On summer vacation with electric motor and battery from Impulse Power – 150 NM with EL and Sail!

Impulse Power has in recent years developed engines and batteries for marine and stationary use. For this season, the portfolio has been further strengthened with, among other things, larger batteries and power electronics for fast charging and offshore alternating current (AC) from batteries. These are products that we ourselves as sailors feel we need, and we wanted to test this in practical use. What could be more natural than sailing down the coastline and seeing how this works.

One thing is range, how far do you actually get, what speed does the boat get with different energy consumption? Another thing is charging in practice, if you find power, how long does it take, do we just charge or should we charge completely?

Test criteria

​To find answers to these important questions (for the electric boat people!) we set out on a long-distance test.

One of Impulse Power's test boats is located at Lille Herberen (Bygdøy Oslo).

It is an Elvstrøm 717, "The Raft". The boat was designed by sailor Paul Elvstrøm in 1976 and just over 50 boats were built. The waterline on this boat is 19.5 feet.

This means a theoretical speed of √19.5 x 1.34 = 5.91 given that the boat does not plan.

It is an easily driven boat. We have previously seen speeds as below:

EFFECT kW	SPEED kn
1	3,6
1,5	4,3
2	4,9
2,5	5,3
3	5,67

Theoretical ranges on pure motor driving are then:

1 kW (approx. 20 A) = max 12 hours      43 nm

2 kW (approx. 40 A) = max 6 hours        29 nm

3 kW (approx. 60 A) = max 4 hours       22 nm

That's speed, ref. formula above. The goal is to achieve a test pull of 40 nm!

Gear​

The Raft» has been equipped with the following products, all from Impulse Power:

• Drivetrain: Impulse 5 – i.e. an outboard 3 kW motor

• Battery: Impulse 9 kWh & Impulse 3 kWh

• ImpVerter: 3 kW AC 230 & 2.4 DC AC charging

In addition, we have a victron DC/DC converter for supplying 12v to the chart plotter. We are now developing a 12v outlet in our ImpVerter for future deliveries. The two batteries can be connected in parallel and together supply 12 kWh on this boat, or run separately. It is possible with a maximum of 4 batteries together - so in theory 36 kWh if there is a large need for power. The “ImpVerter” is connected to one of the battery's two connectors and will charge the entire system when connected to the mains, while at the same time delivering 230 VAC from the battery when we are out sailing. In theory, we would be able to run on engine power at 4 knots for 10 hours and have a range of 40 NM in pure engine power (without sails). At the same time, a sail can also significantly reduce the power requirement and add speed. This was used during the test to save time.

Day 1

We left Oslo at 11:30 on July 13. The tide was going to turn inwards at 12 o'clock, and we would sail directly against the current and that would cost time/speed. Furthermore, heavy rain, lightning and wind were forecast, but this was our last chance to get out, so we chose to sail. The idea was to stay on 1 kW and be able to run in theory for 10 – 12 hours, and possibly supplement with sails if needed, and that would come in handy here.

The Elvstrømmen is a handful to sail solo. It has a tiller without an autopilot that requires a man, bilge rigs that must be prioritized when hitting, and a genoa winch. Impuls Power's delegate was alone on this trip. Given that the priority was to test the driveline on this trip, sailing was put on hold.   But due to countercurrents and low speed over land, as well as promises of cold beer all the way down in Resø, the genoa was made ready for supplementary speed. But first we had to brave the expected bad weather…. Heavy thunder and lightning came in from the west and the LiveLightning app was used frequently. We also went close to Nesodden in the hope of some protection. The strong wind really took hold of the boat and it was choppy, and speed was only slightly over 3 knots. The heavy rain cooled the crew and their motivation.

An hour of rain and wind had been forecast, and YR was right here. At 2 p.m. it was all over and we hoisted the genoa and set sail for Drøbak. Here we made an ice stop and picked up some young people who joined us on the trip. We put the boat on charge for 30 minutes and thus supplemented the battery with some power. From here we continued with genoa and engine (at 1 kW power) until Son, where we arrived at 20:00 on the way.

Unfortunately, we had PC issues that day and were unable to log consumption and data from BMS. We had about 40% left on the largest package, however with 30 minutes of charging with 2.4 kW power from Impvertern in Drøbak. Distance was 26 nm,

we left Oslo at 11:30 and arrived in Son at 19:45 – minus 1 hour in Drøbak was about 7:45 minutes of sailing time – so the speed was slightly below 4 knots. Son Marina was the night's accommodation and one of the boat's eminent 4 berths was used. The reserve crew was sent home for burgers and beers 😊.

Day 2

The PC was replaced and we were finally able to log. Both batteries were fully charged during the evening using the ImpVerter which worked brilliantly throughout the trip. Really useful to be able to charge in just a few hours. If the crew had been able to stand it, we could have sailed on at 23:00. But we chose sleep and started the next day precisely at 09:00 with 97% on the battery. The goal was to get to Hankø at least, maybe Koster. As on day 1, we were lucky with the wind direction, north and this day there was no rain in the forecast, but some wind throughout the afternoon.

PC LOG was started and logging started. This is super exciting for the nerds 😊. Here we can see power consumption over time, temperature, voltage, etc. This will eventually appear in the Impulse Powers APP, but for now only a sneak view…. In the picture on the left you can see the State of charge (how many % of the maximum there is on the battery, Voltage in Volts and Pack Current, i.e. how much power and therefore power we used). Current x Voltage = Power (measured in e.g. kW)

It was an eventful day. Good speed south with the wind at our backs often gave a speed of over 5 knots. Looking at the log, the power (Pack Current) is at different levels. The day before we were at 1 kW. That is the same as 20A x 50 V = 1000 W. We chose to vary the load according to wind and speed. As we wrote in the introduction, the boat's speed is never faster than 5.9 knots (as long as it is not planing). Therefore, we turned down the power so as not to waste energy that does not give any significant speed increase. You can see this on the curve that varies from 5 A at the lowest to 30 A (i.e. roughly 250 W to 1.5 kW. It went quickly and nicely to Hvaler, outside Søstrene there was a lot of sea coming in from the southwest after the wind had changed, and it became hectic in such a small boat. We took the inside of Åkerø to get into cleaner water, and from here we went by engine alone. We kept up such good speed that we made it all the way to Resø on only one battery with a little support from the sail, and arrived in Resø at 9:00 PM. We also managed to have a great pizza at Lexø just before the kitchen closed.

At that time we had 4% SOC on the large (9 kWh) battery. We had drawn 30% on the small (3 kWh) battery - an estimated 80 - 100 W per hour for PC and various consumption. The trip was a full 49 NM over 12 hours. Minus a little break, it gave an average speed of approx. 4.3 knots, 1.5 knots below the boat's max. Almost the entire trip was with the engine on and with support from the genoa + exceptionally a mainsail for a short while before it became too much for a single-handedr on this boat.

The conclusion here is that you can go FAR, but the engine power must be adapted and used smartly.

The return

The return trip was similar after a few days. The route shown below. Resø – Skjæløy without a log this time. The trip is shorter, and there was a bit more sailing. Approx. 30% remaining battery on arrival. The night was spent in Skjeløy for two shorter stretches – Skjeløy Son, and Son Lille Herberen over two days.

Summary

Total sailed – 150 NM

Estimated electricity used:

• Day 1 – Lille Herberen – Son: approx. 75% of 9 kWh                 6.75 kWh used

• Day 2 – Son – Resø: 91% of 9 kWh + 30% of 3 kWh           9.19 kWh used

• Day 3 – Resø- Skjæløy: 60% of 9 kWh                               5.40 kWh used

• Day 4/5 Home: approx. 100% of 9 kWh –                     9.00 kWh used

Total energy consumption approx. 30 kWh, the cost of half a pint 😊. However, with the help of the genoa, but with the engine on 90% of the time at varying speeds.

This was a good test of a practical summer of sailing. Pure electric operation at full throttle as if you were driving with a diesel will shorten the distances, but it is possible with charging with usable power as our ImpVerter provides. Furthermore, the range will be significantly longer if the speed is reduced by 1 – 2 knots from maximum. This can be recovered with a support sail as we did here.

3kW of power on this engine was sufficient even in a little wind with this boat

There was no regeneration on this trip.