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Old 08-07-2014, 19:54   #241
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Re: Electric Propulsion on Catamarans

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Originally Posted by socaldmax View Post
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Interestingly, the US Navy seems to be shifting to electric drive.

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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.
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Old 09-07-2014, 00:07   #242
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Re: Electric Propulsion on Catamarans

And of course a (maybe THE) major priority in submarine propulsion is quietness.

Certainly electric motors can be installed so they don't ever get exposed to seawater. As can diesels, petrol, gas turbine, steam turbine.. you name it.

As a reminder, it wasn't me who started on about water and it's impact on motors. Look back a few posts....

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Water in your fuel disables your diesel engines.
Make sure your boat is not around water to avoid the risks.
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Old 09-07-2014, 00:34   #243
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Re: Electric Propulsion on Catamarans

I think the major factor for subs is air. Remember that diesel is only 1 component of combustion. When running silent the engine is shutdown anyway.


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Old 09-07-2014, 15:32   #244
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Re: Electric Propulsion on Catamarans

I believe the submarines being discussed are in fact nuclear powered.

Anyway, I don't think anyone disputes that electric MOTORS can work. I think the area of debate is where the power to operate these motors will come from, in a cruising situation. Certainly a nuclear reactor would be handy.
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Old 09-07-2014, 15:40   #245
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Re: Electric Propulsion on Catamarans

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I think the major factor for subs is air. Remember that diesel is only 1 component of combustion. When running silent the engine is shutdown anyway.


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Many conventionally powered (non nuclear) make use of Air. Independent Propulsion (AIP). That removes the major factor you listed. The benefit of AIP is that it is incredibly silent, and lacks the downside of traditional diesel electric setups.
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Old 09-07-2014, 23:11   #246
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Re: Electric Propulsion on Catamarans

Here's my thinking so far after considering some of the comments here, as I contemplate our blue water cruising cat for the (mostly) South Pacific.

I have not heard anyone make a knock down case against an electric propulsion cat, yet. Some have made good points about some considerations that would need to be part of the design, and perhaps some limitations such as the period of WOT running, but so far I don't see any showstoppers.

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.

If anyone has some major consideration that has not yet been aired, it would very much be appreciated if that could be discussed. I am discounting arguments that electric motors are somehow just not capable of providing reliable propulsion. Clearly there are quality issues (as with most things) & the spec has to be for industrial duty motors, but there are certainly motors out there that will do the job.

I think the vulnerability of an electric system to lightning is a valid objection, and having circuit disconnects (in addition to breakers) at several points is something I'd like to learn more about in particular.
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Old 10-07-2014, 01:03   #247
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Re: Electric Propulsion on Catamarans

It's not a knock down case, but it's almost certainly going to be heavier than just twin diesels. And more complicated. But if you were already going to have two diesels plus a genset, then probably not much difference in weight.

However, unless you feel the need for AC, I don't believe a diesel genset is necessary or even desirable. JMHO though, for some a big genset may be considered essential.

To me, vulnerability to lightening is something every boat has. Fact is, if you suffer a BIG strike, it's very likely nothing electrical will work afterwards. You'll be lucky if you still have a rig, and are afloat.
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Old 10-07-2014, 01:10   #248
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Re: Electric Propulsion on Catamarans

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Interestingly, the US Navy seems to be shifting to electric drive. The first major combatant to use electric drive was the DDG 1000 (Zumwalt-class destroyer).
The US Navy used electric propulsion for major combatant vessels a hundred years ago -- for example the battleship New Mexico.

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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, Los Angeles class submarines have batteries which can power the auxiliary drive if the steam turbine is not turning.

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The benefit of AIP is that it is incredibly silent, and lacks the downside of traditional diesel electric setups.
AIP overcomes only some of the downsides of traditional diesel electric setups. Overall range is still a limitation. Anyway, AIP seems even less relevant to our needs than nuclear propulsion.
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Old 10-07-2014, 01:54   #249
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Re: Electric Propulsion on Catamarans

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It's not a knock down case, but it's almost certainly going to be heavier than just twin diesels. And more complicated. But if you were already going to have two diesels plus a genset, then probably not much difference in weight.

However, unless you feel the need for AC, I don't believe a diesel genset is necessary or even desirable. JMHO though, for some a big genset may be considered essential.

To me, vulnerability to lightening is something every boat has. Fact is, if you suffer a BIG strike, it's very likely nothing electrical will work afterwards. You'll be lucky if you still have a rig, and are afloat.
Not sure why it would be heavier? Wouldn't the weight of the LiPO4 batteries be about the same (or less) as the weight of diesel? If we are talking extended South Pacific cruising, many boats load up with around 1,000 litres = 1,000 Kg. of fuel & that would be way more than batteries for electric. The electric motors are much lighter than diesels/saildrives as well.
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Old 10-07-2014, 02:19   #250
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Re: Electric Propulsion on Catamarans

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Not sure why it would be heavier? Wouldn't the weight of the LiPO4 batteries be about the same (or less) as the weight of diesel? If we are talking extended South Pacific cruising, many boats load up with around 1,000 litres = 1,000 Kg. of fuel & that would be way more than batteries for electric. The electric motors are much lighter than diesels/saildrives as well.
The diesel-electric variant would use a DC genset, which would be lighter than the AC genset used with the traditional diesel drive. Regardless, most of the weight in a diesel-electric setup would be the batteries and it would be easy to size the batteries so that the overall weight is about a break-even.

Personally, I would be more inclined to have a very large solar array that a genset to supplement electric propulsion. I would rather have unlimited motoring range at 3-4 knots with all the benefits of not having hydrocarbon fuels onboard than limited motoring range at 8-10 knots and all the nastiness of hydrocarbon fuels. Of course, the solar-electric setup without a genset would also be able to do 8-10 knots motoring, but only for very limited ranges of perhaps about 30-60 nm depending on battery capacity.
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Old 10-07-2014, 02:29   #251
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Re: Electric Propulsion on Catamarans

Hi mcarling;

I would rather dispense with the diesel genset as well BUT, just thinking of worse case scenarios like 2 weeks of cloudy weather or needing to motor for a couple of days in very light conditions.

The motors we are considering are the 30kW/40HP Torqeedos, so we would need a really big solar area to feed even just one motor and make 5 or 6 knots. I'm thinking of having a minimum 1kW solar permanently on the coachroof and then several of the thin, 180watt panels that I can clip onto the tramps when needed and conditions allow.
Hence a relatively small genset, maybe 6 kW, and then we could feed 4 kW to a motor and still be putting amps back into the batteries.

Anybody want to chime in on this plan?, and feel free to make suggestions?
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Old 10-07-2014, 02:37   #252
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Re: Electric Propulsion on Catamarans

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Hi mcarling;

I would rather dispense with the diesel genset as well BUT, just thinking of worse case scenarios like 2 weeks of cloudy weather or needing to motor for a couple of days in very light conditions.

The motors we are considering are the 30kW/40HP Torqeedos, so we would need a really big solar area to feed even just one motor and make 5 or 6 knots. I'm thinking of having a minimum 1kW solar permanently on the coachroof and then several of the thin, 180watt panels that I can clip onto the tramps when needed and conditions allow.
Hence a relatively small genset, maybe 6 kW, and then we could feed 4 kW to a motor and still be putting amps back into the batteries.

Anybody want to chime in on this plan?, and feel free to make suggestions?
My suggestion would be to reserve a place for the genset and fuel tank but to try cruising without it. Remember, even on cloudy days one will get some energy from the solar panels. The power required to motor at 3 knots is only about 1/8 that required to motor at 6 knots. In the end, it will depend on how much patience one has. I try to keep in mind that Drake and Magellan circumnavigated hundreds of years before boats had any electricity, motors, or engines. 1KW of solar is not much for back-up propulsion, but would suffice for cooking, laundry, and even some A/C. I would want at least about eight of those 180 watt supplemental clip-on panels if I were hoping to do any long-distance motoring (at 3-4 knots, not 5-6 knots) without a genset.
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Old 10-07-2014, 05:54   #253
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Re: Electric Propulsion on Catamarans

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Hi mcarling;

I would rather dispense with the diesel genset as well BUT, just thinking of worse case scenarios like 2 weeks of cloudy weather or needing to motor for a couple of days in very light conditions.

The motors we are considering are the 30kW/40HP Torqeedos, so we would need a really big solar area to feed even just one motor and make 5 or 6 knots. I'm thinking of having a minimum 1kW solar permanently on the coachroof and then several of the thin, 180watt panels that I can clip onto the tramps when needed and conditions allow.
Hence a relatively small genset, maybe 6 kW, and then we could feed 4 kW to a motor and still be putting amps back into the batteries.

Anybody want to chime in on this plan?, and feel free to make suggestions?
When I started thinking of converting to electric propulsion. I went through a lot of "what if" scenarios as there were no boats that were the size of mine that had done the conversion. Having spent a season below deck trying to get the old diesel working I decided I really did not want to have another engine below deck if I did not have to. Thats when I came upon the idea of using the Honda 2000 generator for charging and possibly extending the range of the batteries if I needed too. I was not sure how well it would work. But, I said to myself if it didn't work out I could always install a diesel generator below deck in the future. I'm happy to say it worked out better than I thought. I would not even consider putting a diesel engine back on board. The reliability is up and ease of maintenance and associated costs are way down and the boat always smells clean even in the bilge. The beauty of electric propulsion is you can try one scenario and see if it will work for your needs. If not it is easily modified and changed. When you install a diesel there you are.
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Old 10-07-2014, 11:00   #254
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Re: Electric Propulsion on Catamarans

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Hi mcarling;



.....

I'm thinking of having a minimum 1kW solar permanently on the coachroof and then several of the thin, 180watt panels that I can clip onto the tramps when needed and conditions allow.

....
....



Anybody want to chime in on this plan?, and feel free to make suggestions?

Very interesting and intriguing project. We have 1.8 kW on our lLagoon 450 cat. That is ample for living a good live with lots of convenience toys, fridges, freezers, fresh water for lots of hot showers and washing the salt off the boat, coffee maker, watching machines, charging LiFrPo for the wife's dinghy. It would not be enough for electric propulsion. I could easily expand it to 2.5 kw in the same place. We extended to cockpit roof aft with the panels. Gives extra shade too. Much appreciated in the tropics. We never use the engine to charge and do not have or want a generator. We could run AC off it (1400Ah LiFePo) but do not need one.

In your case I would still add flexible solar panels to the salon roof. 100W semi flexible can be had at Aliexpress for less than $200 a piece including shipping when you buy multiples.
You should also be able to place another 1-2 kw on the trampoline or forward deck space.

I don't think I would do this under 3kw. Then it should just be doable by solar 90% of the days. You would want to have 30 kwh of battery or more.




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Old 10-07-2014, 11:44   #255
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Re: Electric Propulsion on Catamarans

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By electric I mean one that has sufficiently powerful motors (we're considering twin 40HP for our 46 foot cat)
Why do you need so much power? I would be considering twin 4HP motors on a 46 foot cat capable of pushing you 4 knots on solar power in a dead calm, and much faster in bursts for maneuvering as electric can push well past its rating. You need temperature sensors on the motors.

If there is a little wind (even 3 knots) you can make great speed using the sails and motor together.

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If anyone has some major consideration that has not yet been aired, it would very much be appreciated if that could be discussed. I am discounting arguments that electric motors are somehow just not capable of providing reliable propulsion. Clearly there are quality issues (as with most things) & the spec has to be for industrial duty motors, but there are certainly motors out there that will do the job.
A few thoughts. Use really large propellers spinning slowly. Something close to 1 meter diameter propellers going only a few hundred rpm at top speed. The motor is geared down a lot (30:1 or more) with high efficiency planetary gear boxes to achieve this.

Install a good path from the mast to a ground plate for lightning strikes. This will minimize damage to electronics and thru holes, but will increase your chance of actually getting struck.

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In your case I would still add flexible solar panels to the salon roof. 100W semi flexible can be had at Aliexpress for less than $200 a piece including shipping when you buy multiples.
I think the semi-flexible are good, but beware the more flexible ones have very low output.

Quote:
You should also be able to place another 1-2 kw on the trampoline or forward deck space.
Also consider putting panels on the whole mast and boom, this is quite a lot of area, perhaps 2-3kw. It is also possible to walk on solar panels if they are well supported underneath, but, dropping something can crack them, so use many small ones. This also will make the boat much hotter in the tropics. You can either pump seawater onto the panels to cool them, or, store the last 2kw of panels below, and deploy them when needed. This allows for many arrangements which are impossible in rough weather as well greatly augmenting potential solar area. Consider large panels the whole length of the life lines which rotate to face the sun.

It is best to have many parallel strings to mitigate issues with partial shade.
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I don't think I would do this under 3kw. Then it should just be doable by solar 90% of the days. You would want to have 30 kwh of battery or more.
Large batteries seem nice.. but if they are cheap flooded lead acid for example, they waste a lot of power in self-discharge and are very heavy so there is a breaking point where more will not be better. Lithium batteries would be a much better option if you want a large capacity.
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