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On 11/20/2021 at 9:38 AM, Bull City said:

Nothing like more horsepower when you need it!

And where you need it. The big advantage of an inboard engine - electric or IC - is having the prop down low, where it stays in the water regardless of sea state. Very glad this has all worked out so well for you (after initial software hiccups).

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On 11/9/2021 at 12:24 AM, Bull City said:

Is he like an Irish Lawrence Welk?

FWIW:

A few months ago, I was wondering if it would take the same Watts to move my boat at a given speed regardless of the motor. It seemed to me that if I was using electric power, it should be about the same, and if it wasn't, it would be because of inefficiency in the motor, propeller or somewhere. 

The little bit of data I have is encouraging. I think the eProp pod drive is comparable to the Torqeedo in terms of efficiency. That's enough for me. 

From the data you gave and from the physics, I am pretty sure that the pod drive is more efficient. The efficiency of a brushless motor is close enough to 1 (0.95 may be ?) to not worry about it. The propeller of an outboard is too close to the surface and the numbers show that you are indeed benefiting from the extra depth. Yes, ideally, you would need more data points but the trend is clear and unlike my Irish friend I won't punish you and won't force you to listen to Patrick Bruel (extra points for those who resist finding him on You Tube). :D

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1 hour ago, Jud - s/v Sputnik said:

"The ship will load and offload its cargo, recharge its batteries and also navigate without human involvement.

Sensors will be able to quickly detect and understand objects like kayaks in the water so the ship can decide what action to take to avoid hitting anything, Braaten said."

Oh joy. we are going to be transiting ports with huge drone ships. Progress!

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“We’ve taken away the human element, which today is also the cause of many of the accidents we see,” Braaten said.

That is just... just so reassuring. Everything will be fine.

Seriously, there is a good case made for the reduction in carbon emissions, but will there be no crew member at all?

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58 minutes ago, Israel Hands said:

Sensors will be able to quickly detect and understand objects like kayaks in the water so the ship can decide what action to take to avoid hitting anything, Braaten said."

My and 4 friends go out in our kayaks/jet skis whatever. I bet I can stop a big container ship because it's AI is too simple to know what to do if we surround the bow. If it does detect Bob and runs him over, well that's shame.

This has already been done with Teslas etc. Just stop in a crosswalk and put an orange cone down. The car doesn't know what to do any more.

Self driving ships make as much sense as self driving cars. Maybe you have remote operator on shore for crowded approaches with lots of ships where a human in the loop is a good idea. On the open ocean, where you'll only be dealing with 1 or 2 ships at a time, then the AI can take over and wake the shore operator if it gets confused.

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5 hours ago, Panoramix said:

From the data you gave and from the physics, I am pretty sure that the pod drive is more efficient. The efficiency of a brushless motor is close enough to 1 (0.95 may be ?) to not worry about it. The propeller of an outboard is too close to the surface and the numbers show that you are indeed benefiting from the extra depth. Yes, ideally, you would need more data points but the trend is clear and unlike my Irish friend I won't punish you and won't force you to listen to Patrick Bruel (extra points for those who resist finding him on You Tube). :D

also, the motor is right there in the pod, presumably inline with the prop so I guess the propeller is directly driven. Idk what the losses are for a transmission and various linkages - but spinning all that steel cannot come for free. so, iow, the pod concept all by itself should be more efficient.

the other cool thing about this is the hole in your hull. Just bolts and a cable. I really like that idea - although I don't know how far up it will scale.

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25 minutes ago, floater said:

also, the motor is right there in the pod, presumably inline with the prop so I guess the propeller is directly driven. Idk what the losses are for a transmission and various linkages - but spinning all that steel cannot come for free. so, iow, the pod concept all by itself should be more efficient.

the other cool thing about this is the hole in your hull. Just bolts and a cable. I really like that idea - although I don't know how far up it will scale.

scales well!Siemens_Schottel_Propulsor.jpg

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Efficiency of electric motors usually peaks around 0.95

Bearings / seals - lose you about 1% each

Right angle bevel gears - 2-5%. Depends on type, machining quality etc.

The biggest difference in all these comparisons is this:  BIG props turning slow are more efficient than little props turning fast. For these 2 electric drives one may have a propeller that is better suited to the boat.

The Torqueedo prop is probably too small/fast and better suited to smaller boats, maybe moving a bit faster. (picture using a 3 HP outboard to push your 30' sailboat; it can be done but it's not efficient)

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Those are Azipods (or a copy). The motor is in the hub. They rotate 360 degrees. Some are ice breaking. 

Very popular with cruise ships for packaging reasons (more cabins) and avoiding the use of tugs (because they dock/undock every day)

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1 hour ago, Bull City said:

That is just... just so reassuring. Everything will be fine.

Seriously, there is a good case made for the reduction in carbon emissions, but will there be no crew member at all?

There will have to be a pilot for any runs through congested waters, just as they are needed on conventional ships. So, by necessity, there will have to be at least one person for him to badger for fresh coffee.

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Good point. But maybe the ship's representative and a pilot board together and ship's rep starts up the coffee machine.

In many jurisdictions you don't need a pilot if it is a "local" voyage and the master (ship) is familiar with the route.

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4 hours ago, Zonker said:

My and 4 friends go out in our kayaks/jet skis whatever. I bet I can stop a big container ship because it's AI is too simple to know what to do if we surround the bow. If it does detect Bob and runs him over, well that's shame.

This has already been done with Teslas etc. Just stop in a crosswalk and put an orange cone down. The car doesn't know what to do any more.

Self driving ships make as much sense as self driving cars. Maybe you have remote operator on shore for crowded approaches with lots of ships where a human in the loop is a good idea. On the open ocean, where you'll only be dealing with 1 or 2 ships at a time, then the AI can take over and wake the shore operator if it gets confused.

That will make it easier for Somali pirates to capture ships...

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21 hours ago, Zonker said:

BIG props turning slow are more efficient than little props turning fast.

what about pitch? any pocket-wisdom for the proper pitch to a propeller?

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6 hours ago, floater said:

what about pitch? any pocket-wisdom for the proper pitch to a propeller?

Well, you can calculate the no-slip speed based on pitch * RPM (and converting units as desired). You always need a bit more pitch than the no-load calculation gives you, because in reality there is always some slip. So you need to estimate how much slip there should be. Probably prop specialists know how much is needed in typical use cases. I believe small props need more slip to do their job than large ones. Not sure what the relationship is between speed and slip.

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5 hours ago, weightless said:

With all the other parameters set wouldn't one that absorbs the available power be most desirable?

Not necessarily. An over-pitched prop can generate resistance without generating (much) thrust. Particularly if the pitch is infinite (to just give the most extreme case).

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30 minutes ago, mckenzie.keith said:

if the pitch is infinite

Aha, that makes sense if the most efficient span is infinite then the most efficient pitch must be infinitesimal. ;)

32 minutes ago, mckenzie.keith said:

An over-pitched prop

Sure, but that's a mismatch to the available power, too. Isn't it?

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2 hours ago, weightless said:

Aha, that makes sense if the most efficient span is infinite then the most efficient pitch must be infinitesimal. ;)

Sure, but that's a mismatch to the available power, too. Isn't it?

Well, yeah. It is a mismatch. But my point is that a prop with too much pitch will be difficult to turn for the motor. A prop with too little pitch will be easy to turn for the motor.

Let's say we spin the shaft at fixed RPM and gradually increase pitch, starting with a pitch that is too small. Torque and thrust will both increase, as the pitch is increased, but at some point, when the prop becomes stalled (hydrodynamically) then the torque will increase dramatically, and the thrust may fall off or at least not increase as rapidly as the torque does. If you continue to increase pitch, the torque will continue to go up and the thrust will drop off. The highest torque will occur when the prop pitch is infinite. So I guess my point is that the ability of the prop to absorb the power doesn't seem to be a reliable indicator of a well matched prop.

I guess I could be mis-interpreting what you said, though.

For a concrete example, if you take a typical outboard designed for planing boats and use it to power a big heavy boat, it will have way too much pitch for the application. The motor is still doing work. But you will achieve more economical operation by changing to a lower pitch prop if your boat is slow (a high thrust prop).

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1 hour ago, mckenzie.keith said:

Well, yeah. It is a mismatch. But my point is that a prop with too much pitch will be difficult to turn for the motor. A prop with too little pitch will be easy to turn for the motor.

Amen. I think I was misunderstanding your point. Sorry about that.

I've seen the problem set-up in terms of power. I gather that for any given motor and, if included, transmission there will be a shaft rpm where the motor makes the most power. (Also, there may be a different rpm where it is most efficient. That might be important if efficiency was the goal.)

Some WAGs just to have some numbers to discuss (ie. probably all wrong. Maybe extravagantly so. IDK. Please feel free to correct them):

A small outboard motor might get max power at 5-6k rpm and divide that by around two with a typical transmission. So, I think it'd be desirable to end up at a steady state where the prop shaft is spinning about 2.5-3k rpm and it's working correctly ie. not cavitating or something horrid and pushing the boat in the desired way.

A quick google suggests that some 3kw propulsion BLDC's have a no load rpm around 4k. I suppose they'd make max power around 2k? If that's kinda, sorta ballpark correct then maybe the electrics are running bigger props because when directly connected they have a slower max power shaft rpm than the typical gas OB? Would that tend to make them better at bollard pull type tasks and less good at higher speed tasks? Seems like changing the tranny ratios could move the shaft speed around to match the intended service with either an electric motor or a gas motor. I don't understand the "equivalent" power quoted by the electric folks.

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13 minutes ago, weightless said:

Amen. I think I was misunderstanding your point. Sorry about that.

I've seen the problem set-up in terms of power. I gather that for any given motor and, if included, transmission there will be a shaft rpm where the motor makes the most power. (Also, there may be a different rpm where it is most efficient. That might be important if efficiency was the goal.)

Some WAGs just to have some numbers to discuss (ie. probably all wrong. Maybe extravagantly so. IDK. Please feel free to correct them):

A small outboard motor might get max power at 5-6k rpm and divide that by around two with the transmission. So, I think it'd be desirable to end up at a steady state where the prop shaft is spinning about 2.5-3k rpm and it's working correctly ie. not cavitating or something horrid and pushing the boat in the desired way.

A quick google suggests that some 3kw propulsion BLDC's have a no load rpm around 4k. I suppose they'd make max power around 2k? If that's kinda, sorta ballpark correct then maybe the electrics are running bigger props because when directly connected they have a slower max power shaft rpm than the typical gas OB? Would that tend to make them better at bollard pull type tasks and less good at higher speed tasks? Seems like changing the tranny ratios could move the shaft speed around to match the intended service with either an electric motor or a gas motor. I don't understand the "equivalent" power quoted by the electric folks.

Sheesh. What a can of worms. Typically, the no-load speed of a BLDC is determined by only one thing, the battery voltage. Once the back EMF is approximately equal to the battery voltage, the motor can't go any faster (typically). The back EMF builds linearly with speed.

When we talk about max efficiency of this type of motor, we have to be careful. If we hold torque constant, there will be some max efficiency point in the RPM range. That is the natural max efficiency point. Power is just torque x speed, so if you hold torque constant, the motor power available will be lower at low RPM and only achieve max power at max (or at rated) RPM. For example a 10 HP 4000 RPM electric motor will deliver up to 10 HP at 4000 RPM and up to 5 HP at 2000 RPM, etc if it is controlled with constant max torque.

But if we hold power output constant over some speed range, then you will see that the max efficiency will likely be at max RPM (because that is minimum phase current, and power loss is proportional to the square of the phase current). So if our 10 HP motor is 85 % efficient at 10 HP and 4000 RPM, you can be sure the efficiency will be much lower if you operate it at 10 HP at 2000 RPM.

If you take two motors, one electric and one gasoline powered, and they both put out 10 HP at 4000 RPM, neither one will be better than the other at anything. HP is HP. The only virtue of the electric motor is that it may, depending on the controller and other details, be able to temporarily exceed its rated HP even by 2X. The gasoline motor will stall if you try to do that. But otherwise it is just HP. Electric HP is not better than gas HP.

The other discrepancy is that diesel HP ratings are not sustained operation ratings. So they have to be de-rated a bit. If you try to run a 50 HP Yanmar at 50 HP for 1500 hrs (with maintenance) I don't think it will work. I think it will fail prematurely.

From what I have seen, the people using electric motors on cruising boats are not able to cruise at hull speed or motor into a headwind. They have given up speed, power and range compared to a typical Diesel install.

If you run a 50 HP AC induction motor at 50 HP in a hot room (40 C ambient) it will run 24/7 for 10 years until the bearings wear out. After you replace the bearings you can probably run it for another 10 years. If you run a 50 HP AC induction motor at 100 HP, well, you can actually get away with that for a while. I am not sure how long. But it will definitely put out the power for a while. Lately I have been running a cheap 1 HP induction motor in sustained bursts of 30 seconds to a minute at over 2X that. Somewhere around 2.3 HP. This is a three phase induction motor connected to a 2 HP VFD. BLDC's can also be driven hard for short times, but depending on the supplier, they may not be rated as conservatively as AC induction motors. It is just a reference point.

I am an electrical engineer. I have some experience with BLDC motors and controllers and induction motors and controllers (VFDs). But these are all sub 5 HP motors. I am not a naval architect or a prop expert.

But for sure the first thing you want to figure out is how much shaft HP do you need. Then probably prop size and RPM, then figure out your transmission reduction ratio or try to find a motor with correct RPM for direct drive. To some extent, changing prop pitch and changing transmission ratio do the same thing, at least for small changes. For a cruising sailboat, the motor power should be adequate to reach hull speed, and also to make headway (not necessarily hull speed) in a blow in case you need to re-anchor at night during a high wind event or something like that. I don't care how good a sailor you are, you are not going to retrieve your anchor under sail in a crowded anchorage at night with 40 knots of wind blowing.

If the electric motor rated output power is continuous, then there is no need to de-rate it at all. And if you are sure you don't need full power for long periods of time, then you can use an even smaller electric motor with the understanding that you may temporarily over-drive it for short times if necessary. But marine diesel motors DO need to be de-rated. So if you find you need 40 HP for hull size, you will have to go over 40 HP in motor size.

If you follow this procedure with an electric motor you will end up with a pretty large motor (maybe 50 to 80% of the rated power of the diesel motor) and you will also find that you need a decent sized battery. If you choose to skimp on the battery, that could be a valid choice. It is just range you are giving up. But I think most of the high profile youtube electric motor conversions are not following this procedure.

I already spent too much time typing this. I am not going to re-edit it any more. I hope it makes enough sense.

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3 hours ago, mckenzie.keith said:

The other discrepancy is that diesel HP ratings are not sustained operation ratings. So they have to be de-rated a bit. If you try to run a 50 HP Yanmar at 50 HP for 1500 hrs (with maintenance) I don't think it will work. I think it will fail prematurely.

I think you're wrong on this.

There are - at least for industrial engines - the peak HP figure and the continuous HP figure. If you run the motor at its continuous HP figure, then you will indeed get thousands of hours of running time, assuming proper maintenance.

Diesel air compressors, generators and similar are cases in point.

I guess you are correct for the general run of boat engines, because they're not quoting the continuous HP figure.

As for prop pitch and gearboxes, the 'correct' answer is a controllable pitch propellor.

Unfortunately, in the 50 HP and less range, AFAIK nobody is making one. Hundested still makes a CPP but it is physically quite bulky, you couldn't fit one to anything smaller than 15m or more IMO. I've had my hands on one so I know the size/bulk of the component parts.

I have 2 CPP's in my collection of parts. One still attached to its Sabb 16HP diesel engine and the other a UK manufacture PNP-Duerr unit that came off a Perkins 4-107 engine. I have fantasies of making patterns for the Sabb unit and casting some up, but I doubt I ever will. Too many other projects.

FKT

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5 minutes ago, Fah Kiew Tu said:

I think you're wrong on this.

There are - at least for industrial engines - the peak HP figure and the continuous HP figure. If you run the motor at its continuous HP figure, then you will indeed get thousands of hours of running time, assuming proper maintenance.

 

I could be wrong. But look at the Yanmar 4JH5E. This was the first motor I checked. I didn't attempt to do a full survey of all motors.

Rated power on website: 39.6 kW / 53.8 mhp at 3000 rpm.

Continuous power from datasheet: 36 kW / 48.9 mhp at 2907 rpm.

I believe this is typical in marine diesels for pleasure craft in this size range (let's say 20-100 HP). The rated power is 10% higher than the continuous power. So if you figure you actually need 50 HP to hit hull speed then you need to get a motor rated at 55 or 60 HP. On the other hand, if you were powering your boat with an induction motor for some reason, you would not need to de-rate the motor output at all.

 

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2 hours ago, mckenzie.keith said:

I could be wrong. But look at the Yanmar 4JH5E. This was the first motor I checked. I didn't attempt to do a full survey of all motors.

Rated power on website: 39.6 kW / 53.8 mhp at 3000 rpm.

Continuous power from datasheet: 36 kW / 48.9 mhp at 2907 rpm.

I believe this is typical in marine diesels for pleasure craft in this size range (let's say 20-100 HP). The rated power is 10% higher than the continuous power. So if you figure you actually need 50 HP to hit hull speed then you need to get a motor rated at 55 or 60 HP. On the other hand, if you were powering your boat with an induction motor for some reason, you would not need to de-rate the motor output at all.

 

Yeah but it's not that straightforward because a diesel engine in a boat delivers its power over a range of rpm. An electric motor is rated for one rpm based on frequency.

I know for a fact that electric motors fitted to CNC machine tools are *grossly* oversized because they need to have enough power at relatively low rpm/frequency to drive a cutting tool at the required depth of cut and chip load per tooth. And they don't have gearboxes.

Even with fancy VFD's electric motor power drops off badly when you get under say 10Hz. My diesel motor delivers usable power over 900 to a max of 3600 rpm. That's a 4X speed range so say 15 to 60 Hz for an electric motor.

NB: I'm not an electrical engineer, just someone who's screwed around with 3 phase VFD's for machine tools so I can easily be wrong. I just know that the typical machine tool motor needs to be massively oversized so as to deliver the power needed at low rpm.

FKT

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7 hours ago, Fah Kiew Tu said:

An electric motor is rated for one rpm based on frequency. ...

Even with fancy VFD's electric motor power drops off badly when you get under say 10Hz.

Obviously not an EE so I'll just drop in some characteristic curves and say that the pods and OBs that I've seen are using BLDCs.

image.thumb.png.1b6e659377fb9cd0a924ce2913c0e1a7.png

image.thumb.png.0e6ec2f043090fd5b422a0770ce0d3ae.png

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7 hours ago, Fah Kiew Tu said:

Yeah but it's not that straightforward because a diesel engine in a boat delivers its power over a range of rpm. An electric motor is rated for one rpm based on frequency.

I know for a fact that electric motors fitted to CNC machine tools are *grossly* oversized because they need to have enough power at relatively low rpm/frequency to drive a cutting tool at the required depth of cut and chip load per tooth. And they don't have gearboxes.

Even with fancy VFD's electric motor power drops off badly when you get under say 10Hz. My diesel motor delivers usable power over 900 to a max of 3600 rpm. That's a 4X speed range so say 15 to 60 Hz for an electric motor.

NB: I'm not an electrical engineer, just someone who's screwed around with 3 phase VFD's for machine tools so I can easily be wrong. I just know that the typical machine tool motor needs to be massively oversized so as to deliver the power needed at low rpm.

FKT

When driven with a VFD, and it depends on the type of VFD, too, an induction motor can develop full torque (and then some) from less than 1 Hz up to full speed, and can even drive faster than full rated speed. A VFD is not a good replacement for a gearbox for the exact reason that you mention. Induction motors (and servomotors and BLDC motors) typically have a maximum continuous torque rating. Since power is just torque x speed, as the RPM goes down, the continuous power available also goes down. A motor rated for 10 HP at 60 Hz can only deliver 1 HP at 6 Hz. Also, cooling can become an issue for some motors that have shaft mounted fans. At lower speeds, the airflow is reduced, so the torque has to be de-rated even further. Of course that can be fixed by adding ventilation.

The speed of the motor can be regulated anywhere from very low to full rated speed and beyond. In fact some VFD's support shaft position encoders and can implement full position control with full torque even when the shaft is not moving (almost like a servomotor).

ICE's have torque curves, too. They aren't as flat as electric motor curves, but the power available from an ICE diminishes at lower speeds also. A 50 HP 3000 rpm diesel can only deliver 50 HP at 3000 rpm. It cannot deliver 50 HP at 900 RPM. If anything, electric motors, when controlled properly, are more versatile then ICE motors.

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29 minutes ago, weightless said:

Obviously not an EE so I'll just drop in some characteristic curves and say that the pods and OBs that I've seen are using BLDCs.

image.thumb.png.1b6e659377fb9cd0a924ce2913c0e1a7.png

image.thumb.png.0e6ec2f043090fd5b422a0770ce0d3ae.png

It is unfortunate that the assumptions/operating conditions are not more clearly spelled out. In both cases, for the induction motor and the BLDC, the curves shown are for motors operated at fixed voltage (and in the case of the induction motor, fixed frequency). Those curves do not apply when the motor is controlled by a variable speed control. In effect, the controller is able to vary the voltage and frequency to keep the motor operating near peak efficiency for the particular operating conditions.

The controller will respond to changes in load, so if the load increases dramatically for some reason, and the load torque exceeds the programmed torque limit, the controller will just slow down rather than allow torque to approach stall torque. Or in some cases the controller might "trip" and just stop driving the motor.

Here is a graph of a servomotor torque vs speed curve where the assumption is that the motor is being controlled by an appropriate servo-drive. BLDC and servomotor and induction motor curves are very similar to each other.

 

Servo-motor-torque-speed-curve (3).jpg

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13 minutes ago, weightless said:

It doesn't look like the current crop of marine motors use servo drives.  I haven't seen VFDs either. BLDC seems to the popular choice.

It doesn't matter. The controllers work more or less the same way. A servo drive is just a high performance motor controller. AC servomotors are not really any different than BLDC's for the purposes of this conversation.

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17 hours ago, mckenzie.keith said:

The other discrepancy is that diesel HP ratings are not sustained operation ratings. So they have to be de-rated a bit. If you try to run a 50 HP Yanmar at 50 HP for 1500 hrs (with maintenance) I don't think it will work. I think it will fail prematurely.

That is not quite true.  You can buy diesels that are rated for a certain HP 24/7. The same engine will have a higher output but at a lower rating. For example Caterpillar C12.

345 HP continuous 24/7/365 days per year

390 HP B rating (For vessels operating at rated load and rated speed up to 80% of the time with some load cycling. 3000-5000 hrs/year) 8766 hours in a year by the way

497 HP C rating 

578 HP D rating (For vessels operating at rated load and rated speed up to 16% of the time (up to 50% load factor).
Typical operating ranges from 1000 to 3000 hours per year.) Typical for fast patrol boats which loiter a lot but sometimes sprint

715 HP E rating (yacht planing hull - For vessels operating at rated load and rated speed up to 8% of the time (up to 30% load factor). Typical operation ranges from 250 to 1000 hours per year  This is what you get in your fancy motorboat. Notice you should not run it at full power very often.!

 

Yanmars are pretty good. My old Yanmar 3GM30F had an intermittent rating of 27 HP (1 hr in 12?) and continuous of 24 HP.

Volvo Penta D2. Available in 51, 64, 70 HP.  "Running  hours  less  than  300 hours*  per year.   Full  power could  be  utilized  maximum  1  hour  per 12  hours  operation  period.  Between  full  load  operation  periods, engine  speed  should  be  reduced  at  least  10%  from  the  obtained  full  load  engine  speed." Not much of a de-rate

 

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1 hour ago, mckenzie.keith said:

It doesn't matter. The controllers work more or less the same way. A servo drive is just a high performance motor controller. AC servomotors are not really any different than BLDC's for the purposes of this conversation.

I don't want to impose, particularly on Thanksgiving but if you wanted to flesh that out a bit I'd be grateful. If not, no worries.

IIRC, the Torqeedo control system is throttle encoder-> pwm/h bridge-> motor/commutator. So, while the commutator has a senor it isn't used for feedback in the sense that I think of with servos. It seems to me that the performance would be similar to the graph I posed above with the max rpm varying with the voltage the controller sends. Not?

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34 minutes ago, Zonker said:

That is not quite true.  You can buy diesels that are rated for a certain HP 24/7. The same engine will have a higher output but at a lower rating. For example Caterpillar C12.

345 HP continuous 24/7/365 days per year

390 HP B rating (For vessels operating at rated load and rated speed up to 80% of the time with some load cycling. 3000-5000 hrs/year) 8766 hours in a year by the way

497 HP C rating 

578 HP D rating (For vessels operating at rated load and rated speed up to 16% of the time (up to 50% load factor).
Typical operating ranges from 1000 to 3000 hours per year.) Typical for fast patrol boats which loiter a lot but sometimes sprint

715 HP E rating (yacht planing hull - For vessels operating at rated load and rated speed up to 8% of the time (up to 30% load factor). Typical operation ranges from 250 to 1000 hours per year  This is what you get in your fancy motorboat. Notice you should not run it at full power very often.!

 

Yanmars are pretty good. My old Yanmar 3GM30F had an intermittent rating of 27 HP (1 hr in 12?) and continuous of 24 HP.

Volvo Penta D2. Available in 51, 64, 70 HP.  "Running  hours  less  than  300 hours*  per year.   Full  power could  be  utilized  maximum  1  hour  per 12  hours  operation  period.  Between  full  load  operation  periods, engine  speed  should  be  reduced  at  least  10%  from  the  obtained  full  load  engine  speed." Not much of a de-rate

 

Yeah. The top line advertising power of marine diesels for pleasure craft is not a continuous rating. Some electric motors are rated at continuous power. If you compare the two, just read the fine print. That is really all I am saying.

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13 minutes ago, weightless said:

It seems to me that the performance would be similar to the graph I posed above with the max rpm varying with the voltage the controller sends. Not?

Yeah. That is pretty much it. Essentially, the controller can change the voltage so that the motor is always in a good place on the curve. Some old controllers for E-bikes or RC or whatever may directly translate throttle position to duty cycle and use six-step commutation. But newer controllers are much more fancy and monitor output current and even create a phase shift between output current and output voltage to improve efficiency or allow overspeed operation.

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Why do these lazy engineers imagine a cylinder with a hemispherical nose cone is the best shape to enclose their electric motors??

image.png.48298287a17a466d7f721868757e9185.png

It should have a shape like this:

image.thumb.png.f057f20f640ff1be124121413b0a1707.png

Or look at the ballast bulbs on any IMOCA yacht built in the past few decades (just without the vertical squash to lower VCG on a keel bulb)

 

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2 hours ago, zloitapok said:

Pod 3.0 Evo Folding Propeller appeared at ePropulsion website

https://www.epropulsion.com/product-page/pod-3-0-evo-folding-propeller/

 

Sorry, if you already know this )

@zloitapok I did not know it was available. Thanks for posting it. Are you thinking about a pod drive?

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2 hours ago, Zonker said:

Why do these lazy engineers imagine a cylinder with a hemispherical nose cone is the best shape to enclose their electric motors??

Well, the starting point is that the pod is a cover for an electric motor, whose shape is a cylinder.

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The Cd of something like a laminar flow sort of thing like my sketch is like 0.05. A cylinder + a hemisphere is probably 0.2 or so.

Say diameter = 75mm (3"). 

Draggy cylinder at 6 knots?

F = 1/2 rho Cd A V^2 = 0.5 (1025 kg/m3) 0.2 (pi x .075^2 / 4) * 3 m/s = 1.3 kg so about 1 kg more than a streamlined body.

Now 1 kg doesn't sound like much - but that's about 1% of the drag of a 30' boat at 6 knots. Why give that up?

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On 11/25/2021 at 5:23 AM, Fah Kiew Tu said:

Yeah but it's not that straightforward because a diesel engine in a boat delivers its power over a range of rpm. An electric motor is rated for one rpm based on frequency.

I know for a fact that electric motors fitted to CNC machine tools are *grossly* oversized because they need to have enough power at relatively low rpm/frequency to drive a cutting tool at the required depth of cut and chip load per tooth. And they don't have gearboxes.

Even with fancy VFD's electric motor power drops off badly when you get under say 10Hz. My diesel motor delivers usable power over 900 to a max of 3600 rpm. That's a 4X speed range so say 15 to 60 Hz for an electric motor.

NB: I'm not an electrical engineer, just someone who's screwed around with 3 phase VFD's for machine tools so I can easily be wrong. I just know that the typical machine tool motor needs to be massively oversized so as to deliver the power needed at low rpm.

FKT

In a past life I manufactured air compressors and refrigeration compressors. People would be shocked at how many things require a compressor and how much of an industrialized country's national grid goes towards running them. The smallest unit we made was a 1hp oil-free scroll unit, the largest a 5 kilowatt multistage centrifugal compressor.  We also made rail-car compressors for passenger rail and vane vacuum pumps for trucks.  Anything over 50hp had a fancy three-phase permanent magnet motor and may have had an VCD controller.  VCD reduced a lot of electrical consumption within a narrow band, as you say.  When you looked at the efficiency curve of the screw or turbine and added that to the efficiency curve of the motor itself, the efficient operating band was pretty narrow.  The smaller electrical motors could run for years with no maintenance at all in horrible conditions. The bigger ones needed quite a bit more, especially if environmental conditions were say, hot with lots of SOx, NOx or particulate.  The shortest lifespan were the anti-explosive coal mining units that went down in the pits. They came back looking like they'd been in a war. Anything portable was diesel. 

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3 minutes ago, Elegua said:

In a past life I manufactured air compressors and refrigeration compressors. People would be shocked at how many things require a compressor and how much of an industrialized country's national grid goes towards running the. The smallest unit we made was a 1hp oil-free scroll unit, the largest a 5 kilowatt multistage centrifugal compressor.  We also made rail-car compressors for passenger rail and vane vacuum pumps for trucks.  Anything over 50hp had a fancy three-phase permanent magnet motor and may have had an VCD controller.  VCD reduced a lot of electrical consumption within a narrow band, as you say.  When you looked at the efficiency curve of the screw or turbine and added that to the efficiency curve of the motor itself, the efficient operating band was pretty narrow.  The smaller electrical motors could run for years with no maintenance at all in horrible conditions. The bigger ones needed quite a bit more, especially if environmental conditions were say, hot with lots of SOx, NOx or particulate.  The shortest lifespan were the anti-explosive coal mining units that went down in the pits. They came back looking like they'd been in a war. Anything portable was diesel. 

Anything that goes down a mine comes up looking hideous. I used to photograph the potash mines in Saskatchewan, everything stayed down there for its lifespan except the miners (usually). Take a truck to the surface and it was frozen solid from corrosion in a day and would never run again. The cameras would need a serious cleaning the instant we got them out. 

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54 minutes ago, Zonker said:

The Cd of something like a laminar flow sort of thing like my sketch is like 0.05. A cylinder + a hemisphere is probably 0.2 or so.

Say diameter = 75mm (3"). 

Draggy cylinder at 6 knots?

F = 1/2 rho Cd A V^2 = 0.5 (1025 kg/m3) 0.2 (pi x .075^2 / 4) * 3 m/s = 1.3 kg so about 1 kg more than a streamlined body.

Now 1 kg doesn't sound like much - but that's about 1% of the drag of a 30' boat at 6 knots. Why give that up?

I'd be shocked if there was that much difference. The motor has a faring aft so may well be less than 0.2 and my WAG on your sketch is that it's closer to .1. Depends on the boat but 6 knots seems quite high even free stream. 

wt-diag.jpg

member-freebeard-albums-aero-technical-p

 

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I am pleasantly surprised that my WAG of 0.20 for the cylinder + hemisphere was about correct, as was the the tapered body. I didn't look them up!

OK I agree about the tapered prop hub. But even the one they use is just a frustrum. It's like you gave your kid a CAD program.

Yeah, it's not quite towing a bucket. But why wouldn't you even look at an outboard motor lower hub unit. Their nose fairing ain't no hemisphere.

 

 

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9 hours ago, Autonomous said:

I'm assuming a better shape would require an extra piece and the associated waterproof join. Dunno.

You could put a non-waterproof streamlined fairing or shroud around it. There could be a couple of small drain holes to let water fill up when immersed and drain out when out of the water.

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That sounds economical and good but my concern would be the flora and fauna that could set up house keeping inside. A temporary cover could work but would be bothersome and not idiot proof. Does the motor need water flow on it's immediate case for cooling?

Zonker's illustration above looks good from a hydrodynamic point of view too. My concern with that approach would be the heavier prop shaft and associated structure I suspect would be required.

Both would provide less drag even accounting for the increased frontal area. As stated, the complications concern me. Sometimes KISS is best.

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Take the guts out, mold up a new fancy glass pod with a little area rule dimple on the top and flatten it out a bit so the flow with leeway has a more elliptical path and paint it orange. You could save on fasteners, weight and o-rings and maybe make things a bit cozier by molding the motor in during the layup. Just saw open the pod if you need to fiddle with the motor and glue back when done. Pretty obvious when you think about it, really.

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Like a BMW Auto transmission "sealed for life" 

Ever see the inside of an electric drill? The exterior is whatever crazy shape the designer feels will appeal to the consumer, the inside has a recess for the cylindrical electric motor. You cast or mold the bits that hold the motor in place at the same time as the cover. Zero added cost of machining. 

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12 minutes ago, Zonker said:

Ever see the inside of an electric drill?

I have. It's been a while since I saw one with a metal housing and I haven't inspected any that were water tight.

My WAG is that both the aft plate and the pod have machined surfaces. I haven't seen a diagram but I presume the plate seals to the pod with o rings and that there's a lip seal or two on the prop shaft. The simpler shapes might help with work holding, take a bit less metal initially and waste a bit less metal when machined.

For sure the pod looks like an early development. I suspect they had a long list of bits to make and went for easy and quick and moved on to the next bit. I'm not sure that's "lazy" but yes, it looks like there's plenty of development space left to explore.

 

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15 hours ago, weightless said:

Take the guts out, mold up a new fancy glass pod with a little area rule dimple on the top and flatten it out a bit so the flow with leeway has a more elliptical path and paint it orange. You could save on fasteners, weight and o-rings and maybe make things a bit cozier by molding the motor in during the layup. Just saw open the pod if you need to fiddle with the motor and glue back when done. Pretty obvious when you think about it, really.

The motor can eventually be redesigned to be longer and skinnier, too, reducing cross section, if that helps (I think it would help). Well pump motors, for example, have to fit in the well bore. They are very skinny and operate immersed. They are not BLDC motors but there is no reason a BLDC motor cannot be made long and skinny, too.

 

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21 hours ago, Ishmael said:

Anything that goes down a mine comes up looking hideous. I used to photograph the potash mines in Saskatchewan, everything stayed down there for its lifespan except the miners (usually). Take a truck to the surface and it was frozen solid from corrosion in a day and would never run again. The cameras would need a serious cleaning the instant we got them out. 

Worst work environment I've seen.  

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47 minutes ago, Elegua said:

Worst work environment I've seen.  

Long ride down, too. 1 km deep in the shallow places. They hated to see us coming, they would have to shut the mine down for a day before we could shoot, because the dust was so thick.

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On 11/26/2021 at 9:44 PM, Zonker said:

Why do these lazy engineers imagine a cylinder with a hemispherical nose cone is the best shape to enclose their electric motors??

image.png.48298287a17a466d7f721868757e9185.png

It should have a shape like this:

image.thumb.png.f057f20f640ff1be124121413b0a1707.png

Or look at the ballast bulbs on any IMOCA yacht built in the past few decades (just without the vertical squash to lower VCG on a keel bulb)

 

I suspect this is what happens when you ask an engineer with a mechanical background to draw the housing!

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On 11/27/2021 at 12:23 AM, Bull City said:

@zloitapok I did not know it was available. Thanks for posting it. Are you thinking about a pod drive?

Yes, I building a boat by this project

http://amariner.net/sailing_yacht_design_Tempro_30.html

 

02_long_aft.thumb.jpg.b5a6b1b9543cad65bdeb12af519f4559.jpg

33 ft LOA, 3500 kg total displacement.

Will install ePropulasion 6 kW POD, 48v 600Ah LiFePO4 battery, 800W solar.

I already own a smaller EP sailboat for 5 years, with electric motor based on Toyota Prius hybrid and 60v 230Ah LiNMC battery. Made many wonderful trips, very like EP.

Also, I made multiple ground-based electric projects and converted 3 other boats to EP.

So far I like ePropulsion.

Hope your boat EP will work well )

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On 11/27/2021 at 7:20 AM, weightless said:

Take the guts out, mold up a new fancy glass pod with a little area rule dimple on the top and flatten it out a bit so the flow with leeway has a more elliptical path and paint it orange. You could save on fasteners, weight and o-rings and maybe make things a bit cozier by molding the motor in during the layup. Just saw open the pod if you need to fiddle with the motor and glue back when done. Pretty obvious when you think about it, really.

After that that wee tweak, what will you do in the afternoon? ;) 

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I got a good data point today, during flat, glassy conditions: 3.7 knots, 560 Watts. The battery has 4096 Wh. At this point, the battery was prolly 95%, and the display showed I had 26 nautical miles of range.

I did the following calculation:

26 NM ÷ 3.7 knots = 7.0 hours X 560 Watts = 3935 Wh

When I had my Honda 2 HP, it had a 1 quart internal tank. I used to carry a 1 gallon tank sometimes. Honda says the new 2 HP (with .29 gallon  tank) will run 1 hour at WOT. So, I figure I would get about 4 hours of push at 2 to 3 HP. Although that would be less than 26 NM range, it would be a hell of a lot less weight in "fuel" since the LiFePO battery, at almost 100 lbs. is a lot more than 1 gallon of gas. Even so, I am quite happy with the electric set-up, and I hated the fucking gas motor with a passion. But that's for another thread. :D

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13 hours ago, Bull City said:

I hated the fucking gas motor with a passion. But that's for another thread. 

Glad to see that I am not the only one hating the noisy things with a passion.

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1 hour ago, Panoramix said:
14 hours ago, Bull City said:

I hated the fucking gas motor with a passion. But that's for another thread. 

Glad to see that I am not the only one hating the noisy things with a passion.

Me too!  Stinkpots are Satan's way of ruining your time afloat.  Noisy, smelly, vibratey, spendy, attention-seeking, polluting and climate-wrecking.

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23 hours ago, Bull City said:

and I hated the fucking gas motor with a passion.

lol. I still suffer from PTSD because the outboard on my little 1/4 tonner - and will sail into and out of my slip to this day just to avoid using an engine (even though the knowledgeable souls on this forum claim diesels can be depended upon). However, Steinbeck surely put it best:

"Our Hansen Sea-Cow was not only a living thing but a mean, irritable, contemptible, vengeful, mischievous, hateful living thing. In the six weeks of our association we observed it, at first mechanically and then, as its living reactions became more and more apparent, psychologically. And we determined one thing to our satisfaction. When and if these ghoulish little motors learn to reproduce themselves the human species is doomed. 

PS: plenty more outboard bashing where this came from (see bullet points for a laugh):

PPS: to climb further out on this limb: people are perhaps attracted to electric motors because of hate for outboards? the stinky, messy, heavy turdbox that can be depended upon to let you down when you need it most?

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35 minutes ago, floater said:

PPS: to climb further out on this limb: people are perhaps attracted to electric motors because of hate for outboards? the stinky, messy, heavy turdbox that can be depended upon to let you down when you need it most?

That's me.  An electric motor may not actually be more reliable, but at least it won't be a stinky, messy, heavy turdbox, and it won't be noisy and won't make everything shake.

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2 hours ago, TwoLegged said:

That's me.  An electric motor may not actually be more reliable, but at least it won't be a stinky, messy, heavy turdbox, and it won't be noisy and won't make everything shake.

We could go back to steam engines :P

African Queen boat in Key Largo is thrilling for Bogart fans

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All that aside; the endless pulling of the recoil start (I see that a lot), the smoke, the noise, the gasoline sloshing, watching the act of two - or worse - one person wrestling to get an OB on and off the stern of a sailboat is stessful - even to watch. 

The electric OB are so light, some breakdown. You can set them on the dock, deck, step in your dinghy, take the light easily one handed parts, and install them. 

This guy was simply plucking  his Torqueedo off the aft deck and slapping it on. 

What is harder (for me) to understand is why some people don't row, even with a nicely designed rowing dinghy. Water was flat calm, 1/3 mile to cover.

Is it a male thing, like walking a very small dog? :)

Matinicus.thumb.jpg.2fb613c5fc946176a61667cf6c23d353.jpg

 

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57 minutes ago, Kris Cringle said:

All that aside; the endless pulling of the recoil start (I see that a lot), the smoke, the noise, the gasoline sloshing, watching the act of two - or worse - one person wrestling to get an OB on and off the stern of a sailboat is stessful - even to watch. 

The electric OB are so light, some breakdown. You can set them on the dock, deck, step in your dinghy, take the light easily one handed parts, and install them. 

This guy was simply plucking  his Torqueedo off the aft deck and slapping it on. 

What is harder (for me) to understand is why some people don't row, even with a nicely designed rowing dinghy. Water was flat calm, 1/3 mile to cover.

Is it a male thing, like walking a very small dog? :)

Matinicus.thumb.jpg.2fb613c5fc946176a61667cf6c23d353.jpg

 

I can't see why in a place like Maine you wouldn't row. No anchorages are far away and conditions are generally benign. 

I spent some time as a youth sitting in a rug shop that looked across at a UN refugee center. The hassle that people would go through to avoid a little physical labor was amazing to me. I've never forgotten that. 

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The E craze may not help our national obesity problem. More and more we're seeing bike tours, like Vermont Bike, coming through town.

Don't get me wrong, biking in any form is great. But I sometimes rub my eyes when I see a 'tour' group flying by - uphill - and many of the riders are portly. Oh well, I'd probably opt for the E-bike too. :)

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17 minutes ago, Kris Cringle said:

The E craze may not help our national obesity problem. More and more we're seeing bike tours, like Vermont Bike, coming through town.

Don't get me wrong, biking in any form is great. But I sometimes rub my eyes when I see a 'tour' group flying by - uphill - and many of the riders are portly. Oh well, I'd probably opt for the E-bike too. :)

But you know they paid a lot of money for those lightweight Ti pedals....:D

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10 hours ago, Kris Cringle said:

All that aside; the endless pulling of the recoil start (I see that a lot), the smoke, the noise, the gasoline sloshing, watching the act of two - or worse - one person wrestling to get an OB on and off the stern of a sailboat is stessful - even to watch. 

My Honda 2 HP developed a habit of somehow snatching the starter cord handle out of my right hand and it would smash into my left hand which was on the motor housing. God that hurt. I would curse and swear. It's a wonder the evil little bastard did not end up at the bottom of the lake.

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