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Old 28-12-2015, 05:13   #181
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Re: Tug of War - Electric vs Diesel

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Sigh!
Based on the info on the Elco site: The Elco EP-4000 (40hp) has a max continuous rating of 17kw so you'd be using closer to 15kw than 35kw. With a 5.5 KW generator you could run for 2 days non-stop. If you start and/or end at a marina you would be using shore power to recharge, not the generator. You would need a battery bank consisting of 9 batteries. Interesting fact, the EP-4000 weighs 400 lbs.

Elco Motor EP-4000
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Old 28-12-2015, 05:36   #182
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Re: Tug of War - Electric vs Diesel

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Based on the info on the Elco site: The Elco EP-4000 (40hp) has a max continuous rating of 17kw so you'd be using closer to 15kw than 35kw. With a 5.5 KW generator you could run for 2 days non-stop. If you start and/or end at a marina you would be using shore power to recharge, not the generator. You would need a battery bank consisting of 9 batteries. Interesting fact, the EP-4000 weighs 400 lbs.

Elco Motor EP-4000
Running at 15kW with a 5.5kW generator, that's a deficit of 9.5kWh per hour. 2 days non-stop is 48 x 9.5 = 456 kWh deficit. 456 kWh @ 12V = 38,000Ah. Assuming 200Ah LA batteries and 50% usable, that's 380 batteries required, not 9
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Old 28-12-2015, 05:41   #183
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Re: Tug of War - Electric vs Diesel

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Based on the info on the Elco site: The Elco EP-4000 (40hp) has a max continuous rating of 17kw so you'd be using closer to 15kw than 35kw. With a 5.5 KW generator you could run for 2 days non-stop. If you start and/or end at a marina you would be using shore power to recharge, not the generator. You would need a battery bank consisting of 9 batteries. Interesting fact, the EP-4000 weighs 400 lbs.

Elco Motor EP-4000
So the guy who is your goto for information is the guy trying to sell you the gear.
Much of what you have said has been rebutted in previous posts.
If we are measuring tailshaft power then diesel and electric are identical. If your boat needs 35 kw to drive it at cruising speeds then that's what it needs regardless of the source of power. Electric kw and diesel kw are the same measure.
A 5.5 kwh generator generates 5.5 kw and cannot keep a 17 kw motor running. 9x 12v 200 a/h batteries store no more than 15kwh of electrical energy given that you shouldn't discharge batteries below 60%. That's enough energy to drive the 17kw motor for about an hour. Do the math, the figures elco provide don't add up.

Access to shore power means nothing. your batteries will store 15kw energy regardless of the source of electricity and, as you know that's good to drive the boat for one hour. You can leave the boat plugged in all night but you will still only get one hour of cruising.

You cannot magic up energy.
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Old 28-12-2015, 07:53   #184
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Re: Tug of War - Electric vs Diesel

Maybe Elco's numbers are wildly inaccurate. I'm not affiliated & I'm sure no expert, I just want it to work because I think silent propulsion would be cool as hell. The size of the battery bank is based on the voltage of the motor so that's why the 9 batteries. The site indicates a range of 5 hours at 60% of hull speed & 2 hours at 80% so I guess 1 hour at hull speed makes sense. It does not say what the KW usage at those speeds is estimated at but they are running the batteries to 50%. This motor maxes out at 29.4 KW so it can't even get to 35 kw which would be more like 47hp.

However, by figuring our average burn rate & speed that even believing Elco's numbers my hope of making the EP-2000 work is unrealistic. Our Scout 30 trawler has a full displacement hull with a waterline length of 30'. We typically cruise at 6 knots or about 80% of hull speed burning about .45 gallons per hour which means we're using about 25hp. The EP-2000 would be underpowered & the 4000 is just too expensive, especially when you throw in a generator. But it sure would be cool.

Re-Powering a 1910 Yacht with Electric - Elco Motor Yachts
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Old 28-12-2015, 18:31   #185
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Re: Tug of War - Electric vs Diesel

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Maybe Elco's numbers are wildly inaccurate. I'm not affiliated & I'm sure no expert, I just want it to work because I think silent propulsion would be cool as hell. The size of the battery bank is based on the voltage of the motor so that's why the 9 batteries. The site indicates a range of 5 hours at 60% of hull speed & 2 hours at 80% so I guess 1 hour at hull speed makes sense. It does not say what the KW usage at those speeds is estimated at but they are running the batteries to 50%. This motor maxes out at 29.4 KW so it can't even get to 35 kw which would be more like 47hp.

However, by figuring our average burn rate & speed that even believing Elco's numbers my hope of making the EP-2000 work is unrealistic. Our Scout 30 trawler has a full displacement hull with a waterline length of 30'. We typically cruise at 6 knots or about 80% of hull speed burning about .45 gallons per hour which means we're using about 25hp. The EP-2000 would be underpowered & the 4000 is just too expensive, especially when you throw in a generator. But it sure would be cool.

Re-Powering a 1910 Yacht with Electric - Elco Motor Yachts
The size of the battery bank is not based on the voltage of the motor. You are confusing the need to put batteries in series to provide higher voltages with total power consumption. Let's say you have a 12V and a 24V trolling motor:
- A 12V motor can runoff a single 12V battery but the 24V motor will need a pair of 12V batteries wired to provide 24V...but assuming the motors are generating similar thrust (and at similar efficiency), the 12V will be drawing twice the amperage and thus to get the same range, you need the same number of batteries. There are some efficiency benefits to higher voltage but that is a minor factor. The driving force in determining battery bank size is how many watts you are pulling from the battery bank.

Something doesn't add up. At 60%, a 30kw motor is going to be drawing something close to 1500amp-hrs per hour. 9 - 200amp-hr batteries hold 1800amp-hrs and you really shouldn't use more than 50% if you don't want to damage the batteries. So you would need something closer to 15 - 200 amp-hr batteries to get 1 hr cruise time at 60%. To get a 5 hr cruise at 60%, you are going to need more like 75 - 200 amp-hr batteries. Than again, as you indicated, most people cruise at closer to 80-90% of hull speed.

Even if you accept their numbers, if you get in a tough situation, you better be able to get out of it in less than an hour...actually probably less as battery voltage drops as batteries get used up and the available power will start to go down.
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Old 28-12-2015, 19:06   #186
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Re: Tug of War - Electric vs Diesel

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We typically cruise at 6 knots or about 80% of hull speed burning about .45 gallons per hour which means we're using about 25hp.
I don't know where you are getting your numbers--diesels consume about 1 gallon per hour for each 20 hp output, so 0.45 gal/hr is only 9 hp.
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Old 29-12-2015, 05:43   #187
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Re: Tug of War - Electric vs Diesel

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The size of the battery bank is not based on the voltage of the motor. You are confusing the need to put batteries in series to provide higher voltages with total power consumption. Let's say you have a 12V and a 24V trolling motor:
- A 12V motor can runoff a single 12V battery but the 24V motor will need a pair of 12V batteries wired to provide 24V...but assuming the motors are generating similar thrust (and at similar efficiency), the 12V will be drawing twice the amperage and thus to get the same range, you need the same number of batteries. There are some efficiency benefits to higher voltage but that is a minor factor. The driving force in determining battery bank size is how many watts you are pulling from the battery bank.

Something doesn't add up. At 60%, a 30kw motor is going to be drawing something close to 1500amp-hrs per hour. 9 - 200amp-hr batteries hold 1800amp-hrs and you really shouldn't use more than 50% if you don't want to damage the batteries. So you would need something closer to 15 - 200 amp-hr batteries to get 1 hr cruise time at 60%. To get a 5 hr cruise at 60%, you are going to need more like 75 - 200 amp-hr batteries. Than again, as you indicated, most people cruise at closer to 80-90% of hull speed.

Even if you accept their numbers, if you get in a tough situation, you better be able to get out of it in less than an hour...actually probably less as battery voltage drops as batteries get used up and the available power will start to go down.
I'm no expert but I think the voltage of the batteries has to equal the voltage of the motor. Of course different batteries provide more or less amps but if you have a 24 volt motor you would need two 12 volt batteries. The EP-4000 is a 108 volt motor so it needs 9 12 volt batteries to create that voltage.
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Old 29-12-2015, 05:57   #188
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Re: Tug of War - Electric vs Diesel

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I don't know where you are getting your numbers--diesels consume about 1 gallon per hour for each 20 hp output, so 0.45 gal/hr is only 9 hp.
I used a conversion program.

Measurement unit conversion: gallon[U.S.]+of+diesel+oil/to/horsepower+hour

This site says diesels burn 1 gallon for every 18 hp used. It also says that 35% of the horsepower created by a diesel is given up to the atmosphere in heat. I think it's safe to assume that an electric motor would suffer much less loss due to heat. Therefore an electric motor would need less horsepower to equal a diesel engine.

All About Fuel and Your Boat - BoatSafe.com
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Old 29-12-2015, 06:17   #189
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Re: Tug of War - Electric vs Diesel

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I'm no expert but I think the voltage of the batteries has to equal the voltage of the motor. Of course different batteries provide more or less amps but if you have a 24 volt motor you would need two 12 volt batteries. The EP-4000 is a 108 volt motor so it needs 9 12 volt batteries to create that voltage.
They don't have to be the same, but it simplifies the system if they are. (if they are not the same, you need some sort of converter in the circuit to step the voltage up/.down,)

Also, there is nothing special about 12 Volts. Generally batteries are banks of cells in series. For common battery technologies, each cell is approximately 2 Volts. So a 6V battery will have 3 cells, a 12 V battery will have 6 and a 24V battery would have 12.

In fact many boats use a number of 6 Volt batteries wired in series and parallel to provide 12 or 24V power.

A single 108V battery could well be built as one block of 54 x 2V cells.

And when you say " different batteries provide more or less amps", you are confusing power and energy (as do far too many other people). the number of Amps that a battery "provides" is primarily a function of the resistance of the load put on the battery. Short circuit the terminals on a battery and you will get lots of Amps from it.

What you mean is that different batteries can provide more or less Amp hours.
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Old 29-12-2015, 06:39   #190
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Re: Tug of War - Electric vs Diesel

Elco states that the efficiency of their motors is 85% to 92%. As I understand it the loss is primarily due to heat creation. If a diesel looses 35% of it's power to heat & an electric motor loses 15% there's a 20-27% increase in efficiency with electric. This means you need a lot less electric hp to equal diesel hp.

Based upon Don's numbers which appear to be correct I typically use only 9 hp to run at 80% of hull speed on a 30' waterline length (6 tons). This is further supported by the fact that several Scout owners have replaced their 43hp Volvos with 30 hp Betas & report good results. Maybe the EP-2000, rated at 14.1 KW (19hp) max & 8.5 KW (11.4 hp) continuous would work.
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Old 29-12-2015, 07:29   #191
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Re: Tug of War - Electric vs Diesel

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They don't have to be the same, but it simplifies the system if they are. (if they are not the same, you need some sort of converter in the circuit to step the voltage up/.down,)

Also, there is nothing special about 12 Volts. Generally batteries are banks of cells in series. For common battery technologies, each cell is approximately 2 Volts. So a 6V battery will have 3 cells, a 12 V battery will have 6 and a 24V battery would have 12.

In fact many boats use a number of 6 Volt batteries wired in series and parallel to provide 12 or 24V power.

A single 108V battery could well be built as one block of 54 x 2V cells.

And when you say " different batteries provide more or less amps", you are confusing power and energy (as do far too many other people). the number of Amps that a battery "provides" is primarily a function of the resistance of the load put on the battery. Short circuit the terminals on a battery and you will get lots of Amps from it.

What you mean is that different batteries can provide more or less Amp hours.
I run 4 Trojan T-105s for a house bank so I get that it doesn't have to be 9 12v batteries. I've lusted after Rolls Royce batteries for many years. It looks like, as LI batteries become more common, small cells may become the norm. When that happens marine electric propulsion may be much more viable. Amps is just short for amp hours.
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Old 29-12-2015, 07:45   #192
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Re: Tug of War - Electric vs Diesel

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Elco states that the efficiency of their motors is 85% to 92%. As I understand it the loss is primarily due to heat creation. If a diesel looses 35% of it's power to heat & an electric motor loses 15% there's a 20-27% increase in efficiency with electric. This means you need a lot less electric hp to equal diesel hp.

Based upon Don's numbers which appear to be correct I typically use only 9 hp to run at 80% of hull speed on a 30' waterline length (6 tons). This is further supported by the fact that several Scout owners have replaced their 43hp Volvos with 30 hp Betas & report good results. Maybe the EP-2000, rated at 14.1 KW (19hp) max & 8.5 KW (11.4 hp) continuous would work.
It depends on how Elco measure their HP. Diesels typical measure shaft or prop HP which already takes into account losses.

My 40HP Yanmars deliver 40 usable HP.

If ELCO also report usable HP, then electric HP = diesel HP.
If ELCO are reporting a nominal HP at 100% efficiency, then the true power available from their motors is less than they are saying and you need a bigger engine that the equivalent diesel to get the same power at the propeller.

It's been said before - but deserves repeating: don't size an auxiliary engine on a sailboat based on what you "typically use". It needs to be sized to provide sufficient power to get you safely through adverse situations such as fighting strong currents, headwinds and rough seas.

I can "typically" motor on one engine at 2800 RPM using about 16HP and doing over 6 knots, but there have been times when I was glad to have 50+ HP at a comfortable 3300 RPM (90% of Max continuous RPM) - and to know that I still had another 20 or so available if needed for a short burst.
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Old 29-12-2015, 08:11   #193
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Re: Tug of War - Electric vs Diesel

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Assuming the engine is rated in shaft HP, the only difference would be if you added after market items (oversize alternator, mechanical fridge, etc...). The water pump, standard alternator, etc..., are already accounted for. If you are talking about a diesel/electric system, you are probably need a larger diesel due to the power conversion losses.
In my admittedly limited experience, engines are rated at the crankshaft or flywheel. If HP rated at the flywheel it may calculate for very basic loads like the fresh water pump but not alternators, etc since most engines allow for multiple options on cooling (fresh vs raw), alternator sizes, etc. Shaft HP may be given for a specific boat and engine installation from the boat builder but if you look at the specs from the engine maker they will rate the engine only since they have no idea how the engine will be installed or used.

But yes, the point I was making in my original post, an electric with lower power capacity should give equal performance than higher powered diesel due to the power lost to accessories on the diesel. How much less is a matter for debate and includes too many variable I think to give a pat answer.


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One interesting item:
- Where electric is most practical is for just getting in and out of harbor before hoisting the sails. I sometimes hear purists bragging about only using 5-10gal of diesel per year...of course if you are only using 5-10 gal per year, there isn't much to gain from efficiency.
- For a more typical cruiser (non-sailing purist), who doesn't hesitate to crank up the engine, they aren't going to be satisfied with an underpowered boat with limited range.
- That doesn't leave much of a market for electric drivetrains.
This I think sums it up quite well. I might add that one can go electric and get the range of a straight diesel installation but only with significant added cost and complexity from adding a large generator for the range.
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Old 29-12-2015, 08:39   #194
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Re: Tug of War - Electric vs Diesel

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I'm no expert but I think the voltage of the batteries has to equal the voltage of the motor. Of course different batteries provide more or less amps but if you have a 24 volt motor you would need two 12 volt batteries. The EP-4000 is a 108 volt motor so it needs 9 12 volt batteries to create that voltage.
Nope you are still confusing providing voltage to match the engine with sizing the battery bank.

It's more common to put batteries in series to match the voltage of the engine but it can be done other ways such as thru transformer.

Bottom line, if the engine is consuming X kw, the batteries need to provide X kw regardless of the motor voltage. To provide the same duration of run time at the same X kw draw, you need roughly the same size battery bank regardless of engine voltage.
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Old 29-12-2015, 08:44   #195
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Re: Tug of War - Electric vs Diesel

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In my admittedly limited experience, engines are rated at the crankshaft or flywheel. If HP rated at the flywheel it may calculate for very basic loads like the fresh water pump but not alternators, etc since most engines allow for multiple options on cooling (fresh vs raw), alternator sizes, etc. Shaft HP may be given for a specific boat and engine installation from the boat builder but if you look at the specs from the engine maker they will rate the engine only since they have no idea how the engine will be installed or used.

But yes, the point I was making in my original post, an electric with lower power capacity should give equal performance than higher powered diesel due to the power lost to accessories on the diesel. How much less is a matter for debate and includes too many variable I think to give a pat answer.

.
As I stated assuming both motors are rated in shaft HP (ie:crankshaft), the usable HP is the same as standard auxiliary devices such as the water pump and standard size alternator are already accounted for.

It's only if you start adding after market accessories that it makes a difference. Of course if you are comparing a diesel with a mechanical fridge compressor you have to add in an alternate way to power the fridge. With modern solar systems, these devices are becoming less common as there isn't the need.
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