Oceanvolt Servoprop regen tested by UMA

[tp12]

Originally Posted by Muaddib1116

UMA is a Pearson 36, btw.

Ahhh, thank you!

[tp12]

Originally Posted by Muaddib1116

In what way have I dismissed them? I literally discussed them here. The fact that I have made an accurate observation of them does not mean I have dismissed them.

You were dismissing them. Your latest quote is simply a description and doesn't address the numbers found in any meaningful way

[Muaddib1116]

Originally Posted by tp12

You were dismissing them. Your latest quote is simply a description and doesn't address the numbers found in any meaningful way

So because I was describing the results in the video for people who haven't/couldn't watch it, with no statement about my thoughts on how valid those results are, that means I've dismissed those results? Find a quote from me where I said that their results were not worth anything. Observing the limitation of those results is not a dismissal.

[BillKny]

Originally Posted by Paul L

So how many watts are generated per 0.1 nm of drag?

OK, here is where the real physics comes in... and you'll have to work with me for a bit, because the answer is IT DEPENDS. It depends on how fast you are sailing, and what how easily your boat moves through the water.

I'll use my 52 foot monohull as an example, just because I have all the numbers, and for a first cut, I'll ignore friction and a few other inefficiencies.

To push my boat at 6.5 knots with a propeller takes 54 HP at the shaft. I know this from my engine power curve.

To move a boat through the water, power required increases with the CUBE of the speed.

So if I am sailing at 8 knots (comfortable fast cruising at 15 to 17 knots of true wind), my sails are generating roughly:

(8^3 / 6.5^3)* 54HP = 101HP

If I extract enough power to reduce my speed to 7.9 knots that would be:

101HP - ((7.9^3 / 8^3) * 101HP) = 3.8HP

or about 2.8 kW.

If we are using a good permanent magnet alternator we should be converting that to electrical power at >>90% efficiency, so lets say 2.5kW.

It's important to remember that the 0.1 knot of speed loss you ask about generates a LOT less power at lower speeds. (Remember that cubic relationship?) Going from 5 knots to 4.9 knots in my boat would have 1.4 HP extracted, and less than 1kW available for battery charging.

[Muaddib1116]

Originally Posted by Muaddib1116

I think the results they showed were probably accurate to what they were experiencing, ie they weren't lying. But the brief bit they showed was hardly scientific, and certainly not comprehensive. I think I believe that the system works pretty well, and that it wasn't a fluke. But as NaCLyDog said, it's definitely subjective whether the results are worth the performance loss, and it would be in Oceanvolts interest to come up with some more objective lab results.

These are the only subjective statements I have made. One, that I think they weren't lying to us, the viewers, about what they were getting. And two, that I think the system looks like it works pretty well.

[mglonnro]

Originally Posted by NaClyDog

Something isn't adding up... the OV site states the following;





How is roughly $40K 20-25% more than the cost of a traditional system??? How on earth do you get a ROI in 2-3 years?


More marketing hype it seems...

I got a proposal for our Hanse 388 1.5 years ago. Roughly:

- SD15 ServoProp including cooling fin (21.5 k€)
- LIFEPO4 battery system 14 kWh + BMS (14 k€)
- Shore power charger/inverter + remote controller (1.3 k€)
- Certification by OV (750 €)
- Total: 37.55 k€

I replaced the engine + saildrive in a similarly sized boat in 2014:

- Volvo D1-30 engine, 130-S-B saildrive, *installed* (11 k€)

On Volvo's price list 2021 I see that the same combo costs about 10 k€ today *without* installation, so comparing that to the SD15, the SD15 unit is a bit more than double the price...

[tp12]

Originally Posted by Muaddib1116

So because I was describing the results in the video for people who haven't/couldn't watch it, with no statement about my thoughts on how valid those results are, that means I've dismissed those results? Find a quote from me where I said that their results were not worth anything. Observing the limitation of those results is not a dismissal.

We're going around in circles here. Describing the results is fine for others but you were responding to me; explaining why they're not useful is not addressing the actual numbers in any meaningful way and is dismissing them.

I hope you understand this and apologies if we're just talking past each other here. I don't see any more value in explaining why you think they're not scientific etc - we know that already and to revisit that isn't progressing the discussion. What about the actual numbers, are they good, not good, worthwhile or not, cost effective (unlikely yet) etc

I hope that makes sense

[Paul L]

Originally Posted by BillKny

OK, here is where the real physics comes in... and you'll have to work with me for a bit, because the answer is IT DEPENDS. It depends on how fast you are sailing, and what how easily your boat moves through the water.

I'll use my 52 foot monohull as an example, just because I have all the numbers, and for a first cut, I'll ignore friction and a few other inefficiencies.

To push my boat at 6.5 knots with a propeller takes 54 HP at the shaft. I know this from my engine power curve.

To move a boat through the water, power required increases with the CUBE of the speed.

So if I am sailing at 8 knots (comfortable fast cruising at 15 to 17 knots of true wind), my sails are generating roughly:

(8^3 / 6.5^3)* 54HP = 101HP

If I extract enough power to reduce my speed to 7.9 knots that would be:

101HP - ((7.9^3 / 8^3) * 101HP) = 3.8HP

or about 2.8 kW.

If we are using a good permanent magnet alternator we should be converting that to electrical power at >>90% efficiency, so lets say 2.5kW.

It's important to remember that the 0.1 knot of speed loss you ask about generates a LOT less power at lower speeds. (Remember that cubic relationship?) Going from 5 knots to 4.9 knots in my boat would have 1.4 HP extracted, and less than 1kW available for battery charging.

So is that a rounding error where a theoretical 2.8kw gets demonstrated as 300 watts?

[Muaddib1116]

Originally Posted by tp12

We're going around in circles here. Describing the results is fine for others but you were responding to me; explaining why they're not useful is not addressing the actual numbers in any meaningful way and is dismissing them.

I hope you understand this and apologies if we're just talking past each other here. I don't see any more value in explaining why you think they're not scientific etc - we know that already and to revisit that isn't progressing the discussion. What about the actual numbers, are they good, not good, worthwhile or not, cost effective (unlikely yet) etc

I hope that makes sense

I have never once said that the results were not useful.

What I've tried to do is make sure people don't think they are gospel.

You are fighting the wrong fight here. I have made it clear that I don't think UMA was trying to be deceptive, and that I think the system (implicitly from their results) looks pretty good. If you want me to expound on my thoughts on what they showed in the video or my thoughts on electric propulsion or oceanvolt are, then ask that, don't accuse me of something I haven't done. The only reason I've done any revisiting is that you keep saying that I did something I didn't do.

My thoughts overall on electric propulsion and regen are that the technology is very young. This latest system of UMA's seems very promising. I think that the wattage they are seeing, and losses that they are not, is due to doing ~6.5kts SOG, which has to be near their hull speed. As others have said, I think that that level of regen probably drops drastically as speed drops. I will wait for them to share some impressions after spending more time with the system.

As far as the viability for this type of system overall, I think I mentioned that price is probably an issue, and that utility is limited based on what type of sailing you do. UMA's sailing philosophy, while admirable, is not common.

[BillKny]

Originally Posted by Paul L

So is that a rounding error where a theoretical 2.8kw gets demonstrated as 300 watts?

It is not a "rounding error."

I presented what could be produced with a big, slower boat with sails fully powered up, in a best case. If you slow the boat less that 0.1 knot, or you use a system that is inherently inefficient (like a field coil alternator) you can lose a lot, fast..

To REALLY slow a boat 0.1 knots while it is sailing at nearly hull speed is REALLY HARD. It takes a big prop with variable pitch to extract this much power from the water.

[tp12]

Originally Posted by Muaddib1116

and that I think the system (implicitly from their results) looks pretty good.

My thoughts overall on electric propulsion and regen are that the technology is very young. This latest system of UMA's seems very promising. I think that the wattage they are seeing, and losses that they are not, is due to doing ~6.5kts SOG, which has to be near their hull speed. As others have said, I think that that level of regen probably drops drastically as speed drops. I will wait for them to share some impressions after spending more time with the system.

As far as the viability for this type of system overall, I think I mentioned that price is probably an issue, and that utility is limited based on what type of sailing you do. UMA's sailing philosophy, while admirable, is not common.

I've edited out the unnecessary stuff. Now we're progressing the conversation.

I'd love to see more data, scientific or not, from multihull applications as this will affect the cost benefit argument.

If anyone has more contributions regarding regen at higher speeds I'm all ears.

[mglonnro]

Originally Posted by tp12

I've edited out the unnecessary stuff. Now we're progressing the conversation.

I'd love to see more data, scientific or not, from multihull applications as this will affect the cost benefit argument.

If anyone has more contributions regarding regen at higher speeds I'm all ears.

That's interesting, but regen at lower speeds is interesting as well. The difference in drag/sailing speed in light air conditions regen prop vs folding. If much of the sailing is much slower than "nearly hull speed", how much slower will I sail with a regen prop not doing much regen vs a folding prop folded away.

[mglonnro]

A screencap of the bar chart they showed:

[tp12]

Originally Posted by mglonnro

That's interesting, but regen at lower speeds is interesting as well. The difference in drag/sailing speed in light air conditions regen prop vs folding. If much of the sailing is much slower than "nearly hull speed", how much slower will I sail with a regen prop not doing much regen vs a folding prop folded away.

Sure, it's interesting I agree.

In the multi forum, though, aren't multi applications more interesting? They are to me, at least. Ok, I confess to being focused on the performance end of the multi spectrum. Boats trading accommodations and payload for light weight and speed

[tp12]

Originally Posted by mglonnro

A screencap of the bar chart they showed:

Attachment 245367

You've reminded me of a question I had myself during the video - pinching? Is he describing pointing as high maintaining some speed as you can as pinching? I'm thinking pinching is the first flutter at the luff and losing drive? What's his understanding bearing in mind he's not a racing sailor

I would have thought he'd be wanting to obtain data for close hauled and not pinching; hence my wondering on his definition of pinching.

Oh and I thought I should type pinching one time - pinching...








Pinching