Electric boat conversion - performance

The photo shows the propeller wash for a drive current of about 60A with the boat on its mooring - quite impressive!

We have now run our conversion basically completely successfully for approx. 14 months.

Here are some results:

1. Since so many people ask, no, there is apparently no fuel saving! This surprised me since (I calculated) the system is definitely more efficient ... partly for clearly simpler mechanics but especially because one is absolutely drawing no power when stationary - at least 30% of the time when cruising (I calculated.)

However, electrical measurements show that re-charging is only about 70% efficient - not an issue I've ever heard (or read) discussed.. or even mentioned! However, it seems to be - at least for our equipment - simply a fact that re-charging is only 70% efficient.

Note that we could not hope to save on fuel usage except via increased efficiency - the power input fom the solar cells is negligible compared to the high powers involved in moving... our only prime energy source remains the diesel for the generator... so, no fuel saving (but just about the same as previously - which fits with the crucial physics that you can't get energy from nowhere!)

2. The thrust available is quite stunning - and way beyond what a conventional diesel can provide because the acceleration is so much greater. This makes boat control a world easier - although it takes some re-learning - since one can use brief bursts of intense power to set steering line (or stop or start) and then adjust quietly. N.b, I am referring to acceleration - continuous (illegal) high speed available is only slightly more than traditional drive... and one would have to consider battery consumption more carefully if you ran at those speeds for too long!

3. There is basically NO vibration at all from the drive, even at high power - a quite astonishing effect. (The surface of a cup of coffee placed on the lid of the gas box is completely still at all powers, and even with the generator on!) It is totally reliable whether powered by battery alone or the combination of generator + battery.

4. Although the generator is audible on the boat, the effect is so slight visitors who aren't informed whether it is on or not don't actually realise whether it's on or off unless asked to take notice! Even my wife once asked if it was on or not!

5. The drive batteries have discharged (about 50% max in our useage) and recharged over the 14 months without the slightest indication of any deterioration in performance. This has included long periods inactive on the mooring and other times of intense boating on the river Thames on code yellow when high powers were required at times - and even extended periods of high current running.

6. With "sensible" re-charging we have never been close to loss of battery power. In practice one has huge flexibility of choosing when to run the generator to re-charge.

On the canal, a "good practice" turns out to be to run the pounds electric and turn the generator on whilst locking - and this leaves one basically fully recharged from lock to lock! There is a slight deficit overall using this method, but it is easily made up by running the generator whilst having lunch or equivalent (only about 40 mins MAX needed, less would keep one OK) at the end of the day.....

But, one morning I boated pure electric (canal) all morning as a test. There was absolutely no lack of power available, although the battery plate voltage at cruising speed fell (rather alarmingly!) as low as 60V. However, I then ran the generator whilst we had lunch and went for a walk (as volition, not to leave time to charge!) We happened to meet some people and so total recharging time was 50 minutes. The batteries were now fully recharged - so definitely I could run the next bit, in fact on and against that river Cherwell section of the canal in near spate, "pure electric" with absolute power.

On the river, a continuous run upstream against strong current does require that the generator is on much of the time... which leaves one using hardly any battery! - but there is a vast range of choice about how much of the time. One can chose to run sections "pure electric" without fears of suddenly being out of power!

Downstream, power consumption (and need for generator) is roughly like the canal.

7. I spent ages making an unconventional-method meter to indicate "useful charge left" on the drive batteries. This works very well and supports all the remarks above. However, please note that an equivalent commercial version is now available!!

8. In practice one can tell the state of the drive batteries from the voltage across them (as indicated by our digital voltmeter) under different conditions - where all one wants is a rough idea!

For a few examples:

On the canal, normal cruising, 30-40A drive current, "pure electric", 72 volts means you are pretty-much fully charged. 70V means you've used a bit, easily replaced next lock. 68V means you might need to make up a bit more later. 64V means you've definitely got to do a bit of a recharge at lunch-time(!) (or equivalent at the end of the day.)

Generator on, 72/74V means you're probably not recharging much, but can run effectively forever. 78V-ish means you have masses of battery left if you felt like a patch of silent running...

In practice, with experience, we find you don't really have to think about detail as one comes to learn the kind of number to expect under different conditions!

9. Turn off the generator instantly (easily done - just hit the stop button!) if you see debris in the water or (on the canal) are about to pass where the side is shallow and the exhaust intake might hit or be near bottom (not needed if you cruise the pounds electric!) Check the intake filter every half day - even if only to decide it doesn't need a clean. Given these precautions, no cooling intake problems (and little in the filter!)

10. Hit the switch to run the generator slowly about 5 minutes (allowing it to cool) before actually turning off after a longer burst of running it... if it's convenient. If not, too bad, there's always the over-ride switch if it "claims" to be too hot next time you want to start it.

11. If the generator does indicate "ghost hot", hit the override switch... has to be held down about 15s before the new intake of water cools the thing enough to make the protective cut out shut up(!).

12. No reason to panic if you run aground, the drive has enough thrust to get you off (in reverse!) (seemingly) anything... with no vibration or any fear anything is being over-strained.

13. On the canal, use about 50A to get up to speed but then 30A is enough - if the boat seems slow, probably picked up weed, burst of fast reverse will shake it off.

14. High power reverse makes the boat "pull left" - probably a "paddle" effect since our hull design is far from ideal for reverse water flow!!.... Trick is to give a short burst and then low power to maintain the effect without unwanted spin (of the boat.)

N.B. that overall we find the effect of the drive completely reliable, more useful control power available than conventional drive, always, stunningly, NO vibration, drive noise level for normal running almost zero (except the water!) Absolutely NO disadvantages compared to conventional drive ... given sensible application of the generator, no limit to range, e.g..... and huge advantage of lack of noise (and vibration) in terms of pleasure and ability to talk to one another without aids... and also in certainty of reliability, even in tough current conditions.