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Old 08-02-2015, 20:38   #46
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Re: Using electric motors instead of Diesel on your cat

Hi 44'C,

I appreciate you are offering your opinion on the Torqeedo's, based upon your contact with some users, with a view to helping a fellow sailor and CF member.

But my job is to assess your feedback and determine if it is a valid concern, or not. I have found out the volume of motors sold vs the repair incidence rate, and it is very reassuring. I also like the dedication Torqeedo are showing in innovation and R&D. They are clearly a market leader.

But since I'm not considering the Cruise 4 for my application, but the industrial 30kW inboard Deep Blue motors, what really interests me is how Torqeedo support their products if something does need attention.

I have to say that from what I have learned,including from my talk with Neil recently, their products merit more confidence than what you portray in your posts.

Each to his own opinion, I guess. We'll just have to agree to disagree, on this one.

In my own case, time will tell the tale, if we go ahead with the Torqeedo EP solution.
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Old 09-02-2015, 02:04   #47
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Re: Using electric motors instead of Diesel on your cat

I'd say what has been established here is that Neil's relationship with Torqueedo is not that of the normal paying customer.


The fact that he claims to be so happy with them, when hundreds of thousands of dollars worth of boat has been sidelined FOR MONTHS, due to hitting some JELLYFISH, (FFS!) proves that.


So I'd suggest you bear that in mind when weighing his "opinion".
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Old 09-02-2015, 07:12   #48
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Re: Using electric motors instead of Diesel on your cat

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Also, electric motor output 7hp is equivalent to most 15hp diesel because the system is designed more for efficiency with a larger slower turning propeller. The electric system is much more efficient over a wide range of power output.

watts needed to push my boat (full keel 8,000 lbs)
2 knots - 150w
3 knots - 300w
4 knots - 600w
I think you are mixing up electric motors used in cars with electric motors used in boats.

There are two main design criteria for engine HP are:
- Peak acceleration
- Peak cruising speed

Since acceleration typically starts with an IC engine at low RPM, it is only putting out a fraction of it's max torque. By the time it gets up to cruising speed, the engine is at max torque (or reasonably close).

In a car, that means acceleration controls and you could cut the HP of the average engine by half or more and it could still cruise at highway speeds.

With a boat, in particular a displacement boat, there is no where near the acceleratation expectatons. Also, due to the slow reactions expected, the engine has time to spool up to a speed that puts out decent torque. So while that instant torque of an electric is nice when docking it's not critical and when trying to get her up to cruising speed, it offers no "effective" HP gains. 7HP in a diesel running at peak output is the same as 7HP in an electric at peak output.

So by your wattage estimates, a cheap trolling motor will give you 3kts?

It's still about energy storage and generation. If you could put 20gallons worth of electric in the same size as a 20gal tank within 20% of the cost of a diesel setup, gas and diesel engines would be gone on new boats within 2-3yrs as an option.
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Old 09-02-2015, 13:55   #49
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Re: Using electric motors instead of Diesel on your cat

Valhalla360,

The point of electric and torque is that a larger & higher pitched prop can be used with EP at lower rpm to achieve cruising speeds. This is more efficient ( maximum thrust vs minimum slip) and uses less energy from the battery than trying to spin a smaller prop at higher rpm.

If an equivalent HP diesel tried to turn the same large prop at low revs, the diesel would stall or glaze the cylinders.

To get a meaningful comparison between diesel vs EP, you have to shift your expectation away from maximum speed, because EP should be optimised for cruising speed range where it is in its efficiency sweet spot, ie minimum energy used for maximum thrust produced.

Does that make sense?


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Old 09-02-2015, 14:08   #50
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Re: Using electric motors instead of Diesel on your cat

I guess my objection to all this is - what are you trying to achieve?


If it's reduced fuel consumption, there is IMO a better and proven way of doing it.


Build the boat as light as possible, use the lightest motors available for a given output - ie outboard motors - which also have the benefit of you not having to drag propellers around all the time - and build a boat that SAILS efficiently.


There is nothing more fuel efficient than sailing.
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Old 09-02-2015, 14:32   #51
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Re: Using electric motors instead of Diesel on your cat

For me, it is having a simpler more reliable system, that doesn't generate stink, vibration, and noise. And there is also the challenge of building for the future, not looking to the past.
Sailing is great if there is wind and you pay for the sails, the mast, the rigging, and maintain them, and adjust them, install and remove them,
and zig-zag where you are going, and then have to motor half the time anyway. I am always fascinated that the sailors recommending sailing half way across the pacific and then back again just to go north from mx to sf,
because that is how efficient sailing is.

Stick with your sails and outboards and diesels.
just don't tell everyone else why they should want the same thing as you,
and can't possibly do anything else, even when others demonstrate it is possible.

I know a sailor so cheap..he has a diesel engine.
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Old 09-02-2015, 23:52   #52
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Re: Using electric motors instead of Diesel on your cat

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Valhalla360,

The point of electric and torque is that a larger & higher pitched prop can be used with EP at lower rpm to achieve cruising speeds. This is more efficient ( maximum thrust vs minimum slip) and uses less energy from the battery than trying to spin a smaller prop at higher rpm.

If an equivalent HP diesel tried to turn the same large prop at low revs, the diesel would stall or glaze the cylinders.

To get a meaningful comparison between diesel vs EP, you have to shift your expectation away from maximum speed, because EP should be optimised for cruising speed range where it is in its efficiency sweet spot, ie minimum energy used for maximum thrust produced.

Does that make sense?


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If its all about turning a big prop, just add a deeper reduction gear on the transmission and you achieve the same thing.

Sorry but you aren't getting double the thrust for the same HP just because you turn a slightly larger prop.
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Old 10-02-2015, 01:18   #53
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Re: Using electric motors instead of Diesel on your cat

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If its all about turning a big prop, just add a deeper reduction gear on the transmission and you achieve the same thing.

Sorry but you aren't getting double the thrust for the same HP just because you turn a slightly larger prop.
Really??? Well, why doesn't everyone just do that then? You should call up Yanmar and suggest they re-work their saildrive. There are good reasons they engineer it the way they do. Three factors; torque, rpm & thrust.

Have a look at the tables from the prop manufacturers and see the thrust difference between a 17.5 x 9 and a 20 x 14 prop. at say 1,500 rpm.
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Old 10-02-2015, 01:38   #54
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Re: Using electric motors instead of Diesel on your cat

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Really??? Well, why doesn't everyone just do that then? You should call up Yanmar and suggest they re-work their saildrive. There are good reasons they engineer it the way they do. Three factors; torque, rpm & thrust.

Have a look at the tables from the prop manufacturers and see the thrust difference between a 17.5 x 9 and a 20 x 14 prop. at say 1,500 rpm.
Yes, really.

The reason they don't do it is because the efficency gains are minimal when dealing with reasonably sized props for a cruising sailboat. You aren't effectively doubling the HP when running at cruise speeds. It defies the definition of HP. HP is work done per a period of time. If they both have the same continous rated HP and are both operating at optimal speeds, they get the same amount of work done minus a bit for efficency losses. Those efficency losses are not cut in half with an electric motor.

I have no doubt a much bigger prop with a high pitch turning at the same speed will move the boat faster. The problem is at cruising speed, you need more HP to maintain that speed (diesel or electric). As I said, docking that instant torque is nice (but not neccessary) at cruise speed, there is no advantage.

If the efficencies were really that good, we would be seeing hybrid style boats having taken over the market 15-20yrs ago with a diesel genset powering an electric motor to take advantage of the gains from a larger prop, while providing near unlimited electicity for air/con, stove, fride and other household loads. I'm sure the Yanmar enginers are fully aware of the advantages of bigger high pitch props and realize like I do that they do not double the effective HP simply by using an electric motor while at cruise speed.

Electic motors are great and if we could supply the power to run them in a reasonable package, they would quickly push diesels out of the market but until that happens, diesel will dominate.
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Old 10-02-2015, 14:22   #55
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Re: Using electric motors instead of Diesel on your cat

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Yes, really.

The reason they don't do it is because the efficency gains are minimal when dealing with reasonably sized props for a cruising sailboat. You aren't effectively doubling the HP when running at cruise speeds. It defies the definition of HP. HP is work done per a period of time. If they both have the same continous rated HP and are both operating at optimal speeds, they get the same amount of work done minus a bit for efficency losses. Those efficency losses are not cut in half with an electric motor.

I have no doubt a much bigger prop with a high pitch turning at the same speed will move the boat faster. The problem is at cruising speed, you need more HP to maintain that speed (diesel or electric). As I said, docking that instant torque is nice (but not neccessary) at cruise speed, there is no advantage.

If the efficencies were really that good, we would be seeing hybrid style boats having taken over the market 15-20yrs ago with a diesel genset powering an electric motor to take advantage of the gains from a larger prop, while providing near unlimited electicity for air/con, stove, fride and other household loads. I'm sure the Yanmar enginers are fully aware of the advantages of bigger high pitch props and realize like I do that they do not double the effective HP simply by using an electric motor while at cruise speed.

Electic motors are great and if we could supply the power to run them in a reasonable package, they would quickly push diesels out of the market but until that happens, diesel will dominate.
The original point Boat Alexandra was making is that EP follows the same principles as is well understood in other fields of mechanics, which is that for a given work requirement, an electric motor of approximately half the horsepower is required compared to an ICE, because of the different torque characteristics of electric motors. Is that is disagreement?

I added to that thought with the explanation that the way to go for EP was to get the prop optimized for cruising speed using less energy from the stored battery reserve by going up in prop diameter and pitch. EP does not have to be concerned about max revs like a diesel does to avoid overloading it. You will notice (I believe) that Yanmar warranty is conditional on using a prop that will allow their specified max revs. Right? So the idea of putting on a bigger prop on the diesel doesn't really come into it, does it?

So I'm not sure what you are arguing. Could you state what it is you disagree with in the above more clearly?
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Old 10-02-2015, 15:24   #56
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Re: Using electric motors instead of Diesel on your cat

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The original point Boat Alexandra was making is that EP follows the same principles as is well understood in other fields of mechanics, which is that for a given work requirement, an electric motor of approximately half the horsepower is required compared to an ICE, because of the different torque characteristics of electric motors. Is that is disagreement?

I added to that thought with the explanation that the way to go for EP was to get the prop optimized for cruising speed using less energy from the stored battery reserve by going up in prop diameter and pitch. EP does not have to be concerned about max revs like a diesel does to avoid overloading it. You will notice (I believe) that Yanmar warranty is conditional on using a prop that will allow their specified max revs. Right? So the idea of putting on a bigger prop on the diesel doesn't really come into it, does it?

So I'm not sure what you are arguing. Could you state what it is you disagree with in the above more clearly?
You have a serious misunderstanding of what torque and HP are. I'll try to address your comments:
- There is no well understood principal that an electric motor only needs to be 1/2 the HP of an ICE engine to produce the same HP. You appear to be confusing the acceleration characteristics of electric motors in cars. An ICE at idle has far less than it's rated HP/torque. An electric motor has full torque from zero rpm. So when accelerating a car, there is a noticeable advantage for an electric motor of the same HP since comes off the line with peak torque available and the ICE needs to spool up creating an acceleration lag. Also since the electric motor can put out peak torque at all speeds, it needs fewer gears and acceleration robbing shifts compared to a diesel. If you try to make the diesel accelerate too long in one gear the RPM gets out of the power band and there is a significant drop in available torque. With a displacement cruising boat, the engine and prop are typically sized to take advantage of peak HP/torque while at cruising speeds. Acceleration is of almost no interest to most displacement boat owners.
- An electric motor of the same HP does not allow for larger diameter/pitch...assuming you want to maintain the same RPM (at the prop). I believe you are confusing engine RPM with prop RPM. While it can turn such a prop as you describe, it will turn it at a lower RPM resulting in no significant difference in thrust. By using a reduction gear, you can achieve the same torque multiplication to turn a larger prop with a diesel.
- Yes, Yanmar does recommend that the engine should be able to reach peak RPM. If you want to run a higher pitch prop, you gear it down so the engine achieves the same peak RPM. Of course just like with the electric motor, the prop will be turning at a lower RPM to achieve the same speed.

Basically what is false (not a disagreement) is that for cruising speed when both a diesel or electric motor is running at ideal speeds, HP is HP. The only place there are differences is when you get the diesel away from it's power band which doesn't happen with a properly set up diesel powered displacement vessel running at cruising speed.
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Old 10-02-2015, 20:18   #57
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Re: Using electric motors instead of Diesel on your cat

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You have a serious misunderstanding of what torque and HP are. I'll try to address your comments:
- There is no well understood principal that an electric motor only needs to be 1/2 the HP of an ICE engine to produce the same HP. You appear to be confusing the acceleration characteristics of electric motors in cars. An ICE at idle has far less than it's rated HP/torque. An electric motor has full torque from zero rpm. So when accelerating a car, there is a noticeable advantage for an electric motor of the same HP since comes off the line with peak torque available and the ICE needs to spool up creating an acceleration lag. Also since the electric motor can put out peak torque at all speeds, it needs fewer gears and acceleration robbing shifts compared to a diesel. If you try to make the diesel accelerate too long in one gear the RPM gets out of the power band and there is a significant drop in available torque. With a displacement cruising boat, the engine and prop are typically sized to take advantage of peak HP/torque while at cruising speeds. Acceleration is of almost no interest to most displacement boat owners.
- An electric motor of the same HP does not allow for larger diameter/pitch...assuming you want to maintain the same RPM (at the prop). I believe you are confusing engine RPM with prop RPM. While it can turn such a prop as you describe, it will turn it at a lower RPM resulting in no significant difference in thrust. By using a reduction gear, you can achieve the same torque multiplication to turn a larger prop with a diesel.
- Yes, Yanmar does recommend that the engine should be able to reach peak RPM. If you want to run a higher pitch prop, you gear it down so the engine achieves the same peak RPM. Of course just like with the electric motor, the prop will be turning at a lower RPM to achieve the same speed.

Basically what is false (not a disagreement) is that for cruising speed when both a diesel or electric motor is running at ideal speeds, HP is HP. The only place there are differences is when you get the diesel away from it's power band which doesn't happen with a properly set up diesel powered displacement vessel running at cruising speed.


PE 100-TB 100 Robin/Subaru 4-stroke petrol engine 4.2 42 74 34 42

PE 100-TW 100 Alternating current motor 230V,50Hz 2.2 44 66 35 42

Here is an example of what I'm talking about, the specs for Bauer Poseidon air compressors, one petrol engine driven, the other single phase electric expressed in Kw. To do the same work the ICE is a 4.2 kW petrol motor while the electric is 2.2 kW electric motor, approximately half the horsepower.

You also said above There is no well understood principal that an electric motor only needs to be 1/2 the HP of an ICE engine to produce the same HP.
I never said that at all.That is absurd. As you have rightly said HP is HP. What I said was to do the same work, often you can use a smaller ( in kW or HP ) electric vs ICE.

You also contradict yourself when you say, Basically what is false is that for cruising speed when both a diesel or electric motor is running at ideal speeds, HP is HP.
If that statement is false, then HP is NOT HP. Very confusing, and again, I'm not sure what you are saying.

And anyway, the plain fact is that in EP conversion projects, they often replace an x HP diesel with an .5x HP electric and get equivalent cruising speed performance, assuming the prop has been chosen appropriately for the electric motor.

Let's leave it at that, shall we? You don't think EP can be viable yet (still not sure why) and I do. I am embarking on an EP project ( because I STILL have not heard any showstoppers on this forum) and putting my money where my mouth is, and I'll let you know how it goes with a full report after giving it a thrashing when the boat is launched.

Then either I will be eating crow, or you will. The difference is I will have risked something while you can continue telling people that something can't, won't or shouldn't work, without giving good explanation for your opinion.

Don't get me wrong, I would LOVE for someone (before I spend $$$) to point out clearly, and succinctly, why EP won't work on a bluewater cruising boat with say 2kW solar and a generator to charge batteries when necessary. I have asked a couple of times in the past if anyone could offer showstoppers. But give me substantiated data, not unsubstantiated opinion.

You know what they say about opinions and a certain body orifice?
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Old 11-02-2015, 01:48   #58
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Re: Using electric motors instead of Diesel on your cat

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Then either I will be eating crow, or you will. The difference is I will have
risked something while you can continue telling people that something can't,
won't or shouldn't work, without giving good explanation for your opinion.
The trouble is that you will have risked more than money. My life has been all about innovation and it has allowed me to afford a nice boat and much more besides. No problems when you are only risking money.

However, when you are risking the lives of your loved ones, or even the possibility that others will not sail with you after a dangerous experience, either of these being a real possibility if underpowered, then innovation needs to be balanced with extreme caution having a full understanding of the possible consequences.

One of the key messages I have learned from actually owning and sailing a boat is that what works on a spreadsheet will not necessarily translate to the real world. In fact it rarely does.
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Old 11-02-2015, 04:26   #59
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Re: Using electric motors instead of Diesel on your cat

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The trouble is that you will have risked more than money. My life has been all about innovation and it has allowed me to afford a nice boat and much more besides. No problems when you are only risking money.

However, when you are risking the lives of your loved ones, or even the possibility that others will not sail with you after a dangerous experience, either of these being a real possibility if underpowered, then innovation needs to be balanced with extreme caution having a full understanding of the possible consequences.

One of the key messages I have learned from actually owning and sailing a boat is that what works on a spreadsheet will not necessarily translate to the real world. In fact it rarely does.
Yes, these are good points to raise. Safety is always a primary concern.
But Chris, you know the EP I have been researching, because we've spoken about it. So do you really think having 2 x 40HP (30kW) motors is being underpowered on a fairly light 46' cat? Is that really your concern?

Somewhere there is a thread where those with diesels described serious problems Ie engines conked out) with diesel fuel blockages, blocked filters, fuel sludge, getting a load of bad fuel etc and something like 40% of respondents reported such issues. Should I worry about putting my family at risk crossing a bar with diesels and having the engines fail at the worst possible time? Or should I practice good maintenance & seamanship and do everything I can to prepare my boat to avoid a known possible issue?

Again, what are the specific concerns wrt electric propulsion systems?

Just as a thought exercise, lets examine the possible showstoppers, and see if they've been addressed in my research:
1. Underpowered? EP come in a wide range of HP, so choose what you and the boat designer are comfortable with. Plan for the worst case scenarios such as being trapped by a high wind lee shore, motoring against strong tidal sets, coral passes on the ebb or flow, etc. Work out the wind and wave forces on your boat under severe scenarios. Know what the thrust will be with the EP given the correctly sized and pitched prop.
2. Reliability? Well the MTBF of electric motors is ridiculously high, but what about all the other bits 'n pieces?
Choose an EP system that has quality in every single component. EVERY one!
Choose an EP system that has fault tolerant engineering and fault monitoring and diagnostics built in. You do not want to be poking around your boat at night with a torch (flashlight for our US & Canuk friends) trying to diagnose a faulty switch or connector.
Choose an EP system that is IP67 waterproofed and guaranteed to work if there is water around. Last thing you need is a hull breach/through hull failure and your bilge pumps have no power.
Choose an EP system that bothers to protect the Lithium battery from shock loads in order to prevent battery failure.
Choose an EP system that has quick connectors to replace key components quickly and easily in case of component failure.
3. Vendor support? Avoid EP systems that have been cobbled together from various components from various vendors because, sure as Murphy is an Irishman, the finger pointing will happen if the cause of a fault needs to be diagnosed. If you are an electrical engineer and are totally confident in your ability to diagnose & fix (safely!!!) high voltage EP systems, you can disregard this. Otherwise choose an EP system that the vendor guarantees ALL components and has a workable plan to diagnose and replace components in far flung locations. At least one vendor I am aware of can diagnose and change the system remotely via Internet link.
4. Enough energy to feed the motors? Do your system planning wrt to adequate solar and generator battery charging, and regeneration if possible. It's not rocket science. You need to be able to motor through the calms for several days. Otherwise you can bake and wait
5. Too expensive? Yes it is more than an equivalent HP diesel set up, but there is a TCO payback period that will be feasible for us and what we anticipate our motoring hours per year will be. After the TCO crossover, your diesel will cost you everytime you fill up, if you can get the diesel fuel in the future, depending on location. And then there is maintenance costs & time....

Maybe I've left something out, if so, let me know.
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Old 11-02-2015, 05:12   #60
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Re: Using electric motors instead of Diesel on your cat

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Originally Posted by BigBeakie View Post
PE 100-TB 100 Robin/Subaru 4-stroke petrol engine 4.2 42 74 34 42

PE 100-TW 100 Alternating current motor 230V,50Hz 2.2 44 66 35 42

Here is an example of what I'm talking about, the specs for Bauer Poseidon air compressors, one petrol engine driven, the other single phase electric expressed in Kw. To do the same work the ICE is a 4.2 kW petrol motor while the electric is 2.2 kW electric motor, approximately half the horsepower.

You also said above There is no well understood principal that an electric motor only needs to be 1/2 the HP of an ICE engine to produce the same HP.
I never said that at all.That is absurd. As you have rightly said HP is HP. What I said was to do the same work, often you can use a smaller ( in kW or HP ) electric vs ICE.

You also contradict yourself when you say, Basically what is false is that for cruising speed when both a diesel or electric motor is running at ideal speeds, HP is HP.
If that statement is false, then HP is NOT HP. Very confusing, and again, I'm not sure what you are saying.

And anyway, the plain fact is that in EP conversion projects, they often replace an x HP diesel with an .5x HP electric and get equivalent cruising speed performance, assuming the prop has been chosen appropriately for the electric motor.

Let's leave it at that, shall we? You don't think EP can be viable yet (still not sure why) and I do. I am embarking on an EP project ( because I STILL have not heard any showstoppers on this forum) and putting my money where my mouth is, and I'll let you know how it goes with a full report after giving it a thrashing when the boat is launched.

Then either I will be eating crow, or you will. The difference is I will have risked something while you can continue telling people that something can't, won't or shouldn't work, without giving good explanation for your opinion.

Don't get me wrong, I would LOVE for someone (before I spend $$$) to point out clearly, and succinctly, why EP won't work on a bluewater cruising boat with say 2kW solar and a generator to charge batteries when necessary. I have asked a couple of times in the past if anyone could offer showstoppers. But give me substantiated data, not unsubstantiated opinion.

You know what they say about opinions and a certain body orifice?
So explain why manufacturers aren't outfitting all thier new boats with electric motors. It's a well proven technology and easily adapted. A manufactuer that could put in a small diesel generator to power a 10hp electric motor could put the boat out for the same or less price while giving the performance of a bigger 20hp diesel while getting the benefits of a whole house generator capable of running just about any household load. Your ealier Yanmar comment suggests thier engineers obviously know this and would have taken advantage of it but they know better.

I'm not familair with the compressors you failed to provide details on. My assumption would be there is something else different between the models.

Quote: "What I said was to do the same work, often you can use a smaller ( in kW or HP ) electric vs ICE."


Since HP is the rate at which an engine does work, a smaller HP engine must do less work or it will take more time to do the same work (ie: speed is less). It's the definition of HP.

The only reason I'm engaging you at this point is so some poor shmuck isn't miss informed. I never said you couldn't make an electric powered boat. You just can't do it with the same performance and price. There are trade offs and they are big.
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