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Old 01-08-2020, 14:28   #2056
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Re: Oceanvolt Hybrid Motor

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Old 01-08-2020, 19:27   #2057
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Re: Oceanvolt Hybrid Motor

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For tiny power generation (500W) you are right. But for significant power, say 2kW, it is more complicated. Almost all regen systems use variable pitch props though. A fixed prop is a terrible idea for a regen system.

At significant power like 2kW the efficiency of the system comes into play. Let’s say the system is 50% efficient (that would be a very high estimate) then it needs 4kW of power from the sails. For a moderate cruising boat that means significant drag and that requires more canvas than you would otherwise need. It is akin to trying to get a displacement hull to climb up its own bow wave. More drag means more opportunities to break something.

But if all you want is 500W then fine. But solar can do that with almost no drag. So what is the benefit of regen except when on 24 hour per day passages? That represents what, maybe 0.1% of a cruising boat’s life?
Since we seem to be just throwing numbers around regarding regen, here are some.

Critics of regen seem to be saying there is a terrible boatspeed-drag penalty, and there are stresses on the boat, and you need lots more sail area to compensate for the supposed "losses" caused by the regen. I would say all of these downsides are imaginary, and here is why.

It is obvious that the energy it takes to spin the OV prop in regen mode is at the expense of boat momentum, but the key question is "how much"? The figures for OV regen are about 1.5kW at say 8 knots boatspeed.

On Boat Design.net there is a basic discussion thread Horsepower/Sail Area equivalence that discusses how much wind energy per square meter of sail area it takes to move a given boat travelling at given speed. The actual modelling computations to accurately answer this question will be much more complex than the basics given in the Boat Design thread, but it will suffice to get us in the right ballpark.

From the discussion thread mentioned above, a boat travelling at 5m/sec (or approx. 10 knots) in 10m/sec (19knots) apparent wind on a beam reach has 150 Newtons per square meter of sail area of wind force. Power = Force x Velocity so 150 Newtons x 5 m/sec boatspeed equates to 750 watts per SQM sail area or about 1 horsepower/m2 sail area.

So for a typical cruising cat with a 70 sqm mainsail and 40 sqm jib, it takes 750 watts x 110= 82,500 watts or 82.5kW of wind energy.

If we take away 1.5kW of drag caused by the regen system, we have reduced about 2% of the energy from the boat. ( 1.5kW/ 82.5kW x 100=1.8%)

Do you really think you can practically see the speed loss from 2% of the boats driving sail force? Really? Tell me which GPS you're using, I want one!

Are you going to put up 2% more sail area to compensate? I didn't think so....

From personal experience having been on cruising cats with OV systems in regen mode being turned on and off I can say any loss of boatspeed is very hard to detect at 8 knots. Maybe half a knot on average but very hard to see it amongst the varying speeds as given by GPS SOG readings.

As for supposed stresses on the boat imposed by the regen, I don't get that at all. Sounds like F.U.D. to me unless some numbers can be put towards that argument for support.
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Old 01-08-2020, 19:40   #2058
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post
Since we seem to be just throwing numbers around regarding regen, here are some.

Critics of regen seem to be saying there is a terrible boatspeed-drag penalty, and there are stresses on the boat, and you need lots more sail area to compensate for the supposed "losses" caused by the regen. I would say all of these downsides are imaginary, and here is why.

It is obvious that the energy it takes to spin the OV prop in regen mode is at the expense of boat momentum, but the key question is "how much"? The figures for OV regen are about 1.5kW at say 8 knots boatspeed.

On Boat Design.net there is a basic discussion thread Horsepower/Sail Area equivalence that discusses how much wind energy per square meter of sail area it takes to move a given boat travelling at given speed. The actual modelling computations to accurately answer this question will be much more complex than the basics given in the Boat Design thread, but it will suffice to get us in the right ballpark.

From the discussion thread mentioned above, a boat travelling at 5m/sec (or approx. 10 knots) in 10m/sec (19knots) apparent wind on a beam reach has 150 Newtons per square meter of sail area of wind force. Power = Force x Velocity so 150 Newtons x 5 m/sec boatspeed equates to 750 watts per SQM sail area or about 1 horsepower/m2 sail area.

So for a typical cruising cat with a 70 sqm mainsail and 40 sqm jib, it takes 750 watts x 110= 82,500 watts or 82.5kW of wind energy.

If we take away 1.5kW of drag caused by the regen system, we have reduced about 2% of the energy from the boat. ( 1.5kW/ 82.5kW x 100=1.8%)

Do you really think you can practically see the speed loss from 2% of the boats driving sail force? Really? Tell me which GPS you're using, I want one!

Are you going to put up 2% more sail area to compensate? I didn't think so....

From personal experience having been on cruising cats with OV systems in regen mode being turned on and off I can say any loss of boatspeed is very hard to detect at 8 knots. Maybe half a knot on average but very hard to see it amongst the varying speeds as given by GPS SOG readings.

As for supposed stresses on the boat imposed by the regen, I don't get that at all. Sounds like F.U.D. to me unless some numbers can be put towards that argument for support.
Thank you
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Old 01-08-2020, 20:22   #2059
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Re: Oceanvolt Hybrid Motor

You're welcome cj.

By the way, we also had discussion with a Naval Architect who came up with about 1% reduction of sail force effect of regen with the OV system, so the ballpark figure of 1% to 2% seems about right, as I said many, many months ago when some were saying OV regen was like towing a bucket behind the boat.
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Old 02-08-2020, 00:45   #2060
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Re: Oceanvolt Hybrid Motor

I read through your post with interest as it was an intelligently considered response... and thought "who's writing this?" ... i was delighted to see it was you ss you've been understandably quiet for a while.. welcome back!
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Old 02-08-2020, 01:15   #2061
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post

It is obvious that the energy it takes to spin the OV prop in regen mode is at the expense of boat momentum, but the key question is "how much"? The figures for OV regen are about 1.5kW at say 8 knots boatspeed.
Thanks for the synthesis and links, when you say 1.5kW for OV, does this refer to the Servoprop or the "standard" SD15 saildrive ?

Note : it still baffles me quite a bit that regen works with "standard" folding props, by putting the motor in propulsion mode to open the prop, and then put the motor in regen mode and the prop stays opened.

Any return on experience with that ?
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Old 02-08-2020, 01:37   #2062
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Re: Oceanvolt Hybrid Motor

Yeh, it would be hard to imagine regen causing a significant stress on the rig considering everything else it goes through. Especially given the other critique is that regen only works on passage which is 10% or less of the time.

Sailing Uma and everyone else going that route is very open about the system only makes sense if you understand the drawbacks. Non of them says it can replace a diesel, infact they advice against replacing a diesel if your one is working fine. But if it's a new build or a replacement is needed for a diesel is needed anyway then the option becomes very interesting for a lot of people.

Also, no one is saying or even suggesting it can replace solar but solves the issue of sails shading the solar array underway.

This is a pretty honest discussion of what can be expected out of electric motors:
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Old 02-08-2020, 03:13   #2063
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Re: Oceanvolt Hybrid Motor

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Originally Posted by BigBeakie View Post



So for a typical cruising cat with a 70 sqm mainsail and 40 sqm jib, it takes 750 watts x 110= 82,500 watts or 82.5kW of wind energy.

.
Ha, this is too funny.

So sails are sheeted at right angles to the wind and flat as a board, literally, for the purposes of this example.

So the boat actually moves forward?

Very intesting.

People actually accept what you say??
Or have I missed the just joke'n font??
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Old 02-08-2020, 04:11   #2064
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Re: Oceanvolt Hybrid Motor

Quote:
Originally Posted by BigBeakie View Post
Since we seem to be just throwing numbers around regarding regen, here are some.

Critics of regen seem to be saying there is a terrible boatspeed-drag penalty, and there are stresses on the boat, and you need lots more sail area to compensate for the supposed "losses" caused by the regen. I would say all of these downsides are imaginary, and here is why.

It is obvious that the energy it takes to spin the OV prop in regen mode is at the expense of boat momentum, but the key question is "how much"? The figures for OV regen are about 1.5kW at say 8 knots boatspeed.

On Boat Design.net there is a basic discussion thread Horsepower/Sail Area equivalence that discusses how much wind energy per square meter of sail area it takes to move a given boat travelling at given speed. The actual modelling computations to accurately answer this question will be much more complex than the basics given in the Boat Design thread, but it will suffice to get us in the right ballpark.

From the discussion thread mentioned above, a boat travelling at 5m/sec (or approx. 10 knots) in 10m/sec (19knots) apparent wind on a beam reach has 150 Newtons per square meter of sail area of wind force. Power = Force x Velocity so 150 Newtons x 5 m/sec boatspeed equates to 750 watts per SQM sail area or about 1 horsepower/m2 sail area.

So for a typical cruising cat with a 70 sqm mainsail and 40 sqm jib, it takes 750 watts x 110= 82,500 watts or 82.5kW of wind energy.

If we take away 1.5kW of drag caused by the regen system, we have reduced about 2% of the energy from the boat. ( 1.5kW/ 82.5kW x 100=1.8%)

Do you really think you can practically see the speed loss from 2% of the boats driving sail force? Really? Tell me which GPS you're using, I want one!

Are you going to put up 2% more sail area to compensate? I didn't think so....

From personal experience having been on cruising cats with OV systems in regen mode being turned on and off I can say any loss of boatspeed is very hard to detect at 8 knots. Maybe half a knot on average but very hard to see it amongst the varying speeds as given by GPS SOG readings.

As for supposed stresses on the boat imposed by the regen, I don't get that at all. Sounds like F.U.D. to me unless some numbers can be put towards that argument for support.

Dude,

You didn’t take physics in university did you?
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Old 02-08-2020, 06:33   #2065
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Re: Oceanvolt Hybrid Motor

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Dude,

You didn’t take physics in university did you?
Says the guy that only uses "adjectives" when refering to values, and consider a 500kW power source on a sailboat as "tiny".

Quite funny
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Old 02-08-2020, 08:19   #2066
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Re: Oceanvolt Hybrid Motor

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Says the guy that only uses "adjectives" when refering to values, and consider a 500kW power source on a sailboat as "tiny".

Quite funny

500kW would not be a tiny power source in anyone’s book.
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Old 02-08-2020, 10:10   #2067
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Re: Oceanvolt Hybrid Motor

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500kW would not be a tiny power source in anyone’s book.
Sure, typed too quickly, however around 10 square meters of PV on a sailboat is still a tiny source rigth ?
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Old 02-08-2020, 17:17   #2068
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Re: Oceanvolt Hybrid Motor

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Thanks for the synthesis and links, when you say 1.5kW for OV, does this refer to the Servoprop or the "standard" SD15 saildrive ?

Note : it still baffles me quite a bit that regen works with "standard" folding props, by putting the motor in propulsion mode to open the prop, and then put the motor in regen mode and the prop stays opened.

Any return on experience with that ?
yvest,

That was for the Servoprop, the SD15 and AXC series is about 25%-30% less output at a given boatspeed. I think one of the issues, paradoxically, with the Servoprop is that it might generate too much power at higher boat speeds and the output may have to be throttled back on fast boats. For example at 12 knots the Servoprop is putting out about 4kW of charging PER MOTOR, and that's some serious amps!

Yes the operation of the regen on regular folding props is somewhat counterintuitive at first, but basically, and simply, the motor controller is smart enough to monitor, and control, the prop rpm. So when the flowing water pressure over the blades is trying to collapse the blades ( and drop the RPM), the motor spins the prop just enough to open up the blades so the water can turn the prop. The amount of power it takes to do this is quite low, so as the boat speed increases, the extra RPM from the water flow generates power in excess of what is being used to keep the blades open. The faster the boatspeed, the greater the delta between the power used to keep the blades open and the power being generated.

Does that answer your question or do you have another aspect of it that you're wondering about?
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Old 03-08-2020, 11:09   #2069
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Re: Oceanvolt Hybrid Motor

BigBeakie, thanks a lot for the info, I didn't realize the controller is monitoring the prop permanently in regen mode and can "add power" at any time in this mode.
(also explains why Conrad Colman had a quite sophisticated agreement with the race organisation during the last VG)
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Old 03-08-2020, 17:46   #2070
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Thumbs up Re: Oceanvolt Hybrid Motor

Quote:
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BigBeakie, thanks a lot for the info, I didn't realize the controller is monitoring the prop permanently in regen mode and can "add power" at any time in this mode.
(also explains why Conrad Colman had a quite sophisticated agreement with the race organisation during the last VG)
Actually since the OV motor can be monitored and datalogged for the whole Vendee race, the organisers would have full transparency on all motor use data, i.e. whether the motor was used for propulsion at all, or only regen.

For this Vendee Globe, Alex Thomson racing chose the same Oceanvolt motor we did which is the shaft drive ACX 20kW. He sure won't have any power shortage issues, that's for sure
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