Why hybrid?

[ItDepends]

Let me start with this: I am an old engineer. My father always told me that if you want to know all the reasons things can not work you go to the senior engineer on staff. If you want to solve those problems, go to the young guys. So help me think young here…

The problem: I do not understand why (for a cruising boat) any kind of hybrid propulsion system makes sense.

First, some assumptions:

• A “cruising boat” is a displacement hull.
• It spends almost all of its time under power at a speed that is a high percentage of its hull speed.
• It has a range of at least several hundred miles.
• Its drive train is sized to move the boat at (or close to) hull speed at full power.
• It is driven by a (more or less) standard propeller.
• The propeller’s power curve is (more or less) such that the power absorbed by the prop is proportional the the RPM cubed.
• The hull’s characteristics are such that the power to push it through the water is (more or less) proportional to the speed cubed.

If all those things are assumed true for our design case, why would a hybrid system (either parallel or series) make any sense? The normal drive engine spends virtually all its time running at near full load, there is very little “extra power” available, very different than a hybrid car. You can not install a smaller prime mover in a boat and make up the difference with electric power.

It is possible that by relaxing one or two of my assumptions, the case changes a lot, but I don’t see it as part of the practical world, but would love to be proven wrong (especially with numbers...)

I can imagine a use cases for boats that spends a LOT of time motoring at low output power, but need occasional busts of power might be well served by a series hybrid system (maybe a harbor tug? or some fishing boats?) Some boats have maneuverability requirements where rotating pod drives are needed (many cruise ships) and they go with hybrid drives not for efficiency but for the handling. A vessel that had HUGE needs for electrical power that far exceeded its need for drive propulsion might also make sense to outfit with a series hybrid drive. (cruise ships again?) There are other cases, but again (as far as I know), they are specialized performance designs not efficiency based.

For boats that need a quick assist into the dock after a day sail, then a full electric system can make good sense, but that’s not “cruising.”

[BAD ORCA]

I believe the BETA hybrid engines will also make power when under way without the need to be running. You can freewheel the prop to produce electricity.

Sampson boat video where he is restoring Tally Ho recently talked about this in one of his latest videos. He installed a BETA hybrid engine and will mainly use the electric engine for maneuvering in and out of harbors and the diesel power source for open ocean.

Im contemplating the BETA hybrid "IF" the necessary battery storage needed to run it makes sense from a size/weight prospective and real world electric production is beneficial. Still a couple of years away from this though and not tons of feedback on these motors yet.

My reasoning is that when i start cruising full time, the electrical generating capability of the engine could become very useful under sail. The extra battery storage (energy) as well, and the fact i see myself as someone who loves to go to new destinations and not simply 'park' my boat at anchor when im there. I would be someone that would be constantly day sailing and exploring the area. To me this is a perfect use case for the electric portion of the engine if its just sailing for a few hours a day with some motoring mixed in as well. I will also have solar but not much and i plan on sailing to northern and southern latitudes where there wont be as much sun to make solar my only option for energy generation.

I think these are valid arguments for it but admittedly i have not crunched the numbers yet . It seems like an attractive option to me but they are not cheap engines.

My friend has a pure electric engine on her sailboat and on very light wind days we can maintain near hull speed with full sails while passing everyone else who are luffing with no wind. So, i think from that experience it makes a great augmentation on low wind days.

[ItDepends]

The whole idea of "regenerative power" is WAY over hyped. It's nothing new, boats have had propshaft alternators for decades. I am very familiar with the installations that were put on many of Amel's boats. At 8 knots, they could make about 25A @ 24V, or about 0.5 kW. Enough to supply house power, and slowly add to the house battery charge, but NOWHERE enough for a useful addition to a drive system's energy budget.

At that rate of power generation, it would take about 4 days of sailing (at 8 knots!) to make enough power to push the boat at cruising speed for an hour.

The idea of using the electric motor for harbor maneuvering... if you have the diesel anyway, who cares? How much fuel are you saving? If you are buying it to feel better, fine that's valid. If you think its more efficient, you are doing nothing but repeating salesman's platitudes. NUMBERS!!!!

The Beta hybrids seem like they might make sense as a replacement for a genset for boats with very, very large power needs, or some other special applications... but I just still don't see an efficiency gain over a standard drive system.

For a large, single engine trawler style boat, having a Beta hybrid that was normally its main DC power generator, and was also coupled to an auxiliary shaft to function as a "limp home" engine might be a perfect solution.

[CarlF]

An additional factor is that a rotating diesel engine turning a rotating propeller through a solid shaft is very efficient energy transfer. Modern transmissions lose almost no energy. Storing electricity in a chemical energy battery and then converting it back into rotational energy through wires and speed regulators throws away about 30% of the energy.

[dannc]

Let rephrase the question. Would a hybrid propulsion on a full displacement hull make sense, if:

1. The boat will spend a significant amount of time moving 25-50 NMs per trip.
2. The boat will spend time on canals where there are speed limits.
3. Speed limits would require running the boats diesel propulsion at non optimum RPM levels.
4. The boat has enough solar power generation to move the boat the required 25-50 NMs per trip. In other words, electric propulsion is almost 100% done from solar power.
5. The boat has enough battery storage to store power to move the boat the required 25-50 NMs per trip.
6. The hybrid system is used as a generator.
7. The hybrid system is used as a get home system.
8. The hybrid system makes money sense for items 1-7 compared to diesel only propulsion, being able to operate without a generator and/or a diesel powered get home engine.

Later,
Dan

[HeywoodJ]

Originally Posted by ItDepends

...The idea of using the electric motor for harbor maneuvering... if you have the diesel anyway, who cares? How much fuel are you saving? If you are buying it to feel better, fine that's valid. If you think its more efficient, you are doing nothing but repeating salesman's platitudes. NUMBERS!!!!...

When we aren't off cruising long distances our diesel may get fired up for 5-10 minutes to get off the dock, and another 5-10 minutes to get back on the dock. That is just about the worst way to run a diesel, not getting it up to full operating temperature and allowing acids to form and sit in the engine. So, I can see having an electric option for maneuvering. Still doesn't, for me (and evidently for you), pencil out in the numbers so I still have a straight diesel, but it does make some sense to me in a cruising boat - I end up with a nice, large battery bank that I can use for house loads offshore, a diesel for long range motoring, and electric for quick start/stop functions where a diesel is not best used.

Originally Posted by CarlF

An additional factor is that a rotating diesel engine turning a rotating propeller through a solid shaft is very efficient energy transfer. Modern transmissions lose almost no energy. Storing electricity in a chemical energy battery and then converting it back into rotational energy through wires and speed regulators throws away about 30% of the energy.

That's very disingenuous! The engine and drive train may be very efficient at transferring energy once the diesel is converted from liquid to gas form, but that conversion process is, at the very best, 50% efficient in a turboed, common rail diesel, and can be as low as 35% in a more traditional mechanically injected diesel. The same efficiency occurs in the electric drivetrain, the large losses are in the conversion of the stored energy to and from rotational energy, just as they are with diesel.

Of course, things get even worse if you use that inefficient diesel to charge batteries to then run an electric motor, now you've given yourself the worst of all worlds.

[tenchiki]

Some additional considerations:
1) Regenerative systems have gotten a LOT better recently. There is also solar and wind for charging the batteries.

2) For maximum longevity of your diesel engine, you need to let the engine fully warm up before using it each time, and letting it run for a while fully warmed before shutting down. This could easily be 2x-4x the time to get to/from slip, mooring or anchorage and getting sails up/down. Not to mention that every engine hour adds to maintenance needs.

3) Noise! One of the reasons that I go sailing is to get away from the noises of "civilization". Also, can't sneak out of that anchorage at 3am with that diesel engine running... (of course, the anchor windlass might give you away anyway).

[Jammer]

Originally Posted by ItDepends

Let me start with this: I am an old engineer. My father always told me that if you want to know all the reasons things can not work you go to the senior engineer on staff. If you want to solve those problems, go to the young guys. So help me think young here…

Stop thinking like an engineer and start thinking like a product manager and understand the problem better.

• A “cruising boat” is a displacement hull.
• It spends almost all of its time under power at a speed that is a high percentage of its hull speed.
• It has a range of at least several hundred miles.
• Its drive train is sized to move the boat at (or close to) hull speed at full power.

All of that is true some of the time but it isn't all true at once for all use cases.


Cruising boats vary. Many spend much of their time at sail. Many do not have a requirement to be driven at a high percentage of hull speed all the time that they are being driven. While there is a requirement for a range of at least several hundred miles, most vessels do not motor that distance often.


So there's a case for PEH (plug-in hybrid) since many boats, much of the time, motor only short distances than return to port.

If all those things are assumed true for our design case, why would a hybrid system (either parallel or series) make any sense? The normal drive engine spends virtually all its time running at near full load, there is very little “extra power” available, very different than a hybrid car. You can not install a smaller prime mover in a boat and make up the difference with electric power.

For boats that need a quick assist into the dock after a day sail, then a full electric system can make good sense, but that’s not “cruising.”

Depends. A lot of "cruising" boats do that a good deal of the time, whether to the dock or to an anchor or mooring.


I think hybrid fails in this application on cost and weight grounds but that doesn't mean it's useless, just that it isn't worth it.

[s/v Jedi]

I think the assumptions are wrong. Sailboats spend a minute percentage of time running the engine at all, let alone at full load. We have the 2hp/ft boat length and never used it all during the past 22 years we own the boat. When we run it, we could do it with 20hp or less.

So a hybrid drive would be perfect for us. Especially since we have a large solar array and I think we could run from solar most of the time.

[thinwater]

Originally Posted by ItDepends

Let me start with this: I am an old engineer. My father always told me that if you want to know all the reasons things can not work you go to the senior engineer on staff. If you want to solve those problems, go to the young guys.

That is both brilliant and true! (Another old engineer.)

[Pete7]

Originally Posted by BAD ORCA

I believe the BETA hybrid engines will also make power when under way without the need to be running. You can freewheel the prop to produce electricity.

To be useful, the boat speed needs to be quite high for a small yacht. 5 knots or less, it would be better to stick a 50w solar panel on the deck. 7-8 knots is were the power is really generated. Sailing Uma on their way back from Svalbard talked about this. So if you have regular cruising speed in the 7-8 knot range and are willing to have a fixed big prop* then go for it. Prop size matters too, big is better, on an efficient fin keeled hull to maintain hull speed when you select regen and the drag ramps up, no free ride.

Us with 31ft are probably better off not using regen and going for the folding prop to achieve a better average cruising speed in the 5-6 knot range. Note, average not occasional best speed.

However, if you are using the power generated by a hybrid for another purpose like cooking then perhaps there are benefits to hybrid for a cruising yacht. Just not cheap.

*Apparently and it needs to be checked, a Bruntons Prop can be made to work with some quick switching from fwd drive to regen before the prop slows and the blades change. Ocean Volt also have a folding regen sail drive option, but its Euro 40k for the package, unless your a You Tuber.

[Pete7]

Originally Posted by s/v Jedi

I think the assumptions are wrong. Sailboats spend a minute percentage of time running the engine at all, let alone at full load.

Is that because they are all tied up to a harbour wall or at anchor for 6 days of the week.

[s/v Jedi]

Originally Posted by Pete7

Is that because they are all tied up to a harbour wall or at anchor for 6 days of the week.

True. And when moving, hopefully under sail

[ItDepends]

Originally Posted by Pete7

So if you have regular cruising speed in the 7-8 knot range and are willing to have a fixed big prop* then go for it. .

Actually not at all true. The Autoprop works fine to power a propshaft alternator and so dose a MaxiProp.

But they STILL only make 500 watts at 8 knots with an 18 inch prop.

[ItDepends]

So far, nobody, but nobody, has addressed anything with real numbers, just sales talk and changing the premise. I completely understand (and tried to say so) that I completely understand that a plug-in electric can be a good choice for a day sailor. I completely agree with that premise.

I have a cruising sailboat. We travel about 10,000 miles a year, and use our engine about 350 hours of that time, virtually all of it at about 80% of full engine power where we burn about 1 gal/hr to move at 6 knots. Thats about 350 gallons, and we burn another 60 gallons in a small genset to generate house power. So our total fuel cost in a year is about $2300. Let's call it $2500, inflation and all...

How would a hybrid drive reduce our cost? Explain.