Firstly, thanks Rick for sharing and taking time to educate me.

| The motor/generators in use are ME1003. They are rated at 72V and 3000rpm. They have a claimed mechanical maximum speed of 5000rpm.

If they spin 500rpm at ~7.8kts, why were you worried about over speed at 20kts? Why did you suggest cage induction motors might be needed?

| As a generator we spun up to 3600rpm, which is 85V. It was a generator that flashed over but we had previously run it at 85V in perfectly dry conditions when newly installed without flashing over.

It seems like these generators are not sealed like the submerged ones? Why not?

| So I believe moisture in the engine box and surrounding air contributed to the flashover. The brush cover had some surface rusting inside indicating moisture in the brush housing.
|
| In the new configuration there is a generator for each propulsion unit and they will produce about 60V at full engine revs.
|
| These motor/generators are rated at 200A continuous. The Kv is 41rpm/V.

That is rather efficent.

| You can certainly buy higher voltage controllers. In terms of the overall system cost it is not that significant to go for a higher voltage but you would need to check that its adjustments allow for the conditions you might encounter.

| You may also need to read the fine print though because it may have problems handling a runaway condition. The first controllers used on the 18m proa were not capable of reversing if the prop was still turning. The supplier suggested we should drop the anchor and come to a stop by that means then select the new direction and lift the anchor; not a practical option approaching a marina with a tail wind. The controllers we found that could reverse with props still spinning have a maximum rating of 60V.

It seems there are several MAXv to juggle here. MAXv of drive power to motor, MAXv of (if) reversible, MAXv for regen. What did I miss?

I imagine you have looked at a lot of controllers in you quest to meet your needs. Is controller options a continuous changing field? Would you share the models of your various controllers?

| You can bet you will be at the bleeding edge trying to regenerate on a fast, lightweight sailing boat using the propulsion system.

I just asked a question. It seems neither technically difficult (assuming one has already built a bespoke electrical power system) nor impractical.

| If you can only motor in one direction then you have cut the possible usage to 50%.

I do not understand why you would say that. One can always turn the tender around.

| You will not want to use when going to weather.

Hard to weather? Sure. But one can drag it to weather. Or do I misunderstand and when a sailor says 'to weather' that generally means pointing high?

| You will not use it if sailing below 6kts on any point because it will kill speed just being in the water.

Do you have an idea of how much speed would be lost? My guess is 2@54cm disks would be a LOT of drag. Less so at low speed, more so at high speed?

I do not think it would even be possible for the boat to reach 20kts dragging them, as the boat would not have enough excess power to drag them up to speed. What do you guess the max boat speed of, say, a C50 would be dragging those props?

| You will not want to use it in conditions above 15kts of wind because the sea conditions will be demanding and you will not want to have the complication of a tender in the water.

I'll defer to your expertise as a sailor. Can you explain to a non sailor why the tender would be an issue in the water at 15kts?

| So there could be a useful window for regeneration around 5 to 10% of your sailing time. The limited opportunity to get something out of it means that you should not be relying on it.

Sure. In my original question I suggested it would be a sometimes thing. As we know now, it is unlikely to ever spin fast enough to even reach 60v, it seems compatible with controllers you have on hand.

Again, it is a third generating source, assuming solar and wind, at almost zero extra cost. So why not?

I cannot speak to how often it may be deployed until (if?) it's sailed. But just like the other 3 options, one would not expect them to be always available.