We’ve already shown what the hydro-generation or regeneration feature of our electric motor is capable of at various boat speeds in controlled conditions, but how does it work in practice over the long term?

We have been sailing the boat for almost a year now, with 5,900 nautical miles in our wake. So I thought it was time to give a summary of our experience with the hydro-generation, using different cruising modes and passages we’ve completed this year as practical examples.

Coastal Sailing

In the early months of our voyage, we spent a lot of time on the French, British and Spanish coasts, often staying in marinas where electricity was included in the mooring fee. There was little incentive to use regeneration while sailing, on a typical day’s sailing you would get a maximum of a few hours of productive regeneration at best (1-2 kWh in total), and the large 23 kWh battery, once fully charged in a marina, would easily last us a few days anyway.

Passage: Porto - Madeira

This was a 4 day passage with great sailing pretty much from start to finish. The wind was steady around 13 knots on a broad reach around 130 degrees TWA, conditions where our light wind sail really shines. The average boat speed was 6.5 knots, and we had a light swell on the beam, which is good for regeneration as you’ll see below, because the boat speed is quite stable.

We used regeneration for a total of 18 hours and had to (re)start the regeneration process 38 times. Sometimes we were a bit lazy on the watch and did not bother to restart the regeneration when it stopped, but the best run was 3.5 hours of uninterrupted regeneration, which is the best we ever achieved. On average, the regeneration produced about 330 W, for a total of 6 kWh in 4 days.

The solar panels produced 11.6 kWh in the same period, so regeneration was a significant addition to our energy balance (but still not the biggest producer).

Passage: Canary Islands - Cape Verde

This was a light wind passage with an average wind speed of only 9 knots and an average boat speed of 4.7 knots. The trade winds were disrupted by a low pressure system that was unusually far south, and we were lucky to find a weather window that didn’t have us sailing into the wind. It took 7 days, we used the electric motor for 48 hours and the generator for 30 hours. On the positive side, the hybrid electric propulsion system worked really well and gave us a lot of relatively quiet motoring and motor sailing, but on a passage like this, hydro-generation is simply not possible, we were just too slow for that.

Passage: Cape Verde - Barbados

Now we were really in the trade winds, with winds from behind between 10 to 30 knots, and a combination of wind waves and swell, also from behind, up to 2.5 meters. Most of the time it was great sailing, with exciting surfing down big waves and decent average boat speeds (6.2 knots), not to mention a wonderful arrival in the Caribbean at the end. But surfing a swell from behind means that the boat is constantly speeding up and slowing down. Each slowdown is an opportunity for the folding propeller to fold and stop regeneration, and it did that more often than we expected, even if the boat only slowed to 5.5 to 6 knots. Restarting the regeneration manually every few minutes is not an option for us. So even in 25 knots of wind, which we considered quite strong compared to our previous sailing, and where we expected good regeneration, the regeneration was very disappointing and we hardly used it, except for a few unsuccessful attempts. 2.2 kWh were produced by regeneration in 14 days, compared to solar which produced about 37 kWh in the same period.

Conclusion

We’ve tried a lot to make regeneration work on our boat, but ultimately have to conclude that it doesn’t work as well as we had hoped, and we rarely try to use it anymore. The one passage from Porto to Madeira with relatively useful regeneration has been the exception so far, not the rule. When conditions are just right, regeneration can be useful, but we also know from sailing how often conditions are “just right” - not often. So overall, we now consider the regeneration capabilities of our motor/propeller/boat combination to be a gimmick and not something that regularly plays a role in our energy balance.

What could be changed to get better regeneration? Perhaps the Oceanvolt shaft drive/folding propeller combination would work better on a lighter boat with much better sailing performance than ours. A fixed propeller might also work better, but it has disadvantages when sailing and you need a brake for the shaft to stop it from spinning when you don’t want it to. Oceanvolt’s saildrive offerings with pitching props also seem to offer better regeneration capabilities, but a saildrive wasn’t an option for us because it requires more maintenance/oil changes, is less reliable, and has a higher risk in case of an impact (semi-intentional, when drying out the boat, or unintentional collisions).

We could also add a traditional hydro-generator (like a Watt&Sea) to the boat for an additional cost, which can work continuously with a fixed propeller whenever it is activated. This is perhaps the best addition to our boat that we could consider. But we also know from sailing friends that sargassum seaweed can be really annoying with a hydrogenerator mounted at the stern, so it’s not entirely trouble-free either.

Despite the somewhat disappointing performance of hydrogeneration, our opinion on the propulsion side of our hybrid electric system, and the comfort of cruising/living with a big battery, electric cooking, etc. is still extremely positive. Perhaps that’s worth another post soon.