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valhalla360 · 02-07-2020, 09:26

Quote:

Originally Posted by Bill Seal

Maybe I'm color blind or stupid, but it appears that the electric motor magically increases RPM while keeping torque and power constant. ????

Magic Electric HP that defies physics

yvest · 02-07-2020, 10:39

Quote:

Originally Posted by Bill Seal

Maybe I'm color blind or stupid, but it appears that the electric motor magically increases RPM while keeping torque and power constant. ????

Indeed a problem with these curves ...

The pink curve rise way to quickly
(could not find the original source)

But the basic principle still stands I think.

For instance from :
https://theconversation.com/heres-wh...-torque-115356

Which lead to basically the same analysis.

PineyWoodsPete · 02-07-2020, 12:17

Quote:

Originally Posted by MichaelPrichard

I do apologize for appearing to pile onto PineyWoodsPete, especially since I'm fascinated by your new boat and do largely agree with most of your comments, but I did really want to quibble with this line: while there are some truly lousy TVs out there, and computers the world over generally suck, which I blame on software (as a former Apple HW Engineer), the world is full of refrigerators that run over 30 years with.... and this is the key part.... zero maintenance, ever. Most people don't even vacuum the heat exchanger coils on the back every 10 years. And those lousy TVs will mostly operate as well as they did when they were new up until the $0.25 under-spec'd capacitor burns out 5 years later. But the point is, they'll operate that way with zero maintenance. Running a diesel with no oil changes, replacement belts, impellers or filters will kill the engine in a few hundred hours of use. Of course, no one should ever operate something as magnificent as a well engineered diesel thusly, and I maintain my converted 2003 Duramax powered Suburban (22mpg thank you very much) to the best of my ability because I can't afford a Tesla yet... (end rant)

No apology necessary, Michael! Our last cruising sailboat was a '93 FP Antigua 37 with same Yanmars we bought in Seattle in '96, taking it from near top of Vancouver I. to top of Nova Scotia, then Gulf Coast of FL - from where we had to deliver to Annapolis for full asking price of $25,000 over the $150,000 we paid - and with 4000+ hrs on the engines, which still ran as always.

The only mechanic I've ever called for this or any of the 7 diesels or 9 gas outboard engines I've owned over 60 years was for an oil leak around one of the cat's HP fuel pumps on the leg down to San Diego due to defective gasket. Shimming injection timing not in my skill set. When same happened with the 2nd engine, I simply sealed the perimeter with two coats of epoxy.

What sold us 79 year olders on the Greenline was the full-time 120V through the 48V 12kWh lithium pack and 5kW Victron inverter/charger and 480 kW solar, letting us hang on the hook for at least 3 days with amps to spare even with microwave and electric (not induction-type) stove top - and a reefer/fridge to kill for! For charging, the motor is a 5kW gen @ 2000+ engine RPM.

When the Covid crisis passes, we welcome you to drop down to Seaside for a day or two to check out the Greenline - which was Paul Kaplan's of KKMI lightly used boat, beautifully outfitted and maintained.

**Pete7** · 13-10-2020, 04:35

Quote:

Originally Posted by Adelie

The Cal 34 I want is about 4,000lb lighter so yes, I have plenty of confidence that an electric motor using 1.0kW could push a Cal-34 at 3.0kt, perhaps slightly faster.

Here is another report all be it somewhat older and using 20Kw of AGM batteries. However, some useful numbers at the bottom of the page for speed and range etc.

https://electricyacht.com/wp-content...n-Story-EY.pdf

jack4566 · 14-10-2020, 11:56

So I'm jumping into this discussion with a question for anyone who has done the math.

Is there any weight savings of electric?

Purely looking at sailing performance, lighter is faster right?
On one side you have diesel:
200kg+ diesel long block
200kg+ fuel tanks
50kg in spare parts, filters, auxiliary cooling pumps, etc.

And on the other you have electric:
20kg motor
50-200kg in batteries (which you had already)
10kg in extra wiring and control systems.

So potentially cutting 2-3% off your displacement. That's gotta count for something.

**skipmac** · 14-10-2020, 12:22

Quote:

Originally Posted by jack4566

So I'm jumping into this discussion with a question for anyone who has done the math.

Is there any weight savings of electric?

Purely looking at sailing performance, lighter is faster right?
On one side you have diesel:
200kg+ diesel long block
200kg+ fuel tanks
50kg in spare parts, filters, auxiliary cooling pumps, etc.

And on the other you have electric:
20kg motor
50-200kg in batteries (which you had already)
10kg in extra wiring and control systems.

So potentially cutting 2-3% off your displacement. That's gotta count for something.

Depends on two things.

1. How much battery (IE range under power) you need. Just enough to get away from the dock you'll save a lot of weight.

2. What you have to charge the batteries? Need a lot and off the grid so add a diesel generator, no savings and maybe a penalty. Very small solar or shore power only charger then yes weight savings.

**Adelie** · 14-10-2020, 12:47

Weight comparison is going to depend on the whole system and performance expectation. I want a Cal34 so let’s use that as a basis.

They originally came with Atomic-4s at 325lb. 25gal of fuel is about 150 lb.
tanks, plumbing, filters, add to that. Let’s call it an even 550lb or 250kg
That will get you somewhere around 20hr at WOT (136nm at 6.8kt in calm water)
At 4.5-5.0kt range will be around 250-300nm.

If I convert to 48v electric the motor is 70lb plus throttle, cabling, lugs, controller, readouts: let’s call it 100lb.
The batteries that are in the boat already are sized for house loads, you need extra for propulsion.
Firefly G31s are 74lb each and we need multiples of 4 to get 48v. That’s 300lb for each set of 4 which provides 116Ahr.
With 1 set of 4 batteries I could go about 2-3nm at WOT
At 2.5kt I could go about 22nm. To do that I would be using 500W. If I have enough solar panels installed to average about 1000W I could motor indefinitely at that speed. During the day the panel recharge the traction batteries and propel the boat. At night the batteries propel the boat.
Panels, cabling, controllers, supports: let’s call it 150lb so total weight is now even with the original installation.

To go 4.0kt in flat water I would need right around 2.0kw. A Honda EU2200i is rated for 1800w continuous. That plus solar panels and batteries gives me enough to go 4.3-4.4kt continuously.

If you are traveling off the beaten path finding fuel may be an issue. In high latitudes off season insolation is radically decreased.

Weight is not the only tradeoff.

I am a big proponent of electric propulsion but people need to understand the trade offs when choosing to go that route. For cruising electric propulsion would work just fine. Add an outboard mount if you are worried.

For weekending and local cruising where you have to be home at the end of the weekend at at the very least need to keep a schedule then fossil fuels are the better pick.

**Adelie** · 15-10-2020, 16:32

Something that just occurred to me.

Again using my hoped for Cal-34. Let's say the boat arrives with 2 house batteries running at 12v. I convert to electric drive with 4 fireflies and am even on weight compared to the boat as originally purchased.
If I install another 4 fireflies then I double my range for a given speed (see above) and add another 300lb to the boat over what I started at.

But if instead I add 4 fireflies and remove the existing 2 batteries (assume same weight) and power the house loads thru a step down converter I have the same capacity available for house loads an additional 50% range for a given speed at the cost of 150lb mass.. Actually I probably have a bit extra range and house capacity because the larger bank greatly decreases load per battery and capacity is increased thru the Peukert effect.

There is some extra cost getting the converter and finding mounting points for the extra batteries but there is a slight advantage for traction and a large advantage for house loads.

Keep in mind this won't allow you to have a faster round the clock speed unless you increase your available solar panel wattage too.

zloitapok · 22-10-2020, 15:19

Hello everyone posted in this thread and read it)
Thanks stevenm2016 for your post, one practical experience post cost a hundreds theoretical posts.
Also thanks all other ppl who share their experience with EP speed/power, regen power, etc.

I started to use EP at boats from 2017 and converted two small boats to electric inboards and one old gasoline outboard to electric one.
Also, I have derived a rough mathematical formula to calculate power/speed curves for provided hull params - thanks Fraud and some my observations.

I was not able to check my results at heavy boats and probably calculated data have inaccuracy at power > 20 kW

But for small and medium boats it work well. Hope this will help someone.
I assume is used large effective props.

**Pete7** · 23-10-2020, 03:16

Quote:

Originally Posted by Adelie

But if instead I add 4 fireflies and remove the existing 2 batteries (assume same weight) and power the house loads thru a step down converter I have the same capacity available for house loads an additional 50% range for a given speed at the cost of 150lb mass..

Did that with a previous boat that was 24v. Most things like chart plotters and the fridge ran better at 24v (same wire, higher voltage, lower current) apart from the VHF. I couldn't find a 24v VHF for sensible money, so used a small drop down box which worked fine, but was only powering one device.

If you plan on running CP, VHF, AIS, autopilot and night lights whilst at sea, you will need a bigger drop down box. Perhaps also have a small AGM battery like Odyssey or Red Flash as a buffer and just in case and to even out the loads when the autopilot kicks in at the same time as the fridge.

**Pete7** · 23-10-2020, 03:19

Quote:

Originally Posted by zloitapok

I was not able to check my results at heavy boats and probably calculated data have inaccuracy at power > 20 kW

But for small and medium boats it work well. Hope this will help someone.
I assume is used large effective props.

Thank you, that is neat simple diagram showing examples of different sized yachts.

Interestingly the Cal 34 is more efficient at 4 knots than the smaller and lighter Bristol 27.

How easy was it to calculate the figures and could anyone do this for their yacht?

Pete