Oceanvolt Hybrid Motor

[valhalla360]

Originally Posted by myocean

I agree in principle with what you said but still we should try to be more precise:
1. Depending on the working point an electric motor CAN be much more powerful (e.g. at low RPMs, where the combustion engine is very, very weak)! However at max power it is just max power and I don't think there is any additional magic unless you use very different props with different max RPMs.
2. A comparison with small outboard gasoline engines shows, that they are so bad and wrongly specified, that 1 kW electric is performing a lot better than a gasoline outboard with a similar specified power. (e.g when looking 1...5 hp outboards). So indeed a 1 kW electric motor can beat a 3 hp gasoline outboard in most disciplines (even though max speed is not always the best test for a high torque electric motor)
3. The very short response time of electric motors makes another difference in 'performance' which you feel when maneuvering a boat.

So, as I said, in principle you are right when looking at max. power/max. speed but 1 kW is not always 1 kW because torque curves and dynamics are just not the same.

1&2 are apples and oranges comparisons. You are optimizing the drivetrain for a lot powered electric system and using horribly optimized drivetrain for the diesel.

3 isn't really an issue as quick acceleration is simply not a big issue unless you are significantly underpowering the boat. Of course, if you optimize the drivetrain for a underpowered diesel, you get similar maneuvering benefits. This is essentially what tug boats do. They don't care about top speed so everything is optimized for pulling power.

[SV DestinyAscen]

Originally Posted by valhalla360

1&2 are apples and oranges comparisons. You are optimizing the drivetrain for a lot powered electric system and using horribly optimized drivetrain for the diesel.

3 isn't really an issue as quick acceleration is simply not a big issue unless you are significantly underpowering the boat. Of course, if you optimize the drivetrain for a underpowered diesel, you get similar maneuvering benefits. This is essentially what tug boats do. They don't care about top speed so everything is optimized for pulling power.

And why are we talking about power anyway? Seems like a convenient distraction from why these systems have more to be developed. Range and effective redundancy.

[valhalla360]

Originally Posted by SV DestinyAscen

And why are we talking about power anyway? Seems like a convenient distraction from why these systems have more to be developed. Range and effective redundancy.

Because power determines the performance on a displacement cruising boat. You have to set the performance expectations before selecting the drivetrain for a fair comparison.

If you have a boat with a hull speed of 8kts but you want to design for a cruising speed of 3kts and could care less about achieving hull speed, you can downsize both the electric or the diesel option power as long as you optimize both drivetrains for the performance requirements. That usually means swinging a large low pitch prop thru a transmission that converts HP to lots of low RPM torque. Either can be set up to provide roughly the same torque at the prop at the same RPM (since HP=RPM* torque).

What most of the electric proponents do is compare a diesel drivetrain designed to achieve hull speed for hundreds of miles continuous against an electric drivetrain capable of 50% (or some other low percentage) for a fraction of the range and then point out he diesel isn't at it's most efficient. If you really don't want to achieve hull speed ever, simply spec a smaller diesel so it does run more efficiently.

Twin diesels provide redundancy just as parallel twin generator/twin electric motors provide redundancy, if that's a key design consideration for you. No one is suggesting both can't be reliable, so reliability isn't really a reason to switch.

For similar performance with the drivetrain optimized, the straight diesel will typically win out over a hybrid for range at a lower installation cost. Pure electric isn't even in the ballpark in terms of range.

[valhalla360]

Originally Posted by boat_alexandra

As a possible example: you might want 20kW to negotiate certain situations, but only require 2kW to cruise along at 2-3 knots (with sails helping) in very light wind for extended duration.

This is a nice theoretical assumption but in practical use it doesn't matter much.

Most of this discussion is around twin engine boats, so it's pretty simple to shut one down entirely and run the remaining 10kw diesel at 2kw. Not peak efficiency but efficiency climbs pretty quickly as you add a load, so 20% of peak HP might get you up around 90% of peak efficiency and at those speeds, you are burning such a small amount of fuel that's it's really not worth consideration (are most people really going to care if it's 0.25 vs 0.23 liters per hour?). This is particularly true of turbo diesels that generate peak torque starting at little over idle speed.

[valhalla360]

Originally Posted by valhalla360

This is a nice theoretical assumption but in practical use it doesn't matter much.

Most of this discussion is around twin engine boats, so it's pretty simple to shut one down entirely and run the remaining 10kw diesel at 2kw. Not peak efficiency but efficiency climbs pretty quickly as you add a load, so 20% of peak HP might get you up around 90% of peak efficiency and at those speeds, you are burning such a small amount of fuel that's it's really not worth consideration (are most people really going to care if it's 0.25 vs 0.23 liters per hour?). This is particularly true of turbo diesels that generate peak torque starting at little over idle speed.

Just to follow up on this: 99% of new boat buyers do little or no motoring like this so you won't see manufacturers supplying this any time soon but let's say it is a priority and you are willing to custom order or repower.

A simple solution is to spec a 15kw diesel motor in one hull and a diesel 5kw motor in the other. That means you can motor sail with the 5kw motor running at 40% of peak which is well within the peak efficiency range for even naturally aspirated diesels.

Or as previously suggested a combination traditional large diesel in one hull and a small generator (sized for house loads) and electric motor in the other eliminating the need for a separate generator for electric propulsion when you can use the house generator to keep the batteries up.

[Valiente]

Originally Posted by valhalla360

A simple solution is to spec a 15kw diesel motor in one hull and a diesel 5kw motor in the other. That means you can motor sail with the 5kw motor running at 40% of peak which is well within the peak efficiency range for even naturally aspirated diesels.

Or as previously suggested a combination traditional large diesel in one hull and a small generator (sized for house loads) and electric motor in the other eliminating the need for a separate generator for electric propulsion when you can use the house generator to keep the batteries up.

At this stage it seems to me that with LifePO and Oceanvolt saildrives it all could start to make sense in a 40-45feet cruising catamaran.

My gut aproach is: 1 big Gen in one hull, smaller gen+LifePo bank in the other, with the following usage pattern:
- Slip in/out from Marina under optimal conditions or Help lifting anchor: Electric from lifepo batteries*
- Slip in/out from Marina under less than optimal conditions and economical motorsailing: Electric from small genset+ (LifePo for Peak power)*
- Full Power needed: Marina in/out under hard conditions, or sustained motoring against strong headwinds: electric from both Gensets (+ LifePo for peak power short burst)

LifePo recharging: from small or big genset depending on charge status, other concurrent loads (ac, watermaker....), and time available for recharge.

I believe this setup provides convenience (fumeless /noiseless power on most times), safety (full power available for extended periods), enough redundancy, and just 2 diesels to mantain instead of 3, with a smaller number of engine starts, so mantenance cost cheaper in theory.
Your views?
thanks in advance
Jose

[valhalla360]

Originally Posted by Valiente

At this stage it seems to me that with LifePO and Oceanvolt saildrives it all could start to make sense in a 40-45feet cruising catamaran.

My gut aproach is: 1 big Gen in one hull, smaller gen+LifePo bank in the other, with the following usage pattern:
- Slip in/out from Marina under optimal conditions or Help lifting anchor: Electric from lifepo batteries*
- Slip in/out from Marina under less than optimal conditions and economical motorsailing: Electric from small genset+ (LifePo for Peak power)*
- Full Power needed: Marina in/out under hard conditions, or sustained motoring against strong headwinds: electric from both Gensets (+ LifePo for peak power short burst)

LifePo recharging: from small or big genset depending on charge status, other concurrent loads (ac, watermaker....), and time available for recharge.

I believe this setup provides convenience (fumeless /noiseless power on most times), safety (full power available for extended periods), enough redundancy, and just 2 diesels to mantain instead of 3, with a smaller number of engine starts, so mantenance cost cheaper in theory.
Your views?
thanks in advance
Jose

You could do that and it would work but it would be more expensive up front, heavier and less efficient.
- Generators of the same power output are heavier and more expensive
- Conversion losses with a serial hybrid are higher.

[Valiente]

Originally Posted by valhalla360

You could do that and it would work but it would be more expensive up front, heavier and less efficient.
- Generators of the same power output are heavier and more expensive
- Conversion losses with a serial hybrid are higher.

Heavier? only 2 gensets, one bigger, one smaller versus 2Engines plus 1 genset.

Eficient? May be you are right but Many times you dont even need to start any genset, as a limited power needed can be taken from LiFePo.

For motor sailing in bening conditions (no wind), just small genset.

Big genset is safety net when in need of high power for extended period. (High power motoring against headwind)

I detailed study could be done, but i confess i am just an amateur and lack knowledge in depth, but i still believe numbers could make sense for certain profiles (including lifeaboards) at current state of tech.

[valhalla360]

Originally Posted by Valiente

Heavier? only 2 gensets, one bigger, one smaller versus 2Engines plus 1 genset.

Eficient? May be you are right but Many times you dont even need to start any genset, as a limited power needed can be taken from LiFePo.

For motor sailing in bening conditions (no wind), just small genset.

Big genset is safety net when in need of high power for extended period. (High power motoring against headwind)

I detailed study could be done, but i confess i am just an amateur and lack knowledge in depth, but i still believe numbers could make sense for certain profiles (including lifeaboards) at current state of tech.

If you want a genset for house loads I would go with a single large traditional diesel drive, small genset that can power house loads or a small electric motor (several pages back I laid that out as an option with more details.

No need for a heavy inefficient large generator if it's only for propulsion.

[DotDun]

Originally Posted by Valiente

Heavier? only 2 gensets, one bigger, one smaller versus 2Engines plus 1 genset.

Eficient? May be you are right but Many times you dont even need to start any genset, as a limited power needed can be taken from LiFePo.

For motor sailing in bening conditions (no wind), just small genset.

Big genset is safety net when in need of high power for extended period. (High power motoring against headwind)

I detailed study could be done, but i confess i am just an amateur and lack knowledge in depth, but i still believe numbers could make sense for certain profiles (including lifeaboards) at current state of tech.

My boat has (2) diesels rated at 20.1kw each (and these were the ‘small engine’ option). At cruise speed in your ‘benign conditions’, which covers 90+% of motoring time, each is producing ~9kw (18kw total).

So your small genset would need to be 20kw. That would weigh more than my 2 diesels combined. For the 1% of the time you need more power (your ‘safety net’), how big is your big genset? And for the .1% of the time you’ll need everything you can muster - I have been in conditions where I used the 18kw ea (36kw total) continuous power my diesels will produce for more than 2 hours. The gensets and electric motors to produce that would be multiples in weight and dollars compared to diesel drive engines.

Some will blow off the .1% of the time and state, ‘it’s a sailboat, I’ll have a storm sail’. That tells me they have never been in 40-50kt winds with 4-5m breaking waves trying to claw away from a lee shore. That won’t happen without at least 30kw of drive power and the requisite 32+kw of genset. Forget about the batteries for this task, you won’t be able to afford or carry enough.

Add it all up and it doesn’t make sense anymore.

[BigBeakie]

"Some will blow off the .1% of the time and state, ‘it’s a sailboat, I’ll have a storm sail’. That tells me they have never been in 40-50kt winds with 4-5m breaking waves trying to claw away from a lee shore. That won’t happen without at least 30kw of drive power and the requisite 32+kw of genset. Forget about the batteries for this task, you won’t be able to afford or carry enough."

Can you tell us more about this incident? I'm interested in these infrequent but high impact events.

How did it come to pass that you were on a lee shore in 40 to 50 knot winds long enough to have 4-5 meter breaking seas build up?

How long did it take you to motor out of the situation?

How much battery are you referring to that someone on a liveaboard cruiser "cannot afford" to buy or carry?

[DotDun]

Originally Posted by BigBeakie

"Some will blow off the .1% of the time and state, ‘it’s a sailboat, I’ll have a storm sail’. That tells me they have never been in 40-50kt winds with 4-5m breaking waves trying to claw away from a lee shore. That won’t happen without at least 30kw of drive power and the requisite 32+kw of genset. Forget about the batteries for this task, you won’t be able to afford or carry enough."

Can you tell us more about this incident? I'm interested in these infrequent but high impact events.

How did it come to pass that you were on a lee shore in 40 to 50 knot winds long enough to have 4-5 meter breaking seas build up?

How long did it take you to motor out of the situation?

13 hours into a 14 hour passage, approaching an island and the front/thunder storm that was forecasted to stop 75 miles before decided to visit. Sat on top of us for 2 hours. Steep short interval waves, breaking, 4-5m & 40kt sustained with 50kt gusts. Best way to take the waves is straight into them. With that much wind, it was an effort to keep the noise pointed into it, coming off the top of a wave, the wind would grab the boat fairly severe, and my boat is not near the windage of newer cats. Those waves were not something you want to have on the beam. We did make headway, probably VMG of ~3kts as when it was over we were ~2 hours from the destination. Ran the engines at an RPM that delivers 15-18kw (each).

Originally Posted by BigBeakie

How much battery are you referring to that someone on a liveaboard cruiser "cannot afford" to buy or carry?

If EV powered on battery only, (2) 15kw motors for 2 hours would take about (64) 400ah Lithium batteries down to ~80% DOD. Share the load with a 18kw genset and your still need (32) 400ah Lithiums. Either option is a significant $$ and space.

[Valiente]

Originally Posted by DotDun

My boat has (2) diesels rated at 20.1kw each (and these were the ‘small engine’ option). At cruise speed in your ‘benign conditions’, which covers 90+% of motoring time, each is producing ~9kw (18kw total).

So your small genset would need to be 20kw. That would weigh more than my 2 diesels combined. For the 1% of the time you need more power (your ‘safety net’), how big is your big genset? And for the .1% of the time you’ll need everything you can muster - I have been in conditions where I used the 18kw ea (36kw total) continuous power my diesels will produce for more than 2 hours. The gensets and electric motors to produce that would be multiples in weight and dollars compared to diesel drive engines.

Some will blow off the .1% of the time and state, ‘it’s a sailboat, I’ll have a storm sail’. That tells me they have never been in 40-50kt winds with 4-5m breaking waves trying to claw away from a lee shore. That won’t happen without at least 30kw of drive power and the requisite 32+kw of genset. Forget about the batteries for this task, you won’t be able to afford or carry enough.

Add it all up and it doesn’t make sense anymore.

Makes sense. Will consider just Diesel propulsion for the time being.

[BigBeakie]

Originally Posted by DotDun

13 hours into a 14 hour passage, approaching an island and the front/thunder storm that was forecasted to stop 75 miles before decided to visit. Sat on top of us for 2 hours. Steep short interval waves, breaking, 4-5m & 40kt sustained with 50kt gusts. Best way to take the waves is straight into them. With that much wind, it was an effort to keep the noise pointed into it, coming off the top of a wave, the wind would grab the boat fairly severe, and my boat is not near the windage of newer cats. Those waves were not something you want to have on the beam. We did make headway, probably VMG of ~3kts as when it was over we were ~2 hours from the destination. Ran the engines at an RPM that delivers 15-18kw (each).



If EV powered on battery only, (2) 15kw motors for 2 hours would take about (64) 400ah Lithium batteries down to ~80% DOD. Share the load with a 18kw genset and your still need (32) 400ah Lithiums. Either option is a significant $$ and space.

So you weren't clawing off a lee shore to avoid disaster, you were choosing to claw towards a destination windward shore? It takes about 12 hours of sustained 40 knot winds to develop breaking 4 meter waves, and that is in only 20 meters of water. That's a very long lived thunderstorm you experienced....

And you held station by running your engines, which is a fair choice, because you did not know how long the adverse conditions would last. Another choice would be to sail, but if your cat is not set up for heavy weather sailing, then the iron genny is your only answer; or heaving to, or turning around and running or deploying a parachute anchor might be alternative answers.

What wind speed would you say your boat would NOT be able to hold station? It sounds like it was maybe about 50 knots, because it was difficult to point?
So, what would you do if you got 60 knots on the nose? Would you run full power into it and just try to keep pointing into it while drifting backwards for as long as you had fuel?

A reasonable amount of battery (cost + multihull weight factor) for EP is, IMO, about an hour of full power. If anyone is contemplating EP, they should realise this, and perhaps ensure they have a boat that is suitably rigged and equipped for heavy weather sailing, because you just never know. Going to sea in a boat that MUST rely on engines or motors to deal with heavy weather is a choice, but IMO, a bad choice, regardless of the auxillary propulsion technology.

[four winds]

BB, I think a storm followed DD home, and that wasn't expected.

Then, like a good seaman, he headed back out and stuffed the bows in its face for a while.

Ending up two hours from home instead of one.