Electric motor conversion

[StuM]

Originally Posted by Adelie

If I need to go upwind that’s what sails are for.

"Upwind" ( i.e with the wind forward of the beam) is not the same as "into wind" (i.e. wind on the bow).


Good luck using sails to go "into wind".

[Adelie]

I see, too impatient to sail on a sailboat.

[bluenomads]

Originally Posted by NPCampbell

I'm curious where these numbers come from. As long as you are below hull speed, shaft HP generally increases with the cube of speed. So 50% hull speed should generally equal HP/8 at 100% hull speed. 50% hull speed should require 15.5kW if 124kW is req'd at 100% hull speed. Shaft HP is independent of the method of propulsion. (i.e. HP req'd = disp pounds / (10.665 / SL ratio) ^ 3)

Solar: 50% hull speed or 15.5kW would require around 1000 sq ft of solar operating at 100% efficiency. 1000 sq ft is larger than the footprint of a 45' catamaran.

Battery: 15.5kW would last less than 45 minutes taking 1000 AH of batteries to 100% DOD without running the genset.

The power (kW) come from an Oceanvolt model. While they are theoretical as there's no motor in our particular hull to get empirical evidence, people who have had the theoretical figures and then gone with the company have said that the match with the reality afterwards is very close. I'm using them as a example.

Your HP calulation comes from Gerr (who may have got it elsewhere), who says merely that it's "useful" in predicting power and speed. Importantly, the 10.665 is not something that can be used to apply to all hull shapes and boat types. In short, it's not a universal truth in the slightest!

Regarding solar, and needing more than a 45' cat - we have a 50' catamaran . We certainly plan a reasonable solar array, with about 3.5kW likely.

I haven't looked further at the battery sizing. Your 45mins would not surprise me at all depending on speed, conditions (and battery type of course).

[gmakhs]

Yes , you can get enough energy to run your motor all day but let me know how you plan to cool down the motor when in operation??? Because air-cooled motor don't do well in boat compartments and water coiled ones don't do good at all .

[NPCampbell]

Originally Posted by bluenomads

Your HP calulation comes from Gerr (who may have got it elsewhere), who says merely that it's "useful" in predicting power and speed. Importantly, the 10.665 is not something that can be used to apply to all hull shapes and boat types. In short, it's not a universal truth in the slightest!

I agree. However, even if the 10.665 is hull dependent variable then it still holds that HP varies with the cube of speed.

Originally Posted by bluenomads

Regarding solar, and needing more than a 45' cat - we have a 50' catamaran . We certainly plan a reasonable solar array, with about 3.5kW likely.

Wow, that's a ton of solar! You definitely won't be hurting for on board power

[valhalla360]

Originally Posted by cgm12mgc

We get it, you’re no fan of electric motors. You can stick to diesel... I do in my other boats. People survived for thousands of years without a motor in their boat and as I have stated, mine is to get out of the marinas and under bridges etc. don’t like it? Don’t do it.


Same concept as what you’re saying, I can run my 61’ sportfish wide open throttle for a few hours but i’m up shi*ts creek when I run out of diesel at a burn rate of 120 gallons an hour... atleast with electric I can refill while on anchor 👍🏻

Not at all. For some limited output use cases, it's completely viable. If I need a dingy just to get around the harbor at low speed, it will likely be electric as it's very much viable to operate short distances at low speed and the cost to implement is low and the ongoing maintenance is low.

But lets take your example of a 61' sportfish...you may be able to do wide open for a few hours with diesel...trying that with electric motors, you would be lucky to put out the same power for 5 minutes...but that is a wildly different use case from a displacement hull. You most likely could do hull speed with less than 20% of the available HP in your sportfish (maybe less than 10%). Also a 61' hull will have a much higher hull speed compared to a 35' sailboat. le: speeds in a sportfish to fight a current or storm conditions are far below full throttle.

Let's say you are trying to fight a 5kt current...Your typical 35' sailboat will top out around 7kts, so full throttle will only get you 2kt SOG. If you throttle back to get more duration, you likely come to a stand still. On a 30kt cruise speed (not full throttle) sportfish, you can continue at cruise speed and still are making 25kt SOG...its not a big deal.

I will repeat: IF YOU ARE WILLING TO LIVE WITH THE REDUCED PERFORMANCE, IT'S VIABLE. But understand it is significantly reduced performance.

[Chotu]

Originally Posted by bluenomads

Ease off to 90% of full speed and (nearly) double your time.
Ease off to 80% of full speed and quadruple your time.

People with a 45'/14t cat can motor 4.5-5kn with solar alone - that's people out there doing it, not charging their armchairs.

I'm still charging an armchair too right now, but figures we've received are that, since our nominal hullspeed would be near 9kn, so

nominal hullspeed = 124kW (let's pretend that is 100%)
90% hullspeed = 83kW (59% of max amperage)
80% hullspeed = 30kW (21% of max amperage)
70% hullspeed = 22kW (16%)
60% hullspeed = 11kW (8%)
50% hullspeed = 6kW (4%)

Now your numbers will be different, but the idea is to look at the progression as your go slower.

If you travel at maximum, you won't last long on batteries alone (the comment on only getting 2 hours with the genset running is purely a case of poor choice of matching speed-motor-genset-batteries and not inherent to electric motors!).
BUT, if you're will to come down a little in speed, then there's a lot of possibilities for matching ok speed with distance under batteries alone, or under batteries with genset (maybe solar input too).
So at nominal hullspeed, if the OP had 2 hours of battery draw available at my figures above (an HUGE amount at that speed, but the importance isn't the 100% value it's how much it increases with speed), then the use on batteries alone is:

Nominal hullspeed = 2hrs
90% hullspeed = 3.4hrs
80% hullspeed = 9.3hrs
70% hullspeed = 12.7hrs
60% hullspeed = 25hrs
50% hullspeed = 47hrs

WITHOUT genset!

There's more and more doing it and it works.

In our reality, we see a sweet spot at 60% of hullspeed or about 5.5kn using 11kW total. An 18kW DC genset would work fine giving continuous motoring as long as the diesel lasts (and much quieter and a bit more efficient than diesel only propulsion). We could decide to go 1kn slower, and use about half the power meaning running on batteries-only for short time/distances between endpoints is feasible. Want longer battery-only without genset, then just buy more of them...

Ooof! This is very "uncatamaran-like."

The weight of this system is ridiculous and will definitely ruin the performance of the boat. Also, if you want more range just keep adding batteries?? At 70lbs each even for lithium ion?

Should just get a monohull for this setup.

A pair of outboards is thousand of lbs lighter and you're still burning fossil fuels to run a generator so no environmental advantage.

3.5kw Solar 480lbs
13kw generator 870lbs
Wiring 100 lbs
26 KWH lithium ion Battery Bank 1000lbs
10kw electric motors x 2 is 48lbs (x2)
100 gallons diesel Fuel for generator 700lbs

That's 3,250lbs to get the indicated performance.

Pair of 30hp outboards 187lbs (x2)
100 gallons fuel 700lbs

So 3,250lbs of weight for so-so propulsion where you have to reduce output constantly or 1,000lbs of weight for full, continuous output.

No brainier.

This system is horrible for a catamaran. It's suited to monohulls or condomarans only.

[cgm12mgc]

Originally Posted by Chotu

Ooof! This is very "uncatamaran-like."

The weight of this system is ridiculous and will definitely ruin the performance of the boat. Also, if you want more range just keep adding batteries?? At 70lbs each even for lithium ion?

Should just get a monohull for this setup.

A pair of outboards is thousand of lbs lighter and you're still burning fossil fuels to run a generator so no environmental advantage.

3.5kw Solar 480lbs
13kw generator 870lbs
Wiring 100 lbs
26 KWH lithium ion Battery Bank 1000lbs
10kw electric motors x 2 is 48lbs (x2)
100 gallons diesel Fuel for generator 700lbs

That's 3,250lbs to get the indicated performance.

Pair of 30hp outboards 187lbs (x2)
100 gallons fuel 700lbs

So 3,250lbs of weight for so-so propulsion where you have to reduce output constantly or 1,000lbs of weight for full, continuous output.

No brainier.

This system is horrible for a catamaran. It's suited to monohulls or condomarans only.

not sure where you're getting catamaran from but mine is a 45' monohull

[StuM]

Originally Posted by cgm12mgc

not sure where you're getting catamaran from but mine is a 45' monohull

From Bluenomads stated figures for his powercat.



Obviously, you won't be putting 3.5kW of panels on a 45ft monohull sailboat

[Chotu]

Yeah. StuM is correct. I saw 45' Catamaran, talk about 5-6 knots motoring a catamaran, Blue Nomads, etc and presumed a catamaran discussion.

The weight, of course, has less impact on a monohull.

[Qmansailer]

I’ve been following these discussions on electric propulsion for many years and I’ve learned a lot from the discussions, but I have been reluctant to chime in prior to this because, without hard information, I haven’t felt I could add much to the debate, and, would only add myself as a target for others to push their own opinions. Now that I’ve got some first hand experience, I can hopefully add something to the conversation.
First of all, I am an engineer (in fact most of you have probably owned or used a product that I had a hand in designing at one point), so I do understand “the numbers” and I would argue that there’s plenty of mis-information flying around on both sides of the fence on this one. Second, there’s no definitive answer here, an engineering system, properly designed, meets the intent of the requirements of the intended use. And there are as many intended uses for electric propulsion in the sailing community as there are forum members. What I can hopefully demonstrate is that, for my use requirements, I have been able to apply electric propulsion in a very satisfactory way. It may only apply to me, but it works and I’m very satisfied with it so far.

My set up:
Hull - 43’ Elan GT5 ~ 9000 kgs displacement
Electric Power - 33KW 3 phase AC motor
Batteries - ~ 20KWhr Li-Ion (400V)
Generator - 22KW DC (400V)
Charging - 3KW dockside

With this set up the electric drive is marginally more powerful than the diesel it replaced. I’ve reached a little over 9 knots in pretty flat water, and I can cruise 5 knots at about 10KW. In day-sailing, getting in and out of the marina, I typically use ~ 20% of the battery charge in each outing. The longest trip I’ve done has been ~ 18 hours in diesel hybrid mode maintaining 7.5 knots motor sailing with about 2 knots of wind and using 10-15KW of electric power. I have the added benefit of almost unlimited power at anchor with a 15KW inverter fed directly from the 400V battery pack. I can usually get by on inverter/batteries for a couple of days, and then, it only takes about an hour on the generator to fill them back up again.
Are there downsides - yes there are of course downsides.
- The system is marginally heavier than an equivalent set up of a diesel auxiliary, AC generator, and house batteries, about a 250 kg penalty. I was able to mount all the equipment on the centerline of the boat and minimize the impact to sailing performance. If I could have worked with the hull builder, I would have reduced the ballast, and placed the batteries even lower in the hull to reduce the mass impact, but that wasn’t possible.
- It did take up some room. I essentially had to convert a rear double berth into a single.
- The big one is cost. Many would say it isn’t cost effective. Everyone values everything differently. For me this was worth the money, for others it wouldn’t be. I would say that many people have paid more for a boat than I paid for this all together, and many much less. I could have bought a bigger conventionally powered sailboat for this money, many do, but I wouldn’t get the same satisfaction I get from my boat. To each his own.
The bottom line is, it’s very technically feasible to have electric propulsion on a sailboat. Yes there are compromises and design considerations to take into account. For some it will meet their requirements for other it won’t. I hope this real world example helps to inform the debate.

[wingssail]

Originally Posted by StuM

"Upwind" ( i.e with the wind forward of the beam) is not the same as "into wind" (i.e. wind on the bow).

Good luck using sails to go "into wind".

It's called tacking. And when the poo hits the fan we find we are much better off sailing than motoring, in every way, and that is even with a motor which will push us at 7kts against 50kts of wind. We're still happier under sail.

Less pounding, less stress on the engine and drive train, less shock on the rig, less fuel used, quieter, and the sails get more powerful when the wind blows harder.

Even if the channel is narrow, we can tack against the wind.

Motoring into the wind is for boats that can't sail that way or for captains who simply don't want to.

[NPCampbell]

Originally Posted by Qmansailer

My set up:
Hull - 43’ Elan GT5 ~ 9000 kgs displacement
Electric Power - 33KW 3 phase AC motor
Batteries - ~ 20KWhr Li-Ion (400V)
Generator - 22KW DC (400V)
Charging - 3KW dockside

That's an interesting setup. It's like a scaled down version of a Silent Yacht.

It sounds like it meets your needs. However, it does look like your electrical system has 3 single points of failure? The generator, charger and inverter. I'm assuming you are inverting and then converting down for your 12/24v needs? Whereas a conventional diesel engine can drive a redundant 12/24v alternator that can serve as both a generator and battery charger.

I'm also interested in what the fuel burn rate of your genset is and what speed you can achieve using only the 22kW output of your genset? Around 6 knots I am guessing?

[GrowleyMonster]

As owner of a DIY electric boat, I will chime in.

Do not delude yourself into unrealistic expectations, with electric. First of all, your HP rating. It is for the upper end of the rated voltage range. For large PMAC motors, i.e. rated 10kw to 20kw, this is usually 72v or 96v. For a small boat it is more common to use a 48v bank for enough reasons to fill a small book. You will therefore probably not see your full rated output power. And if you do, you will be looking at a huge current. Lots of amps. Peukert will kill you when you get up over 200a, that is, if your batteries will support a discharge like that. Talking MAJOR wire size, like 0000. But your bank's capacity rating will not even be a thing, at full power. You could go LiFeP04 or similar, but the cost will blow you away. To keep your batteries charged while discharging such high current, you really need at least a 16kw genset. Solar? Not even a thing, at this power level but I will get back to that.

If your power demands are more modest, and you are quite content to motor at 2kts, you can probably motor indefinitely, with enough solar and a touch of the generator now and then. But this will not work so well stemming a current or seas and wind. Just sayin. A big outboard would be good insurance. Not many full time cruisers have found electric propulsion to satisfy their needs. If those needs are modest and if you can carry a LOT of solar and batteries, that is another thing.

Of course every stage of energy conversion adds more losses. You are using diesel engine to turn a generator. Then you are using a charger to input power to batteries. Then you are using batteries to operate a controller, which sends conditioned power to the motor, which turns a prop, perhaps via a reduction gear. Lets just say that on average every component there is 85% efficient, which sounds sucky but is actually not bad. Lets say you have 6 nominal stages of conversion. You have 85% of 85% of 85% of 85% of 85% of 85% power. So about 37% efficiency, using those made up figures. Obviously, cutting out a few middlemen is a good thing. Here is a novel concept... how about eliminating generator, charger, battery, controller, electric motor, and just drive the prop via reduction gear, with a diesel engine?

Okay that sort of covers most of the cons. Oh, I don't care what kind of turnkey system you get installed. You still need to be something of an engineer to figure out what is happening and what you can do or must do to get the best service out of your EP system. You will need to learn especially about batteries. You think you know batteries? No, not really. Not when it comes to a system that will put so much demand on them.

Now, the plusses, and there are many. First of all if you day sail, and mostly use EP for docking, you can fill your tank so to speak, with shore power. You can probably get by nicely with 8 golf cart batteries from Sams Club. No fuel to spill. No fuel to clean up, or to smell, or to buy or pump. Unless you run that genset. For a bank that size it is feasible to install up to about a 2kw inverter (but also install a smaller one, maybe 300w) for sparodic operation of 120VAC appliances. 1kw of solar panels would see you docking with a full bank, most likely. You have instant ON power. Flip a switch and turn a knob and the prop spins less than a second later, with no warmup. Here is the big one. No minimum idle speed. Most guys don't realize how much it hurts to have to "bump" the engine in and out of gear for very low speed maneuvering. We get used to it. But the first time you approach a dock at 50RPM you will be sold on electric for maneuvering. No more bumping a gearshift. Oh yeah electric is great for single hand tacking, if you have a hardnosed boat that just doesn't tack well. Apply a bit of power with that rudder and around and over you go. Electric drives can be anywhere from pretty darn quiet all the way down to nearly silent or even undetectable topside. No exhaust. No heat. No smell. With a day sailer or weekender, electric is THE way to repower. You may be able to skip the solar, forget about a generator, and just charge from shore power.

It sounds to me like you would be happier with a nice tractor engine conversion like a Beta/Kubota. But you really should go sailing on an electric boat before you decide. I love EP, but I love it for some things, not so much for others.

[wingssail]

Originally Posted by Qmansailer

Hull - 43’ Elan GT5 ~ 9000 kgs displacement
Electric Power - 33KW 3 phase AC motor
Batteries - ~ 20KWhr Li-Ion (400V)
Generator - 22KW DC (400V)
Charging - 3KW dockside

For some it will meet their requirements for other it won’t. I hope this real world example helps to inform the debate.

Congratulations on what is apparently a successful conversion to electric (hybrid) propulsion.

It is only through persons such as you who are following though with these projects that will demonstrate to others what is feasible and what is not.

The future of propulsion of all types of vehicles may well be electricity, so it is good to see things being developed.

BTW, your 43’ Elan GT5 is a gorgeous boat.