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**StuM** · 07-05-2017, 23:38

Quote:

Originally Posted by Claude-D

Ok, let me try again. The maximum that can be delivered from the Oceanvolt AX8 is 8kW, maximum 2250 RPM, gear reduction 2.46:1

The Yanmar 38hp give a maximum speed of 6.7knots. The reduction is 3.4:1 I think.

So the question is what will be the maximum speed for the Oceanvolt? Using the same Propeller.

You believe that the Oceanvolt cannot reach maximum RPM in that situation? As the Yanmar deliver 12 kW at 2250 RPM. And Yes we do have to adjust for the difference in reduction gear.

OK, let me try again. Is that 2250 RPM crankshaft (before the gear reduction) or propshaft (after the gear reduction).

You previously stated 2250 RPM when asked what the prop RPM was. Was that an error? If in fact you are now stating that the prop RPM is 2250 / 2.46 = 915 RPM, then this is a different situation entirely.

As an example, a 39HP Yanmar 3JH5E normally has a 2.23 or 2.49 reduction on a sail drive (depending on prop selection).

At 2.23:1 , it would be running at 2018 RPM for the same prop RPM as the OV's max (915 x 2.23).

At 2000 RPM, the prop power curve of the the 3JH5E shows a smidgin over 8 kW.

So yep, your OV AX8 running flat out can match the power output/ prop RPM of a 28HP Yanmar which is ticking over at 2/3 of max RPM and 20% power and the boat speed will be the same.

But if it is taking "full throttle" on that YANMAR to achieve that speed, then the prop is turning at 1345 RPM. To get the same prop RPM from you OV, you'd need to be running it at 3300 RPM, which you clearly can't do. IOW, your boat speed will be limited by your maximum 915 prop RPM and will be a lot lower than that generated by the YANMAR's 1345 RPM.

(Hey, Deja Vu! Didn't I write something very similar several pages ago)

But to get back to your 6.7 knots at full power in calm conditions, is this a hypothetical or is it based on a real example. If the latter, I'd strongly recommend a prop and hull clean for a start, followed by a look at what propellor was fitted if the anti fouling didn't make a difference.

The above 2000 RPM is what I would expect to use in order to get that speed out of that type of engine on that type of boat. And also what I'd expect to get out of your 8kW electric motor at full power in the same conditions.

**StuM** · 07-05-2017, 23:55

Quote:

Originally Posted by Claude-D

Quote:
Originally Posted by SDChristian

Attention OceanVolt: to build credibility, please equip two identical small sailboats w standard diesel and oceanvolt deisel/hybrid for same day, real world comparisons. This would help so much to manage speculation and varying claims/counter-claims. Couple of 35 foot monohulls would do.

There are a few already around. Our problem is that we have not talked about it enough... You may like to have a look here: Monohull Archives - Oceanvolt

Reading comprehension difficulties?

SD asked for a comparison between two identical small sailboats boats in the same conditions,

Your link doesn't give any comparisons whatsoever. Just more glossy puff pieces with zero performance data.

BTW, SD addressed an "open post" to "Attention Oceanvolt".

You replied with "our problem" and "we". Do I take it from that that you are actually an employee and/or official representative of Oceanvolt.

ranchero76 · 08-05-2017, 00:24

Quote:

Originally Posted by 44'cruisingcat

15 kw of solar requires about 75 square metres. Think about it. That's 10m X 7.5m. About the entire horizontal surface area of a 40 foot cat.

Ever heard about retractable panels? We come back to the point that this is not for everyone. It's for big cats, like that Kato, which has ability to carry these retractable panels. I'm throwing very rough numbers, precise calculating of particular boat needs will give better idea. Maybe 8-10 kW will be enough, which will take way less space.

Quote:

Originally Posted by cwjohm

Wow, 10-15Kw of solar to save $1.50 per hour to run the genny. Just shows you need a lot of greenbacks to be green.

It's not about "been green", I've repeated this many time. It frees my mind. I prefer (BY FAR!) to spend money one time, even if it's 100k addition to the boat price. Call it part of purchase price. And then forget about it, never try to separate it from boat purchase price or from other modifications.
And then, when is "no wind" situation, "wrong wind" situation, "not enough wind" situation, and 2-3-4 hours trip is needed, there's no hesitation needed! Just go on EP!
I've seen countless - literally countless such situations. People hesitating - "should we wait for good wind"? Or "should we sail at 2-3 knots"? Or "should we start the engines and spend $10 of diesel plus wear and tear for that short trip"? And it's not last $10 in their pockets, but they ALWAYS will hesitate like this!
Same with everything else. "Should we take hot shower or save water?" "Should we turn on AC?" Or, "let's start generator and start running like crazy, trying to charge laptops, do laundry, charge dive tanks and enjoy air condition, all at the same time!".

Much easier with EP, big solar/battery bank. Just learn how much energy can be used to keep batteries charged, and enjoy free energy for everything (cost of purchase and installation excluded). Nobody adds boat purchase price to annual cruising cost.

cwjohm · 08-05-2017, 00:35

Quote:

It frees my mind. I prefer (BY FAR!) to spend money one time, even if it's 100k addition to the boat price. Call it part of purchase price. And then forget about it, never try to separate it from boat purchase price or from other modifications.
And then, when is "no wind" situation, "wrong wind" situation, "not enough wind" situation, and 2-3-4 hours trip is needed, there's no hesitation needed! Just go on EP!

Could not agree more. As I have stated many times there is no financial justification - only emotional ones. Of course you have to have the extra $100K to spend in the first place, or be prepared to allocate that extra $100K with no financial justification. In reality that eliminates 99% of boat buyers.

ranchero76 · 08-05-2017, 00:43

Request of "comparing two same boats equipped with diesel and EP" doesn't make sense. It is NORMAL that electric cars have all construction optimized for them. So it's also normal that boat with EP will be optimized for EP and won't be same or similar as boat with diesel. And regarding the price (purchase and installation price) - nobody anywhere tells that at the current stage EP (complete proper system with solar/battery) can compete with diesel propulsion price-wise.
EP on sailboat only barely starts making sense. But it's cool, quiet, and it definitely has future. That Kato is dream boat.

44'cruisingcat · 08-05-2017, 00:45

Quote:

Originally Posted by ranchero76

Ever heard about retractable panels? We come back to the point that this is not for everyone. It's for big cats, like that Kato, which has ability to carry these retractable panels. ....

No, I can't say I've ever seen retractable solar panels. Not 75m2 of them anyway.

BTW I think Kato has 1.75 kw of solar.

You need to do some simple arithmetic. Look at how much power a big, heavy cat with multiple aircon units etc will require to move it into a decent wind. Work out how many amp hours of batteries it would take to go for 2 or 3 hours. How many hours any sensible solar array (not 50 - 75 m2) would take to replace it. Then remember you want your air on all night, your multiple fridges freezers, icemakers,hot water, cooking, etc etc etc.....

Solar just won't do it.

This system will be viable on Kato, principally for one reason: that boat is a superb sailing machine. It's not going to motor much.

cwjohm · 08-05-2017, 00:56

Quote:

Ranch says

nobody anywhere tells that at the current stage EP (complete proper system with solar/battery) can compete with diesel propulsion price-wise.

Bigbeakie does!

Quote:

EP on sailboat only barely starts making sense. But it's cool, quiet, and it definitely has future.

I do not think anybody on this forum disagrees with this. It is simply a matter of disagreement of how far off the future is.

It is not so much the solar but the amount of battery storage that you need to retain the solar and sail generated power over night and overcast conditions. Kato has a huge amount of Lithium storage that must have cost a pretty penny. Storage densities are the key and will determine when EP becomes viable.

ranchero76 · 08-05-2017, 01:08

Quote:

Originally Posted by cwjohm

I do not think anybody on this forum disagrees with this. It is simply a matter of disagreement of how far off the future is.

It's not that far, Kato is real, so are few other boats.

Quote:

Originally Posted by cwjohm

It is not so much the solar but the amount of battery storage that you need to retain the solar and sail generated power over night and overcast conditions. Kato has a huge amount of Lithium storage that must have cost a pretty penny. Storage densities are the key and will determine when EP becomes viable.

I've missed that - how much battery storage on Kato? I've mentioned above - there's Sunreef 62 on the market which has 68 kWh of Li-Po batteries and that boat is capable to run AC overnight. That amount of storage seems somewhat adequate, unless something with even more efficiency will show up on the market.

fabgo · 08-05-2017, 01:10

Quote:

Originally Posted by StuM

You may guess that, but a little study of basics physics and hydrodynamics will tell you that you are wrong.

Maybe you could enlighten us?

If I have a fixed prop, and I put the engine in neutral, the prop will spin, correct? I take that to mean there is less resistance from a spinning prop.

Similarly, on an OV system, if there was less resistance without the prop spinning, I assume the whole thing would grind to a halt.

Please explain why this is not so.

BigBeakie · 08-05-2017, 01:26

cwjohm,

Thank you, thank you, THANK YOU

Please see my observations below in red and for unwittingly confirming my proposition by using the Kato example!

Quote:

Originally Posted by cwjohm

Now, this is a classic case of confirmation bias that you are constantly harping on about. You do not understand the math, nor have you tried to, but you are more than ready to pose an opinion as to the implied outcome. If you had bothered to study the papers in question you would have found that STATIC THRUST involves the displacement of water past the props with boat stationary and the DYNAMIC THRUST involves the propulsion of the boat through the water and is strongly affected by the characteristic of the resistive force presented i.e. the characteristics of the boat. To say that the difference is 0.9 is as ridiculous as saying that the ultimate solution to life is 14. OK, point accepted that .9 depends on the boat. Fair enough, but ultimately irrelevant for this discussion because...... Now, what is the difference between 290kgf and 320kgf? It's not even math, it's arithmetic. The DIFFERENCE between the 2 motors is only 10% at worst. Let me say that again. The empirically measured difference between the 15kW (20HP) SD15 and the 33kW (45HP) Beta 45 Turbo diesel at WOT is a measly 10%,
at worst. What is your explanation for this? If you had bothered to study the math you would have found that the relationship is heavily non-linear.

The papers in question refer to idealistic characteristics, and so in reality we have to leave it to the marine engineers to identify the correct propulsion equation. One assumes that they can do the math. Ok,
I get all that, but lets take your real world example just below....

As a guideline however, you have unwittingly provided a real world example of Kato 1 vs Kato 2, which are very similar designs but different weights, Kato 1 having diesel motors and Kato 2 having EP motors. Simple calculations show that if Kato 2 were equipped with 45HP diesel motors one would expect motor speeds of 10-12 knots,Correct, well done... but with 15Kw EP motors you get 6 knots.ATTENTION: Kato II with OV SD15's gets 10 knots. It got, past tense, using just the genset6 knots with the under pitched prop, and now gets 7 knots with the newer higher pitch prop on the genset alone!!! which generates 8 kW. So, you have unwittingly confirmed, with a real world example, my proposition that the performance is about the same.
Remember, that the HP/KW equation vs hull speed is non-linear as well. Thus real world data indicates that OV15KW provides nowhere near the equivalent thrust of a 45HP diesel. I will grant you that the EP motor provides more thrust than predicted from the conversion from Kw to HP but not a great deal more. I accept that if I were to equip 30Kw EP to the Helia it MAY be ok but 40Kw would be my preference.

Following this line I would expect that if you were to equip 15KW EP to your Freeflow you would get about 4kn cruising speed. I have actually checked what owners get with their OV Sd15 installations and I can report that it is always very close, within a knot, of the OV prediction.
It was with Kato II just FYI. OV predicted 9 knots at WOT, and they are getting 10, so if anything they are a bit conservative, which personally I like to see. If I were you I would look at 30Kw which should give you similar results to typical production cats.

Thanks, but no thanks.

ranchero76 · 08-05-2017, 01:35

Quote:

Originally Posted by 44'cruisingcat

No, I can't say I've ever seen retractable solar panels. Not 75m2 of them anyway.
BTW I think Kato has 1.75 kw of solar.

Kato is just one prototype. It's their choice for their needs. I personally think 1.75kW is not enough for boat with EP.

I don't see problem mounting 7x3m panel behind flybridge on big cat, and 2 retractable (sliding) 3.5x3m panels underneath it. Total - 42m2

This light panel is 120W, 46.1"x21.2", which works out to be 190W/m2

https://www.amazon.com/Solar-Panel-K...288519a412ea0d

So 42m2 would give 8kW max. If this is not enough, the are places on the side of flybridge, where more flex panels can be fitted, especially if boat will be designed for that.

Quote:

Originally Posted by 44'cruisingcat

You need to do some simple arithmetic. Look at how much power a big, heavy cat with multiple aircon units etc will require to move it into a decent wind. Work out how many amp hours of batteries it would take to go for 2 or 3 hours. How many hours any sensible solar array (not 50 - 75 m2) would take to replace it. Then remember you want your air on all night, your multiple fridges freezers, icemakers,hot water, cooking, etc etc etc.....

From my post above - "Just learn how much energy can be used to keep batteries charged, and enjoy free energy for everything". It doesn't mean there's endless amount of energy. But combining wind/solar/regeneration will give A LOT of energy. And there still should be generator onboard, for extreme situations when all that amount of energy is not enough. So yes, there still will be small fuel expenses from time to time. Hopefully, not so often.

Claude-D · 08-05-2017, 01:50

Quote:

Originally Posted by StuM

OK, let me try again. Is that 2250 RPM crankshaft (before the gear reduction) or propshaft (after the gear reduction).

You previously stated 2250 RPM when asked what the prop RPM was. Was that an error? If in fact you are now stating that the prop RPM is 2250 / 2.46 = 915 RPM, then this is a different situation entirely.

As an example, a 39HP Yanmar 3JH5E normally has a 2.23 or 2.49 reduction on a sail drive (depending on prop selection).

At 2.23:1 , it would be running at 2018 RPM for the same prop RPM as the OV's max (915 x 2.23).

At 2000 RPM, the prop power curve of the the 3JH5E shows a smidgin over 8 kW.

So yep, your OV AX8 running flat out can match the power output/ prop RPM of a 28HP Yanmar which is ticking over at 2/3 of max RPM and 20% power and the boat speed will be the same.

But if it is taking "full throttle" on that YANMAR to achieve that speed, then the prop is turning at 1345 RPM. To get the same prop RPM from you OV, you'd need to be running it at 3300 RPM, which you clearly can't do. IOW, your boat speed will be limited by your maximum 915 prop RPM and will be a lot lower than that generated by the YANMAR's 1345 RPM.

(Hey, Deja Vu! Didn't I write something very similar several pages ago)

But to get back to your 6.7 knots at full power in calm conditions, is this a hypothetical or is it based on a real example. If the latter, I'd strongly recommend a prop and hull clean for a start, followed by a look at what propellor was fitted if the anti fouling didn't make a difference.

The above 2000 RPM is what I would expect to use in order to get that speed out of that type of engine on that type of boat. And also what I'd expect to get out of your 8kW electric motor at full power in the same conditions.

All of the above is clear and very well explained, thank you. However, a couple of points to clarify: No, the boat is not a hypothetical boat, but an old boat with a 39 Hp shaft drive Yanmar. And yes, 6.7 knots is full throttle, and not at 2,000 RPM and this is with a clean bottom. Yes, maybe the propeller is not ideal for this boat, but it has been on the boat for a long time. However, both the propeller manufacturer and the Australian reseller believe that the propellor is the correct one for this boat. You will also be interested to know that they are also of the opinion that swapping the Yanmar for a 8kW Oceanvolt will considerably reduce the maximum speed.

My view is that it is an interesting challenge since the performance of the boat with the Yanmar is known fact. So since we are planning to keep the original propeller. Nothing will change except for the motor.

cwjohm · 08-05-2017, 02:07

Quote:

ATTENTION: Kato II with OV SD15's gets 10 knots. It got, past tense, using just the genset6 knots with the under pitched prop, and now gets 7 knots with the newer higher pitch prop on the genset alone!!! which generates 8 kW. So, you have unwittingly confirmed, with a real world example, my proposition that the performance is about the same.

This would have to be your 4th go at redefining the performance of Kato. I think you just make up stuff to suit your argument when someone takes a contrarian point of view.

Discussion is pointless when the response to any argument is to simply move the goal posts. I think I will join the others in not pursuing this with you any further.

Claude-D · 08-05-2017, 02:15

Quote:

Originally Posted by StuM

Reading comprehension difficulties?

SD asked for a comparison between two identical small sailboats boats in the same conditions,

Your link doesn't give any comparisons whatsoever. Just more glossy puff pieces with zero performance data.

BTW, SD addressed an "open post" to "Attention Oceanvolt".

You replied with "our problem" and "we". Do I take it from that that you are actually an employee and/or official representative of Oceanvolt.

And I gave SD a place where he will find quite a few production boats where some are fitted with Oceanvolt and others of the same brand with diesel. A bit of the same as when Yanmar tell you "on these Beneteau we fit 30hp and on those Dufour we fit those 40Hp" But you will be pleased to know that Oceanvolt supplies a power and range calculation with every quote that they send.

And yes, I am involved with Oceanvolt.