Oceanvolt Hybrid Motor

[myocean]

Originally Posted by BigBeakie

We did the wind resistance study for the Freeflow 50 and OV helped us with their modelling understand what forces were involved and the power required. We are confident we will be able to motor into 40 knot wind and pick up the anchor, to "get outta there".

This sounds quite exciting! Could you please provide more details about this?

[BigBeakie]

Originally Posted by myocean

This sounds quite exciting! Could you please provide more details about this?

What would you like to know?

[myocean]

Originally Posted by BigBeakie

What would you like to know?

What exactly is the power needed to overcome windage (@windspeed) and what is the power to overcome resistance of the 2 hulls in the water (@kts)?

[44'cruisingcat]

How fast will you be able to motor into 40 kts, and for how long?

There's an electric powered Schionning recently launched in Germany that can motor continuously at only four knots, in flat calm. I doubt it will be able to maintain steerage way into 20-25 kts.

[BigBeakie]

Originally Posted by myocean

What exactly is the power needed to overcome windage (@windspeed) and what is the power to overcome resistance of the 2 hulls in the water (@kts)?

Myocean;

Rather than sell you a fish, I'll teach you how to fish

Meaning, each boat should do it's own analysis because the determining factor
for assessing the wind resistance is the total frontal area of your boat. Be sure to include the total area of mast and shrouds, furled headsails etc. You can count the diameter of the mast and shrouds as a flat surface, i.e. maximum wind force, because round objects are close to flat objects because of parasitic drag behind them.

If you don't have total frontal area from your designers CAD program, you can get a useful approximation by using either a scaled drawing front on, or take a photo front on and make measurements.

With Oceanvolt, they take your boats relevant measurements and they have their own math algorithm that estimates all forces and resistance. So you will get the resistance and power curves for your design, at your displacement. Their calcs have been shown to be a bit conservative as compared to the actual performance that has been achieved by 3 projects that I am aware of the numbers.

With adverse wind conditions, you are not concerned with going fast through the water obviously, so water resistance is not the major factor, by far.

Once you know your total frontal surface area, go to Engineering Toolbox and look up the wind force per square meter curve to determine the total wind force in Newtons for given windspeed. Then look at your Oceanvolt speed vs resistance curve to see what your hull resistance is at full power. Find what wind speed/sqm multiplied by your total frontal area in sqm equals your max speed hull resistance, and you have an estimate of the wind force that will stop your boat.

We also had Oceanvolt validate our calculations with the proper math, and it was close enough to give us a useful metric.

Our worst case scenario we were examining was needing to pick up the hook and get out of a dangerous/poor holding anchorage under heavy wind.

We would never be motoring into 40 knots winds continuously, as there are much better options for a sailboat for that scenario. Our boat is designed as a bluewater boat with a heavy duty, reefing staysail (Cutter rig) and deep third reefed main. So another posters question about how fast and how long we could motor into a 40 knot wind is irrelevant for us.

[BigBeakie]

Originally Posted by 44'cruisingcat

How fast will you be able to motor into 40 kts, and for how long? Irrelevant. Fast enough and far enough to pick up the hook , get through the coral pass against run out (depending on the pass). Would never do that anyway.
How fast can your Oram motor into a 40 knot headwind?

There's an electric powered Schionning recently launched in Germany that can motor continuously at only four knots, in flat calm. I doubt it will be able to maintain steerage way into 20-25 kts.

Perhaps they have undersized their system. So what?

[Claude-D]

Originally Posted by 44'cruisingcat

How fast will you be able to motor into 40 kts, and for how long?

There's an electric powered Schionning recently launched in Germany that can motor continuously at only four knots, in flat calm. I doubt it will be able to maintain steerage way into 20-25 kts.

Interesting to see how much our cognitive bias influences our perception of reality…

I am assuming he is referring to this Catamaran catbuildingblog.com | building a schionning arrow 1200 catamaran A very nice boat, a good design and a nice electric motor installation. And a successful installation. The owner was pretty clear in his wants and needs, and gives a clear description of it in here The electric system on our Arrow 1200 | catbuildingblog.com You know, after reading his blog that the intention is not to build a heavy motor sailor. The boat is meant to be a light performance catamaran. I believe that he succeeded in doing this.

A few points that you may not have noticed;

This boat is not equipped with twin Oceanvolt SD15 developing 15kw each but is equipped with twin GreenStar Marine developing 3.6kW each.

Important to know the maximum output on this boat. We can read this a little further in the post : “Later that week we tested the system in depth at zero wind and these are the figures: Full speed is 6.4 knots, power consumption is 280 Amps @ 24 V what gives us about 80 minutes at full throttle.” This means that the total maximum output on this boat is 6.7kW (280amps X 24V = 6,700w) , pretty close to the same power delivered by twin Torqeedo Cruise 4.0 (8kW) Also interesting to know that the maximum speed reached is 6.5 knots which is the same maximum speed reached by twin Cruise 4.0 on Oram C44 catamarans.

The claimed 4 knots is not in calm conditions but in 15-20 knot head winds.

Here another extract from the blog “Behind the bridge we went full throttle, meaning 4 kn boatspeed into the wind force 5-6.” Not exactly 4 knots in flat calm conditions!

Another interesting quote is this one “Then came the first real challenge for the electric propulsion. To reach Marstal harbour we had to motor against 15 knots of wind and 1.5 knots of current. I did not want to stress the system that was all new to us, so we only went half throttle. The power consumption was 100 Amps, 80 delivered by the Generator and the rest from the batteries.” This is giving us some interesting information: At half throttle this boat is using only 2.4 kW (100amps X 24V =2,400 w) . To be able to motor against 15knots of wind and 1.5knots of current using only 2.4kW of power is impressive.

So, once more the problem is the lack of quantification. This boat has an electric motor installation equivalent to a twin 10 hp diesel installation. (not my words but from the manufacturer's website) Personally I would be perfectly happy with that installation. And yes I would not expect to do much against 40 knot head winds. But then again you will not be doing that well either with a twin 10hp diesel installation. Neither will you with your twin 20hp petrol outboards.

[valhalla360]

Originally Posted by DotDun

The sails have to produce X horsepower to move the boat at the desired speed, let's assume hull speed (HS).

If the sails produce X+, the extra power is typically wasted by trying to push the boat up it's bow wave. Since climbing your bow wave takes a huge amount of power, OV is taking that extra power and using it to produce electricity.

But if the sails are only producing X, the drag produced by the OV will be huge.

It's a good idea, but it's not free.

If you are talking about an old slow monohull, there is some truth to this but they are pushing these systems for high speed multihulls, where traditional hull speed it's really true.

[44'cruisingcat]

Originally Posted by Claude-D

Interesting to see how much our cognitive bias influences our perception of reality…

I am assuming he is referring to this Catamaran catbuildingblog.com | building a schionning arrow 1200 catamaran A very nice boat, a good design and a nice electric motor installation. And a successful installation. The owner was pretty clear in his wants and needs, and gives a clear description of it in here The electric system on our Arrow 1200 | catbuildingblog.com You know, after reading his blog that the intention is not to build a heavy motor sailor. The boat is meant to be a light performance catamaran. I believe that he succeeded in doing this.

A few points that you may not have noticed;

This boat is not equipped with twin Oceanvolt SD15 developing 15kw each but is equipped with twin GreenStar Marine developing 3.6kW each.

Important to know the maximum output on this boat. We can read this a little further in the post : “Later that week we tested the system in depth at zero wind and these are the figures: Full speed is 6.4 knots, power consumption is 280 Amps @ 24 V what gives us about 80 minutes at full throttle.” This means that the total maximum output on this boat is 6.7kW (280amps X 24V = 6,700w) , pretty close to the same power delivered by twin Torqeedo Cruise 4.0 (8kW) Also interesting to know that the maximum speed reached is 6.5 knots which is the same maximum speed reached by twin Cruise 4.0 on Oram C44 catamarans.

The claimed 4 knots is not in calm conditions but in 15-20 knot head winds.

Here another extract from the blog “Behind the bridge we went full throttle, meaning 4 kn boatspeed into the wind force 5-6.” Not exactly 4 knots in flat calm conditions!
.

And not achievable CONTINUOUSLY.

For (try reading this slowly) CONTINUOUS running that boat manages 4 knots in flat calm conditions. By continuous I mean not running the batteries down.

At least the first paragraph of your post was correct.

BTW we've motored into 35 gusting 40 knots. Had ample power, in fact we slowed down because it was so rough.

[valhalla360]

Originally Posted by tp12

You're not having an engineering discussion. You're having a confirmation bias led critique which ignores actual data. No engineer would do that.

And there's no need for your attitude, thanks.

As an engineer when the calculations and the empirical data are drastically different, you look for what is different between the two methods.

As the only ones showing supposedly empirical data is the marketing department, it is questionable. If it was true, I would expect them to be pulling in independent sources to confirm. Boating magazines for example would be all over it if it was so good.

[valhalla360]

Originally Posted by BigBeakie

Now that we have settled the regen issue, except to the liking of some of our fine "engineers"...........

Bring him over. Unless he comes up with a better explanation than you have, I will call him a liar unless he can prove it with an independent test.

[44'cruisingcat]

Originally Posted by BigBeakie

We would never be motoring into 40 knots winds continuously, as there are much better options for a sailboat for that scenario. Our boat is designed as a bluewater boat with a heavy duty, reefing staysail (Cutter rig) and deep third reefed main. So another posters question about how fast and how long we could motor into a 40 knot wind is irrelevant for us.

LOL. Sounds good in theory anyway......

[Claude-D]

Originally Posted by 44'cruisingcat

And not achievable CONTINUOUSLY.

For (try reading this slowly) CONTINUOUS running that boat manages 4 knots in flat calm conditions. By continuous I mean not running the batteries down.

At least the first paragraph of your post was correct.

BTW we've motored into 35 gusting 40 knots. Had ample power, in fact we slowed down because it was so rough.

Yes, that is correct, the boat can only run at 4.3kW continuously from the genset — because it is a very small genset. The customer could just as easily have picked a larger genset, and therefore would have been able to go at full power for as long as he wanted. It is clear that your original post is intended to accuse the electric installation of not delivering what was promised to the customer. This is very clearly not the case.

The motor manufacturer offered an electric motor promising to deliver an equivalent amount of power to a 10Hp diesel at a lower weight, and with the added bonus of being quiet, clean, and having solar recharging. The motor delivered just that, and the customer was obviously happy with the results.

And, since you want to be pedantic about data - let me remind you that you were talking about motoring against 40 knots of wind, *not* 35 knots gusting to 40. The wind loading at 35 is very different to 40. Still, I find it VERY doubtful that you were able to motor against 35 knots with your twin 20Hp. One thing is certain - it would not have been in open water, and not for very long if you did not want to damage your boat.

[44'cruisingcat]

Originally Posted by Claude-D

Yes, that is correct, the boat can only run at 4.3kW continuously from the genset — because it is a very small genset. The customer could just as easily have picked a larger genset, and therefore would have been able to go at full power for as long as he wanted. It is clear that your original post is intended to accuse the electric installation of not delivering what was promised to the customer. This is very clearly not the case.

The motor manufacturer offered an electric motor promising to deliver an equivalent amount of power to a 10Hp diesel at a lower weight, and with the added bonus of being quiet, clean, and having solar recharging. The motor delivered just that, and the customer was obviously happy with the results.

And, since you want to be pedantic about data - let me remind you that you were talking about motoring against 40 knots of wind, *not* 35 knots gusting to 40. The wind loading at 35 is very different to 40. Still, I find it VERY doubtful that you were able to motor against 35 knots with your twin 20Hp. One thing is certain - it would not have been in open water, and not for very long if you did not want to damage your boat.

No accusations, simply stating facts. You might try it some time. They do say a change is as good as a holiday!

As for your other garbage, we motored into 35-40 knots with ease, as far as the engines were concerned. As I said, we backed off because of how rough it was. I have no doubt we could have easily maintained steerage way into a steady 40. We weren't thousands of miles out to sea, but about 20. If you're thousands of miles out there wouldn't be much point motoring into 40 kts, would there? It wasn't for long, but a few hours.

I really don't care if you believe that or not. I've seen you doing your sales pitch for Torqueedo, so I know about your credibility.

[myocean]

I think it is very important to understand, that hybrid systems on a sailing yacht should be designed to fulfill two different power requirements:
1. Have enough reserve power to get out of a dangerous situation (15-20 minutes should be enough and the full throttle power can come from battery only or from battery and genset in combination.
2. Have a reasonable long-distance motoring speed with the power coming from the genset. With a very large genset and moderate speed you can even gain comfort with having diesel noise only for a part the time (for propulsion and battery charging) and full electric, quiet operation the rest of the the time.
How much power is really needed to feel safe and comfortable is an individual decision of the owner. Torqeedo is currently equipping a new Privilege 5 catamaran with a Deep Blue system with twin 50 kW motors. They will provide an enormous power compared with the systems discussed here and the motors are still not much heavier than smaller models: 88 kg each.