 400 amps how long will it take to charge them with a Honda 2000 plugged into the shore power socket?
<O:p
What else am I not considering besides?
  • Resale value of boat (It will stink)
  • If I get into a storm and have 6 foot head seas and opposing current I’ll probably not make it.
  • 12 volt needs, nav lights etc. (Either separate battery or 48 to 12 volt converter)<O:p
There are several reasons I’m considering this:
  • First I think it would be cool to be buzzing around the harbor with no noise.
  • It will be less maintenance than diesel. This is unlikely, I'm sure if I put the extra 5G into a better boat with a decent diesel I’ll bet it would be less hassle overall but I can dream.
  • My wife is deathly allergic to anything petroleum. The fewer petrol fluids on board the better for her.
 

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400 amps from shorepower depends entirely on your charger. An Iota DLS90 90 amp charger would take 4 hours to get to 90% or so and then probably another 4 hours for the final 10%. Or...you could divide the batteries into separate banks with their own chargers A 30 amp shore power can power a couple of chargers which would involve more $$ initially but cut down the charging time.
A Honda will have a tough time powering even a 90 amp charger. So...I would guess about 70-75amps max for that and 5 hours to 90% full.

You may also wish to consider Odyssey batteries as they can be more deeply discharged and very rapidly recharged. This would allow you to go to a smaller bank and have quicker recharging. 400 amphour working capacity could be achieved with 500 amphour total capacity Odysseys going to 80% discharge. They could be FULLY recharged in as little as 2.5 hours with a pair of 90 amp chargers.

Good luck!
 

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Telstar 28
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I think that re-powering a boat currently is unwise... the electric boat propulsion systems aren't really up to the demands of a marine environment on a small sailboat yet.

Fitting 800 amp-hours of batteries, actually, it would probably be more like 1000-1200 amp-hours of batteries since you'd need to have some capacity for your house usage, on a 28' boat is going to be rather tough, even if you've eliminated the in-board diesel. You're looking at about FIVE 8D batteries at 170 lbs. each.
 

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Davidpm,
Pardon the ranting from an old fogy physicist, but you are going to have continuing problems with electrical design if you do not understand the difference between amps and amp-hours. Not only understand the difference but consistently use the correct terms.

This lack of understanding and careless confusion of the terms seems to be widespread in sailing circles and has led to mistakes. It is akin to confusing the difference between speed and distance, which only rarely occurs because people have a more physical understanding of the terms.
 

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Larus Marinus
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Electric propulsion sounds fun, and if you can get a good deal on a sailboat with an engine that needs replacing, it might slightly compensate for the expense. Check that your dock will supply the current you need at a reasonable cost.
 

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David—

GC does make a very valid point. This was a serious problem in the solar thread previously....The battery bank capacity is measured in AMP-HOURS. The power required to move the boat should be measured in WATTS, or Amp * Voltage... and I am guessing that your figures of 30-50 amps to move the boat assumes 12 VDC... because if you need 30-50 Amps at 48 VDC, you're in a lot of trouble. :)

Davidpm,
Pardon the ranting from an old fogy physicist, but you are going to have continuing problems with electrical design if you do not understand the difference between amps and amp-hours. Not only understand the difference but consistently use the correct terms.


This lack of understanding and careless confusion of the terms seems to be widespread in sailing circles and has led to mistakes. It is akin to confusing the difference between speed and distance, which only rarely occurs because people have a more physical understanding of the terms.
 

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Larus Marinus
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SD - The motor he is proposing is 48V, and 50 amps at that voltage would be needed to get near a usable power.
 

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Well

With my easy to move J24 i burned over 6 gallons of fuel this season sailing as many as 4 times a week

In this area no more than 15% of the boats have access to shorepower So a dock to charge will set you back 5000 DOLLARS (MIN PRICE HERE)3300 in Greenport

I would say it is a pretty typical saltwater harbor in that the water moves in and out ;) at about 2 MPH and with the right combo of tide and wind direction it could take you from 30 Minutes to 2 hours sail the 3 miles to Long Island Sound
 

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Idiens—

If he needs to use 50 amps at 48 VDC for eight hours, as he says in his OP...he's actually using 1600 amp-hours at 12 VDC...and he's proposing to have a battery bank of EIGHT GROUP 31s, which is 800 amp-hours at 12VDC.... so that'd be a serious problem right there. :)

SD - The motor he is proposing is 48V, and 50 amps at that voltage would be needed to get near a usable power.
 

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Midwest Puddle Pirate
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I've actually toyed with the idea of electric power on my boat, mostly because I hate my outboard. I looked at a lot of systems, and by far the most complete seems to be the re-e-power system. For lake use it looks like it would work fine, but I'm not sure I would trust it in big water.

With all other electric power systems, you still need to run the prop shaft, stuffing box etc. With the thunderstruck kit, you'll need to run a gear reduction transmission as well. Then it looks like you'll need to make mounting brackets for the motor, the throttle control looks incomplete etc.

I looked at re-e-power pretty hard. The thing I liked most was the ease of installation. It's as close to plug and play as you can get with an electric conversion. The re-e-power 3000 system comes with everything you need to get started except the batteries. Add a charger and a 48v to 12v converter and you're set. I priced the whole setup including charger and converter at 4300 plus batteries.
 

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A useful conversion factor is 746 watts = 1 hp.
Also 1 watt = 1 amp * 1 volt

So to generate 1 horsepower takes a 62 amp draw at 12 volts. (Assuming 100% efficiency for the motor)
 

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The problem then is that 50 amps at 12 VDC is less than one horsepower, and I just don't see how his boat is going to move at 5 knots with less than 1 HP....

I think his numbers are vastly overly optimistic.

A useful conversion factor is 746 watts = 1 hp.
Also 1 watt = 1 amp * 1 volt

So to generate 1 horsepower takes a 62 amp draw at 12 volts. (Assuming 100% efficiency for the motor)
 

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Larus Marinus
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If I understand his proposal correctly he is getting about 3 HP out of a 48V 50 amp = 2400 Watt system that would take his batteries down to 50% in under 2 hrs running. But at only 30 minutes each way that might be feasible. I guess a clean 30ft boat might get 2-3 knots out of 3 HP, which is fine to exit a marina and get the sails up. With only day sailing and overnight charging, it might work out. That motor is capable of regeneration, so with some appropriate electronics, he might charge while sailing....
 

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Oh man. Not this one again.

My 36 ft ship has a 35 hp motor.
It cruises at about 5.5 kt.
Allow that to be (say) 20 hp.
20 hp is 14.9 kW
Run the motor for 1 hour (modest?) would be 53.7 MJ of energy.
1 amp.hr devivered at 12 V is... E = 1*3600*12 = 43200 J
One hour of motoring at 20 hp would then be the equivalent of...

53.7E6/43000 = 1243 A.hr

....assuming 100% efficiency of electrical delivery and electric motor and assuming complete battery discharge.

All that for one hour of diesel equivalent, albeit noisier.

One hour.

Good luck.

Watch you don't capsize.
 

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It's the 2000 pounds of battery that just makes it a heavy decision doesn't it.

If you think you are going green, forget about it. That lead is toxic as hell, and you are burning coal to make the electricity to recharge them (70% of electricity in the US is coal generated, still).Diesels last the life of the boat, those batteries maybe 5 years before they fill up a land fill somewhere (or get recycled, minus the acid).

Okay, I can get rid of my 300 pound diesel, 175 pound drive leg, and 200 pounds of fuel, and replace that 27 hp engine with a run time of 55 hours at cruise speed with a 2500 pound replacement that needs plugged into the dock for 8 hours after 1 hour of run, oh, and it cost twice as much too.
No deal.

One Gemini did a refit. Props to him, I think it's stupid as all hell and a waste of a fine cruising boat for a reduction in decibels when you are motoring.

It's just not ready yet.
 

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Discussion Starter #18 (Edited)
I'm not talking about a 36' ship or even a 30'. I totally agree that a real sailboat of 30' to 36' can not be run by todays battery. I'm talking about a 25' to 28' boat which probably needs a fraction of the thrust of the bigger boats. With electric the draw is much, much higher for the bigger boat and since it is barely adequate for a 28' (I hope) it makes no sense at all for the 36'.
Jerome Fitzgerald, admittedly a bit of a character, states in his book 'Wind and Tide' Wind and Tide: An Introduction to ... - Google Book Search

that he can row his 8,000 pound boat at about 1.5 knots. I'm sure that a guy on oars if putting out much less than one hp.
The curve of power usage on electric is dramatic. At 2 knots you can go for hours. At 6 knots your battery is used up in minutes.

What I'm really interested in is the formulas for the calculations and advise on an appropriate boat. This is the the only way I can get on the water with my wife so significant compromises are expected.
 

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Discussion Starter #19 (Edited)
Electric sailboat motor - The WoodenBoat Forum

I know of someone who put a Solomon Technologies ST-37 electric drive in their Westsail 32. The weight of the electric drive plus all the extra batteries was about the same as their old volvo engine and fuel tank, so, weight was a wash. They spent about $15,000 for the refit, said it took them about 600 hours of their time.

Run times, at 2 kts they can go for about 15 hours, at 3 kts for 6 hours, at 4 kts for 3 hours or at 5kts not long and not far. For me, that is a little too underpowered, particularly if you are sailing anywhere there is considerable tidal current. But, if you really only use it to get on and off the dock, then it might be worth it."
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That westsail is at least double the boat I'm thinking about so if I could get 4 knots for 6 hours it just might be good enough for me.
 

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Does this site give any usefull Info?
Electric Yacht - Libertine, Catalina 27

From the website- "Since we sail on a lake that is no more than 5nm in any direction, long range was not really a concern."

'nuff said.

Electric marine propulsion has it's place- calm inland waters. Here's my thinking:
In a pinch, if you have to, if you have no other choice and don't mind sacrificing engine components, you can conceivably motor along for a short length of time with a disabled petro-engine using the starter motor. On an electro-yacht, with dead batteries, and dead wind, you are dead in the water.
If you get pooped in breaking seas, chances are your petro-engine will stay running. what happens when an electric motor gets wet?
If a petro-engine gets snuffed by rising bilge, or descending greenwater, it might, maybe possibly be revivable. A drowned electro-motor is history. the downside of "plug and play" is "remove and replace."

Bottom line- would you replace your family car with a golf cart?

If you really want peace and quiet, invest your money in light wind sails, sailing lessons to improve your skills, and more time under sail. The better your equipment and your skills, the more time you spend quietly under sail.
 
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