Electric Boat News from Dusseldorf Boat Show

[gregcope]

How long does one take to charge at 12v?

1l petrol is about 35MJ

So even if you can provide 10 amps from your 12 v circuit, it's going to take over 2 days to provide the same energy as you can pour in to a tank in 20 secs.

I can see electric engines being the future, but there needs to be a massive investment in charging infrastructure.

Agreed.

In our real world pottering use at anchor, ie no long trips, but we do not do those, we do not find that an issue so works for us. My gut feeling is most tenders are like cars. Some do long journeys, most just pop round the corner. YMMY.

The reports from Ian @nestawayboats suggest this area is expanding with new companies and wider product ranges, with better features are entering the market. This can only be a good thing.

 

[nestawayboats]

That's just plain wrong.
Power is force times speed.
Or in rotational machines, torque times angular speed.

An electric motor may give the same thrust as a more powerful petrol engine, but you could get that same thrust from a smaller petrol engine with a different prop and gear ratio.

In real use, people may find electric outboards are as effective as certain petrol engines, but that's usually because the petrol engine has a prop not optimum for the job.
Where electric scores is that the torque is constant or may be higher at low rpm, so there is less sensitivity to having the wrong prop for the conditions.
Most people never get 3hp out of their 3hp outboard, because the boat doesn't go fast enough for the engine to reach peak power.

Making spurious claims does the industry no favours.

We try to avoid equations because they put a lot of people off reading, but maybe it is unavoidable. I'm not sure about "Power is force times speed" but the common definition of Power is Work over (ie divided by) Time.

Without going into SI units etc which would put even more people off, the "Work" we're interested in here could be defined as "pushing a boat through the water at a useful speed". Other outputs such as heat and noise are not what we're after.

And if our comparison is over the same amount of time then it becomes a constant so we can take that out of the equation.

So for our fictional yachtsman with no understanding whatsover of Physics but wanting some form of propulsion for his tender, Power could be said to be "how effective is it at pushing my dinghy along?"

Scenario 1. Very lightly loaded, single 50kg crew, flat bottomed dinghy. That will probably plane with a 3.5hp petrol outboard, speed will be dependent on many factors but let's be optimistic on all of them and say 14 knots. It will definitely not plane with a Torqeedo or Epropulsion 1kW electric outboard as both of them max out at about 6 knots, again dependent on many factors but we were generous to the petrol one so let's go with 6 knots. The effective "Power" in terms of what's useful to the yachtsman is quite a lot more for the 3.5hp petrol than the 1kW electric. (In fact in this scenario the electric outboard will probably achieve that speed at about half power, and using more throttle won't make any difference, but let's not worry too much about that.)

Scenario 2. Medium load dinghy, 2x 90kg crew with some other stuff. That will not plane with a 3.5hp motor, there is not enough power to get it into planing mode. A reasonable guess would be 5 knots. The 1kW electric outboard might actually be faster, but let's say it achieves the same speed. As far as the yachtsman is concerned he's getting the same amount of work or power.

Scenario 3. Heavily (probably over) loaded dinghy, 4x 90kg crew plus gear. Again it won't plane and the petrol motor with its propeller that's designed to spin around fast will be slower, 4 knots is probably generous. The electric outboard with its larger slower turning propeller and massive low down torque is in its element and barely (if any) slower than Scenario 2. As far as our Physics-hating yachtsman is concerned, the electric outboard seems to be more powerful.

Yes it is a lot about the propeller and "gearing" (the direct drive electric outboards we recommend don't have gearboxes, that's been covered elsewhere), but I'm not even sure if most manufacturers offer alternative propellers for their small petrol motors, certainly they are not supplied. And without changing the gearing the petrol engine wouldn't have enough torque to drive the propeller that would be "efficient" in scenario 3, ie it would be more likely to stall at idle in gear. Which we don't want.

"Most people never get 3hp out of their 3hp outboard, because the boat doesn't go fast enough for the engine to reach peak power."

Yes as well, absolutely. That is because their 3hp outboard as supplied to them as standard isn't optimised for what they actually do with it. For whatever reason that is... one would imagine the manufacturers have a reasonable idea, by now, of what they're used for. Petrol outboards have been made for quite a long time, and a lot longer than these upstart newfangled electrical things which seem to do the job more effectively for most people most of the time, despite having less absolute power. In this respect (and probably this respect only!) the Seagull outboards were better than most if not all petrol outboards that succeeded them (in that they turned a relatively large propeller relatively slowly - if you could get them started (I will duck for cover!)).

I agree making spurious claims isn't helpful but I don't think it is unreasonable to suggest that a 1kW electric outboard has quite a similar output to a 3hp petrol one, in terms of what the typical user wants and gets from it. But if you want to get a really lightly loaded dinghy on the plane it is not equal or equivalent. In most scenarios where the 3hp petrol can't plane (ie with more than one person aboard) the electric one will probably be better. Saying it's equal is wrong and if I've ever said that it was by accident of typing or not thinking enough beforehand. "Equivalent" (or even one would hesitate to suggest "roughly equal") is a less definitive term and if you need to get the point across reasonably quickly it is not unreasonable to use it. IMHO

Ian, Nestaway Boats

 

[nestawayboats]

How long does one take to charge at 12v?

1l petrol is about 35MJ

So even if you can provide 10 amps from your 12 v circuit, it's going to take over 2 days to provide the same energy as you can pour in to a tank in 20 secs.

I can see electric engines being the future, but there needs to be a massive investment in charging infrastructure.

To which the answer is another question ie which manufacturer and which battery and how much is it discharged?

Assuming you've used the battery's entire capacity - which is becoming increasingly unlikely as battery capacity increases - then at 12V:
- Torqeedo 532Wh battery approx 11hrs from flat
- Torqeedo 915Wh battery approx 19hrs from flat
- Epropulsion 1018Wh battery approx 11hrs
- Epropulsion 1276Wh battery approx 13hrs

As most people don't flatten their batteries completely on a daily basis usually they charge overnight to full or near full for the next day.

Mains charging is faster if you have access to mains, or an inverter on board. Epropulsion are ahead of Torqeedo on fast charging, you can have a mains charger that will get their 1276Wh battery to 80% in about an hour if you are willing to pay for it (that is not the standard one). But bear in mind faster charging does have a slight detriment to battery cycle life, you shouldn't do it when you don't need to.

Ian, Nestaway Boats

 

[DoubleEnder]

I have no commercial interest in any outboards of any type. In my experience using various small electric and petrol outboards in a range of hard dinghies and small RIBs on flat water, the electric engines are generally ‘better’. Performance has always seemed at the very least adequate, sometimes startlingly good. They are easy to handle when mounting or removing. The pieces are small and light. Some of the batteries float! They are clean and very very quiet. You don’t get oil on your clothes or car. They always start! I own a Suzuki 2.2 and it’s a smelly oily b@gger.

This is completely unscientific I know but just my impression of using both over the last couple of years. I haven’t had to worry about range but I think that holds true for a lot of people; not everyone I agree.

Electric motive power was everywhere at Düsseldorf. Noticeably more than 2019, for yachts, motor boats, day boats etc etc. Also fast RIBs and other fancy stuff. I loved the electric foiling board.

I looked at one small 23 ‘ sailing boat on show. It was a nice little boat but it had a petrol outboard in a well in the cockpit. The engine was a modern 8 or 10hp. And I was struck how startlingly old fashioned it looked compared to all the similar sized boats I’d seen with some variant of electric power. Positively anachronistic.

Yes I know for many owners electric power isn’t really viable. I have on occasion motored for over 100 miles, and I could not do that with electric power. But I wish I could....

 

[lw395]

We try to avoid equations because they put a lot of people off reading, but maybe it is unavoidable. I'm not sure about "Power is force times speed"....

Ian, Nestaway Boats

That's cse physics, chap.
If you don't understand that, we're wasting our time.

 

[lw395]

I have no commercial interest in any outboards of any type. In my experience using various small electric and petrol outboards in a range of hard dinghies and small RIBs on flat water, the electric engines are generally ‘better’. Performance has always seemed at the very least adequate, sometimes startlingly good. They are easy to handle when mounting or removing. The pieces are small and light. Some of the batteries float! They are clean and very very quiet. You don’t get oil on your clothes or car. They always start! I own a Suzuki 2.2 and it’s a smelly oily b@gger.

This is completely unscientific I know but just my impression of using both over the last couple of years. I haven’t had to worry about range but I think that holds true for a lot of people; not everyone I agree.

Electric motive power was everywhere at Düsseldorf. Noticeably more than 2019, for yachts, motor boats, day boats etc etc. Also fast RIBs and other fancy stuff. I loved the electric foiling board.

I looked at one small 23 ‘ sailing boat on show. It was a nice little boat but it had a petrol outboard in a well in the cockpit. The engine was a modern 8 or 10hp. And I was struck how startlingly old fashioned it looked compared to all the similar sized boats I’d seen with some variant of electric power. Positively anachronistic.

Yes I know for many owners electric power isn’t really viable. I have on occasion motored for over 100 miles, and I could not do that with electric power. But I wish I could....

You got it in one with 'fashion'.
Battery everything is the fashion of the moment.
What you need to work on is your desire to motor 100miles. Why?
I have done 100mile trips with no engine.
To do a 100mile trip under sail with a little electric whisk to aid parking seems a much more sensible, and environmentally viable, aspiration?

 

[dunedin]

What you need to work on is your desire to motor 100miles. Why?
I have done 100mile trips with no engine.

As ever, these things depend a lot on cruising grounds and type of sailing.
We like sailing and spent a lot of extra money to buy a boat with plenty of sail area, laminate sals etc which can be enjoyable to sail upwind in 5 knots true wind. Great fun.

BUT. Sometimes we do need to motors for longer distances. Few boats go very fast downwind in 5 knots true. And few of us like doing long distances upwind in 40 knots true.
Hence when faced with getting from Sweden to the U.K. with a 4 day calm spell before a series of gales, we filled up the diesel tank and a couple of spare cans and set off Eastbound, 300+ miles. We couldn’t afford to drift at 2 knots as would get severely pasted by the North Sea gale (and the North Sea is a bit bigger and wilder up where we are), so motored for the first 24 hours, then able to sail the rest of the way.
Also other times away from electric supplies for 2 weeks or more, and 150 miles or more.

But clearly for tenders, marina based RIBs and day boats electric will soon be the preferred solution, subject to resolving the price order of magnitude gap.

 

[JumbleDuck]

That's cse physics, chap.
If you don't understand that, we're wasting our time.

Power = force x speed is all very well, but it's not at all easy to apply to a propeller, because the same force does work on both the boat and the water, and they are moving at different speeds. Which is why we have delights like Kelvin-Froude Actuator Disk Theory.

 

[jordanbasset]

Re charging, we have solar panels and I use an invertor, takes a couple of hours to charge from 50%

 

[RupertW]

How long does one take to charge at 12v?

1l petrol is about 35MJ

So even if you can provide 10 amps from your 12 v circuit, it's going to take over 2 days to provide the same energy as you can pour in to a tank in 20 secs.

I can see electric engines being the future, but there needs to be a massive investment in charging infrastructure.

For main boat propulsion yes, for most tender propulsion it’s been fine for a few years.