Oceanvolt Hybrid Motor

[Stumble]

Originally Posted by exMaggieDrum

I have always wondered if pushing a cat with only one engine is less efficient since rudder would have to be used to counteract the push to one side or the other. I'm sure it must some but not sure how that compares to the savings of only one motor running. Talking about long distance offshore here.

A cat with just one engine one is going to be slightly less efficient that a cat with the prop down the center line, but it's a pretty trivial amount. Probably just the drag induced by 1-3 degrees of rudder applied. Not zero, but not a whole lot either.

The goal with a well designed diesel is to have it operate at around 75% of max load. This is the fuel efficency peak in kw/h/grams fuel.

So let's assume our cruising cat is operating one engine at 75% max load and is making 6kn. If we crank up the other engine and set it to the same rpm you would expect the boat to now be doing around 9kn (rule of thumb... Double the HP increase speed by 50%).

But what happens if we turn on both engines BUT lower the rpm to maintain the same speed of 6kn... It's easy enough to do, but fuel efficency drops by about 10% PER ENGINE. The net result is an increase in fuel burn of about 20% total. See the right hand fuel burn graph below (dropping from 75% load to 37.5% load).

It would take a lot of rudder deflection to make up for all that excess fuel burn.

As a note, this ignores two things

1) ancillary systems like alternators and pumps that take up some engine power. Adding these in makes running one engine more efficent.
2) it also assumes that the boat is operating at <75% of hull speed. Why for a cruising cat is almost guaranteed.

[SDChristian]

Originally Posted by Stumble

A cat with just one engine one is going to be slightly less efficient that a cat with the prop down the center line, but it's a pretty trivial amount. Probably just the drag induced by 1-3 degrees of rudder applied. Not zero, but not a whole lot either.

The goal with a well designed diesel is to have it operate at around 75% of max load. This is the fuel efficency peak in kw/h/grams fuel.

So let's assume our cruising cat is operating one engine at 75% max load and is making 6kn. If we crank up the other engine and set it to the same rpm you would expect the boat to now be doing around 9kn (rule of thumb... Double the HP increase speed by 50%).

But what happens if we turn on both engines BUT lower the rpm to maintain the same speed of 6kn... It's easy enough to do, but fuel efficency drops by about 10% PER ENGINE. The net result is an increase in fuel burn of about 20% total. See the right hand fuel burn graph below (dropping from 75% load to 37.5% load).

It would take a lot of rudder deflection to make up for all that excess fuel burn.

As a note, this ignores two things

1) ancillary systems like alternators and pumps that take up some engine power. Adding these in makes running one engine more efficent.
2) it also assumes that the boat is operating at <75% of hull speed. Why for a cruising cat is almost guaranteed.

So based on this information, once one gets beyond the mental uneasiness of asymmetrical power (electric on one side and diesel on the other), perhaps that is the best of both worlds???

[Cap Erict3]

One of the most attractive aspects of sailing is the lack of engine noise. Simplicity is another but that starts slipping out the window as boats get larger.

Cost is a major factor for all but the financially elite and $ per mile keeps many a fine vessel tied to the dock or forever on the drawing board.

Electrically propelled ships have been around for many years. They are not simple or cheap. The diesel gen sets make plenty of noise.

The perfect hydrogen generator may be perfected tomorrow. Solar radiation has enormous potential.

Who knows? A sweet potato may power communities someday.

None of my research indicates that electric propulsion is a viable option for my sailboat and I made a comfortable living off of knowing a bit about electricity.

Build a better mouse trap and the world will beat a path to your door, is an old and accurate saying. Easy to understand. I would not mind following a well worn path to an aux engine but have no time for smoke and mirrors.

[Stumble]

Originally Posted by SDChristian

So based on this information, once one gets beyond the mental uneasiness of asymmetrical power (electric on one side and diesel on the other), perhaps that is the best of both worlds???

Maybe, but not really in my world for two reasons...

1) the time when you really need both engines on is for low speed maneuverability. Inside an anchorage, or in a marine or threading your way up a narrow channel. In these circumstances you need the second motor on anyway, so you would have one electric motor, and one diesel motor going... It's going to be very difficult to rev match the props when the throttles are so different.

2) What happens when you need a lot of power a very small percentage of the time?

Generally speeds and efficiency are assuming flat water, no wind, a clean bottom, and lightly loaded. But what happens when you are dragging anchor in a 50kn squall with a bottom that was last done 18 months ago, and into a 2kn surface current wth 6' waves? This is a rare but realistic situation in my world, and the answer is enough HP at the prop to make headway even under less than ideal circumstances. This requirement can't be met without a large EP motor and a generator sized to match... But I don't think I want to rely on a large generator that never gets turned on to save my boat in a bad situation.

The only way I could see an electric on one side and a diesel on the other is if the size of the diesel were increased to make up for the missing HP on the other side and the EP was just for manuvering. The problem here is that then when running at our nominal 6kn you are outside the efficency band of the motor. Worse, you would need a larger prop (or different pitch) to apply all that HP when you really need it. This kills your efficency at all other speeds.

[44'cruisingcat]

Originally Posted by GaryJones

This is what you are saying and it is totally correct:
You are sailing at speed x (let's say 15 knots -- you do have a nice fast cat)
You turn on regeneration and the friction causes you to reduce speed to 14 knots.
Then either immediately using the other engine or at another time when you are doing 14 knots you use the same power drawn at the same rate to get you back to 15 knots.

As you rightly point out this is only possible in an ideal world with zero losses and hence not happening.

But this isn't what Stumble is saying.

Engine power to boat speed on a boat isn't linear.
Install 2x 5hp engines on your fast cat and run at full throttle you'll probably get 5 knots.
Install 2x 10hp engines and you'll probably get 7 knots.
Install 2x 20hp and 9 knots.
Install 2x 40hp and 10 knots.

You got me thinking. As it happens, a lot of different engines have been used on our sisterships.

2 x 10 gets 7.5 kts.
2 x 20 gets 9.5 kts.
2 x 25 gets 10.5 kts
1 x 60 got 12 kts.

It's actually surprisingly linear.

But I do see your point. However the ability to, in light wind, use power stored when sailing fast is going to be limited by the size of the battery bank. And any useful sized battery bank is going to impact on sailing performance...

[44'cruisingcat]

Originally Posted by exMaggieDrum

I have always wondered if pushing a cat with only one engine is less efficient since rudder would have to be used to counteract the push to one side or the other. I'm sure it must some but not sure how that compares to the savings of only one motor running. Talking about long distance offshore here.

It doesn't take much rudder. On our boat usually 1 - 2 degrees. Our most fuel efficient way to motor is with one engine and fairly slowly.

[StuM]

Originally Posted by Stumble

1) the time when you really need both engines on is for low speed maneuverability. Inside an anchorage, or in a marine or threading your way up a narrow channel. In these circumstances you need the second motor on anyway, so you would have one electric motor, and one diesel motor going... It's going to be very difficult to rev match the props when the throttles are so different.

This would be a biggy. The completely different torque characteristics of the two types of engine ( ) would make balancing thrusts when manouvering a real PITA.

[StuM]

Originally Posted by Stumble

So let's assume our cruising cat is operating one engine at 75% max load and is making 6kn. If we crank up the other engine and set it to the same rpm you would expect the boat to now be doing around 9kn (rule of thumb... Double the HP increase speed by 50%).

But what happens if we turn on both engines BUT lower the rpm to maintain the same speed of 6kn... It's easy enough to do, but fuel efficency drops by about 10% PER ENGINE. The net result is an increase in fuel burn of about 20% total. See the right hand fuel burn graph below (dropping from 75% load to 37.5% load).

Spot on. To put this into a real world example. For my boat:

One engine 2800rpm = 6.2 knots @ 3.7lph total
Both engines 2200rpm = 6.2 knots @ 4lph total
(and twice the engine hours so twice the maintenance cost )

[BigBeakie]

exMaggieDrum,

Thanks for that summary of Calders article, very interesting. But a couple of your comments seemed off the mark from what I know about Nigel Calder.

"My thought - of course, Calder will have significant sponsorship from the vendors to promote them to his wide audience. "

I think Mr. Calder has established enough credibility and professionalism in the industry to warrant some respect. Questioning his credibility by inferring he is "on the take" from vendors to give a good review, says more about your cynicism than his ethics.

Also, he has "ripped out a few systems in the past" because his boat is a test bed for electric propulsion and he has tried many, many motors and other components of EP. He has written extensively on EP for several years, in case you were not aware.

[Stumble]

Originally Posted by BigBeakie

exMaggieDrum,

Thanks for that summary of Calders article, very interesting. But a couple of your comments seemed off the mark from what I know about Nigel Calder.

"My thought - of course, Calder will have significant sponsorship from the vendors to promote them to his wide audience. "

I think Mr. Calder has established enough credibility and professionalism in the industry to warrant some respect. Questioning his credibility by inferring he is "on the take" from vendors to give a good review, says more about your cynicism than his ethics.

Also, he has "ripped out a few systems in the past" because his boat is a test bed for electric propulsion and he has tried many, many motors and other components of EP. He has written extensively on EP for several years, in case you were not aware.

Calder also headed up the EU sponsored hybrid drive research project. I have zero doubt about his facts.

There is a legitimate debate about what the model usage profile should look like. How many hours at what speed, range require, etc. where I would disagree with him, but that's just a priority issue not one of honesty.

[leftbrainstuff]

The energy density of diesel is significantly more than a magnitude better than lion batteries.

No matter how you spec or package your hybrid / elec drive the math kills it for range and recharge time.

Arguing about fuel consumption variances is insignificant.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app

[Northstarmulti]

We're busy constructing two Schionnings that are getting full oceanvolt shaft driven systems, a Gforce 15C and a moulded bilge Arrow 1360. The conservative performance numbers we've been given for the OV systems are actually quite good and they are based on lower hull beam to length ratios. Its true that there is not much weight saving compared to the same boat using twin diesels, provided the diesel boat also has no genset. If she has a genset with her diesels then the OV system is lighter by approx the weight of the genset, so 160 to 220 kg. In the OV setup though the weight can be far better distributed as the shaft drive units only weigh around 28kg each.
I do think that these systems in their current form are better suited to the lighter, more easily driven hull forms found in the performance cat sector. We also have a shaft drive twin diesel GForce 15C in the shed, so we'll be able to directly compare the two propulsion systems between the exact same boats, both of which are pretty slippery.
Ash D

[Northstarmulti]

Forgot to mention that my weight comparison is based on lighter diesels in the 30-40 hp range (yanmar 3ym30 and Nanni 38hp). If using Yanmar 45hp (which is very heavy @ 220+ kg) then the OV is approx another 140+ kg lighter.

[GaryJones]

Originally Posted by Northstarmulti

Forgot to mention that my weight comparison is based on lighter diesels in the 30-40 hp range (yanmar 3ym30 and Nanni 38hp). If using Yanmar 45hp (which is very heavy @ 220+ kg) then the OV is approx another 140+ kg lighter.

Hey Ash,

I have been following your progress on facebook with these builds for a while. They are really starting to take shape.

If I am not mistaken, the OceanVolt system you are installing is 2x 8.3kW engines? Do you feel this is going to be enough to replace the Yanmar / Nanni you are putting in her sistership? I guess they were selected as they are the largest shaft drive model that OceanVolt sell?

What size generator are you installing to run with the electric engines?
What size battery bank?

I am really looking forward to seeing the whole thing complete and in the water. Exciting times!

Gary

[Cap Erict3]

http://oceanvolt.com/

Am able to access various distributor sites but not OV.