Electric Propulsion

[Richard McCluney]

Hi - I need to re-power my boat (its an ex-fleet boat with 4500+ hrs and ongoing engine issues). Does anyone have an experience with electric propulsion, I have been looking at companies like Electric Yacht and OceanVolt.
Thanks
Richard

[DaveBMusik]

 Heck out sailing Uma on you tube.

[Richard McCluney]

Thanks - some good insights.

[Noah]

Caveat: not an electric owner nor expert, just an observer (with a diesel): IMO, for in and out of your slip or your mooring, an electric retrofit is an expensive experiment that MAY be worth considering. For passagemaking or powering more than 1-2 hours, nope. You would need lots of expensive lithium/iron batteries (and a variety of ways to recharge them underway) to get any range or comfortable safety margin to get out of trouble if required.  I would rebuild or replace the diesel.

[mainesail]

You've not really defined your usage, and this is a critical part of the equation, so it is tough to answer other than in a general sense..

As a marine electrician, involved in electric conversions (EC's), all I can say is learn as much as you can and use real math... A lot of the proponents of EP conversions tend to mislead folks or tell partial truths in order to get in the door. I am on a number of electric boat forums and rarely do I hear someone mention Peukert, battery temps or actual cycle life at 80% or 100% DOD which is where you can wind up if you ignore Peukert etc..

Weight conversion claims are also very often misleading. They often pick the heaviest old school engines like the older Perkins 4-108 & the heaviest reversing gear, not a standard and considerably lighter Universal like the M25 or M35 which are well under 400 pounds with the gear.... They then very often entirely leave out the house banks weight or the windlass bank when doing EP conversion math. You can't really do that with a straight face. A number of years ago I worked a boat show right next to an EP conversion company. The mistruths that flowed from the sales reps mouth were absolutely astounding. During a slow period I pulled him aside and asked whether his data considered Peukert, temp and cycle life? I got blank stares. This is not all all to suggest all of these guys are selling snake oil, some are very good and reputable, just that you as a customer need to educate yourself on this well ahead of talking to an EP sales rep..

When we discuss battery weight we need to be cognizant of the fact that you will still need a 12V house bank. EP guys often like to tout a DC to DC step down converter pulling from the propulsion bank but remember these things can't drive large DC electric motor loads such as a windlass and your house use is now eating into your already precious EP capacity.

This was from an actual quote one of my customers received;

The 48V propulsion bank weighed 520 pounds but then the house bank may was another 130 or so pounds making for approx 650 pounds of batteries on a 28 foot boat. The house bank weight was left off any conversion calculations. If you are real energy conscious you could get away with a single 65 pound house bank but he wanted a minimum of 130Ah's to be able to easily power his windlass at 50% SOC. In general your house bank use won't change so, in most cases, you'll still need the same Ah capacity at 12V that you use now.

With diesels you also have fuel capacity weight, which is not very light weight. A 20 gallon tank when full would weigh about 140 pounds +/-.. So in his case he had a 175 pound engine + 140 fuel = 315 pounds. With fuel filters and misc spares he was at about 360 pounds for engine and full fuel.

He was told the EP conversion for his boat would weigh less? Really? Basic math far too often flies out the window when EP salesmen get the quote moving so please be careful...

His quote was for an 8 battery bank which alone was approx 160 pounds heavier than the diesel engine & full fuel plus filters and spares. Of course the battery bank weight did not include the weight of the electric motor and associated gear which can be another 100 pounds +/- with wire, controller, mounts, motor etc. In total this made his conversion nearly 260 pounds heavier, not lighter as he was quoted.. You really need to be able to do the accurate math for your own vessels conversion and not relay on others to do that.

On top of this he now had two on-board battery systems, house/12V & electric & electric motor/48V at two different voltages but no large current source that could be directed at either. Sometimes an EPC will weigh less but with lead acid batteries it very often does not.

On a 34 footer be sure you can physically fit enough solar and wind to charge two banks adequately in the time frame you would want to in order to achieve the desired max distance you expect to be able to travel. EP currently works best for boats that don't venture too far and essentially only use it for getting back into the marina/slip/harbor. E-propulsion very often requires a boat that is tied to a dock when done sailing or you wait a long while between uses to recharge via solar & wind..... By the time one gets done building a system like this, unless you 100% DIY, fixing an aging diesel can look like a Kmart Blue Light special in comparison.

This is not to say e-propulsion can't be done, it can be done very suitably, if your use fits into your desired use box.. Unfortunately "EP" currently fits into a pretty tight box, range wise, for "E" only power.

To do these systems right, & many are done using inaccurate assumptions & using shoot from the hip math, it can be quite expensive and then you still need to replace an expensive EP bank every few years. Or yearly, as one of my customer learned the hard way. He was mislead, with fuzzy math, on his installation. :doh:

One must also keep in mind that the EP conversion is only part of the expense. You also want wind and solar, (unless using it for marina in/out use only). Also don't forget that you are charging two banks not one and at two different voltages.. Tapping off the propulsion bank for 12V is wrought with problems and I would not do that to any of my customers with cruising boats.. 48V to 12V converters are often quoted, cheap & dirty and okay for a day sailor but rarely a cruiser. This is another long involved discussion but the best course is usually to keep your house bank.

In colder climates, with cold water, or early or late in the season, you can literally cut your capacity by 30% or more due to physical battery temp. Another "rarely discussed" snafu with the EP sales guys. Batteries are rated at 77F-80F and at colder temps they simply can't deliver the same Ah capacity. One of my customers was quoted an EPC with AGM batteries using 80% DOD as average use. The math was also totally bogus and Peukert and water temp/battery case temp for the location chosen was completely and utterly ignored. His very expensive bank, over 2K, lasted one season. That's a lot of diesel and diesel maintenance..

Sure, you can get multiple years out of LifePO4 at 80% DOD but not a heck of a lot out of FLA or AGM unless you are geting back to 100% as fast as is humanly possible. Even the best AGM's (other than Firefly @ $500.00 each) can only claim 400 cycles to 80% DOD (LiFePO4 2000+ cycles) but this is in a LABORATORY.. Real world, not lab derived numbers, done under carefully controlled conditions, converted to 80% DOD numbers in the real world barely break 100-200 cycles for lead acid and this is with immediate and full recharges done soon after discharge. If you dilly-dally on recharging from 80% DOD, using solar or wind, sulfation will kill these banks much faster than the cycles will.

Here is some more math from one of my customers quotes:

This customer was told he could easily go 50nm, the system was lighter and solar and wind could recharge him in 24 hours. None of it was true and it bordered on criminal, IMHO. The only part that was true was that he was told he just had to run his boat slower. Sill the 3 knot figure they threw out defied simple battery physics and made zero sense mathematically.


To go 50nm takes 16.6 hours at 3 knots

A 5kW motor is pulling 104A at 5000W at 48V

If we figure he was using only 70% of that 5kW to do 3 knots that is a 73A load to the battery bank...

A 73A load on a 200Ah 48V bank with a 1.11 Peukert (AGM) gets you a 159Ah bank not 200Ah. Wait, we just lost 41Ah's??? Peukert must always be accounted for in good system design.

They also told him the batteries were best located in the keel sump (long full keel boat). At mid summer his keel sump temps peak at about 62F and off season in the 40's & 50's. This can bring usable bank capacity down to the 120Ah range. 80% DOD of 120Ah's (real capacity) = 96 usable Ah's...

With EP your Ah capacity is NOT the 20 hour rating yet most sales reps use the 20 hour rating to size your system... Frustrating to say the least.

If you want to use 80% of the bank capacity at 73A you need to start at a Peukert corrected capacity of 159Ah's not at 200Ah's. If not you will be drawing the bank way below 80% DOD due to the high loads applied to it. EP loads are well beyond the 20 hour rate, which for this bank was a 10A load at 80F to deliver 200Ah. This is the most often ignored math EP conversion guys forget or choose not to tell you about. The battery temp should also be accounted for when sizing an EP bank.

In the end this customer  really only had approx 127 (realistic) Peukert & temp corrected Ah's to use before he hit 80% DOD with a 73A load with his AGM bank (Lifeline).

If each hour of run time at a 70% load was burning 73Ah he could not even go 5 miles at 3 knots before hitting 80% DOD. How did they get to that lofty 50nm claim? I have no idea......??????

Even if we figure the motor at just 50% load/52A/48V you have a 165Ah bank (Peukert corrected/excluding temp) and 132 usable Ah's before hitting 80% DOD with a Peukert of 1.11... I am completely ignoring battery temp in this math which would make it even worse here in Maine....

Even a 50% load still barely gets to 7nm.... Again, how on Earth did they do the math that shows his boat getting to 50nm..?

At 1000 watts or just 20% motor load you are still burning 21A at 48V.

21A X 16.6 hours @ 3 knots/50nm = -348.6 Ah's consumed....

There is no physical way he could get 16.6 hours out of a 200Ah "rated"  bank even at just a 20% load using realistic math. Unfortunately the lofty, and completely bogus, 50nm range was a complete and utter lie based on the actual quoted system.

The only thing I can say to help you keep everyone around you honest in this research is to:

Trust Ohm's Law - Many will try to rewrite it, but as of yet no one has been successful..

Convert Watts to Amps at fixed voltage:

Watts ÷ Volts = Amps

eg:
5000W ÷ 12V = 417A
5000W ÷ 48V = 104A


Never Forget Peukert - When dealing with high load applications such as e-propulsion one simply can not ignore Peukert when dealing with lead acid batteries..

A 100Ah lead acid battery is only a 100Ah battery when used at, and loaded at, 5A at 75-80F, when new or just broken in. At any load higher than 5A it is no longer a battery that can deliver 100Ah.

Every other load & temp range either above or below the 20 hour rate and 75-80F results in changes to the batteries deliverable Ah capacity. Cycles, DOD, sulfation and plate erosion also impact Ah capacity and it only ever gets smaller.. Anyone telling you otherwise is really not qualified to be doing so.

LiFePO4 cells have virtually no Peukert's corrections but they are still not a Peukert of 1.0..  Like lead they too are affected by temperature. A 100Ah battery with a 1.0 Peukert would provide 100Ah at a 300A load and conversely 100Ah at a 0.5A load. This simply does not exist in the real world.  The reality is that a 100Ah LFP pack might provide about 95Ah at 300A (3C) and 110Ah at 0.5A. Far better than lead acid but still not a Peukert of 1.0..

Do that with a flooded lead acid 100Ah battery:

100Ah Battery - 300A Load = 33Ah

Please do your research & prepare yourself before you sign on the dotted line.

[McSalish]

I've been toying with the idea of electric propulsion myself.  Mainsail seems to give good advice.  I'm considering it because I sail in the Puget Sound/Salish Sea and connect to shore power in my marina and lots of places I visit so I don't thing prolonged PSOC would be a problem for me.  Even so, I would only do it here with solar and an ICE generator for supplemental charging away from the dock.

The testimonials I have read stress the importance of keeping a clean bottom, something I can be less fastidious about with a diesel.  There's a C30 based in Oak Bay, BC that has offered some info on the internet about their experience with the conversion.  Search for that and as many other real world conversion stories as you can.


On a recent trip (with somewhat dirty bottom) I fought a strong adverse current under power through a narrow passage.  Something I wouldn't want to do with electric propulsion.  I could have waited for more neutral conditions but it was late Sunday afternoon and I wanted to get home.  Having the diesel allowed me to follow a pod of orcas the day before and wind up 10 miles further from home than the place I'd planned to stay.  With electric power I would have had to skip the whales and stick to my plans or spend another day on the boat, a luxury I don't always have.


I plan to track my engine use more closely over the next couple of years before I consider switching.  Perhaps by then there will be a cost effective hybrid option.


Cheers and good luck with the decision (and the math).  Please keep the forum posted on your experience if you do go electric.

-Mark

[Richard McCluney]

Thanks for the great responses - I am starting to get quotes, do the math, and figure out my real requirements and oh yes brush up on Ohm's law! The attraction remains - reduced maintenance and an improved carbon footprint. Buying an electric car was the best purchase I ever made, and it would be fun to try and make it work in the boat as well.