Electric propulsion for a sailboat

Hi, This has to be the right place and this question has probably been asked but I think this is a great idea and need some help. I have a Dawson 26 ketch. I took the inboard out and wanted to replace it with an electric trolling motor or something like that. My intention is to use the electric system to move around in a marina under power or pull away from the dock when I don't have a shore breeze. I thought about creating a well in the back cabin as this is a center console boat and putting it in when needed. I have no idea how much motor I need to push a 6000 lb. boat or the amount of electricity it would need even at slow speeds. Part two is to use our solar panels to recharge the batteries as necessary. Could anyone steer me to the right place or provide guidance? Thanks.

 

Think about it some more....

To move your boat against the wind, you need at least 5 KW. A brand new 100 AH battery can store 1.2 KW, but to make sure it stays healthy for a number of years you can draw only half of than, so .6 KW.
Your 5 KW electric motor will run for 7 minutes before the low battery warning light comes on. That is probably not what you're aiming at, so you need much more storage capacity. With 4 such batteries you have almost half an hour.
If that suits you, put the batteries in series and buy a 48 V DC 5 KW electric motor.
The motor must be able to deliver the power at only a few 1000's rpm or you need a gearbox that does the conversion.

As for solar panels: You have the disadvantage that you are a sailor, so it is difficult or impossible to place the panels where there are no shadows. Even a thin rope casting a shadow over a panel causes the power generation to drop sharply.
You probably have space for 300 Watts of solar panels; if you manage to keep these in unobstructed sunlight you need 17 hours to recover half an hour of electric sailing.

This is all theory of course. I omitted mechanical and electrical losses, but you may consume less than the 5 KW if you move slowly and there is no wind.

 

Plenty of electric boats around. Have a look at

http://www.electric-boat-association.org.uk/

 

I have been working on a design for an electric auxiliary sail boat for almost a year and I am still a long way from a working model. Torqeedo makes a 48 volt 4 k out board that would suit your purpose as well as 26 v lithium ion batteries that are light enough that you could have a bank of sufficient capacity to push the boat at 4 or 5 knots for an hour. This will cost you more than $15,000. Forget about the solar panels. With a hull half the weight and twice the length and a fifth the beam as yours and somewhere to put 10 250 w panels you might run at five knots continuously in full sun at half throttle.

 

I'm kinda struggling with the same questions. I have a DIY new build rather than a re-power situation.

Like you I went with the idea of a well, as I found the near-180 degree rotation of an outboard very appealing when manoeuvring in tight places.

I came across this, which in my case addressed my questions and concerns. So much so, that I have committed to purchasing one.

http://www.torqeedo.com/

I found several other options, but have not kept the links. These all seemed to be poorly "packaged" systems cobbled together from a range of different manufacturers and mainly focused on substituting a fossil fuelled engine with an electric one.

 

Oh... Should have remarked... substituting an inboard fossil fuelled engine with an electric one.

 

Yank the engine and trans out, but leave the shaft. Attach an appropriate motor, with chain sprockets, gearing to a desirable prop RPM, then place batteries in the engine bay to account for the engine weight removed, minus the electric motor weight. I did precisely this on a 25' racer about 20 years ago when the gas engine took a dump. I used a 24 VDC commercial washing machine motor and it was enough on the 4 deep cycles, to get me out to the river, clear the channel marker, where I hoisted to the starting area, then return home. The weight was within a few dozen pounds of the gas assembly and I got about an hour and half before noticeable power lose could be heard. The boat was charged at the dock with a standard shore based rig. Unless you only sail once a week, forget about the PV panels for this size of recovery.

 

Now thats a really cleaver idea. I had no idea a washing machine motor could be used in such a fashion.

And I suppose, therein is the tone of my earlier post. I have little knowledge of electrical systems, had seen some seemingly complex solutions on-line that looked a little too amateur from my ignorant perspective.

Some of us have the knowledge and aptitude to construct such a thing, which I envy you for.

Me, well, I'll leave such things to the Germans and their ingenuity for me to enjoy after parting with a little too much cash. Knowing at least that I have a great setup and one I can have faith in.

I would however, greatly enjoy and surely learn from a more detailed explanation of what you build and how you went about it, as I'm sure other would too.

 

Many will declare that electric is popular, and for occasional use where your boat is kept at a marina or on a trailer and the batteries can be charged from mains supply and your use is occasional weekend outings - THAT WILL WORK.

BUT

for live aboard independent operation the technology as a complete system is not sufficiently mature to be confident in meeting the propulsion and other needs always when called upon. - - Expect quite a few years to pass before all components meet the reliability of the friendly diesel auxiliary.

Torqedo is good, but does not like 'long' battery runs so NiFePO4 high-tech batteries near the stern are a must. - - These batteries demand special charge management systems. - - To extend runtime, a special generator is needed and must charge through the specialised management systems. - - So now the old diesel aux looks very good in its reliability and simplicity.

I tried to implement full electric, - but, before launch I opted for the diesel. - - I still have the diesel powered battery charger for 24v or 48v battery bank - (cost Au$14000).

My 48v battery bank is now split into a 24V system and runs the house, galley and nav. - - My 20hp pair of saildrives have their own batteries. - - Under power I do 6 knots on either engine and both give 10 knots all at 3000 rpm which gives me 3 litres/hour burn on each engine. - - I have 1400W of effective solar panels, (except when the seagulls leave their deposits), and a potential to fit 2340W of PV panels.

So in summary, and by dent of practical experience, (quite expensive) - the technology is not ready yet for long-term-live-aboard-cruising if one is not an expert with fat bank accounts and you remain in the local area where parts and support is not an issue.

 

I agree with Masalai.

Did the same thing. Went through every conceivable possibility to do diesel-electric propulsion in my case. Everything there is, including custom systems.

They were all way too heavy for a catamaran. Went with outboards instead in my case.

 

About the time fusion reactors come on line, PV panels will begin to develop enough wattage in a small enough for print to be viable.

 

Hi Par,
You and I might wish, but I doubt it will happen (either option) within our budgetary constraints unless you are that billionaire who has been badgering me with offers of 500.000 pounds something. "You have been rewarded 530,000.00 GBP ( Five hundred and thirty thousand great britain pounds ) in the facebook Award. Contact Micheal Hammond on demo@bcsconsultants.com and call +447035905064 to claim. " by the name of eventmanager@facebookpromo.com?

 

A large Hilti with a long shaft to an 16" X 16" prop will give you portable, directable thrust.

Great for mixing large quantities of margaritas too!

 

Sailing

All of the comments are well placed as far as I can tell. I have considered converting a dc motor for this use and connecting it to the existing prop shaft. What I have ended up doing is putting in the well and fitting out for a small outboard that should push the boat to near hull speed if necessary. It just seems that folks have been sailing for a few millennia without any auxillary power. We can convert solar energy to power a battery and batteries can power motors. It seems odd that we can not accomplish this in this time. I worked most of my life as a mechanical engineer and can do the math but sometimes a clever person will create something that will do what convention says is impossible. We will just have to keep working on this and perhaps it will be one of us.

Thanks for all the thoughts. Jack

 

Good on ya Jack.

Don't forget, wind is solar powered and moves sailboats with ease.