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Old 08-08-2021, 12:44   #316
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Re: Replace Diesel with electric engine

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Originally Posted by wingssail View Post
On what basis do you think that 20hp will drive Jedi at 6kts? I'd guess that it will be 2-3 times that power required. For 6 kts, what RPM do you run your Yanmar at? The horsepower/rpm curve for that motor should tell you what it is putting out to get you that speed. I'd say that at 1800 RPM that would be about 48 hp, or 40kw. Well, whatever.

The point is that you'd need a 16kw gen set for 20hp, and a 50kw gen set for 60hp. Somewhere in that range would get you 6 kts. I don't see why it is "no question about it" why you'd replace one diesel with another AND the electrical drive equipment, etc. Why are you so sure about it?

The Brake HP/Torque figures for any engine are taken at WOT - the results being the counter-power needed to brake the engine down to the selected RPM to make the curves.

The Prop Power/Demand (PD) curve is what you want here - the actual power absorbed by the prop at different RPM, the only assumption being that engine reaches max RPM at WOT. It's a non-linear cubic relationship. So it appears on the below curve that @ 1800RPM, PD is only roughly 22HP needed, assuming 100% efficiency - so maybe 25HP actual, or a bit less than 20kW.
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Old 08-08-2021, 14:47   #317
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Re: Replace Diesel with electric engine

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Adelie, You are absolutely right. But my point is that if they had to purchase the OV unit (and the ancillary items, and the cost of the haulout and installation) it would not have been a DIY EP system for someone extremely short on money. It would have cost them a substantial amount.

That is the "trap": It looks cheap but the needed ancillary equipment, the installation, and upgrades for desired power, range, and dubious regen, raises the cost.

A friend with a CT 41 described the realities of his electric drive system:

"It didn't cost much but it wasn't free, and you have to learn how to sail."

Actually, not bad, if you think about it.
I get the impression that the DIY unit was satisfactory to them and they only switched to the OV because the unit itself was free. The advantages would not have been worth it to them if the had to pay retail.
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Old 08-08-2021, 14:59   #318
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Re: Replace Diesel with electric engine

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Adelie, I don't get your calculation here. Studentdriver is talking about a 48000lb 52' boat and you are saying it can go 2kts on less than 2/3 of one horsepower? (and who thinks 2kts is sufficient?)

And even then, using your 500watts for 24hours means 12kw, which is a lot to collect in solar in the normal 6 hours of full solar sunlight. However big a battery he has, eventually he has to replenish 12,000 watts per day.

I don't think this is practical for most cruisers.
Sorry I did not make it clear, less than 500W is for Uma which is what I had writing about for several posts. Actually at 2kt demand will be on the order of 350W for Uma. That would be about 700Ahr at12v. I don’t see a convenient way to fixed mount k2100W of panels on the boat but I can think of a way to put 1000W on a temporary tracking mount which would provide similar output. Not convenient an most people wouldn’t do it butyrate doesn’t mean it’s impossible.
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Old 08-08-2021, 16:17   #319
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Re: Replace Diesel with electric engine

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Originally Posted by s/v Jedi View Post
I base that on the calculator. 20hp = 15kW and I think it evenshows more speed than 6kts for me. At 40kW, your suggestion, my speed will be 8.5 kts.

I guess that explains it. In 99% of the time I would not need diesel at all, but if needed I can motor for days. Not sure yet what size genset would be optimal, wish I could get more resolution in this graph.
If you hover the cursor over each data point it will give you the power used. For 19.5m LWL and 25t it says 3.5kW at 6kt. I'm not buying it.
I don't think the equation used is very good when the speed is below 1.0SLR

For 0.75SLR Skenes indicates about 8lb resistance per long ton at the high end. Let's assume a 55,000lb boat loaded. That's 24.5 LT. which translates into 196lb resistance. Let's call it 200lb. Let's assume 20lb thrust per hp. That's 10hp to make 6kt. I assume 20lb/hp because it is an outboard geared and propped for planing speeds pushing the boat at displacement speeds so it's going to lose efficiency.

Jedi if you ever mount the engine, I would be very interested in what speed you can make with the dinghy motor at WOT throttle. Let me know, I like collecting this kind of data.
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Old 08-08-2021, 16:32   #320
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Re: Replace Diesel with electric engine

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Originally Posted by PineyWoodsPete View Post
The Brake HP/Torque figures for any engine are taken at WOT - the results being the counter-power needed to brake the engine down to the selected RPM to make the curves.

The Prop Power/Demand (PD) curve is what you want here - the actual power absorbed by the prop at different RPM, the only assumption being that engine reaches max RPM at WOT. It's a non-linear cubic relationship. So it appears on the below curve that @ 1800RPM, PD is only roughly 22HP needed, assuming 100% efficiency - so maybe 25HP actual, or a bit less than 20kW.
Has Jedi ever indicated what RPM the engine needs to hit 6kt?
6kt may be off the chart.
Alternatively does Jedi have a fuel flow meter? That can be used to estimate HP at various speeds.
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Old 08-08-2021, 20:54   #321
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Re: Replace Diesel with electric engine

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Originally Posted by Adelie View Post
Has Jedi ever indicated what RPM the engine needs to hit 6kt?
6kt may be off the chart.
Alternatively does Jedi have a fuel flow meter? That can be used to estimate HP at various speeds.
No, that was Wingsail's number. But Jedi has a big problem if his Sundeer 64 takes anywhere near his Yanmar's WOT 3300 RPM/140 HP to reach 6kt with it's very sleek canoe body, 64' WL and hull speed near 11kt.

A fuel flow meter curve will be a much closer match to the prop-demand curve at all speeds than to the engine's max (WOT) power curve at those speeds.
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Old 08-08-2021, 21:02   #322
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Re: Replace Diesel with electric engine

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Originally Posted by PineyWoodsPete View Post
No, that was Wingsail's number. But Jedi has a big problem if his Sundeer 64 takes anywhere near his Yanmar's WOT 3300 RPM/140 HP to reach 6kt with it's very sleek canoe body, 64' WL and hull speed near 11kt.

A fuel flow meter curve will be a much closer match to the prop-demand curve at all speeds than to the engine's max (WOT) power curve at those speeds.
Using main engine rpm at 6kt and the prop curve you can estimate hp required at that speed. Likewise you can estimate HP from fuel flow at various speeds.

The question I asked Jedi was: "...if you ever mount the engine, I would be very interested in what speed you can make with the dinghy motor at WOT throttle." There was no question about what speed the main engine can push the boat at WOT, that's going to be 11kt and change, possibly 12kt but I think that would be a stretch.
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Old 08-08-2021, 21:42   #323
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Re: Replace Diesel with electric engine

Quote:
Originally Posted by Adelie View Post
Using main engine rpm at 6kt and the prop curve you can estimate hp required at that speed. Likewise you can estimate HP from fuel flow at various speeds.

The question I asked Jedi was: "...if you ever mount the engine, I would be very interested in what speed you can make with the dinghy motor at WOT throttle." There was no question about what speed the main engine can push the boat at WOT, that's going to be 11kt and change, possibly 12kt but I think that would be a stretch.
The reason the question came up is because we were trying to image how many kilowatts (hp) was needed for studentdriver's Empacher 52 (like he wanted to put in a 100kw genset so he can achieve his desired speeds (LOL)).

But Jedi is a good test case to start getting some ballpark figures.

When we look at hp/prop curves we see very shallow slope down low, getting steeper as speeds go up. I know from the published curves for my motor, and from actual fuel usage measurements, that 6 knots requires around 11hp at the prop and approx 22 hp output from the engine itself (that is 2200 rpm on my 3JH Yanmar).

I guess that the Sundeer 64 is going to take twice that. Jedi says no, just 20hp, but he has not told us the rpm he needs to use for six knots, or the fuel usage.

studentdriver wants to put 100kw gen set on his imaginary project, which is a bit too far the other direction. Probably needs about 35hp or about 40kw.

It all goes back to how big of an electric drive system one needs to be able to maintain 6 knots continuously running an electric motor on the output of a genset.

And this leads us to think about the regen issue. If it takes 35 shaft HP (40kw) to push the boat six knots, then it would take (forgetting losses) the equivalent of an extra 35HP on the sails to extract 40kw in regen mode. (wow, that would be good, 40kw is 3000 amps at 12 v, 800 amps at 48v!) but the total drive required is equivalent to 70 hp on the sails. Hard to see when that is going to happen. So regen is a fraud.
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Old 08-08-2021, 23:40   #324
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Re: Replace Diesel with electric engine

Uaaarghh, I am really getting tired of EP. Everyone believes in it like in the immaculate Conception. As backpack a few AAA Monocells and the remaining will be done with recuperation.

Look at the capabilities of your bowthruster. See how slow it moves the boat.
Did you know that is has got 6 Kw?

So how can someone believe in 10 Kw?
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Old 08-08-2021, 23:47   #325
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Re: Replace Diesel with electric engine

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Originally Posted by moseriw View Post
Uaaarghh, I am really getting tired of EP. Everyone believes in it like in the immaculate Conception. As backpack a few AAA Monocells and the remaining will be done with recuperation.

Look at the capabilities of your bowthruster. See how slow it moves the boat.
Did you know that is has got 6 Kw?

So how can someone believe in 10 Kw?
...now don't knock EP! on a lot of our lakes here in "the forest" everybody is using it...very popular https://www.minnkotamotors.com/ - because combustion engines are prohibited...
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Old 09-08-2021, 00:04   #326
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Re: Replace Diesel with electric engine

With my Yanmar I’m not sure how many rpm for 6 knots. I think this is highly dependent on the propeller as well, right? We run 6 kts at very low rpm. At 1,800 rpm we are at 7kts I think.

The diesel does not always output the same power at the same rpm… it depends on the load at the shaft. Fuel consumption would be a good indicator but of course I don’t have that.

For testing I could even just use my dinghy tied next to the boat. Never tried what speed can be made that way.
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Old 09-08-2021, 00:13   #327
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Re: Replace Diesel with electric engine

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Originally Posted by moseriw View Post
Uaaarghh, I am really getting tired of EP. Everyone believes in it like in the immaculate Conception. As backpack a few AAA Monocells and the remaining will be done with recuperation.

Look at the capabilities of your bowthruster. See how slow it moves the boat.
Did you know that is has got 6 Kw?

So how can someone believe in 10 Kw?
I agree entirely.

One gallon of #2 diesel contains 38 KW of energy and weighs 7.1 pounds.

No other energy storage media today in even close.

Maybe someday there will be a viable alternative but not today and probably not for decades.

Unless you are a day sailor and never get more than 5 miles from your home port or are someone willing to sit on your boat until the wind comes up electric drive from battery and solar just won't work.

Anyone can spend a fortune on a solar-battery-regen system and kill the resale value of a boat if that makes them happy but do so knowing that you are wasting your money.

I own a Tesla model 3. I plug it into the power grid every night. I can go to a charging station and put 40 KW into the battery in less than half an hour. There are no super chargers in the ocean.


https://en.wikipedia.org/wiki/Gasoli...lon_equivalent
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Old 09-08-2021, 00:21   #328
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Re: Replace Diesel with electric engine

double u Yes used it myself at a lake for 22 to 26 ft "yachts" and it was ok as last aid when the wind died completely but not for 30 to 60 ft seaworthy cruisers that rely on engine power as the last and only power not to sit on a reef.
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Old 09-08-2021, 00:36   #329
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Re: Replace Diesel with electric engine

This manmade CO2 hype is a good accelerator for economic well beeing and very good for these leechers.

What I have has an ecological footprint. 100%
When I throw it away I produce and ecological footprint. 100%
When I buy it new I produce an ecologial footprint. 100%
When I repair it my footprint is usually < 10%

No, I do not need a new car every 3 years.
The break even point of Ecars is 240.000 km.

In middle Europe people drive around 10.000 km /year.
They need 24 years to reach the break even point.
BUT: they need a second set of batteries too.
THEREFORE: An Ecar is at minimum 1,5 times more harmful to nature than any diesel.

So, let us wait for the E-Fuels and it seems that everything is fine with it - on the first sight.

Remember: a small eco diesels CO2 output is the same as of two people running the same distance.
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Old 09-08-2021, 00:40   #330
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Re: Replace Diesel with electric engine

But it is a good reminder NOT to fire up the engine on every purpose but to sail away a lot more.

REMEMBER: it is better to preserve what you have got and NOT to buy new things.
I bet we can reduce the CO2 output by more than 40% by NOT buying new things
but repairing and buying old things,
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