View Full Version : retro electric re-fit
05-01-2010, 04:33 AM
im contimplating a electric convertion for my 31 foot strip built scooner. i have heard that electric is "the way of the future" less polution high instant talk and with new battery technology sheould be macking its way onto our waters sooner rather than later.
i like the sound (well lots les sound) of not having noice or that horible diesel smell that makes my wife sick, floating around my boat.
has anyone had any experience with electric motors on this site yet? if so what are the ups and downs.
also keen to here convosation from boath sides:- the hard core old school deisel or die fans and the stop living in the past and protect our waterways hippy beatniks.
05-01-2010, 10:38 AM
I have an old issue of classic boat that talks of an electric conversion. They used a Thoosa brand motor. Came with all the parts needed. I'm super interested in that too. Did some research online. They have a line of motors that should fit most needs. Right now the battery technology isn't there for cruising but if you're just using the motor to get away from the dock on the weekend or something you should be fine. It's a bit costly to install. If you're converting, selling the old motor tanks etc should return some of the cost but not much. You'll be saving on gas later though if you're set up to generate with wind. The great thing about the Thoosa is that it's set up to regenerate when under sail. Shift into ahead, throttle to the slowest speed. If you're moving at a decent speed through the water, it will regenerate for you. They had trouble with the regeneration. Seems you need a big slow turning wheel to get it to regenerate well. If you're screw is stuck in an appertur or otherwise restricted in diameter it might not work. They ended up cutting away some of the rudder and enlarging the appertur to swing a bigger wheel. Seemed to help. I'm planning on using an offset screw to keep the laminar flow smooth and allow me to use a larger diameter screw.
05-01-2010, 12:43 PM
I researched electric power for my boat and came to the conclusion that there are still too many negatives for it to make sense. The negatives as I see them are as follows:
1. Cost - An electric installation with sufficient battery capacity for an endurance of more than a couple of hours costs about twice as much as a new diesel engine install.
2. Endurance - Except at very low speeds (less than 3-4 knots) endurance of more than a couple of hours requires a weight of batteries 3-4 times the weight of a diesel engine, full fuel tanks and starting batteries. Even if you can accomodate several thousand amp hours of battery capacity, you are still limited to a day (8 hours) or less under power.
3. Charging - there are only two practical charging setups. One is to plug the boat into shore power after each use and the other is to have an on-board diesel generator. With the generator, you do have the option of running diesel electric. However, if you are going to run diesel-electric, why not just go straight diesel. Solar panels and a wind generator can be used to charg your batteries, but not if you run for more than an hour or so a day.
4. Weight - The batteries for even a minimal endurance setup are going to weigh 600+ lbs. More likely you will want 1,200-1,800 lbs of batteries.
5. Environmental - The batteries will have to be replaced every few years at substantial cost (minimum $600 for lead acid batteries in a minimal endurance setup to as much as $4,000-$5,000 for AGM batteries in a longer endurance setup. on top of the cost you will be putting a minimum of 100 lbs of lead a year into the reprocessing stream. Lead foundries are not exactly good players environmentally, nor is lead minig and smelting. Finally, the cost of batteries will be equivalent to about 40 gallons of diesel a year for a minimalist setup.
Basically, unless you have lots of spare cash, a boat that can handle a lot of battery weight and volume and access to shore power for recharging, I think electric just doesn't make sense now.
05-01-2010, 01:18 PM
I think the technology is catching up with the demand.
These units look good and the price is cheaper than a diesel.
05-01-2010, 02:48 PM
thanx for your posts.
i have looked at the Therosa 7000 rg model online. i can not get hold of the NewZealand importer at present so having trouble finding a price??
anyone know what they ask for one of these units?
im interested in this ajastable prop concept, any idea of the corellation between incerasing the lamaner flow for regenerating and decreasing it for propoltion.???
still find it hard to belive that 4 12 volt 12o AH batteries and an electric motor weigh 3 times more than the deisle and tank i already have!
05-01-2010, 02:57 PM
imcurious about the weight statistics above that say 600lb of bvatteries is needed. thant a minimum of 10 batteries and up to 14 ? 120 AH 12 volt batteries weigh 33 kg?
05-01-2010, 03:21 PM
Ultimately what you have to remember is that you drain your batteries a lot faster than you can charge them. Keeping that in mind, now consider your typical usage and that should give you an idea if electric propulsion is the way to go or not.
05-01-2010, 04:09 PM
What you need is Mister Fusion.
05-01-2010, 04:21 PM
Most of the electric systems I considered like 72 or 96 volts that is 6 or 8 batteries. If you go with group 31 batteries (115 amp hours = 1380 watts available for one hour), 6 batteries weigh approximately 6 x 69 lbs = 414 lbs and 8 batteries weigh about 552 lbs.
Consider a 10,000 lb displacement, 32' LWL boat. 6 knots speed requires about 10 hp. If you consider a 72 volt system with 6 115 amp hour deep cycle flooded lead acid batteries and it takes 10 hp to push your boat at 6 knots, the 6 battery bank will give you an endurance of about 56 minutes assuming the electric propulsion system is 85% efficient. If you drop the speed to 4 knots the power required drops to 3 hp and the endurance increases to 188 minutes. In both cases the run time totally flats the batteries. If you limit your battery drain to 50% of capacity, the run times are cut in half. Consequently, achieving a run time of 2 hours at 6 knots at 50% battery drain with my hypothetical boat requires 24 grp 31 batteries for a total battery weight of 24 x 69 = 1656 lbs
Doing the same calculations for a 48 volt system (4 grp 31 115 amp-hr batteries) gives an endurance for 50% battery draw down at 6 knots of 19 minutes. At 4 knots the endurance is 63 minutes.
A more practical 48 volt system would use 4 4D or 8D batteries. The 6 knot endurance of my hypothetical boat would be 32 minutes with 4D AGM batteries and 40 minutes with the 8D batteries. The weight of the 4D batteries is about 500 lbs and the 8D batteries would weigh about 670 lbs.
Clearly a system with only enough grp 31 batteries to generate the required system voltage is only useful for short runs from the dock out to a spot where you can set sail and vice versa. If you want the system to have the endurance to provide a couple of hours of run time for when the wind dies, you need some serious battery capacity. Hence, the large weights and costs of batteries.
Finally, it makes sense to go with AGM batteries because they withstand a larger number of discharge/recharge cycles than flooded batteries. That will increase your battery cost by about a factor of two and decrease your endurance by about 5-10% because AGM batteries tend to have lower capacities than the same size flooded batteries.
05-01-2010, 05:45 PM
Another boat to consider. My 36' sailboat has a 27' waterline length and a 15,000 displacement. It takes about 5.8 hp to push the boat at 4 knots. So, if I equipped it with a 48 volt electric propulsion system with four grp 31 AGM batteries (105 amp-hr capacity), the endurance at 4 knots would be about 30 minutes before the batteries were drawn down by 50%. That gives me a range of 2 nautical miles. My boat hangs on a mooring and it is about 0.7 nm from my mooring to the outer edge of the moored boats. Consequently, I could use a 48 volt electric drive to power out past the moored boats to set sail (11 minute run) and then power back in after dropping sail outside the moored boats (11 minute run) and still have about 8 minutes of endurance at 4 knots left. The 22 minute run would drop my batteries to about 63% of capacity. Recharging the batteries will require about 200 amp-hours (4 hours with a 50 amp charger). Since my boat is on a mooring I would have to rely on either solar or wind power to recharge the batteries. If I put 2 65 watt solar panels on the boat (130 watts), I would need about 20 hours of full sun to recharge the batteries. That means that I could use my boat every third day if there was full sun for the days between sails. If there was fog, or the weather was cloudy, I would have to wait much longer to recharge.
If I kept the boat at the local marina, I could use shore power to recharge the batteries. However, the run from the marina to the outside egdge of the moored boats is just over a mile. I could still manage with 4 grp 31 AGM batteries, but I would be drawing the batteries down a bit more than 50% by powering out and back. If the wind died when I was 5 miles from the marina, my only option would be to motor back at a speed below 4 knots. If I had run the mile out at 4 knots to clear the moored boats before I set sail, I would have drawn the batteries down to approximately 75% of capacity. If the wind quit when I was 5 miles from the marina, I wouldn't have enough battery capacity to get back at 4 knots. I could make it at 3 knots, but it would completely drain my batteries and it would take me 1 hour and 40 minutes. To be on the safe side I would probably need to reduce speed to 2 knots (2.5 hour return time) to avoid drawing the batteries down more than 60%.
If I wanted a range under power of 10 nm at 5 knots, I would need about 32 grp 31 AGM batteries to only draw the batteries down by 50% during the 10 nm run. That would come to about 2200 lbs of batteries and would cost $8,300. My boat does not have space for that many batteries and the added weight of the batteries would shorten my endurance under power because the weight of the electric propulsion system would increase the displacement of my boat by more than 1800 lbs.
electric power is a good option if you have a light boat, access to shore power and don't need to motor far. For a heavy boat with the need to power for than 4-5 miles, it just isn't practical as a retrofit.
05-06-2010, 02:56 PM
thanx Todd, for you well resurched and well put infomation. it has inspired me to do more of my own reasurch on the topic. im fast being convinced that a nice shiny new Yanmar 22 hp diesel would look rather nice in my engine bay, and get me a lot further than an electric convertion. maybe one day things will change and electric motors will me efficiant enough, and alternative power will becom effective enough to validate electric motors for the serious passage makers amoung us....
05-06-2010, 04:36 PM
Actually electric motors are more than adequately efficient. The difficulty comes in storing electrical energy to run the motor. The only affordable batteries are lead acid and they simply don't have the energy storage capacity to run an electric powered boat for very long unless you install a LOT of batteries. Furthermore lead acid batteries are going to need to be replaced every 5-7 years. The cost will come close to the cost for diesel fuel for the same period plus you have the environmental consequences of disposing of lead and getting the lead for the new batteries.
I think that if fuel cells come down to reasonable prices that they make make electric propulsion a more viable alternative. However, then you still have to provide the fuel for the fuel cells and deal with the costs of the catalysts in the fuel cells.
Incidentally, a 22 hp diesel is equivalent to a 16 kilowatt electric motor. I know that the electric propulsion web sites like to say that you can get away with less power if you go electric. However, I think that is only trus if you design the boat from the ground up for electric propulsion. That design would incorporate a large, relatively slow turning, high pitch prop to take advantage of the high torque available at low rpms from electric motors. However in the case of a retrofit, you are generally stuck with a relatively small prop that is optimized for higher rpms. In other words, you really can't take advantage of the plusses of an electric motor because you can't fir a big enough prop in a typical retrofit situation.
In summary, if you want to go electric, the only applications that make sense now are either a diesel electric system with sufficient batteries for an hour or so of low speed cruising before you have to fire up the generator. That sort of system gives you quiet low speed operation for short runs with the gen set for longer runs. However, you need a pretty beefy gen set. The other viable option is a diesel/electric hybrid that basically incorporates an electric motor between the diesel engine and the prop. You can run all electric until you draw the batteries down then the diesel engine takes over. Steyr motors make a diesel/electric/hybrid system. Both diesel/electric and hybrid systems are MUCH more expensive than a pure diesel system at present.
05-06-2010, 09:30 PM
There is a yahoo group dedicated to electric boats - check it out, there are several posters who have electric aux power, lots of pictures of installs and lots of tech info if you have the perseverance to read through the archives.
You can see my 25' electric boat at www.wolfeboats.com (http://www.wolfeboats.com). It will go 7 mph for 40 miles with 500# of batteries but is light weight and slender.
You don't say what the displacement of your boat is but that and WL length is what will determine the speed/power relationship. Most successful projects use 5-6 hp motors. 48 volts is a popular voltage where components are available and not too expensive.
If you need to motor in and out of a harbor and sail the rest of the time AND can plug in to recharge from shore power an electric system could work for you. I don't think a hybrid with a big gen set makes much sense unless you have huge house loads. Wind and/or solar can recharge on a mooring but are expensive and bring their own complexity.
A typical E system's weight and cost will be in the same ballpark as a diesel and full tank of fuel. If you are handy good at keeping the blue smoke inside of electrical equipment you can build your own system and save a few thousand dollars over a package unit like solidnav or Thoosa.
Electric won't go as fast and range will be a tiny fraction of a tank of diesel fuel. If you buy fuel once a summer, as many sailors do, electric could work. Electric has other advantages, mostly esthetic. It also needs practically no maintenance if you use AGM batteries, which should last many years if you don't often run them flat and keep them charged.
Lithium Iron Phosphate battereis are becoming available at more reasonable cost, driven by the huge demand for electric bicycles in China. Google "Thundersky". They are about 1/3 the weight and 1/3 the volume of lead acid but between 3 and 10 times the cost. They claim a long life even under deep discharge. For a boat that is carrying a lot of lead in the bilge anyway substituting lead batteries for lead ballast can work.
If you need to run the engine all day to get back home on windless Sundays forget electric. If you need to run your engine to punch into 30 kt head winds forget electric.
Electric isn't better or worse than ICE, it's different. Heck, lots of people think you are crazy fooling with all those ropes and rags to go only 6 kts!
05-07-2010, 01:21 PM
I don't want to chime in here on a topic that I really am not versed in but I think that with regards to charging one thing has been missed. Could a bank of batteries not be recharged while under sail by a regenerative process? This would of course impact sailing performance but is a viable method which can help to supplement shore power or solar and wind generation... no?
05-07-2010, 04:51 PM
My "Mr. Fusion" remark was only slightly tongue in cheek.
As above, your problem is energy density.
Batteries don't have much.
Have you considered a yuloh?
05-07-2010, 09:43 PM
Regarding regeneration, most of the folks on the yahoo EB site who have tried to actually document how much energy flows back into the battery bank under sail report "not much".
Ampair makes a towable log type generator with a 12" prop which puts out 72 watts at 6 kts - that's 1/10 hp. I would bet the frictional losses in a typical drive system with a 1" shaft, thrust bearing, motor bearings, cutlass bearing and packing gland could be that much.
05-08-2010, 08:33 AM
We converted our plastic CAL 34 to electric propulsion about five years ago and it has worked out very well for us as an auxiliary propulsion system. All of that time spent cruising in the Caribbean.
We went with the Electric Yacht system (http://www.electricyacht.com) as it seemed to have the best controller and regen system. We use a simple 48V bank of eight 6V golf cart batteries and we have never been without power for the system when needed in spite of never being plugged in to shore power ( using only regen, solar, wind and Honda 2000 from time to time).
As far as cost goes it was much less than a new diesel would be and in terms of weight I think I figured that the entire system actually weighs in about 75 pounds less than the old atomic 4 and fuel.
In all seriousness, about 25+ years ago I was involved in building a couple of electrically powered launches (22' fantail, similar to original Elco's in design). For power the owner of the yard I worked at had me drive to a golf cart dealership & pick out a couple of used electric golf carts ($100 ea), had them delivered to the yard & I cannibalized the drive systems for the launches. I don't know how well they held up over time, but they seemed to work ok for my involvement.
Here is one of the ones I put together (not me in the pics).
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