Thoughts on a viable and MARKETABLE Electric Drive Train

[valhalla360]

I want to start by saying I encourage meaningful and technical debate on the proposed drive train. If I made a mistake in assumptions or calculations, the goal is not to shut down discussion.

So most of the proposed electric drive train threads either focus on use cases that represent tiny percentages of the new boat market (such as ocean crossings or boats that claim average speeds in the mid teens, etc...) or quickly wander off into magic thinking (5kw of power will get a 50ft cat up to 5kts kind of stuff).

Hybrid drive trains don't work very well on boats. Base hybrid technology really benefits from a highly variable power demand where the hybrid system evens out the loads on the ICE, allowing it to stay at peak efficiency matched to the average power demand. Perfect for a car in stop and go traffic. Since displacement cruising boats largely run at a steady power demand, there are no peaks and valleys to take advantage of. They are already running close enough to peak efficiency that there really is no efficiency gains to be had and potential losses due to additional energy conversions.

Battery-Electric drivetrains quickly run into limits on how much power can be stored and how to replace it. Fine if you just want to get in and out of harbor but very limiting if you need to power for any significant distance.

Probably the most common displacement cruising boat use case is weekend cruisers who go out many weekends per year with 1 or 2 longer week long trips covering more ground.
- Battery-Electric could typically cover the weekend day trips but on the longer trip, if you need to cover some ground to get back in time for work on Monday, covering 50-60 miles in 8-10hrs is beyond their capability if the wind doesn't cooperate.

This brings us to a Plug-In-Hybrid option.
- I'm assuming this is a new boat so no retrofit costs, it's all built into the original design other than the cost difference in the drivetrain components.
- It likely will be a cost increase but probably not a huge cost increase. Though I doubt it will pay off in terms of fuel costs saved.

I'm looking at the outboard powered 34ft Gemini as the base boat. This is an established model that is a popular cruising boat so it's only the drivetrain that is really in question (if you have a general dislike of Geminis take it to another thread if it's not tied into the propulsion system). Also, since we had one fitted with a 25hp outboard (call it 20kw for ease of calculations...I know it's off a bit), I'm familiar with the performance and capabilities.
- 20kw outboard was plenty to maintain a 6.5kt cruise speed (roughly around half throttle so call it 10kw for cruise speed) and could push the boat up to full hull speed, so we aren't under powering the boat to make the calculations look good. So lets assume a 20kw electric outboard is mounted in place of the gas outboard.
- Ours had 2 - 18 gal built in tanks plus a 6 gal outboard tank, all plumbed to a 3way valve.
- A Tesla 80kwh battery bank weighs about 1200lb, so rough estimate if we install a 40kwh battery bank, probably around 600lb. If we place 300lb of batteries where the built in gas tanks go and another 80lb where the 2 - BBQ size propane tanks go, and 240lb where the 4 - 6 volt golf cart batteries went...so far we haven't added any weight.
- Modify one of the rear compartments to fit a 5kw generator (remember, new design so no retrofit costs and it can be done properly). Retain the 6 gal portable tank (could be made built in if desired). This would be a swap out for our 2400w generator...so a small increase in weight.
- Fridge and stove are converted to electric operation, so it's fine to replace the propane tanks with batteries.

Typical Use case which I believe is common for typical new boat buyers:
- Boat lives at the marina plugged in all week.
- When you arrive on Friday, battery is fully charged and until you leave the dock, it stays that way.
- Day trip, 10kw draw from the 20kw motor is plenty for normal cruise speed. Even with a couple hours of motoring, you still have 20kwh of battery storage available for use at anchor if you choose not to return to the marina for the night.
- 20kwh of remaining battery bank should be plenty for house loads including electric galley and even air/con operations for a weekend if you wanted to anchor out.
- Longer trips. 40kwh battery bank drawing at 10kw to maintain 6.5kt will get you 4 hours or 26 nm range under pure battery. Crank up the 5kw generator and that should go up to around 8hrs or 52 nm range. If you have to go beyond that, you can continue on using purely the 5kw generator output but at a decreased speed. In moderate conditions that probably drops you to around 4-5kts until the fuel runs out (Might want to carry a 5gal fuel jug or two for longer trips...which we did anyway).
- After a long run, we tended to marina hop so usually would have been able to recharge off shore power. Assuming there is 1.5kw excess capacity for charging after house loads on a 30amp, 15hr would replace 22.5kwh. If fitted with a 50amp shore power, you could dump 4kw into the batteries, easily fully recharging overnight. (in a pinch if anchored out, the generator could be used to top up the batteries overnight. It wouldn't be the ideal scenario but if only done rarely, at least you didn't give up capability)
- Even a lot of longer distance coastal marina hopping cruisers (great loop cruisers for example) could get 75% or more of miles from shore power sources. We usually stayed under 30miles per day except for a handful of longer 50-60miles days, so the bulk of the miles could be done under battery power from shore power with only modest generator assistance.
- In an emergency, you can run full out 20kw output for 2hr under battery alone and 2.5hr if you start the generator immediately and even after the batteries die, you have at least some power (5kw) until you run out of fuel. While it's possible you need max power for longer, that's really moving into a situation where it's so rare I would argue I can live with it. It's certainly not the examples where you have 20-30min at max power and I can see situations we've been in where that isn't enough.
- Of course, this assumes a pure motoring scenario...if you get any miles from sailing, it should reduce the generator run time.
- Even if you are on a mooring, a 750w solar array could reasonably be fitted on a Gemini generating say 3kwh per day or about 21kwh per week. It will be limiting if you motor a lot but for modest motoring needs, it would be enough.

Cons:
- It will be more expensive but not drastically. I would estimate probably under $10k more but on a boat with a base price north of $250k, that's not beyond being reasonable.
- The operator will need to understand the operation to maximize performance...example: For short trips, leave the generator off. For longer trips, they need to start the generator almost immediately after departing. For intermediate distance say 30 nm, the operator will need to estimate when to crank up the generator and how much reserve capacity battery they want to maintain.

Pros:
- Eco street cred...probably 75% reduction in carbon emissions.
- Ability to run the house loads without cranking up the generator (while not giving up the capability if the situation calls for it)
- Instant power with no need to wait for an engine to warm up.
- Eliminates concerns of having propane on board.
- Able to boost thru a light wind tack while sailing by just a quick push of the throttle.
- And the big one...this is a common use case so larger manufacturers would be interested and could offer it as a standard option.

Alternative option: Trawler cat (still sailboat speeds). You could probably up the solar to 3kw and bump up to a 60kwh battery bank at net zero cost/weight by eliminating the sailing rig. Now you have a 6hr/39nm range under battery alone and are generating around 12kwh per day from solar. For weekending it would be perfect. Even for longer distance coastal cruising (like great loop), you would probably be pushing upwards of 90% of miles under electric power.

[Bill O]

Wow, a lot of thought and detail for this theoretical boat.

IMO the sailing vessel would better than the trawler to be able to fill in w/wind power when needed. Also should be less power to move the sailing cat vs. the trawler unless your trawler was power cat based.

Would think you could add as much solar on the cat as you could for the trawler so a solar farm of >1kw would be a cheap add on.

Overall I like the concept!

[valhalla360]

Originally Posted by Bill O

Wow, a lot of thought and detail for this theoretical boat.

IMO the sailing vessel would better than the trawler to be able to fill in w/wind power when needed. Also should be less power to move the sailing cat vs. the trawler unless your trawler was power cat based.

Would think you could add as much solar on the cat as you could for the trawler so a solar farm of >1kw would be a cheap add on.

Overall I like the concept!

The trawler option was basically take the Gemini and skip the mast and sails. We have done a lot of motoring on the Great Loop with the mast down and it works fine in what we call trawler-cat configuration. The idea is we could up the battery power storage and solar significantly, while remaining largely cost/weight neutral comparted to the sail option. If you aren't into sailing, saves some hassle and maintenance and makes up for limitations that the sails would have addressed.

In sailboat configuration, 750w is a pretty good size without getting exotic or wasteful in terms of putting on a ton of solar that's always shaded by the rig. The Gemini only has a 14ft beam so it's not comparable to a big 25ft beam cat in terms of available solar panel areas. Then again the solar was a small bonus as the primary propulsion was going to be via shore power. 3kwh per day is going to only give you about 20min at cruise speed per day.

[Bill O]

Yes the whole idea still sounds good. Is this where you are headed?

I know you said you would do all this on a new Gemini, just wondering if this would be a viable idea for someone if they didn't mind doing the work and retro a used one w/your planned conversion in mind?

[valhalla360]

Originally Posted by Bill O

Yes the whole idea still sounds good. Is this where you are headed?

I know you said you would do all this on a new Gemini, just wondering if this would be a viable idea for someone if they didn't mind doing the work and retro a used one w/your planned conversion in mind?

No, not planning to do it.

Just a thought process based on some of the recent threads where people either are completely unrealistic or are saying electric propulsion is going to take over based on an exotic designs and use cases that do not represent the typical new boat buyer.

A Gemini was just an example of a popular production boat and since we owned one and knew it well, the changes that would be needed to make it viable were better known to me. I'm sure a lot of 30-40ft boat designs could be modified in similar manner such that you could get most miles from battery power while not driving the price thru the roof and keeping the performance profile while motoring pretty reasonable relative to what your average buyer expects.

[marshmat]

It sounds like you are talking about a homebrew equivalent to Torqeedo Deep Blue?
https://www.torqeedo.com/us/en-us/pr.../hybrid-drives
The difficulties with this class of system - aside from cost, which is significant - are controls integration and fault tolerance.


On the first point: It's one thing to round up a pile of high-power parts; it's quite another to make them work together, reliably, under all conceivable conditions with zero risk of accidentally blowing something up or electrocuting yourself.



On the second point: Fault tree analysis on these kinds of systems often reveals several dozen single points of failure that, if they go, leave you with the whole thing dead. The risk is that you spend so much time fixing the thing and bringing in specialty technicians that there's no time left to enjoy the boat.

[dougweibel]

Just a qualitative note on the current state of electric propulsion - Jimmy Cornell just abandoned his zero-emission circumnavigation attempt. I have not followed it but reading only his post about why he gave up it sounds like the power produced with the regenerative system (sail drives I believe) produced far less power in real world ocean conditions than they did during test sails in smoother water conditions.

This is not directly relevant to the OPs proposal but is interesting.

[Adelie]

A first assessment is that Cornell’s boat was a power hog.

I’m awaiting published analysis by him or somebody on his team before coming to a final opinion.

[StuM]

Marketable electric drive train? Hornby have been making them since 1925

https://www.hornby.com/uk-en/about

[Adelie]

To the OP comparisons of marine hybrid to auto hybrids is inappropriate because of the drastically different loading expectations.

it looks like what you are proposing is a series hybrid boat that can plug in instead of a parallel hybrid boat that could also be plugged in.

In a series hybrid plug the battery is fully charged at the dock from shore power. A 20kW electric motor is coupled to the propeller and all motive force comes from that motor. Batteries power the electric motor for short to medium periods, the faster you go the shorter the period must be. If one knows that the boat is going long distance then a generator (let's say 10kW) is run which can power to electric motor for long periods at moderate speeds, with occasional periods of higher speed where battery power is also used as well as generator power.

In a parallel hybrid the battery is fully charged at the dock from shore power. A 10kW internal combustion engine (ICE, diesel or petrol) is coupled to the propeller thru a transmission and clutch. A 10kW electric motor is coupled to the propeller shaft on the propeller side of the clutch and transmission. The electric motor can be used to propel the boat at low to moderate speeds, once again the faster you go the shorter the period you can go that speed. If you know that you are going long distances, you can start the ICE and engage the transmission and proceed at a moderate speed.

The series hybrid you outlined offers a few advantages. The ICE can be placed anywhere convenient and is structurally simpler. Quickly recharging the batteries from the ICE while at anchor is simple, power goes from the generator straight to the batteries.

The parallel hybrid offers different advantages, chief among them being increased efficiency. While being propelled by the engine the transmission involves about a 3% energy loss. The drag of spinning the electric motor, pulleys and belts incurs some more loss. Let's be conservative and say it is another 3%. That's a total of about 6% lost. In the series hybrid there is 7-10% lost when generating the electricity, and another 7-10% lost in converting it back to mechanical energy at the prop. There is also some lost in the control electronics. Let's say 16% loss for series hybrid. That means the parallel can go about 10% further than the series per gallon of fuel. Beyond that, at the same power settings it will go slightly faster, not 10% faster because the speed-power relationship is a curve, but maybe 6-7% faster (1/4-1/3kt).

Also the parallel is a bit more fault tolerant.
In the parallel if the electric motor or it's controller fails the ICE can still propel the boat long distances at slow to moderate speeds.
In the series if the electric motor, motor controller, generator controller or the electrical part of the generator fails then the boat is limited to shorter distance and slower speeds.

In both instances the user needs to accept the fact that the boat will only be able to reach a modest speed if going long distances (>25-30nm). For distances under that a combination of ICE and battery power will be able to propel the boat that far at something near hull speed (1.2-1.3 X sqrt LWL). Beyond that most reasonable sized batteries will be depleted and the boat speed will have to drop to what the ICE alone can acheive (0.85-1.0 X sqrt LWL).

So for a 35' sailboat you could motor from LA to Avalon on Catalina island at about 6.5kt. If there was a dock with power there you could recharge overnight or more likely in 36hr and then return to LA at the same speed.

If you started from San Diego (about 70nm) , you would be limited to about 5kt running just on the ICE or maybe 5.25kt using the ICE and a bit of battery the whole way. The return would be the same.

11 years ago the EU funded a research project to develop a roadmap for hybrid marine drive (HyMar). Initially they pursued a series system but quickly realized that the parallel system was better for a number of reasons.
https://cordis.europa.eu/project/id/233718/reporting
https://cordis.europa.eu/project/id/...lts?format=pdf


Whatever system you envision the buyer will need to accept a modest cruising speed for all but the shortest distances.

The downside to the parallel system is recharging. The ICE needs to be engaged in propelling the boat in order to use the main electrical motor as a generator or there needs to be an extra clutch in the system which is a modest extra cost but also an extra potential point of failure. The Betamarine parallel hybrids offer this option.
https://betamarine.co.uk/he-hybrid-propulsion/

Further reading though a bit dated:
https://www.morganscloud.com/2013/04...oyaging-boats/
https://www.morganscloud.com/2014/04...ectric-drives/
https://www.hybrid-marine.co.uk/

[valhalla360]

Originally Posted by marshmat

It sounds like you are talking about a homebrew equivalent to Torqeedo Deep Blue?
https://www.torqeedo.com/us/en-us/pr.../hybrid-drives
The difficulties with this class of system - aside from cost, which is significant - are controls integration and fault tolerance.

On the first point: It's one thing to round up a pile of high-power parts; it's quite another to make them work together, reliably, under all conceivable conditions with zero risk of accidentally blowing something up or electrocuting yourself.

On the second point: Fault tree analysis on these kinds of systems often reveals several dozen single points of failure that, if they go, leave you with the whole thing dead. The risk is that you spend so much time fixing the thing and bringing in specialty technicians that there's no time left to enjoy the boat.

I was actually looking at the Elco electric outboards. They have a 20kw model (BS rated 50hp equivalent) for $8k which is only $2k more than a 25hp gas outboard.

First Point: No, this was just a rough outline of what was needed to check for viability. Of course it would all have to be put together in a well designed professional manner.

Second Point: Sure with a single engine, there are single points of failure. Not much different from when we cruised with a single outboard as the main propulsion (bad fuel, starter issue, starter battery failure, etc....) Again, not talking about a home brew system.

Of course unlike the Cornell fiasco, if I was running the company, I wouldn't be showcasing the boat until it was ready for real world use.

[valhalla360]

Originally Posted by dougweibel

Just a qualitative note on the current state of electric propulsion - Jimmy Cornell just abandoned his zero-emission circumnavigation attempt. I have not followed it but reading only his post about why he gave up it sounds like the power produced with the regenerative system (sail drives I believe) produced far less power in real world ocean conditions than they did during test sails in smoother water conditions.

This is not directly relevant to the OPs proposal but is interesting.

It's actually one of the two recent threads that got me thinking about this. I feel it's was a silly publicity stunt in terms of actually selling boats:
- Very few new cruising boats are sold to be primarily used offshore. The vast majority wind up weekend and coastal cruising, so it makes not sense to focus on offshore.
- Hydrogenation as the primary power source makes no sense...even for cruisers doing ocean crossings, you will find the typical long distance ocean crossing cruiser still spends 90% of time operating in coastal cruising mode where hydrogenation provides nothing. My idea relies primarily on shore power. The generator and solar are intended primarily as supplemental.
- Cornell's boat is a high performance boat and they were planning on 8kt average speeds to get the rated output...that's way outside the norm for your average cruising boat.

I wanted to set up a use case that is applicable to your average cruiser. If this can be made viable, you have a product that can be sold in numbers significant enough to make it financially viable and not just a stunt.

[Yihang]

On a similar note I think the NEEL 43 has a lot of potential. Only a single motor needed like the gemini, 3 (6000lb) ton pay load all deep down in a centralised storage area. And a fairly light performance oriented design. Although you would probably always try to motor sail to get as much of the windward Ama out of the water to reduce wetted surface while motoring.

[valhalla360]

Originally Posted by Adelie

To the OP comparisons of marine hybrid to auto hybrids is inappropriate because of the drastically different loading expectations.
..........

If you read the first part of my original post, I talked about hybrids and why a standard hybrid isn't viable on a boat.

It would be a series hybrid but that's not really the point. Using automotive terminology:
- Your basic hybrid is primarily powered by the ICE with a small battery bank only providing additional power when there is a surge in demand (such as start up from a light). They can be either serial or parallel...but since power demand when motoring is pretty much constant with a cruising boat, there are no surges in demand for the most part unlike a car in stop and go traffic.
- I'm looking at a Plug-In-Hybrid model where it's intended to operate for most miles as a battery electric (charged at shore power) but there is a backup ICE ready to add power if needed for longer trips. The biggest difference is unlike a car, there is a point where I expect the system to drop back to a reduced capability. From our experience doing the Great Loop (7000 mile coastal cruise), 50miles in a day was a longer run, so no power drop if you run the generator for the entire run and most runs were 20-30miles where little or no generator use would be needed. It's only when you get over a 50 mile run that you need to consider dropping back on speed...but even there, if you dropped from 6.5 to 6.0kts, the improved efficiency would increase range while not being onerous like some of the silly examples where they assume 2-3kt speeds under power (As mentioned previously, one downside is the operator needs to understand when and how to apply the generator...but it could be as simple as a table of speed vs range with proposed generator run times needed to achieve the speed/range combination)

With the system as outlined, there really wouldn't be any performance loss unless you have a run in excess of 50miles in a day. 40kwh battery bank drawn at 10kw to give a 6.5kt cruise speed for 4hr if in pure battery mode (26nm range). If the 5kw generator is running, that jumps up to 8hr at 6.5kt for a little over 50mile range. After that you would be limited to the 5kw output, so around 4-5kts. (this is based on our usage of a Gemini with a 25hp outboard and power levels to make 6.5kt). The user doesn't have to accept modest cruise speed except for rare very long runs.

I was thinking in terms of US east coast where 70mile runs (while possible) is not going to be a common thing. If you follow the Great Loop websites, there is much angst over the crossing of the armpit of Florida (Carabelle to Tampa) because it's more than 50 miles that must be done in a single day. That's really about the longest 1 day run. (Mississippi River section is longer but since you have the current running with you, we throttled was back and still made 7-11kt SOG the two times we did it)

In your San Diego to Catalina example, it's offshore so most times, you could motor sail to increase range without loss of speed. If you switched to the trawler option with 60kwh battery bank and ran the generator, that's about 12hr at 6.5kt, so no issue with 70miles under power.

The whole point of my idea is the buyer wouldn't be expected to accept reduced cruise speeds in most common coastal cruising situations...which I believe is the biggest hurdle to a viable electric drivetrain.

[valhalla360]

One loop back to my prior post...I'm still targeting weekend cruisers. Great Loop cruisers are still a relatively small percentage of new boat purchases...though far more common than ocean crossing cruisers.