Solar sails and the future of hybrid cats

[valhalla360]

Originally Posted by ssmoot

What's a "33kW" diesel? Is it one you can hook up to a 25kW generator and run for a whopping 30 minutes every 10 hours? Because that's the type of engine we're talking about here.

No? That'd be silly?

The feigned ignorance gets old. You can disagree and make a case for what is most important to you without coming off like a child who thinks he's caught his parents in his clever word-games trap.

What sort of magical thinking does it take to pretend we're talking about a "33kW" engine, and not a ~10kW engine that's only capable of 33kW in short bursts when putting ~3.5X the fuel into it? You might want to get the genny manufacturers on the phone. Clearly you're better at this than them and can inform them how to produce a generator for a fraction of the weight and fuel cost they're managing.

Except you can run a 45hp diesel at a lot more than 15kw output for extended periods of time. Even if you derate it to 35-40hp, that's still a lot more than a 15kw electric motor....which a 15kw diesel generator won't be able to feed continuously either, so there is no net gain.

[ssmoot]

Originally Posted by valhalla360

If you are driving a car in stop and go traffic, this all makes perfect sense. On a displacement cruising boat set at 6.5kts and just chugging along, it's irrelevant.

The car would be more efficient if it were just chugging along. That's a fact. If you don't understand why that's the case, I can try to help you understand it if you'd like.

Nothing obtuse about it. If you claim a 15kw electric motor has the same hp as a 45hp diesel, that is a lie and there is no way around it.

This looks like moving the goalposts. I don't think anyone ever made the claim that you could get 45hp out of 15kW. Just that they're about equally fit for purpose of moving around a cruising catamaran.

But let's flip this whole thing on it's head and maybe you'll understand why this is unnecessarily melodramatic:

If you claim a 45hp diesel is equivalent to a 33kW electric motor, that is a lie and there is no way around it. The diesel will need to be throttled back after 30 minutes but the electric motor can keep going all day long. By the time the electric boat travels 100NM, the diesel boat will be hours behind.

BTW, in case you weren't aware, the same is likely true for the 15kW electric motor assuming the M1 RPM of the diesel is 2,000RPM [1] since the 4JH45 doesn't hit 15kW until about 2,350RPM and fuel consumption almost doubles. So even though the diesel gets a better start with 30 minutes of WOT, the 15kW motor is putting out 50% more power the other 14 hours.

Is a 15kW still not equivalent then? Is the only metric that matters here the 100-yard-dash time of your setup? That's your prerogative. But that doesn't make anyone else a "liar" just because they don't agree.

[1]: I'm guessing at the M1 on the Yanmar because it's not published as far as I've found, and a YachtWorld test pegged an efficient cruising speed for the 4JH57 equipped Lagoon 42 at 2,000RPM.

[ssmoot]

Originally Posted by valhalla360

Even if you derate it to 35-40hp, that's still a lot more than a 15kw electric motor.

To be clear, you're claiming the M1 for a 4JH45 is somewhere between 2,700 and 2,900RPM? [1]

[1] http://www.yanmarmarine.com/theme/ya...heet_4JH45.pdf

[Thalas]

I guess I'm not understanding the importance of spending pages and pages arguing about kw vs hp. Diesel has more energy density. Electric has more simplicity and possibility to renew at sea.

Most sailors would probably agree that a 6kt cruising speed at 2200rpm is desirable if you HAVE to motor. If a 15kw motor can also hit that 6kt speed without burning through electricity at an unreasonable rate, why not compare the engines using that metric to get a better idea of the tradeoffs?

What is the range of the average cat with full diesel tanks? What size motor and battery bank could reasonably fit in a cat to balance weight and range? What about half that range? What kind of deficit would we be running with a 3kw solar array in different conditions? What kind of regeneration would we expect to see at 8kts under wind power? What size genny would be the minimum to recharge the larger battery bank on overcast days? What future advances are on the horizon regarding solar fabric integration into sails? What are the advantages/disadvantages of running a bank at 48V and stepping down to 120V or 12V for house needs?

There are so many interesting questions to explore here and certain people just go back and forth with rude accusations debating minutiae. This is a thread about implementing solar and electric motors into an all/electric boat. We know for a fact that both electric and diesel can hit 6kts so size your motor accordingly and help elucidate some of the questions raised above or raise your own questions. But name calling and beating a tiny point to death feels like a thread hijack into negativity.

[valhalla360]

Originally Posted by ssmoot

The car would be more efficient if it were just chugging along. That's a fact. If you don't understand why that's the case, I can try to help you understand it if you'd like.

Apparently, you don't understand why hybrid power works great in cars. In stop and go conditions, the power demands vary greatly.
The hybrid allows the engine to operate at an efficient power output. In fact, it's fairly common for hybrids to be more efficient in stop and go compared to freeway driving.

With a displacement cruising boat, it's not common to have stop and go conditions, so the engine already runs at a very efficient output. There is nothing to gain with a hybrid.

This looks like moving the goalposts. I don't think anyone ever made the claim that you could get 45hp out of 15kW. Just that they're about equally fit for purpose of moving around a cruising catamaran.

Talk about moving the goal posts. The common parlance among electric power advocates is EQUIVALENT, not equally fit. As I've said multiple times, if you are willing to accept reduced capability with electric power, an honest comparison would have you compare to a similar power diesel.

But let's flip this whole thing on it's head and maybe you'll understand why this is unnecessarily melodramatic:



BTW, in case you weren't aware, the same is likely true for the 15kW electric motor assuming the M1 RPM of the diesel is 2,000RPM [1] since the 4JH45 doesn't hit 15kW until about 2,350RPM and fuel consumption almost doubles. So even though the diesel gets a better start with 30 minutes of WOT, the 15kW motor is putting out 50% more power the other 14 hours.

HP and RPM are not equivalent. It depends on the loading.
HP = Torque * RPM. If you are spinning a very small prop at 2000RPM, it doesn't take a lot of torque, so HP will be much less. A 45hp diesel can put out far more than 15kw on a continuous basis so, no it's not going to win the "other 14 hours.

Is a 15kW still not equivalent then? Is the only metric that matters here the 100-yard-dash time of your setup? That's your prerogative. But that doesn't make anyone else a "liar" just because they don't agree.

Again, I think you don't understand how hybrids work.
An electric motor can have a lower HP and win the 100-yard dash because of the low end torque means it builds to that peak HP much quicker but thats not how displacment engines get sized.

[1]: I'm guessing at the M1 on the Yanmar because it's not published as far as I've found, and a YachtWorld test pegged an efficient cruising speed for the 4JH57 equipped Lagoon 42 at 2,000RPM.

Again, if you want to claim the Lagoon is overpowered, that's fine but it's a totally different discussion from saying a 15kw electric motor is equivalent to a 45hp diesel.

[cwjohm]

Thalas said

Most sailors would probably agree that a 6kt cruising speed at 2200rpm is desirable if you HAVE to motor. If a 15kw motor can also hit that 6kt speed without burning through electricity at an unreasonable rate, why not compare the engines using that metric to get a better idea of the tradeoffs?

Herein lies the problem. On a normal production catamaran a 15Kw motor cannot hit 6kn speeds.

Not that I want to enter into this silly discussion, but in reference to the performance of Kato 2, I decided to discuss with Tony rather than listen to the Oceanvolt propaganda.

Firstly, adjusting for all factors the boat goes over a longer period (hours not seconds) around an average of 7Kn. Tony is quite happy with this but remember this is a custom build boat designed for speed.

Secondly, with the lack of torque associated with the electric motors, Tony has fitted bowthrusters, for close manouvering and he believes they are mandatory.

So, extrapolating from this the average production boat would probably get around 4-5Kn with 15Kw electric motors and in adverse conditions go backwards, and without bow thrusters in close in manouvering would be an absolute PITA.

As I have stated many times here a dual 30Kw electric motors would equate to 45Hp diesel and give similar performance. If you want to spend on these and the generator and batteries then no problem other than the pain in your bank account.

All the rest of the discussions here is like arguing how many angels you can fit on a pin.

[valhalla360]

Originally Posted by Thalas

I guess I'm not understanding the importance of spending pages and pages arguing about kw vs hp. Diesel has more energy density. Electric has more simplicity and possibility to renew at sea.

Most sailors would probably agree that a 6kt cruising speed at 2200rpm is desirable if you HAVE to motor. If a 15kw motor can also hit that 6kt speed without burning through electricity at an unreasonable rate, why not compare the engines using that metric to get a better idea of the tradeoffs?

What is the range of the average cat with full diesel tanks? What size motor and battery bank could reasonably fit in a cat to balance weight and range? What about half that range? What kind of deficit would we be running with a 3kw solar array in different conditions? What kind of regeneration would we expect to see at 8kts under wind power? What size genny would be the minimum to recharge the larger battery bank on overcast days? What future advances are on the horizon regarding solar fabric integration into sails? What are the advantages/disadvantages of running a bank at 48V and stepping down to 120V or 12V for house needs?

There are so many interesting questions to explore here and certain people just go back and forth with rude accusations debating minutiae. This is a thread about implementing solar and electric motors into an all/electric boat. We know for a fact that both electric and diesel can hit 6kts so size your motor accordingly and help elucidate some of the questions raised above or raise your own questions. But name calling and beating a tiny point to death feels like a thread hijack into negativity.

As I have said multiple times, if 6kts is good, set that as the bar and then pick the HP/KW for both the electric and diesel.

You are handicapping the diesel because your average 40-45' catamaran cruises at 7kts and is capable of 9-10kts, so if you want to set 6kt top end as the bar, you could downsize the diesel HP probably by 50% or more.

[ssmoot]

If you want to understand this better, look up “hypermiling” and task yourself with figuring out why a BMW i3 only gets 39MPG combined. Until you can answer that question, and why the BMW i3 specifically, I don’t think discussing the hybrid car analogy further is going to be productive.

Here’s an easily digestible article you might start with: https://www.edmunds.com/fuel-economy...l-economy.html

And here’s the money quote:

Every time you stop and start, you waste fuel.

Originally Posted by valhalla360

A 45hp diesel can put out far more than 15kw on a continuous basis so, no it's not going to win the "other 14 hours.

I think such claims should require some sort of proof? I’ve linked Yanmar’s own data sheet, fuel consumption and power graphs. Several times now. You’re just… saying things.

I feel like you haven’t actually looked at the charts.

Again, if you want to claim the Lagoon is overpowered, that's fine but it's a totally different discussion from saying a 15kw electric motor is equivalent to a 45hp diesel.

“equivalent” is entirely arbitrary.

I’m not suggesting the Lagoon 42 is overpowered. I’m suggesting that the peak rating isn’t meaningful. If Lagoon could put 30hp engines on the boat that provided 12kW at 2,000RPM for a lower price, they totally would. But they can’t. That engine doesn’t exist.

[ssmoot]

Originally Posted by cwjohm

Herein lies the problem. On a normal production catamaran a 15Kw motor cannot hit 6kn speeds.

So the Nautitech Open 40, with 18.8hp standard engines, can't do 6kt?

[sailingharry]

Originally Posted by ssmoot

I think such claims should require some sort of proof? I’ve linked Yanmar’s own data sheet, fuel consumption and power graphs. Several times now. You’re just… saying things.

I feel like you haven’t actually looked at the charts.

I've just spent the last 1/2 hour reading, re-reading, searching, and pouring through this thread. I must be blind, I can't find your links. Could you post it one more time, or tell me which post it is in? Thanks.

[Just Another Sa]

Originally Posted by ssmoot

If Lagoon could put 30hp engines on the boat that provided 12kW at 2,000RPM for a lower price, they totally would. But they can’t. That engine doesn’t exist.

http://www.yanmarmarine.com/theme/ya...et_3YM30AE.pdf
This one can put out 16 kW at 2000 RPM if propeller is selected for that task. Doing so for any longer period would be stupid, but it can do so. Using just 12 kW at 2000 in a sailboat, which might spend a lot of time at anchor or being moored, and thus not using engine at all, and when using engine, not using 12 kW/2000 rpm all the time, but only when going upwind a few hours continuously when not wanting to sail (less than 25% of engine usage) would be just fine.
Yanmar is certainly not the only manufacturer producing engines capable of achieving that task.
For anyone doing so, it would be unwise to ever using WOT with that propeller.

[Just Another Sa]

Originally Posted by cwjohm View Post
Herein lies the problem. On a normal production catamaran a 15Kw motor cannot hit 6kn speeds.

Originally Posted by ssmoot

So the Nautitech Open 40, with 18.8hp standard engines, can't do 6kt?

With just one engine or with 2 of them?
And with what overall weight? Empty boat or one carrying full cruising gear and some growth on the bottom.

[ssmoot]

Originally Posted by Thalas

I guess I'm not understanding the importance of spending pages and pages arguing about kw vs hp.

We're talking about doubling the size of the motors. If you want to, go for it. Because why not? But if we're talking about doubling the energy required, that's different. Because it's the difference between a viable system, and one that's not.

So 15kW motors. 30kW motors. Who cares? But delivering 30kW reliably continuously? That's a big deal. Because it must be continuous. With perfect efficiency, you'd burn through a pair of even 60kWh batteries in just two hours to move the boat ~15NM. And that's just ridiculous.

What is the range of the average cat with full diesel tanks?

My guesstimate, based off the Lagoon 42 article I linked, was about 257NM for the Lagoon 42 with it's 79 gallon tank under diesel power, and 220NM with 15kW motors. That was based on 7.5kt at WOT. I don't remember where I got that number.

What size motor and battery bank could reasonably fit in a cat to balance weight and range?

At under $15K and 960lbs, I don't see much advantage in going lower than 60kWh unless you just can't stand the idea of using an EV battery pack? The Bolt pack is really the state of the art in cost, capacity and weight AFAICT.

What about half that range?

You'll only be able to run silent for a few hours at most before firing up the generator. So 15kW motors with a 60kWh battery sounds about right to me. I'd be tempted by twin 32kWh batteries (the i3 battery pack), but they'd weigh more for the same capacity and at double the cost you might as well just have twin 60kWh batteries even though that seems a bit silly.

With all that spare capacity they should last basically forever at least.

What kind of regeneration would we expect to see at 8kts under wind power?

That's a good question. I wonder if Oceanvolt makes any claims. You might peg that as a best-case-scenario then at least. I also think propeller design might end up playing a bigger than expected role: Folding and feathering propeller test

What are the advantages/disadvantages of running a bank at 48V and stepping down to 120V or 12V for house needs?

Since most of the capacity would only be there for the motors, and step down converters are very efficient, I think you'd consider that a rounding error. Because of wiring and battery pack advancements (which in EVs are due almost entirely due to basic engineering, and not chemistry), I do think high-voltage packs are the clear winner for weight, density, cost.

There are so many interesting questions to explore here and certain people just go back and forth with rude accusations debating minutiae.

I really want to agree, but a 200% difference in power requirements means an extra ~3,000lbs and ~220% higher fuel consumption. To even begin to think about making that economical, we'd have to have some sort of new generator technology that some how produced twice as much power with the same amount of diesel. And I'd be surprised if that ever happens.

So do I need 10kW or 30kW to maintain 6.5kt? That really does matter. It's easily the most important question if you're wondering if electric propulsion is viable on your 42' cruising catamaran.

[Just Another Sa]

Originally Posted by ssmoot

Here’s an easily digestible article you might start with: https://www.edmunds.com/fuel-economy...l-economy.html
And here’s the money quote:

From the link you provided:

"Pulse and glide" This is perhaps the most complicated technique employed by hypermilers. On a Prius, the optimal speed for this tactic is around 30-40 mph, said Prius owner Cullen. The first step in the pulse-and-glide technique is to pulse, which is to accelerate the vehicle to around 30 or 40 mph. In the Prius, once the speed has reached 40 mph, ease slightly back on the accelerator until no energy arrows appear on the energy monitor, indicating that the vehicle is neither relying on the engine nor recharging the battery. As a result, the car begins to glide. When the vehicle slows to about 30 mph, repeat the whole process again, pulsing and then gliding.

The pulse-and-glide technique improves fuel economy by minimizing use of the internal combustion engine. There is a version of this technique that can also be applied to non-hybrid vehicles, but be aware that it is outlawed in several states because it would require actually turning the engine off, which causes the power-assist for the brakes and steering to fail. If the key is in the off position, the steering will also lock.

So don't stop and start your car, instead stop and start the engine of the car!

[ssmoot]

Originally Posted by Just Another Sa

http://www.yanmarmarine.com/theme/ya...et_3YM30AE.pdf
This one can put out 16 kW at 2000 RPM if propeller is selected for that task. Doing so for any longer period would be stupid, but it can do so. Using just 12 kW at 2000 in a sailboat, which might spend a lot of time at anchor or being moored, and thus not using engine at all, and when using engine, not using 12 kW/2000 rpm all the time, but only when going upwind a few hours continuously when not wanting to sail (less than 25% of engine usage) would be just fine.
Yanmar is certainly not the only manufacturer producing engines capable of achieving that task.
For anyone doing so, it would be unwise to ever using WOT with that propeller.

This is great. Using real, published numbers. Thank you.

We should be looking at the propeller power curve though. If you're going to look at the 100% load graph, then your fuel numbers change drastically and now we're looking at bigger generators and motors to try to figure out a comparable solution.

I'm definitely not trying to suggest you can run a pair of electric motors at 30kW and consume less power than a diesel solution putting 30kW into the props directly.