Electric Propulsion on Catamarans

[BigBeakie]

Thanks valhalla. Good info about motoring upriver and into the wind. I think it's a better plan to have more horses than you need in most situations rather than find yourself in a situation that can get out of control. Within reason, of course.

BTW, I've been thinking about the objection to electric hybrid that goes something like "if you're going to burn fuel for a diesel genset to run your electric motors, you might as well just use diesel engines."

A variation goes something like, " Electric propulsion is not efficient because of all the energy conversions. You get the most efficiency by burning diesel and converting directly to thrust by a diesel engine."

Both of these arguments have a certain logic, and I've read with interest all the threads that batted these propositions back and forth. But FWIW, it dawned on me that you have to consider a couple of conditions to see whether those ideas are true & it depends on your style of cruising and geographic area. To cut to the chase, if you are expecting frequent and long periods of motoring, especially at higher speeds or in significantly cloudy areas, then there is a certain logic that may justify diesel propulsion. If however, you motor infrequently, for short periods or at modest speeds, and it's normally sunny, then it seems to me electric has many advantages. I cannot see how storing the sun and wind amps and then using them to power the boat and motor, is inefficient. Especially over the long term and especially since you can do it again and again essentially for free. That sounds pretty efficient to me.

Does that seem like a "fair and balanced" view? This is an important decision for us, and a bit daunting as we realise that it is still early days for recreational marine electric propulsion in terms of reliability of all components. But so far it seems if the system is well designed, has high quality components properly installed, and there is excellent vendor support & warranty, then for our chosen cruising lifestyle in the South Pacific, electric propulsion is the way to go.
But we are newbies to cruising, so as always, feel free to question our assumptions and/or share your experience.

[mbianka]

Originally Posted by BigBeakie

BTW, I've been thinking about the objection to electric hybrid that goes something like "if you're going to burn fuel for a diesel genset to run your electric motors, you might as well just use diesel engines."

If that were they case a lot of ferries would not be operating as diesel electrics. But, they are. Another problem with diesel engines for propulsion is you have to locate them so they mechanically provide power to the shaft(s). This may or may not allow space for easy maintenance. With electric you can mount the generator in a location where it can be easily maintained. From my experience the electric propulsion system (including the motor) will require minimal maintenance compared to the internal combustion portion of the system.

[deckofficer]

Very fair and balanced.

I look at it this way, whatever solar harvesting your panels do in a day, if it exceeds your hotel loads it becomes "fuel" in the (lithium) tank. If the lithium tank is large enough, this daily overage of harvesting solar can propel the boat for free.

[BigBeakie]

Capt'n Mike - Yep, yet another advantage of electric is less weight and better weight distribution. Considering our 46 ' cat design has weight as centred fore and aft as possible, where do you think a good place for the diesel genset would be? The LiFePO4 bank will be under the salon seats, the electric motors will be shaft drive and fairly central in the hull fore-aft.

deckofficer - SPOT ON! In a nutshell that is exactly what we are trying to accomplish. I'm hoping the diesel genset is pretty much only when we are in very light airs for extended periods and need to drive the electric motors from the genset.
If the motors are 30 kW, the genset is a 6 kW unit (maybe 8 kW), and we drive one motor only off the genset, the 46 FreeFlow design has quite "slippery" easily driven hull shape > what is the best way to estimate motoring performance eg hull speed? Assuming a fairly large feathering prop? Does this need a naval architect to work through it or are there cats that you know of that would be a good guide?

[leftbrainstuff]

Originally Posted by Tropic Cat

Ever met Richard? Solid guy. If he says it, you can make book on it.

Derate all Solar panels to 75% of advertised power output to mirror reality.

Unless the math has changed since I was in my EE classes 747 watts still = 1 horse power.

Where are the efficiency numbers for the electric motor drives?

In anyone's power calculations, you're left with an electric drive system that can give you hull speed for around 10 minutes or 2-3 knots of boat speed for a couple of hours or so.

Electric motor drives will be disabled by a lightning strike, so not usable in tropical climates. (I live there and have been struck by lightning... not a lot of fun) and in short is just not ready for prime time. If it was, I'd have it on my boat as I love the concept, but not the reality.

No boat owner should rely on electric drive with current technology, as there are times you need your engines when things go bad out there.

When these systems can motor at 6 knots for a minimum of 5-6 hours and the batteries weigh less than 600 pounds, and I can recharge batteries in less than an hour (WITHOUT A GENSET) ... I'll buy one myself.

For now, a diesel just works.

Can't argue with the math. As a Mech Eng the energy density of diesel can't be beat.

We also have wind and solar but they rarely keep the house batteries charged. As liveaboards for cruising electric propulsion isn't ready for primetime.

Sent from my GT-I9300 using Cruisers Sailing Forum mobile app

[44'cruisingcat]

Except that 75% is probably optimistic for the solar. Unless you're in the tropics in summer. We have 800 Watts, and MPPT and rarely see 500 watts output, in subtropical Qld in winter, with perfect blue skies.

Our 800 Watts runs our refrigeration, watermaker, breadmaker fine, even in winter. As long as it's sunny. But if we wanted to use it for cooking, or hot water, well, we'd be having a lot of salad, cold coffee and cold showers. Spare amps for propulsion? Unrealistic.

[deckofficer]

Originally Posted by BigBeakie

deckofficer - SPOT ON! In a nutshell that is exactly what we are trying to accomplish. I'm hoping the diesel genset is pretty much only when we are in very light airs for extended periods and need to drive the electric motors from the genset.
If the motors are 30 kW, the genset is a 6 kW unit (maybe 8 kW), and we drive one motor only off the genset, the 46 FreeFlow design has quite "slippery" easily driven hull shape > what is the best way to estimate motoring performance eg hull speed? Assuming a fairly large feathering prop? Does this need a naval architect to work through it or are there cats that you know of that would be a good guide?

Back when I last cruised, many boats were running a separate prop shaft with a prop mounted backwards so the pitch was perfect for taking energy from the passing water medium while under sail. Steve Dashew in his book mentioned another advantage of the MaxProp with its ability to stay pitched in astern propulsion without feathering during sailing like it does when you drop into neutral from forward propulsion.

I don't know of any sailing cats that have a prop shaft positioned to swing a large, slow turning prop that would be efficient for electric propulsion.

[mbianka]

Originally Posted by BigBeakie

Capt'n Mike - Yep, yet another advantage of electric is less weight and better weight distribution. Considering our 46 ' cat design has weight as centred fore and aft as possible, where do you think a good place for the diesel genset would be? The LiFePO4 bank will be under the salon seats, the electric motors will be shaft drive and fairly central in the hull fore-aft.

deckofficer - SPOT ON! In a nutshell that is exactly what we are trying to accomplish. I'm hoping the diesel genset is pretty much only when we are in very light airs for extended periods and need to drive the electric motors from the genset.
If the motors are 30 kW, the genset is a 6 kW unit (maybe 8 kW), and we drive one motor only off the genset, the 46 FreeFlow design has quite "slippery" easily driven hull shape > what is the best way to estimate motoring performance eg hull speed? Assuming a fairly large feathering prop? Does this need a naval architect to work through it or are there cats that you know of that would be a good guide?

BigBeakie:

I'm no navel architect or designer so my recommendation is to speak to one. But, since you don't have the weight of diesels in each side. I would think centered somewhere aft in the cockpit in a good soundproof enclosure with removable sides. It could be used as a bench or the top of the enclosure could function as a table with fold down sides. Just orientate it so you can get to both sides easily. It will make any maintenance much easier than in some hot confined space below.

As far as feathering props you may not need them. As I discovered just using 10 amps of EP on my 30 foot mono hull my boat is moving along at 2 knots in no winds. As the wind picks up and the sail takes over powering the boat the amp draw goes down but, the effect of the electric powered prop is it negates any prop drag. As my boat speed starts to reach around 6 knots the motors start to regen and charge the batteries. It's a win win situation IMO and one that I happily discovered as I used EP. Something to think about anyway before you spring for feathering props.

[SVNeko]

Originally Posted by BigBeakie

By electric I mean one that has sufficiently powerful motors (we're considering twin 40HP for our 46 foot cat) & a diesel genset to run the electric motors for longer periods when becalmed. The cat will need sufficient solar and regeneration to put back the amps into the LiPO4 house bank and the dedicated LiPO4 motor batteries. That is a given.

Do you ever think about, like, um, sailing it? With all that kit your boat will be weighed down so much your waterline will be halfway up the hulls and the boat won't be much fun. We are talking about a sailboat here, right?

Sent from my SM-T210R using Cruisers Sailing Forum mobile app

[yamez4u]

I have nothing against composting heads (except maybe the name, as they don't really compost) They are similar to my Dry-flush in that they store waste to be dumped in the trash on land.

Originally Posted by valhalla360

No composting system sterilizes the waste. That was never a consideration. It allows oxygen in so it breaks down drastically reducing the weight and volume. Given a month or so without new deposits the vast majority of pathogens die off on their own because they developed to live in a host at body temperature and a moisture saturated environment.

We looked at incinolets, they work great on commercial boats where the motors run 24-7 and you have an endless supply of electricity. In the context of this thread, they would be a huge consumer of you limited supply of solar generatated electricity or if you go generator, would require significant additional generator run time.

See section on "Sterilizing Weed Seeds and Pathogens"
A Compost Thermometer Leads to Increased Compost Quality

None of the small composting heads are going to reach the temperatures needed to kill pathogens and should never be dumped overboard. You could infect sea turtles and other humans with human pathogens. Many of you may have seen Logger heads with tumors these come from human Herpes.

So as long as you treat the waste from your composting head like "human waste" and dispose of it in a sanitary way I would say they are better then normal holding tanks. I just choose different heads that work better for me. I have used neither long enough to have a strong option one way or the other. Ask me again in three months. I have a 3KW array on my boat so for me the Incinolets tiny draw for one hour has little impact on my house bank. And of my two heads it is the only one I could use safely living off the hook for long periods.

[yamez4u]

Originally Posted by SVNeko

Do you ever think about, like, um, sailing it? With all that kit your boat will be weighed down so much your waterline will be halfway up the hulls and the boat won't be much fun. We are talking about a sailboat here, right?

My boat (not a sailboat) after the conversion with a 48volt 1000AH LiFePo pack is much lighter then before, I am up almost an inch on the water line. I really need to add some weight at some point for safety reasons. I think you under estimate how much weight your engine takes up in tank and fuel weight.

[deckofficer]

Originally Posted by yamez4u

My boat (not a sailboat) after the conversion with a 48volt 1000AH LiFePo pack is much lighter then before, I am up almost an inch on the water line. I really need to add some weight at some point for safety reasons. I think you under estimate how much weight your engine takes up in tank and fuel weight.

Have I missed your description of your boat? What kind of range do you have at what speed before you plug in at the next marina and suck down 3600 watts continuous for a 1 day stay?

[yamez4u]

Originally Posted by deckofficer

Have I missed your description of your boat? What kind of range do you have at what speed before you plug in at the next marina and suck down 3600 watts continuous for a 1 day stay?

I have a 3kw array so depending on the sun and the speed I pick, possible infinite, but not fast. I am still testing the range on battery alone and have a few prop issues to work out, but even with the current prop the number are not bad:

Knots | Watts |Motor RPM | Pack life | Range
5 kts 7800 950 6 hrs 45 miles
6 kts 15600 1100 3 hrs 18 miles
7 kts 26520 1340 2 hrs 14 miles

I could probably go all day at 4 knots. I do have a 48kw pack. When the prop reduction is right those numbers could get much better. Either way I would be happy with what I have now.

[deckofficer]

Originally Posted by yamez4u

I have a 3kw array so depending on the sun and the speed I pick, possible infinite, but not fast. I am still testing the range on battery alone and have a few prop issues to work out, but even with the current prop the number are not bad:

Knots | Watts |Motor RPM | Pack life | Range
5 kts 7800 950 6 hrs 45 miles
6 kts 15600 1100 3 hrs 18 miles
7 kts 26520 1340 2 hrs 14 miles

I could probably go all day at 4 knots. I do have a 48kw pack. When the prop reduction is right those numbers could get much better. Either way I would be happy with what I have now.

Thank you for the cold hard facts. What is the size, hull type, and displacement?

I was hoping for a bit better efficiency than what your getting, but your out doing it and I'm still crunching numbers.

[yamez4u]

Originally Posted by deckofficer

Thank you for the cold hard facts. What is the size, hull type, and displacement?

I was hoping for a bit better efficiency than what your getting, but your out doing it and I'm still crunching numbers.

It is a big heavy boat with a semi-displacement hull. 41 foot with 13 tons of displacement. Your cat will be much more efficient then my boat. By how much I could not even guess.