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BigBeakie · 07-12-2015, 22:05

Quote:

Originally Posted by StuM

Full throttle does not necessarily equal max revs. It depends on the respective gearing and prop designs (Try putting your foot hard down while driving a manual car up a hill)

Yes, that is true, the gearing on the diesel would most likely be higher so it is more efficient at cruising speed range. But consider the other boat as just a load. Like high wind, or strong current, or water that you are trying to push a displacement hull through, etc.

My point is, which type develops more thrust per HP when under load? You clearly have smaller HP electric providing more thrust than larger HP diesels, assuming all the other mitigating factors are equal. Which I agree, we do not know. As I said, it is not a controlled experiment.

But in other threads on EP, it was incessantly mentioned that a horsepower is a horsepower & whether it was electric HP or diesel HP would make no difference to the prop. I think someone mentioned that if two boats were trying to pull each other, as in the video 1 electric and 1 diesel, and they had equivalent HP, then it would be a standstill.

Our arguments about the usefulness of EP torque at low revs for cruising met with derision. Our contention is simply that the torque at low revs is excellent for maneuvering, docking in high wind, pushing against high high/waves/currents, and indeed plodding along at modest cruising speeds or motor sailing.

The issues of range anxiety are another matter, and those are handled by good system design for recharging, regeneration etc.

That's all the EP proponents have ever said.

Terra Nova · 07-12-2015, 22:12

Quote:

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...

So what? Few in their right minds would ever consider converting to or buying an electric cruising yacht.

BigBeakie · 07-12-2015, 22:42

Quote:

Originally Posted by Terra Nova

So what? Few in their right minds would ever consider converting to or buying an electric cruising yacht.

Ah ha! Didn't take long for the typically open minded diesel afinionados to come out, did it?

Terra Nova · 07-12-2015, 22:54

Anything is possible when you don't know what you're talking about. Electric could even seem like a good idea.

Bertie68 · 08-12-2015, 01:34

Torque and HP have nothing to do with this. What counts is just the propeller's parameters and the rpms. Of course, the engine has to be able to supply enough torque so as to keep the propeller turning at the given rpms while overcoming the hydrodynamic resistance, for which in turn the engine must have enough power.

dlymn · 08-12-2015, 02:06

Engine efficiency might be one issue but so is energy density. Diesel fuel stores far more energy kilo for kilo than a typical storage battery. 25 kilos of diesel will allow me to cruise at 6 knots all day. the same mass of battery allows a similar boat to cruise for less than 15 minutes. the diesel boat gets lighter as it uses fuel, the electric stays the same.

The refueling network for diesel is comprehensive. A days cruising will take me less than 10 minutes to refill (25 litres). It takes a special system to recharge a bank of batteries to say cruise for a day ( 6hrs x 10kw, a 110 volt system running at say 25 amps will take 20hrs of flat out charging to refill). I carry enough diesel to cruise 6 hours per day for 8 days. I need 200+ x 12v x 200 ah batteries to do the same and remember the recharge demand. An easy way to recharge the batteries would be to have a 30kw diesel generator on board. This could recharge a days cruising in 2 hours.
So we could go electric with enough batteries for a days cruising ( 25) and a 30 kw diesel generator. Wait a minute...........

PS all ballpark figures

valhalla360 · 08-12-2015, 03:48

Many flaws in the tests:
- The boats are clearly moving the direction of the electric boat meaning the diesel has to overcome both the electric motors and momentum.
- Cavitation may be hampering the diesel since it is moving backward it isn't getting a clean bite on the water where the electric boat is moving into clean water presumably getting a better bite.
- There was no indication what propellers were used on each boat.
- There was no indication of what gear ratio was used on each boat.
- With the Diesel moving backward was it able to get the prop up to speed and take advantage of the larger HP (vs the electric which was moving forward making it easier to get the prop up to speed).

Of course, it's a pointless test:
- If this was a key performance aspect of cruising boats, it would be easy to add a reduction gear to the diesel so it would have even more torque than the electric motor and could turn an even larger prop. The fact is off the line thrust isn't a key cruising need. Cruising boats don't need fast starts so there is time for the diesel to spool up and generate the thrust.
- If they had kept the video going you would have seen the diesel charge back across the screen as the batteries quickly die and the diesel gets up into it's ideal power band and can keep it there for hours or even days.
- As far as powering into waves, the diesel would do much better than is implied here as it would be up in it's power band and putting out more thrust than the electric.

Electric will put out more torque off the line but after that, HP is torque times RPM. If you want more torque, it's easy to add a reduction gear. They don't use lower reduction gears on diesels because that's not a key performance feature on cruising sailboats.

Put it in a car where you need a lot of torque to get the car moving and then very little HP to keep it moving and electric make a lot of sense. For a cruising boat, no one really cares about acceleration (wow, 0 to 6mph) max HP is needed at cruising speed (or slightly above to account for bashing into waves). As such the low end torque of an electric motor isn't an advantage.

Dave22q · 08-12-2015, 09:30

Am eagerly awaiting a practical and affordable electrical yacht motor/solar recharge/battery system. Sadly I see nothing that indicates success is likely in the next 5-10 years. What are the main problems? To cite two; range and weight/space.

**skipmac** · 08-12-2015, 09:35

Quote:

Originally Posted by BigBeakie

Ah ha! Didn't take long for the typically open minded diesel afinionados to come out, did it?

I am an electrical engineer and would LOVE to go electric for many reasons, some very specific to my boat and the current engine installation. But it doesn't make sense, due to cruising range and cost.

To get a cruising range of 200-400 nm is impossible with batteries. Even 100 nm range is impossible with the typical cruising boat. That leaves the only option to install a diesel generator to power the electric motor. BUT, now you have put an engine back into the boat and at a much higher cost than just using a diesel for power directly. I've checked the costs and it is roughly triple the cost to go with electric drive with a generator than it is to just install a diesel to drive the boat. Also, until recently there were no commercially available electric drives that had the power to replace my 58 HP diesel.

So tell us the solution to these issues and I will be the very first to jump on the electric band wagon and as soon as I have the spare change, will install the system in my boat.

Cheechako · 08-12-2015, 09:40

My "discussion" would be... let's see that after they have been pulling for a couple hours...

**skipmac** · 08-12-2015, 09:43

Quote:

Originally Posted by Terra Nova

Anything is possible when you don't know what you're talking about. Electric could even seem like a good idea.

Electric motor on a boat powered by batteries is a GREAT idea..... as long as you never have to motor any further than a mile or so from your slip to open water, never cruise the ICW or transit any canal, always keep the boat plugged in at a marina or have solar and a generator for backup to keep the batteries charged.