Turbines and electrical propulsion for a schooner

Hi,

I have a new project:

http://djalbat.com/cecelie

I was pondering whether it's possible to make do without a diesel engine. Originally she would have had a very small engine, around 40hp. Some vessels her size make do without any engines, although admittedly they sometimes need a tow:

http://winewomantravel.com/2011/11/17/fair-transport-the-ship-tres-hombres/

The ship yard suggest putting a 400hp engine in her but I'm thinking, why not just put an electric motor in her? The technology for motors and inverters has become affordable and mundane. If I went for a 250hp motor and inverter this would be no problem. The big cost would be the battery bank but then 400hp diesel engines and everything that goes with them aren't cheap, either.

So I think this would work, provided you could charge the large battery bank. I was thinking of having two turbines with vents in the bows around the same location as the bow thruster with tubes along the length of the hull, exiting some way back.

The more I come to think about it the idea of messy diesel and hydraulic systems with their high running and maintenance costs, not to mention the environmental costs seems barmy. Admittedly the idea of turbines in the bows is whacky but if that can be made to work, I think the system would be a good one.

Any comments?

Kind regards,

James

 

James,
You are doing some beautiful work on her 'mid-life' refit. 1921 was the same year the original schooner Bluenose was launched, and the same year my dad was born.

The original 40 hp seems small in horsepower by today's standards, but back then it was probably a very large in size, and slower turning and more easily matched to a large diameter propeller. I am a bit surprised by the bow thruster but I suppose it is a practical necessity today. I am sure it is not original. The other thing different today is your electrical needs are much higher. We have gotten soft.

I like the idea of a central diesel generator, and from their I presume power can be diverted to the electric motor for the bow thruster, the electric motor for the main propulsion shaft, and all of the electrical needs of the ship. I understand maximum efficiency is achieved at about half the rated horsepower. If you are comfortable keeping your cruising speed at maximum efficiency low you can use a smaller engine, where the horsepower requirement for house needs, or bow thruster when docking, or power requirements when powering through calms or in and out of ports, might all match one another more closely.

I am not exactly sure of the economics of these things either, but another option if you had 250 horsepower in mind might be to split it into two 125 horsepower diesel engines. This will allow you to run only one at a time when the other requires maintenance, or when running one is more efficient than running both. If both are identical they can use the same spare parts, and expertise.

Then I was thinking, is there a way to have it so that you still only have one generator, and have it so that either engine, or both, can supply the generator, or the main propulsion shaft? This would add a lot of gearboxes, but reduce the need for large electric motors. The large electric motors might be cheaper to purchase and easier to locate in your ship and easier to maintain however, which might be your thinking. Cheers.

 

Hi,

I don't think you've quite gotten the idea. The idea is *not* to have a diesel onboard, but to charge the battery bank with turbines located in the bows.

And you're right, of course the bow thruster is not original.

Thanks otherwise.

 

It simply is not practical to drive propulsion from batteries for any length of time. I haven't done the calculations on a vessel this size, but frankly you would probably have to convert that entire 20' section of the boat into lifepo storage to be able to motor more than a few minutes from battery power.

The turbine idea is new to me, but generating power from the flow of water isn't. The problem here is that to harvest much power you need high average speeds. On a vessel this size you may have those speeds, but the systems will still add lots of drag. I am not sure that a turbine in a tunnel would generate much more power than a tow behind generator. But they still wouldn't generate an appreciable amount of power compared to your propulsion needs.

My guess is that a reasonable system would require 30-40 hours of high speed sailing for every hour of motoring time. Assuming the batteries could handle the charge rate, and storage capacity. And assuming no engine losses.

 

Hi Greg,

> It simply is not practical to drive propulsion from batteries for any length of time.

Agreed. This would be for manoeuvring only. If you look at the link, you'll see Tres Hombres needed towing into port on that occasion and presumably often does. My reasoning goes that Cecelie had to make do with a relatively tiny engine when she was built and probably for the majority of her time thereafter. She is, after all, first and foremost a sailing vessel. So for propulsion, yes, but only in and out of port.

Interestingly, on the size of the battery bank I have some raw data. I looked into an electric power boat not long ago. To power a 125hp electric motor for five hours at maximum power required batteries weighing around 500kg. Their cost was considerable, probably about double the price of a 125hp diesel engine at £20,000. Going on those figures, Cecelie would need an investment of no less than £50,000 for the batteries alone to drive her 400hp motor for a few hours. This is the sticking point. I think with many electrical propulsion systems, whatever the application, the price of the batteries usually is.

Finally, I'd hope to get quite some power out the turbines. She's a big girl and under full sail will generate enormous oomph, for want of a better word. Two 125hp generators or thereabouts would recharge the batteries in less than a day.

 

Sorry Sir but you do not know what you are talking about.
To power a 93kW (125HP) motor for five hours you need 465kW. For a 93kW continuous duty motor you are looking at a minimum of 400V. Since you also need the associated controllers presumably you are looking at light rail technology at 600V. But lets assume 400V. LiFePo4 batteries at 3,2V and 1000Ah exist. So you need a string of 125 batteries to make the voltage. This brings you at 400kW. A battery pack this size costs at least 150,000 pound sterling. That is for Made in China prismatics without any BMS. And this battery pack would drive your proposed 400HP motor for an hour.
In real life you will need a motor, power electronics, BMS, chargers, etc. In real life you are a commercial vessel subject to commercial regulations so you are more likely to use a battery system like the EST50-1050 witch has Lloyds approval, and a motor and controller designed for a tram or trolley bus.
As for charging the batteries from turbines under sail you are delusional. If you could operate two 125HP generators under sail power that would mean that you have 250HP braking your vessel. That is "enormous oomph" indeed. Mounting the turbines in tunnels would destroy the underwater profile and you would never achieve the necessary speeds to operate them.

Just to ease your mind about the diesel, Tres Hombres has a diesel generator running to power all the SOLAS mandatory electronics.

Last thing. I presume you know that your new project is a commercial vessel and you will need a licensed captain and crew.

 

Rumars, hi,

>To power a 93kW (125HP) motor for five hours you need 465kW

Really? I thought to power a 93kW motor for five hours you'd need 465kWH not 465kW. Forgive me but you seem to be confusing work and power and in doing so you're multiplying the size of the problem by 5.

Aside from this miscalculation you're what we call violently agreeing with me in stating that the cost of the batteries is the limiting factor. Although, as I've pointed out, you're out by a factor of 5. If you take this into account I think you'll find your calculations are more optimistic than mine.

> If you could operate two 125HP generators under sail power that would mean that you have 250HP braking your vessel. That is "enormous oomph" indeed.

This is a fair point. I wonder how much power Cecelie would be generating under sail. Smaller turbines could be used, I suppose, but obviously they would take longer to charge the batteries.

> Mounting the turbines in tunnels would destroy the underwater profile and you would never achieve the necessary speeds to operate them.

I think this is an exaggeration. Well designed vents would cause less drag than a comparable turbine chucked over the stern behind her and many take that route.

Another possibility that I've only just thought of is to use the propeller although I doubt it would ever be very efficient. Better than trying to make Cecelie look like Red October, though...

> ...Tres Hombres has a diesel generator running to power all the SOLAS mandatory electronics.

Now this is news, thanks for this tit-bit. I have wondered whether she'd ever get certification without some kind of back up.

Which brings me onto your last point. Others have made the very valid point on this forum that in taking on large projects it is about precisely that, taking on the project for its own sake. If the goal is to get Cecelie to the point where she actually needs a captain and crew, then even that goal is too far off for me and believe me, I'm not deluding myself. I will take Cecelie as far as I can, it may be for others to take her all the way.

Finally I would have to agree with you, although I hope not violently, that doing without at least a diesel generator on board would preclude any chance of certification, so I'd have to accept that. I think a hybrid system with the propeller driving the main generator could work. This is nothing new, see here:

https://www.youtube.com/watch?v=JH3xMWplVxk&feature=player_embedded

 

So many questions.

If the boat can get along on 40 hp, why put in 400, just to maneuver into port?

What is the environmental foot print of all the batteries that will only last maybe 8-10 years compared to a diesel system with double or triple the lifespan?

What is the difference of costs over a 30 year span?

What are the dangers of fire/explosion with such a large battery bank?

What sort of toxic gases would the batteries put out in the event of a fire?

How do you go about extinguishing a large battery bank fire that is possibly emitting very toxic fumes?

Why, at a monumental cost, would you limit yourself to a few hours of motoring time, and probably give up the capability of motoring your way out of the path of a storm, or to motor your way to port if it was impossible to deploy the sails?

Why would you need 'commercial' certification and a licensed captain and crew?

How much crew will it take to operate this boat?

What does this mean?

 

Hi,

> If the boat can get along on 40 hp, why put in 400, just to maneuver into port?

The shipyard owner suggested an engine of this size. I'm guessing the original engine would only have been for manoeuvring, whereas he had something more like propulsion on the open sea in mind. For example, he, and others in fact, have suggested I bring her back to Britain under her own steam, or rather diesel, in something close to her current state. I declined. In suggesting electric motors of around 125hp-250hp I was trying to go for some sort of halfway house, to be honest.

> What is the environmental foot print of all the batteries that will only last maybe 8-10 years compared to a diesel system with double or triple the lifespan?

I honestly don't know. I need to do lots more research into this. That's partly why I'm asking questions on this forum. To argue on a reasonably high level, however, I could ask why go for electric cars rather than diesel or petrol ones? Because electricity is believed to be becoming cleaner? Obviously if that electricity is being generated by Cecelie herself while underway under sail, few would argue that it's not a cleaner option than a diesel generator. But yes, you're right to ask the question, you cannot escape the environmental cost of producing these products in the first place, or disposing of them.

> What are the dangers of fire/explosion with such a large battery bank?

Good question, as are the two that follow. I've just googled and come up with this:

http://www.hemmingfire.com/news/ful...ging_the_lithium__ion__battery_fire_risk.html

An interesting bit of information on this subject that I'll share, I remembered this after answering this morning...Stena ferries from Harwich to Holland are now charged in port. All electricity demands on board, which are obviously considerable, are met from storage batteries. No electricity is generated from the engines, either the main ones or auxiliary ones for that purpose. The ferries are literally plugged in and charged up when in port. Obviously not straight from the mains, it's a dedicated 11,000V supply run underground from specially commissioned substations. Stena cite efficiency and environmental concerns as the reasons behind this.

> How much crew will it take to operate this boat?

I don't know. I'm guessing two watches of six crew at least, so a compliment of at least twelve altogether. But this is just a guess. I'd suggest going and asking Fair Transport if you really want to know.

 

Some more thinking on this...

* The silly vents in the bows idea is out, but it got me thinking.
* You can't do without a diesel engine on board as a backup,
* BUT you don't have to use it for propulsion, at least not directly.

So you have an electric motor and main generator connected to the prop-shaft, a large battery bank, plus a diesel generator to charge the battery bank in the event that the main generator cannot.

* Hopefully on long voyages the main generator will be enough.
* The electric motor, main generator, inverter and converter are all relatively cheap and trusted technologies these days.

I still think all of this would be quieter, safer, possibly slightly cheaper and definitely more environmentally friendly than a bloody great diesel engine, but then I would say that and I'll admit the comparison is pretty much a moot one anyway.

 

Not really. This subject has been beaten to death. In particular applications, with 3 phase AC motors a diesel/electric may have some advantages. Otherwise, when you add all the losses from the generator to the charger to the battery to the controller to the electric motor, it is much greater than the 3% of a gear box. A 40 HP engine will be adequate as a main auxiliary engine, can run a generator head and have a PTO for hydraulics so you can have capstans, winches etc.

 

First thing, the vessel is over 24m (78 feet) so under european regulations it is not a pleasure vessel anymore. This means the captain (and crew) will need at the minimum the RYA Yachtmaster offshore with commercial endorsement (200GT) or better a MCA Master 200GT (this is fully STCW95 compliant). In addition the OP wants to engage the vessel in cargo shipping and that means merchant marine territory with all the associated regulations.

Tres Hombres (28mLOD, 32mLOA, 128GT, brigantine) sails with 5 professional crew and up to 10 trainees and Nordlys (20mLOD, 25mLOA, 48GT, ketch rig) sails with 3 professional crew and up to 6 trainees so I would expect the Cecelie to have something similar.

James.Smith hi,

You are right I forgot the "h". A battery contains a limited amount of power. A 400V 1000Ah battery will contain 400kWh. You can extract this power over 1 hour at a rate of 1000A per hour, or you can extract the power for 5 hours at a rate of 200A per hour. This means that you can either power a 400kW motor for 1 hour or a 80kW motor for 5 hours. At the end the energy spent is exactly the same. And this is an ideal calculation not counting efficiency losses in the controller and motor. So no, I don't think I multiplied the problem by 5.

I am glad you ditched the turbines. You can use a shaft generator if you like and still generate electricity. This is a method used on enough yachts to know it will work. Even better if you have a variable pitch propeller. Maybe you can compensate for the hotel load underway. Installation in series or parallel is a matter of preference and technical details.
As for DE it does not pay for your vessel. Install a diesel big enough to have independence for entering ports and be done with it. How big it will need to be needs to be calculated by a NA according to prospective use.
I also think you should make contact with the people from http://fairtransport.eu/ to see what it means to prepare and operate such a vessel. After all they operate 2 engineless traders. And maybe they can provide you with enough volunteers to ease the financial burden of refitting.

Anyhow you need a proper NA to design the rig and supervise the conversion to working sail. There is no other way around it, at least not in Europe. It may be different in Africa, see http://musafir.org

 

Rumars, hi,

thanks for the reply. I'm glad you like the shaft generator idea. I need to do some mugging up on motor/generators. The propeller is currently fixed pitch, but I could trade it in for a variable one if need be I guess.

As for contacting Fair Transport, I am years away from daring to do that. At some point I will volunteer but I'd want to get Cecelie well down the road before expecting to be taken seriously. Really, not this year.

Good to have the crew figures but again, not something to worry about for a few years.

I hadn't come across Musafir, so thanks for the link.

 

Still plugging bad information?

The 3% loss from a gearbox ignores the all-important losses in the engine beforehand.

Diesel electric means the engines run a peak efficiency all the time, while in "normal" diesel propulsion the engines will suffer losses whenever the rpm leaves peak efficiency.

For many vessels the losses in the engine(and gearbox) for a diesel setup are/would be greater than the losses for converting energy in diesel-electric.

Real life examples are everywhere, and easy to find.
Here's Wartsila saying their new diesel-electric tugs will save 25%: http://www.mpropulsion.com/news/vie...cy-boosts-for-tugs-and-ahts-vessels_40605.htm
The UK navy installing electric hybrid systems in destroyers so they can run on electric when operating at speeds that would be away from peak efficiency for their main engines: http://news.usni.org/2015/09/23/nav...c-drives-in-destroyer-fleet-staring-next-year

 

The weight of the batteries is also a limiting factor, but also capital and maintenance costs, and energy losses. Batteries have their place, but a very weak one here. The case for electric motors is independent of the case for batteries. Diesel-electric propulsion systems can offer some versatility, but there needs to be some good reasons to justify their use over transmission systems. It depends on the application. If you can reduce your cruising speed requirements, when operating without wind, so that there is more of an even balance between propulsion needs, bow thruster and maneuvering needs, and house needs; and their are also some potential for power generation from wind and solar; then their might be a case for using multiple diesel engines and diesel generators and electric motors, but very limited battery capacity. Perhaps 5 hours, perhaps 20 hours, but not 20 hours or even 5 hours of full power. 20 hours of minimal emergency needs, certainly.

One of the biggest thing that diesel-electric systems provides is more versatility in where you locate your equipment, and to provide more reliability by locating redundant equipment further apart. Heating needs is also something to look at. Produce your hot water needs from the diesel engines. Combined heat and power. This is also easier to do more effectively if you have more freedom in placement of equipment. Sometimes you lose in economy of scale, but medium sized equipment can sometimes be less costly, and more reliable, because it is produced in greater numbers. Cheers.