Sail boat engine choice - electric or diesel

[jtaylor]

Keep in mind what I mentioned earlier about windage and current impacting range... I have been out in more or less ugly conditions for my area. a 25kt headwind and short chop can bring a boat near to a standstill. I was able to make only about 2kts over ground against the wind, chop and current. With a "2 hour" battery, will you be able to get to shelter within 4nm? You may need to switch plans and head for cover downwind, in which case its a completely different ballgame.

My boat under diesel only had a 3gallon race-compliance tank. Those 3 gallons could move my boat for 12 hours at more or less full throttle with my 7hp continuous rated YSB8. That was enough to move my boat under the same conditions at about 2.5-3kts.
My boat under electric propulsion can do the same but for only 1 hour. The "bigger battery" that we are looking at will be able to manage about 3 hours of that. In the above mentioned conditions, as soon as we turned around, instead of making 2kts at 50A, we were making 5.5kts at 12A. Is amazing what wind and current will do to the performance envelope. That excursion ended with us back at the dock with a 70% drained battery bank and only having covered about 5nm total (there and back).

In short, you cannot assume a speed for x hours. You need to know what happens to the performance of *your* boat under various circumstances, and have a plan for all situations, even in "my local little lake where nothing goes wrong..." But that carries true for diesels as well.

[Another anecdote]
A few years ago, we headed out to a race with a storm brewing well to the north of us. Once we saw some lightning further down the lake, we cancelled the race and the intrepid fleet turned back to the club. That's when a microburst hit. We could see the boats in front of us, one by one get pushed over to about 45 degrees under bare poles. It lasted for under a minute but wind instruments had clocked winds in excess of 45kts (again, on our gentle little lake where nothing bad happens). My electric boat performed wonderfully. A beautiful Tofinou 9.5 had their fuel tanks shook up a little sediments in the tank were stirred up and their fuel lines clogged and starved the engine, which cut out... right at the turn into the club where there's a 2kt cross-current and rocks downstream. The skipper was able to anchor and wait for a tow, but not before his 6' draft got to know a bit of the topography. I don't know what else happened out there, but his season was essentially over and he had extensive work done on the diesel, saildrive, rudder and keel. My take away? Different systems, different problems. I electric boat will work at all angles of heel that the boat can operate at. When I winterize, I simply remove the key and I'm done. I don't miss diesel maintenance. My system gives me extremely fine-grained performance and efficiency data. My diesel had the oil and water dummy lights. Not even a tach.
[end of annecdote]

Converting to electric propulsion requires that you learn a lot about your boat's propulsion system and its efficiency. With diesel, you can always ge a bigger tank and range variances amount to fractions of a day's motoring. With electric, you've basically got a day-tank and that's being generous. I classify my system as a "1 hour" setup -- my battery bank kWh equals my motor power (5kw). A better setup would be at least a 2-hour setup. 10kwh storage for a 5kw motor. Any kind of cruising/travelling would require some sort of on-board power generation, ideally sized to motor cruise output, about 50% max continuous output. In my case, my 4000kg boat with a 5kw propulsion system would be well-served by a 2.5kw genset. With a permanently installed genset, you can reduce battery capacity back to the 1hour level. The devil is in the details however, and getting all this equipment to work well together more or less autonomously is where the industry is concentrating their efforts at the moment. Get things happening, but it's still very much in development and/or $$$$$.

To plan the conversion here are the basic steps I would take:
1) determine the power requirements of moving your boat. Tow it and put a strain gauge on the tow line to see how much resistance your boat generates at given speeds. This gives you your minimum power curve.
2) determine the largest diameter propeller you can fit with adequate hull or aperture clearance. Size your prop to this diameter.
3) determine propeller pitch. Assume about 50% prop efficiency. Aim for cruise speed (about 1 knot lower than the hull speed or where the "knee" in the power curve is) at 1000rpm. Convert that to pitch -- how many inches in a nautical mile, what speed, how many RPM would that take for a zero-loss prop to screw through the water, double that and there's your pitch.
4) size the controller to be able to hit hull speed continuously, but your ideal is 50% power at cruise speed. In my case, I can hit about 6kts (less than my 6.7 theoretical hull speed but, compromises... at 80A. Max throttle will settle at about 88A, but can burst to 110A if there's significant resistance from seaweed, dirty bottom, wind, etc).
5) identify the transmission ratio that will match motor RPM at that power level with shaft output at your 1000rpm. In my case, that is about 2.55:1. Your motor has a k-value or how many RPM per volt with no resistance. I believe the Motenergy 0913 was about 50rpm/volt and it seems to be a common k-value.

And the rest is balance of system, data logging#dispaly, energy conversion, charging, battery management, throttle choice, etc.
It's a long path. If you're into that sort of thing, it's a lot of fun. IF you just want to get the boat back in the water, it can be a source of endless frustration and resentment. YMMV.

Ok, sorry for the brain-dump. I learned a lot doing my conversion and that information loves to come out from time to time...

/J

Originally Posted by carstendenmark

Thanks, beachbumlou

I use the main engine (the sails) as much as possible.
By saying "bad conditions" I didn't mean motoring when unnecessary. I mean BAD.

[mcon12000]

Have you done something this invasive to a boat before? Boy are you into self inflicted pain!

I'm a huge fan of electric propulsion on land and really want to like the idea for a boat but just can't justify the expense vs range. I also have a four year old onboard so safety and or ability to maneuver is more important now vs me alone. So for "me" it only works with a genset capable of delivering the required energy to the electric motor (defeats the purpose) or possibly in your case day sailing where you plug in at the end of the day.

Sticking with the OP's scenario of an aging/dying motor and associated basic electrical system I'd say rebuild the diesel. If you have the stomach for months of electrical work, fabricating and a bit of carpentry then go for the conversion but holy crap it's going to be expensive. I'm betting you could buy two possibly three brand new engines for what the conversion is going to cost.

You also mentioned going to an electric cook top I assuming you plan on spending some evenings away from the dock? Personally I can't find enough space on my 38' boat to put the solar panels I would need to go to an electric galley. I love the idea though!

While we're on the subject I'm almost finished rewiring my boat's electrical backbone and it was far from cheap to accomplish correctly (ABYC Standards). I also do this work for others and your scenario only makes sense as a DIY project unless your boat is rather pricey and your passion for perfection is priceless. It's my opinion that anyone who starts a process like the one you're considering should be prepared to gut the boat's electrics. You'll find that one change leads to another necessary change until you run out of boat lol.

I'd recommend spending a MUCH smaller amount of time and money educating yourself about the diesel you currently have and upgrade your electrical system to lithium for that electric galley. Anyway you've already made some good choices or we wouldn't be talking about this... So good luck with the project and enjoy the journey!

[Gonsena]

Originally Posted by carstendenmark

I live in Denmark, and most people do coastal sailing.
My setup is not meant for world cruising.
However, please watch Youtube "Sailing Uma", a pure electric live-aboard 36' sailboat who criss-crossed the Caribbean and now also crossed the Atlantic.
The electric motor can recharge when sailing by sails.

People buy a sailboat for sailing, not motoring, in my mind :-)

If I remember correctly they had a home made and got as a gift and ocean volt but the propeller rescharges once they get 7knots plus if not is not worthy as it loses all the speed

[jtaylor]

Sailing Uma had an OceanVolt system gifted to them, yes. However it was making noises and while in holland, they had it replaced with a new unit. The original gifted unit had been on a boat that was struck by lightning so they think there may have been something wrong with the gear meshing from that incident. Apparently, the transmission oil was black and full of metal filings when they did the leg-swap. The new unit is so much quieter and even more efficient. Some good videos on that on their channel.

[misfits]

Logged in twice in one day, omg.

I've had an electric boat for 4 seasons now. It spends the summer swinging on a mooring or at an anchorage up on Penobscot Bay in Maine.
Yes there are limitations but I have no plans on being a world cruiser. I have a Honda generator in addition to 260 watts of 24 volt panels that are wired in series.
This spring I motored 24 NM in 5 hours from it's winter home to my mooring using the generator to drive a 25 amp charger. I arrived at my destination with the battery bank at 65% SOC. My propulsion bank is 150 AH, 48 volt, FLA. I also have a separate 12 volt house bank that powers a 2000 watt inverter for a microwave, plus refrigeration in addition to the other normal stuff.

I realized my propulsion bank just sits most of the time so I installed a 48 volt DC water heater element. I came up with that approach after a thread here on this forum 5 years ago about heating hot water.

95% of the time the solar system provides all the energy to run this boat .

For me the way I use my boat, electric works. Are there times I wish she had diesel, abso****inlutely. But I don't miss the maintenance or smell.

[jknight611]

Originally Posted by waterman46

What? Photocells on the sails?

Regeneration, an electric motor when turned becomes a generator

[jtaylor]

Originally Posted by mcon12000

Have you done something this invasive to a boat before? Boy are you into self inflicted pain!

Sticking with the OP's scenario of an aging/dying motor and associated basic electrical system I'd say rebuild the diesel. If you have the stomach for months of electrical work, fabricating and a bit of carpentry then go for the conversion but holy crap it's going to be expensive. I'm betting you could buy two possibly three brand new engines for what the conversion is going to cost.

I have done almost everything imaginable to my boat. I recored the decks from inside. I have replaced every. single. goddam. electrical. wire. and. fitting. on this boat. It's a long process. Every year she gets a little better, a little nicer. The repower in 2014 was fun. I didn't launch until mid-august (in a part of the world where haulout starts shortly after labour day and runs until early November). A lot of pain, yes, but a lot of learning, and many excuses to buy nice tools...

As for the cost, I went the engineered system, installed by myself. There just isn't (or wasn't) a network of "certified" system installers specializing in electrical repowering so I would have been paying their rate for them to learn. Besides, I'd been planning my conversion since the first year I bought the boat (5 years previously). My engineered system was complete, except for batteries and charger. That included propeller, wiring harness (don't underestimate the value of a pre-made wiring harness), contractor, controller, motor, mounts, gearbox, prop, coupler, throttle, key switch, controller display panel, etc... Even with that, I had lots of work to do installing it. Building a box for the throttle to mount it, aligning the prop with the motor, power cabling, etc. All told the system, the batteries and BMS, SoC meter, charger, cables, wires and connectors, tools, all came to just under $10,000CDN, not including my time. A BetaMarine 13hp diesel would have been about $8000CDN, plus whatever installation changes would be needed, exhaust, engine stringer modifications, etc. So probably about the same, plus installation. I have a system with which I am thoroughly confident and know inside out. I know what components do and what they can be bypassed or replaced with. Electric propulsion is interesting that way. Individual parts of the system can be upgraded and changed as you go. The system can evolve with the boat and you are never really tied to a specific vendor of a specific product that may or may not be obtainable. DCDC converters can be swapped out as needed. AS with relays, contractors, fuse blocks, etc. You can even change the controller from a Seven to a Kelley if that floats your boat. It will all still function. Maybe not at optimum efficiency, but it'll get you going again.
For best flexibility, I would recommend being able to change your charger profile on the go. Should you lose a lithium bank while on holiday and can't get a replacement, you could install AGMs instead and change the charger profile and get back out there. Life with electric propulsion is not all worrying about being caught off a lee shore in a gale. I think that fear is not unique electrically propelled boats. Yo can imagine any kind of edge case where this system falls down, and I can imagine the same around trusty old diesel.

As it stands today, voyaging on pure electric is a thing that *can* be done. It just takes special people that have electric propulsion as part of their voyaging program... But something that can be done is not the same as something that can be done by anyone anytime. Electric voyaging is not there yet. But it is coming.
Daysailing, club racing, and weekending is something that is here now. Today. For nearly everybody. The systems and energy storage are able to handle that vast majority of situations. System integration still has a way to go but it is more than doable. If you use your sailboat as a motorhome, let's say you have a long weekend off and you have to spend it at a specific spot 25nm away no matter what, then yeah, you'll be wanting that diesel to guarantee that you can get there and back on your schedule. Or if you're in Montreal and heading up the St. Lawrence to the Thousand Islands and Lae Ontario, an electric propulsion is probably not your bag. I'm panning on doing this eventually, but I'll need a bigger charger and a couple of 2000w combined generators. In the mean time, I don't need to carry that weight with me every day.

Electric gives you options options options...
As long as you're willing to work within its limitations.

/Jason

[newhaul]

Originally Posted by jknight611

Regeneration, an electric motor when turned becomes a generator

Owevet regen requires a minimum speed to be effective ND smaller vessels just can't do it .

[jtaylor]

I only start seeing regen above 5.5kts, and that's only 1A at 52V... The most I've ever seen is 2A when sailing downwind in 15kts and hitting hull speed of 6.7kts. On a daysail, that's not very useful. On a passage, it could be interesting. 50W * 24 hrs is 1.2kwh/day. Not that bad... Probably more than enough to recover electronics load, if not refrigeration.

when in Flroida a few years back, I was talking with the engineer of Tang! a 60' carbon/kevlar catamaran with an electric propulsion system that had just crossed the Atlantic. they had to run the water maker, take hot showers and make ice cubes for drinks and still run the dump-loads to shed excess power they were generating while sailing at 17+kts.

The power available goes up with the cube of the speed... 5kts just doesn't have enough available power. But multihulls have huge regen potential.

[Ryan]

If it was me, I'd rebuild that Volvo, fix your fuel leaks, get the injectors tested and serviced. It might be all you need is a better propeller and some gaskets.
Put in good filters, clean/replace your tanks, and use the considerable about of money you saved to go sailing.
Having repowered myself (MD3B --> 4JH4), expect it to either be very expensive and time consuming if you do it yourself or extremely expensive if you have someone else do it. Even more so for the switch to electric.

The only reason I can see justifying a new diesel are that it has always been the wrong size. In my case 36 hp was no where near enough for the boat.

[mcon12000]

Originally Posted by jtaylor

The repower in 2014 was fun. I didn't launch until mid-august (in a part of the world where haulout starts shortly after labour day and runs until early November). A lot of pain, yes, but a lot of learning, and many excuses to buy nice tools...


/Jason

I'm living this right now! Boats in the water but hasn't moved the whole season and the local stores have the winterizing displays up.. lol

[mcon12000]

Originally Posted by jtaylor

I have done almost everything imaginable to my boat. I recored the decks from inside. I have replaced every. single. goddam. electrical. wire. and. fitting. on this boat. It's a long process. Every year she gets a little better, a little nicer. The repower in 2014 was fun. I didn't launch until mid-august (in a part of the world where haulout starts shortly after labour day and runs until early November). A lot of pain, yes, but a lot of learning, and many excuses to buy nice tools...

As for the cost, I went the engineered system, installed by myself. There just isn't (or wasn't) a network of "certified" system installers specializing in electrical repowering so I would have been paying their rate for them to learn. Besides, I'd been planning my conversion since the first year I bought the boat (5 years previously). My engineered system was complete, except for batteries and charger. That included propeller, wiring harness (don't underestimate the value of a pre-made wiring harness), contractor, controller, motor, mounts, gearbox, prop, coupler, throttle, key switch, controller display panel, etc... Even with that, I had lots of work to do installing it. Building a box for the throttle to mount it, aligning the prop with the motor, power cabling, etc. All told the system, the batteries and BMS, SoC meter, charger, cables, wires and connectors, tools, all came to just under $10,000CDN, not including my time. A BetaMarine 13hp diesel would have been about $8000CDN, plus whatever installation changes would be needed, exhaust, engine stringer modifications, etc. So probably about the same, plus installation. I have a system with which I am thoroughly confident and know inside out. I know what components do and what they can be bypassed or replaced with. Electric propulsion is interesting that way. Individual parts of the system can be upgraded and changed as you go. The system can evolve with the boat and you are never really tied to a specific vendor of a specific product that may or may not be obtainable. DCDC converters can be swapped out as needed. AS with relays, contractors, fuse blocks, etc. You can even change the controller from a Seven to a Kelley if that floats your boat. It will all still function. Maybe not at optimum efficiency, but it'll get you going again.
For best flexibility, I would recommend being able to change your charger profile on the go. Should you lose a lithium bank while on holiday and can't get a replacement, you could install AGMs instead and change the charger profile and get back out there. Life with electric propulsion is not all worrying about being caught off a lee shore in a gale. I think that fear is not unique electrically propelled boats. Yo can imagine any kind of edge case where this system falls down, and I can imagine the same around trusty old diesel.

As it stands today, voyaging on pure electric is a thing that *can* be done. It just takes special people that have electric propulsion as part of their voyaging program... But something that can be done is not the same as something that can be done by anyone anytime. Electric voyaging is not there yet. But it is coming.
Daysailing, club racing, and weekending is something that is here now. Today. For nearly everybody. The systems and energy storage are able to handle that vast majority of situations. System integration still has a way to go but it is more than doable. If you use your sailboat as a motorhome, let's say you have a long weekend off and you have to spend it at a specific spot 25nm away no matter what, then yeah, you'll be wanting that diesel to guarantee that you can get there and back on your schedule. Or if you're in Montreal and heading up the St. Lawrence to the Thousand Islands and Lae Ontario, an electric propulsion is probably not your bag. I'm panning on doing this eventually, but I'll need a bigger charger and a couple of 2000w combined generators. In the mean time, I don't need to carry that weight with me every day.

Electric gives you options options options...
As long as you're willing to work within its limitations.

/Jason

Also I wasn't referring to you in my first post but after re reading it I can see where it would appear that way.. I'll likely be sending you a PM in the future when I decide to take the plunge...

[john manning]

As you can see from other answers here, its just a matter of how you expect to use you boat.

The main problem I see in your plan is that you are going from a 10HP motor that is no longer giving full power to a 24HP (18KW) electric drive. Why all the extra power. The current state of battery technology means you need to go with minimum electric power for your purpose.

I am currently considering repowering my 39ft catamaran with a diesel electric system. As part of doing that I built an electric drive. I ran my propellers at the rpm needed for 6kts and measured power used. It turned out to be one third of the diesel engine power used. My guess is that you will get the same propulsion you have now from a 3KW or 4KW electric drive.

[misfits]

Originally Posted by john manning

As you can see from other answers here, its just a matter of how you expect to use you boat.

The main problem I see in your plan is that you are going from a 10HP motor that is no longer giving full power to a 24HP (18KW) electric drive. Why all the extra power. The current state of battery technology means you need to go with minimum electric power for your purpose.

I am currently considering repowering my 39ft catamaran with a diesel electric system. As part of doing that I built an electric drive. I ran my propellers at the rpm needed for 6kts and measured power used. It turned out to be one third of the diesel engine power used. My guess is that you will get the same propulsion you have now from a 3KW or 4KW electric drive.

John, you're correct about KW. I'll typically motor between 30-40 amps at 48 volts. At 40 Amps thats 2.5 HP. I have a 10KW drive, probably could have gotten by with a 5KW & saved a couple of bucks in the process.

[jtaylor]

@John Manning: see one of my previous posts about the main steps to converting. The tow test is actually fairly important if you wish to get a fairly otpimized system. That's the only way to get real data of hull resistance through the water without factoring in efficiency losses of components of the drive system.

As for the 18kw system proposed by the OP, always be wary of power claims of systems. That 18kw is probably peak power. Peak power in marine diesels is the 1-hour rating. Peak power in industrial motor/controller systems is a 1 or 2 minute rating.

The Sevcon controller in question is the Gen4 Size 6 controller.
The 550A rating is 2 minute.
The continuous rating is 220A.
And the motor in that kit has a continuous rating of 157A.
So the continuous (24/7 usable) power of the setup is limited to pack voltage * 157A.
So about 12kw at 72V nominal or 7.8kw at 48V nominal (just over 10hp)

In my system, the 2 minute rating is 275A.
The continuous rating is 110A.
110A @48V nominal is about 5.5kw or just over 7hp.

My Yanmar YSB8 has a 1hour rating of 8hp and a continuous rating of 7hp.
My boat claims to displace 7500lbs, I've always used 8000lbs or even just 4000kg in my estimates.

My system is/was sold by Electroprop as a 5.5kw system.
The same components are sold by others (Thunderstruck among them) as 10kw systems.
One thing I really like about ElectroProp is his apparent under-rating of his systems. He always quotes continuous power. Marine propulsion applications are always going to be continuous power. We never have a need for those 1 or 2 minute peaks so anyone who advertises them is being a little disingenuous.

His boat is probably fairly similar to mine -- about 30', about 8000lbs.
His power needs will also be similar.
Lets assume he fits that 18kw system.
Even if he puts the throttle all the way down with a prop that can get him to hull speed the following will happen:
1) the boat reaches hull speed and the prop reaches the rpm requested by the throttle but max power is not developed. Not a big deal, but you may have bought more motor/controller than your boat can use. It's only money... You could probably turn off the water cooling and just run the motor as a sealed unit without overheating.
Or...
2) the prop is way too big and aggressive. Again at full throttle, the motor will try to spin at 2500rpm. It will use all available power to do so. If the prop is too aggressive and is trying to spin at 1000rpm but hitting too much resistance from the water, more power will be drawn. Some sort of equilibrium will be reached. if 2500rpm can't be reached, then controller max power will be hit and that's where things will stay until battery runs out or things heat up too much and the controller claws back power.

Basically, you want to have your controller max power being reached at the same time as your boat hits hull speed, at the same time as your prop is hitting that 1000rpm and motor at its max rpm for your voltage.

The prop on my boat could actually stand to be a little bigger. I am hitting max throttle before I'm hitting max power. But performance is good enough. 6kts at 80ish amps is fine. The controller and motor coils never get above 65C in 6 years / 7 seasons. However, going for a 14" did 14" pitch would have been more expensive and not as readily available. I went for readily available anywhere, easy to find and relatively affordable standard components instead of per-optimized exotic bespoke engineered components.

The thunderstruck kit uses the same Sevcon Gen4 line of controllers which are amongst the most efficient brushless motor controllers on the market. They support regen, and allow an insane amount of configuration (if you have the equipment). ElectroProp configured my controller and gave it its personality. Thunderstruck will do things a little differently. Perhaps the acceleration/deceleration ramps are different. Perhaps throttle behaviour is different (linear as opposed to logarithmic or some other custom curve. Perhaps they characterize their motor differently than has ElectroProp. That is definitely something to get from a knowledgeable source - a complete system integrator, such as ElectroProp, Electric Yacht, Thunderstruck, etc will all have configured their controller for a specific motor. Had I just bought a pile of components, I would have been stuck with defaults or I would have had to purchase the controller interface (hundreds$$ if I recall). Anyway, ElectroProp built in a few tweak-able parameters that I can change from within their Sevcon ClearView Display menus and they have served me well in optimizing my setup. If I change props, I'll have to revise those option, but I know they're there.