Electric Propulsion on Catamarans

[socaldmax]

Originally Posted by tomfl

I did not see anything in your post about batteries. You did seem to say the electricity was generated from a turbine which might mean no batteries are used. Is this the case.

Yes, all US Navy subs are nuclear powered. So the current subs create steam off of a secondary coolant loop, which drives 2 turbines for propulsion and 2 turbines for electricity. They also have motor/generators for DC and 400hz power generation. There is a huge bank of batteries, but it is used as a backup electrical power source until the diesel gen can be started which then powers the pumps and control systems to restart the nuclear reactor or flash the TGs and restart the reactor. Subs always have secondary and tertiary systems, as well as hybrid systems like electro-hydraulic, or hydro-pneumatic, etc.

So they are removing 2 huge propulsion turbines and a huge reduction gear and replacing it with a direct drive motor mounted on a 21" dia. propulsion shaft. This is obviously going to require much more electrical power generation to propel a 560 ft long sub, with a full crew, missiles, etc.

What this tells me is that this is all efficient enough to warrant the expense of all of these changes and there is a net gain somewhere - either costs, quieter operation (that's a given), maintenance, etc.


IMHO, the only real impact this has on an electric propulsion catamaran is to signal us that the technology has matured enough that large craft like freighters and mission critical propulsion on a sub is being entrusted to electric motors.

I'm still in the daydreaming stages, but I've been thinking about a 47' catamaran with 8x300 watt panels across the rear above the davits, with an additional 3 panels attached outboard of each hull, to the safety rail. A total of 14 x 300 w panels should produce close to 4Kw under bright sun. If the wind isn't blowing then either an electric motor (not sure what size, but let's say equivalent to the original diesel engine it replaced) or a diesel/electric hybrid would propel the boat at normal cruising speeds.

If one removed both engines and replaced them with the correct sized DC motors, you'd have a lot of room left over in the engine compartments for a lot of LiFe batteries, enough to help propel the boat if the sky is a bit cloudy.

[44'cruisingcat]

It's already (IMO) accepted that electric motors can do the job. But given that few cruising boats have nuclear reactors on board, it's where the POWER comes from to drive the motors that becomes problematic.

For most, solar and wind generation simply isn't going to be anywhere near enough. Many people can't even run their house demands purely off solar/wind. And propulsion demands would be orders of magnitude greater.

So that calls for a genset. But if you have a genset, you're back to burning fuel and relying on an internal combustion engine again. But with extra points of mechanical/electrical vulnerability added. And weight. And expense.

And to gain what?

[Cotemar]

You can make this work well. Just hook up with Kodak as they have one of the smallest nuclear reactors ever made hidden in their basement for over thirty years.

Kodak had weapons-grade uranium and its own nuclear reactor! Ever since 1974 the well known experts on photographic film and inkjet printers.

This little nuke should power your catamaran for a few life times.

[BigBeakie]

Thanks Guys for all your comments and ideas. To adress some of the points made;

I don't think the electric propulsion solution with DC Genset would be heavier than regular diesels/saildrives plus fuel, I think it will be lighter. Unless you go crazy on having excess LiFePO4 capacity.

mcarling - points noted, thanks.

mbianka - I don't think a Honda will put out enough juice for the motors we are considering. I like the idea, I love our Honda for camping, but I would rather carry diesel than petrol for safety reasons. We will consider electric for the tender as well and also an electric dive compressor, so we are investigating having a petrol free boat.

roetter - great information, much appreciated Rolf!

boat alexandria - we spent alot of time analysing the power required for blue water cruising in the South Pacific. Small 4 hp electrics are not adequate for adverse conditions and put the boat at risk. Examples: getting into and out of lagoon passes with current, big tidal races, getting off a lee shore in a big blow etc etc. The power it takes to overcome windage on a cat this size is surprising!
A meter prop is a daunting thought! I understand your thinking, but really? Who makes a 1 meter diameter feathering prop? Part of the solution to electric propulsion is how you put amps back in the batteries as efficiently, and sometimes, as quickly as you can. So prop regeneration is an important aspect to consider. We are also looking at the new Watt & Sea Hydrogenerator that puts in 48 amps at 9 knots boat speed and 16 amps at 6 knots. As well as regeneration from the shaft drives using feathering props. So if we run down the bank at anchor during some cloudy weather, we just go sailing for half a day to recharge the batteries.

[yamez4u]

I re-powered a similar sized boat, (not a cat but is dual prop) The motors and batteries, and support equipment where pretty strait forward. My biggest issue so far has been prop size and reduction. Garrs prop book helped a bunch. You can see my setup here http://www.deny.org Even with a bad match on the prop, at 4 knots I could probable run all day. At 5 knots about 6 hours.

[BigBeakie]

Thanks yamez4u, always good to hear from those who have been through it.
I agree the prop choice is crucial so that the regeneration will work properly.

Some great info on your site! You didn't consider composting toilets? So far my research on them seems really positive. Is there a reason you didn't go that way?

[yamez4u]

I decided against composting heads, because very few really compost. To compost you need a large container that gets to a sterilizing heat, for months. Other wise you are just storing your crap and dump it some place. Pretty much exactly like the current boat waste tanks, but less smelly. They may not smell, but don't fool yourself, any head you have to empty weekly has not had enough time to compost. So for me the options where incinerating or storage without a tank. I am trying both. The "composting" head would be similar to the Dry-flush. IE store the poop without the smell, then trash it when done. Peat moss should cost less, but you would have to handle it when emptying your head. The Incinolet truly sterilize the waste and unlike the composting heads or the Dry-flush I could honestly dump the waste overboard at sea without braking any laws.

[BigBeakie]

OK understand. But from speaking to users who are cruising with the composting toilet, they report that for the 2 persons they do not have to empty it weekly, but perhaps monthly. They just bag it in a rubbish bag and take it to shore to feed a tree. They are delighted with it, so that's why we are interested.

It is true that the composting process goes on for a long time to completely get to end product, but there is no reason you can't empty it earlier if it is full. While cruising they are using dried copra fibres (coconut husks) which seems to work fine, and there is plenty of supply of those around the South Pacific

[seandepagnier]

Originally Posted by BigBeakie

boat alexandria - we spent alot of time analysing the power required for blue water cruising in the South Pacific. Small 4 hp electrics are not adequate for adverse conditions and put the boat at risk. Examples: getting into and out of lagoon passes with current, big tidal races, getting off a lee shore in a big blow etc etc. The power it takes to overcome windage on a cat this size is surprising!

First of all, keep in mind the power required is zero. This was proven a long time ago. It does not put your boat at risk.

The most annoying example people use is to motor against a big blow. Why would you ever do this? You risk losing control if the wind really builds, whatever your engine may be. Your sails are what you should be using, and a whole lot more reliable.

I am currently using only sail and (engine people) are constantly trying to justify all the time and money they waste on their engine by telling me some "Bar entrance is impossible" or you cant get in a lagoon etc.. only for me to find when I get there that it's all nonsense.

There are not many places where the tidal current is above 4 knots which is the point where the 4hp motors would struggle (remember you can go a mile or so pushing them each 10hp, and the efficiency is more than 4x that of a typical diesel with this horsepower, with the right propeller setup.. you should be doing 6 knots) but in this case, or if one motor fails etc.. you can simply wait a few hours for the tidal rush to diminish to enter the lagoon. You just spent 500 hours sailing across the pacific, one more hour is not a problem.

The power requirements you are looking at are based on spinning tiny propellers above 1000rpm which is incredibly inefficient, and using it to motor against a tropical cyclone in 60 knots of wind which if you are doing, you have made a big mistake, because when it gusts to 80 you will completely lose control anyway. In these situations you should be in a proper place to ride out the storm before it arrives.

A meter prop is a daunting thought! I understand your thinking, but really? Who makes a 1 meter diameter feathering prop? Part of the solution to electric propulsion is how you put amps back in the batteries as efficiently, and sometimes, as quickly as you can. So prop regeneration is an important aspect to consider. We are also looking at the new Watt & Sea Hydrogenerator that puts in 48 amps at 9 knots boat speed and 16 amps at 6 knots. As well as regeneration from the shaft drives using feathering props. So if we run down the bank at anchor during some cloudy weather, we just go sailing for half a day to recharge the batteries.

If you want to regenerate with good efficiency with the same motor, you will absolutely need a completely different propeller than for powering. It is not possible to use the same propeller unless you want to make a much smaller amount of power for the same drag. This also means different size regenerating propellers for different speeds. This also allows you to remove the main propeller to reduce drag when sailing.

Because the forces are lower on the propeller at a maximum 200 rpm, you don't need bronze, you can make your own.

If you get a 40hp electric motor to match existing diesels that people use, and use a tiny 16 inch bronze propeller etc... you are going to end up with a system that is not very efficient, and your range will be a fraction of what it could be. You would be ignoring physics, and joining the people who use diesel engines, because they care about convenience only and absolutely nothing else, except in this case, your system will be much less convenient because you can only go really slow, or really short distances.

[BigBeakie]

Originally Posted by boat_alexandra

First of all, keep in mind the power required is zero. This was proven a long time ago. It does not put your boat at risk.
A. You mean like on all those romantic sailing ships that sailed up and down the Australian east coast? The ones that are now marked as shipwrecks on a map I have? Those hundreds of shipwrecks? I bet a few of those Captains wished they had a good strong motor to get off the lee shore or be able to get around the reef that was smack dab in front of them! Read the stories of how the sailing ships with somewhat limited windward sailing abilities were blown onto reefs on the GBR.

The most annoying example people use is to motor against a big blow. Why would you ever do this? You risk losing control if the wind really builds, whatever your engine may be. Your sails are what you should be using, and a whole lot more reliable.
A. Yes of course you sail off it (lee shore) if you can. But depending on the shape of the lee shore, what if you can't point high enough to get past that point? What if you are headed up a river entrance and the wind is funnelling down the river? You going to tack at 90 degrees up a river?

I am currently using only sail and (engine people) are constantly trying to justify all the time and money they waste on their engine by telling me some "Bar entrance is impossible" or you cant get in a lagoon etc.. only for me to find when I get there that it's all nonsense.
A. Well I am truly impressed! Jump on Google Earth and have a look at the Wooli River entrance on the north New South wales coast. See how narrow the breakwall is? Now imagine either getting in, or out, on sail with 2 meter seas running. There are lots more like that, too. And I have been through enough coral passes, even with my limited experience, to know that proposing to sail in and out is just high risk stuff. But good luck with that.

There are not many places where the tidal current is above 4 knots which is the point where the 4hp motors would struggle (remember you can go a mile or so pushing them each 10hp, and the efficiency is more than 4x that of a typical diesel with this horsepower, with the right propeller setup.. you should be doing 6 knots) but in this case, or if one motor fails etc.. you can simply wait a few hours for the tidal rush to diminish to enter the lagoon. You just spent 500 hours sailing across the pacific, one more hour is not a problem.
A. There sure are many places where the tidal race is more than 4 knots. All of the Kimberley coast, throughout the Indonesian archipelago between islands come to mind immediately. And the wind can drop &/or disappear faster than you can say "Oh sh*t, better start the engine!"

The power requirements you are looking at are based on spinning tiny propellers above 1000rpm which is incredibly inefficient, and using it to motor against a tropical cyclone in 60 knots of wind which if you are doing, you have made a big mistake, because when it gusts to 80 you will completely lose control anyway. In these situations you should be in a proper place to ride out the storm before it arrives.
A. Bigger prop for electric propulsion is agreed. But you proposed a meter diameter prop. If it is not a folder or feathering prop, imagine the drag with just one of them,never mind two. If it is a folder or feathering prop, I asked who makes one?

If you want to regenerate with good efficiency with the same motor, you will absolutely need a completely different propeller than for powering. It is not possible to use the same propeller unless you want to make a much smaller amount of power for the same drag. This also means different size regenerating propellers for different speeds. This also allows you to remove the main propeller to reduce drag when sailing.
A. I don't think so, I believe you can use a Gori of the right diameter, which is bigger than for the equivalent diesel power, and get good regeneration AND thrust.

Because the forces are lower on the propeller at a maximum 200 rpm, you don't need bronze, you can make your own.

If you get a 40hp electric motor to match existing diesels that people use, and use a tiny 16 inch bronze propeller etc... you are going to end up with a system that is not very efficient, and your range will be a fraction of what it could be. You would be ignoring physics, and joining the people who use diesel engines, because they care about convenience only and absolutely nothing else, except in this case, your system will be much less convenient because you can only go really slow, or really short distances.

A. Oh the last thing I would do is ignore physics

[mbianka]

Originally Posted by BigBeakie

Thanks Guys for all your comments and ideas. To adress some of the points made;

I don't think the electric propulsion solution with DC Genset would be heavier than regular diesels/saildrives plus fuel, I think it will be lighter. Unless you go crazy on having excess LiFePO4 capacity.

mcarling - points noted, thanks.

mbianka - I don't think a Honda will put out enough juice for the motors we are considering. I like the idea, I love our Honda for camping, but I would rather carry diesel than petrol for safety reasons. We will consider electric for the tender as well and also an electric dive compressor, so we are investigating having a petrol free boat.

Understood. I was just pointing out how I found that a $900 Honda has met all my needs in moving my 16,000 lb boat. Less is sometimes more with EP. My boat moves along quite nicely at 3 knots using just 900 watts of power. Which is well within the range of the Honda 2000 max output. They also make larger generators but, I would not be able to move them around as easily. I did find that I fire up the Honda less than I thought as I gained experience in using the hidden benefits of EP. I'm sure you will find that you will not be using the generator as much as you think with your much bigger solar array too. Mine is only 120 watts. You still might want to consider carrying something like a Honda 2000 on board. It's light and does not take up much space and if(when) the diesel generator breaks down you can still charge the batteries while you work on the generator. Relatively cheap as a backup. Another thing it's also easy to overlook that your boat will be making fuel(energy) while sailing or even when at anchor via solar and/or wind turbine. I get a kick out of that.

[bryguy67]

Originally Posted by BigBeakie

(we're considering twin 40HP for our 46 foot cat) & a diesel genset.

Our system will also use typical size diesels (55hp in our case) but NO generator. When the electric motor is in line with the diesel on a shaft drive then the motor BECOMES the generator when you start your engine(s)...AND when you choose to hydrogenate while sailing. It's like having two generators on board and they can be operated via diesel or wind. I agree with others that you won't need a generator, but you'd be really missing the boat if you don't connect the two.

[BigBeakie]

bryguy67,

One of our main motivations in going electric is the trend in the South Pacific island nations to start moving from fossil fuels to solar arrays and battery storage for their electrical needs. Several places are already de-commissioning their diesel generators and switching to solar storage solutions. The UN says this trend will become stronger in the next decade and we will be planning of cruising for the next 10 years, so.....

We think over time the supply & cost of diesel will becoming an issue for cruisers to these areas.
So for us it makes no sense to have both diesel motors AND electric motors, the so called parallel system. I never have been able to wrap my head around the concept unless cruising in high latitudes with lots of cloudy periods.

Yes the redundancy of the parallel is attractive at first, but considering the cost/weight/maintenance/ TCO value proposition, we are leaning towards an electric-diesel genset solution for a cat in tropical cruising.

[valhalla360]

Originally Posted by BigBeakie

Valhalla 360: Yes I've been looking at long river entrances as one scenario. Bundaberg has a reasonable length passage but the tidal current is pretty modest, so not an issue. One thing I am investigating is what adverse current and wind conditions would stop the boat, but havn't reached a conclusion yet.
!

We were going up the St. Clair River (north of Detroit) a couple years back. We were fighting a 2kt current for around 30miles. If we had to drop back to 4kts, we would have only made 2kt COG.

For about a mile under the blue water bridge, the current went up to 5-6kts if you stayed in the slow water on the canadian side, so a lesuirly 4kts would be losing ground. We were full throttle making 1.5kts for about 45 minutes before breaking free and then were were at higher than normal throttle for another hour or two before we got fully clear of the currents.

We've also gotten into situations in narrow channels with 30-40kt winds on the nose where we have had to spend a fair bit of time opening her up if we want to make headway.

Can you make due with poor performance? Sure, but we are a long way from getting the same performance out of an electric system

[valhalla360]

Originally Posted by yamez4u

I decided against composting heads, because very few really compost. To compost you need a large container that gets to a sterilizing heat, for months. Other wise you are just storing your crap and dump it some place. Pretty much exactly like the current boat waste tanks, but less smelly. They may not smell, but don't fool yourself, any head you have to empty weekly has not had enough time to compost. So for me the options where incinerating or storage without a tank. I am trying both. The "composting" head would be similar to the Dry-flush. IE store the poop without the smell, then trash it when done. Peat moss should cost less, but you would have to handle it when emptying your head. The Incinolet truly sterilize the waste and unlike the composting heads or the Dry-flush I could honestly dump the waste overboard at sea without braking any laws.

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 thier own because they developed to live in a host at body temperature and a moisture saturated environment.

The primary advantages for a cruiser:
- We can go around a month between emptying the solids tank.
- Emptying the liquid tank can be done at any shoreside toilet or overboard if offshore.
- Because the decomposition is aerobic, odors are negligible.

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.