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Discussion Starter · #1 ·
Hi EVerybody,

I'm looking into the most affordable route to get myself (and a friend in the same predicament), out of the Diesel engine doldrums, and onto an EV powertrain.

The boat currently has a knackered (not currently functioning) old 55hp marine diesel engine, but I'd really like to ditch the rotten old oiler and install a nice lithium-based battery EV system, at a budget that won't bankrupt me, but allows for battery capacity expansion as time goes by.

However, I need to get past the lack of knowledge & experience hump, so that I can actually proceed. If I list my loose requirements, please could you more knowledgeable EVers let me know what exactly (approximately) I need to go shopping for, or if there's a great resource for all of the things I'd need, in kit form, who's out there and not going to rip me off. I'm not averse to purchasing a kit, but also not exactly rich, so need it to be reasonably priced.

Loose Requirements
  • Motor with similar performance to the 55hp diesel @ 1800-2500rpm (after all, it's pushing the same load)
  • Direct drive (I think this is best, so that we can get regenerative power, while under sail (unless there is a better way)
  • Ability to charge the battery from shore-power (which generally ranges from 100-220V @ 50-60Hz)
  • Ability to invert the battery power to various voltages (220V for consumer equipment, 24V for some high-draw devices & 12V for the standard navigation equipment)
  • Range... I'm going to say 1-2 hours of continuous running at max power (this is a sailboat after all, so it's likely only going to be motoring onto & off difficult anchorages/mooring balls, and entering & exiting ports/harbours where sailing would be inappropriate. This bit seems like the area we can save on & save up for future expansion, if we make the right choices, up front)
What have I missed out, or forgotten to ask, or specify? I might have been a mechanic in a past life, and an EV owner at the moment, but I've never converted from an ICE vehicle to an EV :)
 

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The REALLY big challenge with an electric boat (I've built three now) is that they have a power requirement that is radically different from a car. A car uses around 15% to 20% of it's rated engine power on average, whereas a boat tends to use about 70% to 80% of it's rated engine power on average. This means that a 100hp car will typically use around 15 to 20hp in reality, but a boat with the same size engine will use around 70 to 80hp. This places a pretty hefty demand on the battery pack, motor controller and motor, as they will all be operating at a much greater percentage of the rated power than if used in a car.

As an auxiliary in a yacht with a fairly easily driven hull then it's quite possible to fit a reasonable electric drive system, but there will probably be a loss of manoeuvring thrust. There are ways around this by using an electric thruster, for example. We've chartered a yacht with an electric auxiliary and it was generally fine, but did suffer a bit from being a little short of power at times. That yacht had been purpose built for electric power, with a hollow, rather broad, keel, into which the battery pack was fitted, as ballast. Finding space for the battery pack is a bit of a challenge on a boat that hasn't been designed for one, as space low down in the hull is usually at premium.

One useful advantage of electric power, if your shaft arrangement will allow it, is the lower rpm and hence larger diameter, higher efficiency, prop that can be used. Improving prop efficiency is key to making electric drive work well; my 18ft river boat uses a 350mm diameter two blade prop that is around 80% efficient, perhaps around double the efficiency of a more typical 150mm diameter three blade prop driven by an ICE. This helps a great deal, by halving the motor power needed, and hence halving the battery pack size.
 

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Range... I'm going to say 1-2 hours of continuous running at max power
My immediate concern is the cost and weight of the batteries.
55 bhp is 41kW. Ignoring losses, 2 hours is going to need an 82kWh battery. That's bigger than most EVs and I'd guess would cost north of £10,000 - maybe even 15k.

I suggest you look very hard at the amount of power you will actually need, both motor and battery, and check that you can obtain and afford the batteries before going into any more detail.

These big packs need some clever management systems too, and of course must be totally waterproof (see Audi eTron news).

That all assumes lithium cells like cars. Using lead-acid would be less difficult but the weight, and size, could be even more of a problem.

[Cross posted with JH]
 

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Discussion Starter · #4 ·
@mikegs Lead Acid is hard nope.

I threw out the 1-2 hours thing, with zero idea; 1 hour would likely be more than I ever intend to use, and the usage profile is much more likely to be a few minutes at a time, at a much lower duty cycle, and only ever using the full beans, to perhaps get out of trouble, or through a particularly bad current (though I would hope that a decent sailor would have planned better).

The sort of thing I was envisioning, was using the powertrain from a written-off EV and £10-15k is actually still not as bad as spending a similar amount on a reconditioned marine engine.
 

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Most EV motors run at a much higher rpm than is sensible for use in a boat. Better to look at some of the larger diameter, lower rpm, motors that are around, as used in some EV conversions. The boat we hired had a Lynch motor, which directly drove the prop shaft. This was pretty efficient, although the relatively small 18" three blade prop wasn't the most efficient around, but the 30ft yacht was pretty heavy and the shaft arrangement wasn't ideal for electric power.

Forget about regen under sail. The boat will just stop dead in the water if you try it. I tried it in a fairly stiff blow, on a broad reach, and it knocked about 3kts off our speed and felt like we were towing a sea anchor.
 

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New Electric in the Netherlands, have done a number of EV boat conversions. Including a dual motor, and diesel hybrid tug. It can run on the motors in Amsterdam, it can then charge with a charge location, or go out of the city limits, and use the Hybrid feature to run the motors to charge the pack. Or they can run all three together for extra power.
They have now purchased some of my LG Cell blocks, for use in future conversions. They have fairly limited red tape with boat systems, and so they wont have to get any new certification to use the Pack Monitoring units we have developed to use these Cell blocks. Also having the capability for liquid cooling built in, high charge /discharge rates can be readily managed .
The bigger problem they have found is that most EV motors dont give good performance in the RPM range required for the design of the boats, so they normally use simple very wide tooth belt reduction systems, but that also means they can alter the RPM to suit the existing props, and get the best possible performance from both.
HPEVS make some sealed Stainless motors but these have proved to be less than successful. The motors were flooded with oil as a cooling media which cavitates as the rotor goes around, and loses cooling capabilities. The oil filled motor also tended to leak, the shaft seals not being appropriate for the oil. All held together with 4 off 6mm tierods, that also didnt survive the constant high loads.
They now use a fully sealed liquid cooled, Siemens motor with about 60KW. They are also looking at some 100kw Motor / reduction boxes I have supplied them to play with.
The big advantage with Li Ion is the huge weight reduction. Im doing conversions on vehicles called Polaris rangers, these had 8 Trojan Traction batteries, that I have replaced for 8 Li Ion cell blocks. Gives higher voltage, longer run time and saves 130kg. Lead drops steadily and constantly throughout its charge. Subsequently they get to about half charge and well below 12v / battery, whereas the Li Ion is still going strong holding a usable voltage down to around 20%.
So there are weight and usability advantages .
I currently sell at around £150/ (+VAT) kwh + control system, But I always price on the specific pack required, if the buyer wants cell mounting trays , and of course the number of Pack Monitoring Units required.
 
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