serious discussion about electric power in large boats

[john61ct]

Sorry I can be a bit literal, from "I can't imagine x" I inferred "I've never heard of x in reality" as a subset, as opposed to "I strongly believe x is inferior", with which of course I agree

[Michael Gunning]

We have converted about 100 boats of that size to electric. The 100NM range at 5kts is not reasonable with today's battery technology. See the chart below. The sailing experience is superior as electric provides a superior quiet slow speed and can be used while sailing to increase speed and/or point of sail. Regeneration is significant and expect up to 300w/hr when sailing close to hull speed.


Speed & Power QuietTorque 30.0LC 48v Liquid Cooled dual powerhead Motor System
Kts Amps Watts
1.6 10 480
2.6 20 960 This is what a portable 2kW generator would push the boat
3.3 40 1920
3.7 60 2880
4.1 80 3840 23NM with a 400ah 48v – 19kWh battery pack
4.4 100 4800
4.7 120 5760
4.9 140 6720 15NM with a 400ah 48v – 19kWh battery pack
We would recommend an 8 to 12kW genset to provide continuous cruising speed
5.4 170 8160
5.9 230 11040
6.4 290 13920
6.9 370 17760
7.0 390 18720
7.6 490 23520
8.0 590 28320
30000 Max power of 30kW motor

Hull speed 7.93


Mike

Electric Yacht

[john61ct]

Originally Posted by Michael Gunning

The 100NM range at 5kts is not reasonable with today's battery technology.

I'm guessing that "not unreasonable" is a Freudian typo? 8-)

Could you maybe (either way) run the kWh per hour numbers for us on a known working setup in that length / displacement ballpark,

then the size LFP bank, genset and recharging time required?

[skipmac]

Hi Mike,


Thank you for posting to this discussion. Always good to have input from someone with real world, hands on experience in the area under discussion.


As an EE with serious interest in electric but also serious concerns about suitability for my situation I would like your opinion on a few issues. Please note this is not meant to be critical or negative, just sincerely want to better understand some of the finer points and to confirm that I'm more or less correct in my conclusions.


First a comment, I really appreciate your addressing the range right off the bat. I can't count the number of discussions on this forum where someone chimed in with their plan to go electric with wildly exaggerated claims on the range they expected. To me this is the biggest concern considering the cruising I do currently.


First questions. I looked up the system you recommend and see that it's rated in max and continuous input power. Seems a little odd to rate it that way. What is the efficiency accounting for losses in friction, heat and any parasitic loads or what it the max and continuous output power?


The specs show a rating of max input power of 30kW which converts to a hair over 32 HP. Yes I know this doesn't address the lower efficiency and higher parasitic loads of an ICE compared to electric and the always continuous issue of torque vs rpm for the two technologies. Still I would guess in very round numbers this electric would give an output in the 25-28 HP range. My 42', 25,000 lb boat has a 58 HP diesel with maybe 45-50 HP output max. 99% of the time I'm only using a fraction of that but occasionally when I have to maneuver in a very tight fairway in a marina with a strong wind and/or current I need every bit of that to back and fill to get away without smacking another boat. What feedback or experience have you gotten from the installations you've done in this regard?


One thing that has always mystified me is the cost of marine electric. Early on I investigated a DIY system and found industrial motors rated 25kW or more, continuous duty for under $2000. A new 65 HP electric motor for my wife's Prius lists for under $1000. Yes I understand economy of scale vs custom, marine vs nonmarine etc but the marine systems are listed at 10-20 times the cost for a similar sized industrial or commercial motor. Even allowing several thousand for controllers, brackets and installation there's still a difference of many thousands. For that much I could buy 3-4 spare industrial motors and just swap them out ever couple of years.


This leads in to the final issue that makes electric not practical for me, cost. I need cruising range so I would have to add a diesel generator to the electric system. When you add a 12kW or larger gennie to the $15k for the electric drive (not even counting batteries and upgraded charging systems) you are now at least double the cost of a new ICE that also has a good bit higher power rating. Plus you have replaced one engine with another so the same or even more maintenance and repair issues.


Bottom line as I see it, electric only works for someone that only motors from dock to open water or for someone willing to spend the extra for a green system.


Love to hear your comments on this.


Thanks
Skip

Originally Posted by Michael Gunning

We have converted about 100 boats of that size to electric. The 100NM range at 5kts is not reasonable with today's battery technology. See the chart below. The sailing experience is superior as electric provides a superior quiet slow speed and can be used while sailing to increase speed and/or point of sail. Regeneration is significant and expect up to 300w/hr when sailing close to hull speed.


Speed & Power QuietTorque 30.0LC 48v Liquid Cooled dual powerhead Motor System
Kts Amps Watts
1.6 10 480
2.6 20 960 This is what a portable 2kW generator would push the boat
3.3 40 1920
3.7 60 2880
4.1 80 3840 23NM with a 400ah 48v – 19kWh battery pack
4.4 100 4800
4.7 120 5760
4.9 140 6720 15NM with a 400ah 48v – 19kWh battery pack
We would recommend an 8 to 12kW genset to provide continuous cruising speed
5.4 170 8160
5.9 230 11040
6.4 290 13920
6.9 370 17760
7.0 390 18720
7.6 490 23520
8.0 590 28320
30000 Max power of 30kW motor

Hull speed 7.93


Mike

Electric Yacht

[Michael Gunning]

This is the prospective of an electric marine propulsion company about the state of electric propulsion.
Mike Electric Yacht



Skip,
I agree with most of your observations. Marine propulsion is much more difficult than other electric applications. I am not an EE but the professional motor system builders are marine engineers.



Cost for the semi-custom products that are sold by electric marine propulsion companies are not even in the same ballpark as the auto industry. We all use industrial based components but at much smaller production runs and therefore much more expensive and then we have to make it work in a bilge/engine room.



These are some quality marine companies we see in the market: AquaWatt, Bell Marine, Elco, Electric Yacht, OceanVolt, Torqeedo and Thoosa. Their systems run from 48v to 345v with power capacity from 2.5kW to about 80kW. Can not speak to DIY systems.



For your first and second questions. Electric marine propulsion companies normally call their systems what the public understands, KW or something like that. From what I know from talking to industry builders, all electric propulsion systems apply about 80-84% of the power from the battery to the motor to the propeller but with native rotational torque. It is really difficult to compare to a diesel unless you stop using hp and only look at torque. Finally no transmission, alternator, pumps, etc, which for small motors can have significant parasitic losses ranging from as high as 20% to low of 5%. The kW numbers you see in the projection is actually power at the propeller.

Your last question is cost. The electric motor solutions are less expensive then their counter parts. Batteries and gensets may increase the cost considerably. Think in terms of operation and power management on the boat. For a dedicated cruiser you will find some advantages in total power generation and management that may make the electric less expensive over years of operation. This is based on Nigel Calder's work for cruising boats power management and cost to produce power with genset, solar, or from a propulsion motors alternator.

[StuM]

Originally Posted by Michael Gunning

We have converted about 100 boats of that size to electric. ... speed and/or point of sail. Regeneration is significant and expect up to 300w/hr

If someone has converted 100 boats to electric, the least you would expect is knowledge of basic electrical units.


How anyone making that claim can talk about "up to 300w/hr" is beyond me.

[SwellGuy]

Originally Posted by Michael Gunning

Regeneration is significant and expect up to 300w/hr when sailing close to hull speed.

‘w/hr’ is a nonsense unit in this context.

Either you mean to talk about power, in which case you’d say ‘300watts when sailing’, or you mean to talk about energy, in which case you’d say ‘300 watt*hours/hr’ otherwise known as ‘watts’.

Pro tip: don’t take advice on propulsion systems from someone who doesn’t have a firm grasp on the difference between power and energy.

[dougweibel]

Originally Posted by SwellGuy

]Pro tip: don’t take advice on propulsion systems from someone who doesn’t have a firm grasp on the difference between power and energy.

Agree!! I see a lot of advice being offered on all sorts of electrical issues using the wrong sorts of units. It is frustrating how many people don't seem to understand the underlying quantity being measured with units of amps, volts, watts or watt-hours.

Amp-hours is forgivable as a unit of energy for most battery powered systems as it is a reasonable proxy; it is easy to measure, not that measuring watt hours is that much more difficult, and useful for managing batteries.

[john61ct]

300W on average, comes out to 300Wh per hour

I think y'all are taking pedantry to a harsh extreme.

Being "technically right" is not the best kind of right.

Especially if it discourages members - none of us being perfect - from contributing valuable experience and knowledge to the forum.

[GrowleyMonster]

I own an electric Cal 2-27. When the fuel tank sprung a massive leak I had to pull the atomic to get the tank out, and decided not to put it back in. I went with a Motenergy 5kw motor, Kelly controller, and golf cart batts from Sam's. Total cost after getting $400 for the Atomic was about $2400. Very practical setup for under 30' boats that don't motor long distances. Over 35' and a 48v system starts to show serious inadequacies. And higher voltages calls for a different set of electrical standards so if you go bigger, then go a lot bigger, at least 144v nominal. 96v minimum. 300v is not excessive so big boats should take advantage of off the shelf electric car components and batteries. For golf cart batteries more than 96v gives you a huge weight and space penalty so lithium is your best bet for bigger boats. Talking big bucks, now.

My GC2 batts are now 7 years old and starting to show their age. I am replacing one next week. When I have to replace a second one I will start saving my nickels for a new set. $85 each. Not bad, but it takes a bite out of my fuel savings. I figure another year or two at most. But you have to maintain them properly to get this much life out of them. Without proper care you will toast them in two years.

The trick to getting max range out of a shore power charge is to go slooooow. Talking 2-1/2kt or so. Then it will amaze you. Go 5kts and the range will disappoint you sorely.

I had planned to put up 2kw of solar panels in a full solar canopy but that project was shelved indefinitely due to other priorities with a newer and bigger boat with a sound diesel. I intend to sell the Cal as is.

I won't wax poetic on the advantages of electric except that maneuverability is greatly enhanced. Nothing beats it. Instant on, no minimum idle speed, crazy torque on demand.

If my big boats diesel craps out I probably will put in a Beta though electric definitely would be considered.

Full systems can be expensive. Designing your own system is much cheaper but not for the uneducated neophyte. It is sort of complex.

[StuM]

Originally Posted by john61ct

300W on average, comes out to 300Wh per hour

I think y'all are taking pedantry to a harsh extreme.

Being "technically right" is not the best kind of right.

Especially if it discourages members - none of us being perfect - from contributing valuable experience and knowledge to the forum.

Guess it's time to repost this
http://www.cruisersforum.com/forums/...ml#post1933764

[StuM]

Originally Posted by john61ct

300W on average, comes out to 300Wh per hour
I think y'all are taking pedantry to a harsh extreme.

Being "technically right" is not the best kind of right.

Especially if it discourages members - none of us being perfect - from contributing valuable experience and knowledge to the forum.

He said "up to 300 w/hr".

So did he mean that you would see "up to 300 watts" or "up to 300 watt hours" in a specific period of time. Per hour? Per day?.

Assuming "per hour", there is a big difference between the two. If you are getting "up to 300 watts", you can be fairly certain that you will get a lot less than 300 watt hours over an hour. If you get 300 Wh per hour, you will certainly see more than 300 W at times.

[mdenize]

Originally Posted by StuM

If someone has converted 100 boats to electric, the least you would expect is knowledge of basic electrical units.


How anyone making that claim can talk about "up to 300w/hr" is beyond me.

I think this a very unkind statement and fairly typical of this forum of flat eathers. As an EE I can say that here on this side of the round earth a watt/ hour is just as vaid as a kilowatt/ hour ( Just smaller units). Anyone with electrical knowledge would recognise 300w/hr as 0.3kW/Hrs per hour. Anyway just saying that stum's statement makes perfect sense to me😁

[Pelagic]

Originally Posted by SwellGuy

For that boat, folks would recommend at least a 40HP diesel, right?

Let's be overoptimistic and assume you only need half that to get to a useable cruising speed (5mph?), so 20HP.

At 5mph, it'll take you 20 hours to get your 100 miles. So the energy you need for your journey is (20 HP) times (20 hours).

20HP = 15 kilowatts. So you need 15 kilowatts * 20 hours = 300 kilowatt hours of energy to make your 100 mile journey.

300,000 watt hours / 12 volts = a 25,000 amp hour 12V battery bank..

(if you are thinking "but wait, i'll be charging along the way", just remember: Your panels are 0.13 kilowatts. You need 15 kilowatts. They aren't making a dent for charging en route.)

That's amazing, right? Almost makes me think I have an arithmetic error here. But let's do it another way. Let's find out how much battery capacity I need to replace 1 us gallon of diesel fuel.

1 gallon of diesel = 139,000 btu = 40 kilowatt hours. Even if the electric system is 100% efficient, and the diesel is only 33% efficient, you are talking (40kw * 0.33)/12V = 1,100 _usable_ amp hours of capacity to replace one gallon of diesel fuel. Wow!

Another way of looking at it: Your 130 watt panel, in perfectly bright sunny conditions, will take 40kwh / .13kw = over 300 hours to produce the energy of _one gallon_ of diesel fuel. Again, if the electrical system is 100% efficient, and the diesel is only 33% efficient, that's still 100 hours to replace one gallon of diesel! Wow!

Great explanation by putting things in perspective.
Have not read all the threads on this electric power feasibility, but wonder if a large capacity permanent magnet shaft alternator could be used in whilst sailing to recharge at the expense of boat speed.

[StuM]

Originally Posted by mdenize

I think this a very unkind statement and fairly typical of this forum of flat eathers. As an EE I can say that here on this side of the round earth a watt/ hour is just as vaid as a kilowatt/ hour ( Just smaller units). Anyone with electrical knowledge would recognise 300w/hr as 0.3kW/Hrs per hour. Anyway just saying that stum's statement makes perfect sense to me��

You claim to be an EE and can make that statement? Where did you get your training?

"/" means "per", "divided by', "for each".

300 W/hr is 0.3KW/h not 0.3 KW/h/h.

A watt is a unit of power. Watt/hour is another way of saying "watts per hour".
Anyone with electrical knowledge would recognise that 300 W/h means a change in power over time.

Or to put it another way, watt/hr is the rate of change of power. If at 07:00 you solar panels are producing 100 W and at 08:00 they are producing 400 you have 300 W/hr. That is the only type of situation in which W/hr makes any sense.

I can't think of a case where 300 watts per hour per hour would be useful information. It is the rate of change in the rate of change in power. An example of a real life 100 W/h per hour (Let's pretend these are solar panels)

07:00 - 300 Watts
08:00 - 400 Watts ( A change of 100 W/h)
09:00 - 600 Watts (A change of 200 W/h and 100 W/h/h)
If that continues at 100 W/h per hour you would be getting 900 Watts at 10:00 and 1.3 KW at 11:00.