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mszczepa 07-04-2010 11:43 PM

electric motor
I am buying a Bristal 33 with an electric motor I am wondering if there are others out there with an electric motor I was wondering if you get a honda generator and plug in battery charger 20 amp will this extend the range by a large factor what kind of generator do you need to push the motor thanks Mark

scottyt 07-05-2010 12:34 AM

well that depends on what kind of motor... is it a trolling motor, or a larger inboard motor?

a trolling motor, sure it will, and for a long time too

a built in motor, not even close.

there are 3 honda inverter gennys. the 1000, 2000, and 3000. each is not really the full size of what they are called, its closer to 85 % of the name.

so you have a 1k, a 2k and a 3k. to convert watts to hp is about 750 watts per hp, so the 3 k could produce about 4 hp. so for about 30 hp you would need about 25 k watts, a huge genny. now electric works in boats slightly different than diesel so you might be able to get away with say 10 k watts ( a "normal" genny size ) for extended running but you wont get hull speed on just the genny, so the battery bank would start to run down to get hull speed

now for battery banks, i would think you want at least 2000 amp hours at 12 volts, but the bank would probably be a 48 volt bank. which would run a 25 hp electric motor for about an hour ( 2000 amp hrs at 12 volts or 500 at 48 volts )

mszczepa 07-05-2010 01:29 AM

The survey says it is a Briggs and Stratton Etek model 48 volt 8 hp continuous 15 hp peak I know there is a 4 battery bank with a 20 amp charger My question is it possible to put another battery bank of 48 volt and run a 2ooo honda gen to charge other one as you go along so that you could get a 40 mile range thanks Mark

tomwatt 07-05-2010 08:36 AM

Your current battery bank is 4x12v, so a second bank would double your Amp Hours... how much weight is that going to add to your boat?
Interesting rig... post some pictures.
I considered something similar for myself, but in the end decided that weight of battery storage was going to make it impractical and expensive... that fuel wasn't that expensive yet.

eMKay 07-05-2010 12:20 PM

What is the capacity of your bank now? That motor is designed to draw 400 amps peak, and 150 amps continuously at 48 volts. It can run on up to 72 volts though. The generator can extend the range but not very much if you are trying to run at hull speed. An off the shelf controller is available to run it up to 250 amps with a regeneration feature that can put back up to 4 amps into the batteries. If you are daysailing this can recharge the current you used to get out of your marina while sailing. I am planning a similar system for my boat with a targeted range of 20 miles, and a small generator to help with recharging if I need to run up to max range. You must plan your battery banks capacity to be double your targeted range, if you continuously run down below 50% charge you will destroy the batteries quickly.

As for the weight, remember the average diesel engine weighs 200 to 500 lbs (my tiny 8hp Renault weighs 200lbs) while the Mars ETEK (Briggs doesn't make it anymore) weighs 24lbs.

mszczepa 07-05-2010 01:15 PM

I have not picked the boat up I will after the 15 th I do not really want to put an outboard on the back but I need at least 20 miles out of her I don't mind 4 knots so I am looking for a 5 hr run time The boat has 4 Trojan 130 ah each in a series Is it worth putting another 4 battery bank and will it get me there thanks Mark Am I understanding this right from what you said that my honda 2000 could run to a controller that would run motor at 250 amps I do enjoy your feedback because this area is not what I am good in thanks again

scottyt 07-05-2010 01:48 PM


Originally Posted by mszczepa (Post 619603)
.... Am I understanding this right from what you said that my honda 2000 could run to a controller that would run motor at 250 amps ...

at 48 volts a honda 3000 will put out about 50 amps, of coarse thats going thru a charger taking 110 v from the genny and making it 48 volts for charging.

so a 10k watt genny would run your motor at normal current levels if emkay was right on what it draws. now you need to look at the price and size of a charger that can put 150 amps at 48 volts.

Mark F 07-05-2010 10:26 PM

Hi Mark,

I have an Ericson 27 with a similar size motor built by Mars. To give you an idea of performance, at 20 amps I get 4 knots of boat speed. I have motored in calm conditions for 7 hrs at 4 knots and used half of my capacity - two 100 amp hr battery banks. On your 33 you should be able to add another bank pretty easily. My system is set up so I can motor on one bank while charging the other using an external generator (Honda 2000). I have never done that but there are others using Honda 2000's to extend their range. Check out the Yahoo Electric Boat Group to find out what other's are doing. It is a growing industry with more people making the switch all the time. You're going to like the relative simplicity, quiet, odor free, immediate power motoring you get with Electric propulsion :-).

mszczepa 07-06-2010 12:39 AM

Thanks for getting back to me there is hope. I really did not want to stick an outboard on the back or put an engine well in . I did dream about making special rigging so that I could attach my dingy with its 15 hp motor to the side of the boat and using this when I had to do any distance in calm waters. I looked at other battery chargers that put out 40 amps and thought again of charging one bank while running on the other if I needed distance Question ? when you said you had a hundred ah battery did you mean that all four batteries added up to 100 or did you mean each battery was a hundred amps when I look at mine on the other boat they say 180 ams reserve so that does mean you add up the four does it not??? I am trying to get my head around this so when I make my presentation to my wife ** the keeper of the funds } I know what I am talking about thanksMark

Mark F 07-06-2010 01:50 AM

I have two separate banks (sets) of batteries. One is made up of four 12 volt group 27 AGM batteries connected in series. Each battery is rated at something like 90 amp hrs, by connecting them in series you get 48 volts and the amp hrs stay the same - 90 ah. The other bank is four group 31's rated at 110 ah, so 48 volts and 110 ah. Your 130 ah Trojan's are a real good start and should do fine for local stuff. I like having the redundancy of a second bank even if I rarely need to dip into the second bank. You should find out what the amp draw is for 3, 4 & 5 knots of motoring boat speed. Also the proper prop is important to performance. I started with a fixed two blade 11x8and got 3 knots at a 20 amp draw. Now with a fixed three blade 12x10 I get 4knots at 20 amps. Does the Bristol have a way to monitor the batteries?

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