Tug of War - Electric vs Diesel

[donradcliffe]

Originally Posted by valhalla360

So conveniently, they were "aligning" the boats and it just happened to create a significant momentum advantage for the system they are pushing.

As far as the other example, you have a boat that appears to be limited to 5.5kts when comparable diesel boats should be able to easily cruise at 8-9kts for extended periods of time. Of course, you can drop back to 5.5kts and get similar efficiency with a diesel powertrain.

I have no axe to grind either way, but the reason one cat was able to tow the other one backwards had a lot more to do with the propellers than momentum. If you put larger diameter props on the diesel cat and optimize them for lower speeds, it would tow the electric cat backwards.

[Scout 30]

Originally Posted by donradcliffe

I have no axe to grind either way, but the reason one cat was able to tow the other one backwards had a lot more to do with the propellers than momentum. If you put larger diameter props on the diesel cat and optimize them for lower speeds, it would tow the electric cat backwards.

I'm not sure about that. Both boats should already be propped to achieve max rpms at WOT. However, it would be interesting to know how the 2 boats are propped.

[a64pilot]

Even if they were propped to reach max RPM, an 18" prop will usually out pull say a 12" prop, or even say a three blade 18" compared to a two blade 12".
Lots of way to game this and get the result you want

[Scout 30]

If they wanted to skew the result they could just give the diesels less throttle. Who really cares anyway. We all know some tugs use electric motors. The real question is can electric be a viable alternative to diesel & I think it can but only if you include a generator.

[44'cruisingcat]

Originally Posted by Scout 30

If they wanted to skew the result they could just give the diesels less throttle. Who really cares anyway. We all know some tugs use electric motors. The real question is can electric be a viable alternative to diesel & I think it can but only if you include a generator.

In which case there's little point doing it.

[44'cruisingcat]

Originally Posted by BigBeakie

OK, back to the OP for a second re the tug of war test. FWIW I can confirm after speaking with those involved that the electric was used to position the boats, to align them at the beginning and that accounted for the boats moving slightly left at the beginning of the video, and then both boats went to full throttle at same time. So the fact is the electric at approx. half the HP pulled a diesel ICE boat at twice the HP.

A real cruising example of a serial diesel hybrid electric propulsion cat that has been using electric without incident for about a year coastal cruising off east coast Australia is as follows:
44 foot cat with 2x 4kW electric Torqeedo, 10kW LiFePO4 bank and 5kW Eniquest DC genset.

I gotta ask, what's not to like?

What's not to like? Can't speak for you, but I'd be pretty cheesed off if I broke a gearbox by hitting a jellyfish.

[BigBeakie]

Originally Posted by 44'cruisingcat

In which case there's little point doing it.

Hi 44'

There may not be a point ideologically if by that you mean using a diesel genset for extended motoring invalidates the whole concept of EP being a fossil fuel free technology, but I don't think you need to throw the baby out with the bath water. Put another way, let's not make perfect the enemy of the good.

It is completely obvious that if you want to, or need to, motor for long periods of time continuously with electric motors, you will need a generator. And actually that is not strictly speaking true either, because you could have lots of solar and motor at a few knots directly off solar output if becalmed and it would be better than just sitting there as they did in the old days.

But depending on where you are cruising, being becalmed might be a fairly infrequent event, in which case you would hardly ever use the genset for recharging and you'd use EP most of the time off battery storage from solar and regeneration. In this case, EP has lots of benefits.

So if we want to have a serious discussion about EP and whether it is viable for cruisers or not, fine. I'm up for that and think it could be quite valuable.
Yes you need adequate power for adverse conditions. Yes you will need a genset to recharge batteries, at some point. Yes the investment in solar and an EP system that delivers efficient regeneration is a good thing. Yes with diesel you can go as fast and for as long as you want to burn your money. OK, we get it.

But raising silly objections like you need enough batteries to equal a tank of diesel, or a demo of electric vs diesel in a pulling contest must have been gamed because the poor diesel could not overcome a bit of initial momentum, and so forth, is not really advancing anyones knowledge, is it? It is just taking an entrenched position against EP and finding justifications, like classic confirmation bias.

Now, what is the killer reason EP is not viable as an option for cruising catamarans? I am asking seriously.

[44'cruisingcat]

It's probably viable. But is it better? Is it worth the substantial extra cost?


The initial cost is far greater. Will running costs really be less?


Your example of the 44 foot boat doing 5.5 knots at 1 litre per hour - that could also be achieved with a Yamaha 9.9 HT. At an initial cost of maybe $4500 for the whole setup, fuel tanks and all. And with the Yam you'd also have the option to go faster for sustained periods if you wanted to.


Will it really cost less to service a 5 kW diesel genset than a 9.9 outboard? How long would it really take to recover the difference in cost?


How about reliability? Certainly electric motors are very reliable. But the high power speed controllers, the generator, the diesel that runs it... is a genset motor going to be any more reliable than a propulsion motor? Why would it?


So you have more possible failure modes.


And as far as I can see you really don't gain anything.


If you go for an "all electric" boat the costs escalate quickly. Unless you're happy to run the genset every time you make a cup of tea or cook a meal, you need a very large inverter, and a big battery bank.


You might argue better safety, by not carrying propane or petrol, but what about a barbecue, and a dinghy?


I looked at it when I was building my boat. A near identical boat was being built with diesel/all electric not far away. I simply couldn't afford to go that way, and felt the investment would take far too long to be returned.


There would have been around a $25,000 price difference. I haven't used anywhere near that much fuel yet, in 27,000 miles and 5 1/2 years full time liveaboard.


And today that diesel/electric boat has outboard motors.

[Rustic Charm]

Originally Posted by BigBeakie

TCO being all costs over 5 years, the initial capital investment to put the system in, plus all the on costs to run it, maintain it, service it. Depending on how many hours per year you run the engines (therefore how much diesel you use), there will come a break even point when electric propulsion will become cheaper to run than diesel engines.

In the tropics where we will do alot of cruising, there will be a great deal of calm conditions and we expect to motor more than "average", so our crossover break even point will come sooner than someone with low engine hours. We will also be trolling for sport fishing so that would increase engine hours as well.

For us, EP makes a lot of sense. The trick is to put together a well designed and efficient system.

As they say, we didn't make it out of the stone age because we ran out of stones

So, me being the novis in this stuff and trying very hard to ignore the clearly dogmatic bias that it can't work for cruisers,

I have a 36 foot mono with a 38hp that will push my boat at 6 knotts max with 2500-2800 revs. I'm going to have to re-power in a couple of years as my VP2003T is becoming too expensive to keep fixing things. I have a 170 litre keel tank. I have two 240 solar panels (I think?) and 4 120Amp AGM house batteries.

What size electric motor and gear box would I need to reasonably equal this? What sort of price are we talking about?

What size diesel generator would I need to compliment it?

[valhalla360]

Originally Posted by Terra Nova

It is easy to overlook facts when your main objective is to rationalize a radical departure from what makes sense to nearly everyone else.

Please share the facts I missed.

A group pushing electric drivetrains set up what appears to be a flawed test. The burden is on them to prove it's not flawed.

[valhalla360]

Originally Posted by donradcliffe

I have no axe to grind either way, but the reason one cat was able to tow the other one backwards had a lot more to do with the propellers than momentum. If you put larger diameter props on the diesel cat and optimize them for lower speeds, it would tow the electric cat backwards.

Very true. It's similar to a 40hp tractor will easily beat a 400hp diesel 1 ton dually pickup because the tractor it built entirely for low end power.

[BigBeakie]

Originally Posted by Rustic Charm

So, me being the novis in this stuff and trying very hard to ignore the clearly dogmatic bias that it can't work for cruisers,

I have a 36 foot mono with a 38hp that will push my boat at 6 knotts max with 2500-2800 revs. I'm going to have to re-power in a couple of years as my VP2003T is becoming too expensive to keep fixing things. I have a 170 litre keel tank. I have two 240 solar panels (I think?) and 4 120Amp AGM house batteries.

What size electric motor and gear box would I need to reasonably equal this? What sort of price are we talking about?

What size diesel generator would I need to compliment it?

Two suggestions would be to contact OceanVolt and Hybrid-Marine UK. The vendors will have different approaches and suggestions on what would be suitable for your boat and cruising requirements. There are lots of others as well. Mr Google can help you find them.

[charliehows]

Originally Posted by 44'cruisingcat

It's probably viable. But is it better? Is it worth the substantial extra cost?


The initial cost is far greater. Will running costs really be less?


Your example of the 44 foot boat doing 5.5 knots at 1 litre per hour - that could also be achieved with a Yamaha 9.9 HT. At an initial cost of maybe $4500 for the whole setup, fuel tanks and all. And with the Yam you'd also have the option to go faster for sustained periods if you wanted to.


Will it really cost less to service a 5 kW diesel genset than a 9.9 outboard? How long would it really take to recover the difference in cost?


How about reliability? Certainly electric motors are very reliable. But the high power speed controllers, the generator, the diesel that runs it... is a genset motor going to be any more reliable than a propulsion motor? Why would it?


So you have more possible failure modes.


And as far as I can see you really don't gain anything.


If you go for an "all electric" boat the costs escalate quickly. Unless you're happy to run the genset every time you make a cup of tea or cook a meal, you need a very large inverter, and a big battery bank.


You might argue better safety, by not carrying propane or petrol, but what about a barbecue, and a dinghy?


I looked at it when I was building my boat. A near identical boat was being built with diesel/all electric not far away. I simply couldn't afford to go that way, and felt the investment would take far too long to be returned.


There would have been around a $25,000 price difference. I haven't used anywhere near that much fuel yet, in 27,000 miles and 5 1/2 years full time liveaboard.


And today that diesel/electric boat has outboard motors.

well put; in theory it can be done, in practice its just not anywhere near feasible unless you are making some kind of point - i doubt any of the people arguing for electric propulsion have actually put their money where their mouth is, and those few who have dont seem to be piping up enthusiastically.

[Scout 30]

Originally Posted by Rustic Charm

So, me being the novis in this stuff and trying very hard to ignore the clearly dogmatic bias that it can't work for cruisers,

I have a 36 foot mono with a 38hp that will push my boat at 6 knotts max with 2500-2800 revs. I'm going to have to re-power in a couple of years as my VP2003T is becoming too expensive to keep fixing things. I have a 170 litre keel tank. I have two 240 solar panels (I think?) and 4 120Amp AGM house batteries.

What size electric motor and gear box would I need to reasonably equal this? What sort of price are we talking about?

What size diesel generator would I need to compliment it?

I have the same motor & think the EP 2000 would be the way to go. $9,000 for the motor which is about the same price as a Beta. You'll need a charger & 6 12 volt batteries for the EP 2000. For the Beta you'd need a charger but fewer batteries for a house bank & separate starter battery. So up to this point the costs are pretty similar. If you are going to install or already have a generator for air conditioning, water making or whatever, then you are ahead of the game & I'd really consider electric. Under batteries alone Elco estimates a range of 6 hours at 60% of hull speed so for a boat with a 30' waterline length that would be 26.4 miles at 4.4 knots. However with just a 2.5KW generator running you would increase that to 539 miles at 5.5 knots. That would work for most people.
Elco Inboard Electric Motor EP-2000 | Elco Motor Yachts

[leftbrainstuff]

Originally Posted by BigBeakie

The video shows a pulling match between 2 equivalent cats, one with 2x 10kW OceanVolts and the other with 29HP diesels.

Assuming this was done legitimately, ie that both boats had full throttle on, this shows the torque advantage of electric motors vs diesel.

Discussion?

And the relevance is?

In the water a dc motor having max torque at zero rpm is irrelevant. Due to slippage due to inertia.

You could run a large prop and turn it slowly. But this would increase drag, when sailing, and not fit in most efficient hull shapes.

But for trains and mining dump trucks its an important design characteristic.

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