Re: [electricboats] Sizing motor for 45-50’ boats

Consider that you want to operate your motor in the sweet spot which is usually somewhere close to full throttle. If you overpower too much you might be running in the 20-40% capacity range which is not going to be as efficient and could contribute to overheating, especially in your controller. This may not apply as much with some high end motor/controller combinations but generally variable drive electric motors are not as efficient when running at low speed so avoid killing a mosquito with a sledge hammer.  I wouldn't go much more than 2 kw/ton displacement. 

On Monday, March 15, 2021, 01:57:28 PM EDT, orest iwaszko <orest@albernicharters.com> wrote:

ratios vs heat:

      My  10 kw motor can spin 5000 + rpm 

Intuitively I topped my ratio at  2700 ( for longevity i thought )

      But at slower rpm the cooling fan is also slower = less cooling .

      I mostly use the electric for fishing at 1200 rpm and the cooling can be an issue

Wondering if it was a mistake to go with the slower rpms.

and while Im here ,    any cooling ideas for running continuously 

.  

 Sincerely, Orest 

 Alberni Charters

 250-735-6503.

On Mon, Mar 15, 2021 at 9:37 AM twowheelinguy via groups.io <twowheelinguy=yahoo.com@groups.io> wrote:

Randy,

I can give you a benchmark for how LOW you can possibly go. 

I've been pushing a 45',  20 ton, concrete bilge keel hull with a 48V, roughly 8 kW, "golf cart motor on steroids" for about 8 years now, although the boat's been on the hard for over a year while I've been doing other things lately. 

If all you want to do is build a system that will get you in and out of the marina to go sailing, then you can feasibly get by with a much smaller motor but if you plan on being an electric boat with auxiliary sails, then the old 1 kW/ton of displacement is a good rule of thumb and you'll want a generator big enough to feed it at whatever speed you want to operate. 

The Arc was always meant to be an "experimental water craft". With a 5500W single axis tracking solar array and a goal of cruising directly off real time solar input, there wasn't much point in putting in a bigger motor. Although it's fair to say the boat is a "bit" underpowered lol, we learned we could cruise nicely at about 4 mph all day on nothing but sunshine and have enough power to keep the vessel under control in all the circumstances we encounter in the ICW. Albeit often in slow motion.

Seems we get about one mile per kWhr of energy. So on a partly cloudy day, we can collect about 30 kWhrs and go about 30 miles. Or record is 42 miles on a clear winter day. We've never cruised in the longer summer days.  It's a little slow but we're usually not in a hurry and if we are, we can switch back to the original 38hp diesel and do about 50 miles per day, rain or shine.  Or at least we could until a couple years a go when 40 yo transmission started acting up.  At full throttle, using the batteries in tandem with the solar, I can get 5 knots out of the electric but this is not sustainable for very long with my 5 kWhr golf cart battery bank. (16-6V GC2s at 50% dod).

We started building the boat 12 years ago with a LOT of help from this forum. Thanks to anyone that remembers.  It took about 3 seasons to get it operational and another season or two to tweak things out a bit. We've been cruising it up and down the SE U.S. intracoastal for about 7 years.  

Since I need to repair the diesel's transmission, I plan on just upgrading the entire system in the next few years with higher eff. solar panels that will deliver 8.5 kW and a 12kW motor that is a little more efficient than my current shunt motor.  At that point I will also change from a parallel hybrid configuration, to a series hybrid, add a 20 kWhr Lithium battery bank, and install an 8 kW, 48V DC genset.  Just have to sell the house first to get the money. 

Based on the data I've collected on the Arc so far, I think this configuration should allow me to cruise at 5 knots on solar alone, about 7 knots at full throttle, and get about 10 mpg in hybrid diesel mode at 5 knots. Hope to be in the yard getting started this spring.

Capt. Carter

www.shipofimagination.com  

  

On Monday, March 15, 2021, 10:19:12 AM EDT, Randy Cain <randylcain@gmail.com> wrote:

The ME1616 with the Sevcon Gen 4 Size 6 will give you 24kw of power continuously (48kw peak) at 96v. I'm building my conversion with 2 of them (48kw continuous, 96kw peak) via saildrives on my 34' 4.5 ton catamaran. If I were driving a single shaft then I would use a separate belt from each motor to a single shaft. 2 controllers would be required.