Arto

I like electric drives too.  This is my little trimaran under electric power at 440W drain from the battery:

https://www.youtube.com/watch?v=WRzr63FkAPM

It has a range of 50nm at 5kts under battery alone; no generator and also no intention to regenerate.  I have 400W of solar panels and can do 5kts drawing 200W from the battery.

However a 38ft mono is a different boat to a lightweight, bi-directional HP.  The battery could be placed low in the hull as extra ballast and to improve righting moment. The boat is not as sensitive to added weight as a HP.  Unless the boat has the ability to plane, it is limited to around 9kts under sail and takes considerable force to achieve that speed so adding drag to regenerate is not significant..  The wave drag will rise rapidly above 5kts so regenerating at speeds above 5kts would not have much impact on boat speed.  They would notice the drag in light winds.  And even more noticeable in light wind going to weather.  Do you know the make of the boat? 

10 hour operation would cover most circumstances but 40nm under battery without recharging is still a limitation.  It would not get through a windless night.  On the other hand it is possible to recharge with sun or wind almost anywhere.  By contrast, you cannot purchase fuel away from land. 

For extended cruising on a larger HP,  I would opt for a small diesel generator around 3kVA and at least 20l of fuel - about 100kg of added weight for around $1000.  Almost any modern electric propulsion will have the ability to regenerate.  However the diesel adds tremendous utility over an extra 100kg of battery.  Still place the maximum number of solar panels you can fit on locations that are not working areas.   

Rick

On 29 Aug 2019, at 10:22 pm, Arto Hakkarainen ahakkara@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:

To continue a bit on this topic:

Some high profile ocean racers are choosing Oceanvolt now. See Alex Thomson and Hugo Boss Racing https://www.alexthomsonracing.com/oceanvolt/ 

Also two weeks ago in Helsinki floating boat show I talked with the owner who was presenting his boat with Oceanvolt and 22 kw battery. He said he can motor 10 hours at 4-5 knots (38 foot Swedish made monohull that sails well) and that he is never going back to diesel.

So still pricy but to me more and more attractive option. Of course better the boat sails including light weather the more attractive the electric option becomes.

Also they have a bit different system to charge while sailing. The system limits the folding propeller to rotate at 600 rpm or 10 rps that is enough to keep the blades open. Also they claim that the slowing down is negligible. Seems like they limit the charging and also the slow down of the vessel. 

Arto