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Nigel Calder Hybrid propulsion Part I
Nigel Calder Science of Hybrid Part II
Ocean Volt
Interview w/ Top Secret Owner a Hybrid Voyage 580

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What does Volt-in-a-Boat mean?

We want to make a boat that behaves like a first generation Chevy Volt.  This would be a boat propelled solely by an electric motor connected to batteries, but with a diesel generator to charge those batteries if they run out.  This serial hybrid drivetrain is how the first Chevy Volt was powered. 

Background & Terminology

When cars first were developed, it was actually a fairly even race between electric and Internal Combustion Engine (ICE) motors, but the convenience of refilling a tank in a few minutes vs a few hours killed electric cars.  Electric boats managed to survive where pollution is an issue, like lakes and rivers, but only in small boats and where range is not a problem.  Elco has been around since 1893 making boats and motors.  So normally folks use an ICE to power their car or boat, but recent technological advances have enabled electric motors to make a comeback.  There are three ways electric propulsion can work:
  1. Electric Only - In the car world this is called an Electric Vehicle (EV).  There is only an electric motor with batteries.  When your batteries run out, your motor is done.  This how a Tesla or Chevy Bolt works.  There are two ways to recharge: an external source like house power or solar panels, or recharging using the vehicles momentum either when braking or coasting downhill.  We have become so good at using the motor to slow the car down that we have never replaced the brake pads on any of our EVs and we didn't have to replace the pads on our Prius until 95,000 miles.  However if the batteries are fully drained you can't just grab a can of gas, pour it in, and drive 20 miles to the gas station.  You need a special charger and at least half hour of charging to drive that 20 miles.  This is what causes something called range anxiety, a fear of draining one's batteries too far. 
  2. Parallel Hybrid - In this system two motors, electric and an ICE, are both connected to the drivetrain, so the vehicle can be directly driven by electric, the ICE, or both.  You can drive for as long as you have gas.  There is some efficiency loss when the battery for the electric motor is charged by the ICE, but there is recharge from braking and momentum just like the EV.  Since the electric motor is used mostly below 10mph that, combined with regen braking, means that a typical parallel hybrid gets better mileage in the city than on the highway.  This is how Toyota Prius works. 
  3. Serial, or Series, Hybrid - This also has two motors, an electric and ICE, but only the electric motor is connected to the drivetrain.  When batteries get low, the ICE kicks in to recharge the batteries.  Battery only propulsion usually is good for 20-30 miles, but as long as you don't burn more energy than the generator can put into the batteries, you can also drive for as long as you have gas with a serial system. The electric motor is also used for regen when coasting and braking.  This is how the original Chevy Volt or BMW i3 with a range extender works.  For a boat we call this a Serial Hybrid Propulsion (SHP) or SHP System (SHPS). 
The hybrid solutions eliminate range anxiety, which is why they have become accepted today.  The parallel hybrid system is the most efficient (and most popular) when the ICE motor needs to be used b/c the ICE can power the vehicle directly.  This inefficiency is why the Chevy Volt drivetrain dropped the serial mode in 2016.  Because there is a loss in between the batteries and the ICE generator, the serial system will always have an efficiency loss especially at higher speeds as the ICE charges the battery.  It is also critical that the generator be sized correctly so that it can run at it's most efficient RPM at all times and not all car companies have that size engine available in-house.  For this reason the first Chevy Volt got 3-4 less mpg on long trips compared to the Cruze (gas only) model it is based on, but the BMW i3 does better than the smallest BMW ICE thanks to the motorcycle engine used as a generator.  Since many car users want to be able to drive more than the batteries will take them, typically 20miles a day, the parallel system is still the most common in cars. 

However all of these systems cost significantly more than an equally equipped ICE vehicle, so they are only popular with people who can afford them. 

Why is Hybrid Propulsion a good idea on a Bluewater boat?

The obvious benefits to electric power are instant on, relative silence (however the props do still make a lot of noise moving thru the water), low maintenance, no smell, and no water pollution.  The other huge benefit is that with electric motor in a boat, just like coasting downhill in an EV with regen active, you can recharge your battery bank while you are sailing.  This means you are essentially creating engine fuel as you sail.  The boat will slow down compared to sailing with no regen, but purportedly by less than ½ knot. 

Hydro-generation is not new, products like the Watt & Sea, which look like engine-less outboards, are becoming fairly common these days but most brands cannot generate more than a 200 watts.  However with an electric motor, more than a kW can be generated at 8 knots, which adds up fast in a catamaran w/ its two motors.  Also with all that energy generation, one can have more power for A/C and switch to electric appliances in the galley (instead inefficient propane which heats the galley more than the food).  Another benefit of using motor regen is mentioned in the O'Kelley interview of the Top Secret owner.  He states that regen can help control the boat while surfing down waves.  I haven't heard that before, but he believes regen reduces the boats acceleration as it goes down the back of a wave which helps keep the spinnaker loaded.  If that is true, then claims that regen only has a ½ knot effect on boat speed is probably not accurate. 

The intent would be to only use the motors to get in and out of harbors/anchorages and sail more than 90% of the time.  This is what Sailing Uma has been able to do with electric only propulsion and no regen (but they just upgraded to an OceanVolt which gives them regen).  However the more I read, the more it seems that 90% sailing is wishful thinking when it comes to catamaran cruising.  Since most Cats stink sailing upwind, there will be days were you end up using the motor for a few hours when the wind is on your nose.  But if we can time it so that we're sailing at least most of the time, things should be pretty self sufficient power wise.  While sailing, we take a hit on speed using regen for a bit to recharge the batteries from the night before and the motoring until the sails were raised.  If the sun is out, there is no need to completely top off the house batteries b/c there will also be solar charging going on.  So there is a slow down while doing regen, but we aren't racing and since we will have a performance cat (and not a condomaran) we should still make good time overall. 

However this is not all without cost, both a financially and possibly in reliability.  Given the estimates we've had so far, it is going to add around $100k to the build cost of new 45ft catamaran.  Retrofitting will be at least another $40-50k more b/c you will need to discard motors, AC generator, inverters, and chargers (that you are going to get pennies on the dollar for selling on eBay) and then spend serious cash on labor running new wiring.  No matter how much diesel fuel you save, you aren't getting that money back.

On the reliability side: with all this technology comes complexity and fragility.  Everyone knows that anything that can go wrong on a boat generally does at least once.  A non-functioning diesel motor can usually be resurrected on the water, but an electric motor with a fried IC on the controller is dead weight on the boat until you can get a new printed circuit board.  That is why just about every bluewater sailor you talk with will say that this is an absolutely insane idea for an offshore boat, verging on dangerous.  However, thanks to articles like this Yachting World article I think they are wrong, and this is argued in detail on my hybrid Myth/Reality page

Proposed System

As with any project, there was a proposed system and then what ended up being built.  A Voyage 480, Maverick 440, or Vision 444 will fit this design no problem, the Seawind 1260 or Balance 451 will take some thought b/c of the aft head but should be workable. 

Fortunately we found a builder that is not only willing to install a hybrid system, but is willing to work with us to create the system that we want.  What did we end up with? Well it is described Adamson Vision 444 Hybrid page.  Redundancy turned out to be too expensive and difficult to achieve other than having the solar panels directly connected to both battery arrays.  As unlikely as it is that the Engine Battery Array (EBA) could shut down, the fact remains that a lot of things in the boat will not function without the main engine battery array, so the crew will need to be very familiar with how to resurrect that array if it goes down.  Unfortunately, it requires some skill with software configuration, both Valence and Victron, to complete.  Hopefully I can convince OceanVolt to change that situation by making the firmware more self-configuring after a catastrophic battery failure. 

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