Arto,

  It'd say it's mostly a percentage issue, like weight.

  Another 500 pounds on a 10,000 lb 30' monohull is tough to notice, while another 500 lbs on a 1,500 lb 30' multi makes a huge difference, particularly on a lightweight and easily-driven one like an HP.

  It takes so much energy to get that 30' lead mine moving through the water that the saildrive generator is often a non-issue.  And since hull speed tops out at under 8 knots, there's a limit to the resistance it can create on the upper end.

  That 30' HP, though, is going to fly in light winds, at least in comparison to the monohull.  But with so little energy going into the movement, the drag from the saildrive will be very noticeable.  It will be less significant around 5-10 knots of boat speed, but then become a whole new issue at 15 to 20 knots -- at that point it's applying a lot of force to both the hull and the prop.

---

  I would not consider a sail drive, or fixed rudders for that matter.  There's too much that can go wrong in too many areas.

  If I were going electric, I'd either go for pod motors that swing down, or alternately, a continuous propulsion rated thruster that retracts into the hull (will be less efficient, but will have its own nozzle to increase thrust, plus will work equally in both directions).  I imagine it would work as a generator if you could introduce a proper charge controller into the system.

  Either way:

    - There's nothing valuable to destroy when you hit the bottom, a log, a whale, or a container,

    - There's no resistance in ghosting conditions because nothing is in the water, and

    - There are no worries about exceeding design limits when flying at double-digit speeds.

        - Mike

 

Rick

To help me verify if my thinking is right please correct me if I'm wrong. But like you wrote a monohull sailing faster than 5 knots consumes so much energy moving forward that taking some power from regenerative charging slows the boat only some non significant amount. That I understand well and no counter arguments there. Also since moving a sailboat at slow speed say 2-3 knots takes so little energy that there is no power to use for regenerative charging. 

But when talking about multis that are not limited to hull speed it still takes a lot more energy to sail faster. Velocity squared? So accelerating from 5 to 6 knots takes a lot less energy than from 10 to 11 or 15 to 16. So does that mean that taking for example 1 kw of regenerative charging slows the boat less when moving 15 than 10 knots? And a lot less than when moving 5 knots? And that you shouldn't even think of regenerative charging at speeds below 6 knots?

Also to me it seems that any electric propulsion on sailboat requires the boat to be so well sailing and easily sailed that people really sail and don't motor. To me that means several requirements to make sailing convenient and effective:

1) Boat sails well on light wind conditions.

2) Setting and dousing sails is easy and convenient.

3) Reefing is as easy possible, preferably a non-issue. Nothing like grinding in the one line reef through zillion blocks on modern monohulls while keeping the boat bow to wind and having the main sail boom and all the lines flogging just above your head while grinding in the reef. It must be a lot less of hassle and stress.

4) Sea kindly motion in heavy weather and big seas. 

Just my thoughts while doing the planning. And hope my English is understandable… 

Arto

On Friday, August 30, 2019, 05:32:39 AM GMT+3, Arto Hakkarainen ahakkara@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:

 

Cool!

Boat is Arcona 380. See https://arconayachts.se/boat/arcona380/ 

Thanks for well informed response.

Arto 

Lähetetty Samsung Galaxy -älypuhelimesta.

-------- Alkuperäinen viesti --------

Lähettäjä: "Rick Willoughby rickwill@bigpond.net.au [harryproa]" <harryproa@yahoogroups.com.au>

Päivämäärä: 30.8.2019 2.42 (GMT+02:00)

Saaja: harryproa@yahoogroups.com.au

Aihe: Re: [harryproa] Dragging a prop

 

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