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Old 17-07-2014, 21:53   #391
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Re: Electric Propulsion on Catamarans

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Originally Posted by BigBeakie View Post
I do not know if Torqeedo supplies a "one size fits all" prop for the shaft drive. I doubt it because there would be a wide variety of boat parameters to consider such as single hull or multi, DWL displacement etc.

Basically I'm wondering how anyone who has EM's on their cat sized the propeller? I hope there is some rationale to it other than guesswork.
I tried to use the simple rules of thumb to find the right prop for my boat and failed. Though I learned a lot. It was not till I bought Dave Gerr's "Propeller Handbook" that I got the solid answers you are looking for. You can skip to page 45 and start there. It will take about two hours to read and fill in all the formulas. But you will have exactly what you want at the end.
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Old 17-07-2014, 22:00   #392
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Re: Electric Propulsion on Catamarans

Yamez4u,

Yeah! Thank you, that is a great suggestion. I am hearing so many crazy things from propeller companies that, you're right, I better sort this out myself.

So he talks specifically props fr electric motors and the considerations specific to EM's?
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Old 18-07-2014, 02:07   #393
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Re: Electric Propulsion on Catamarans

Re sizing props for electric catamarans, I have spent some time looking at the forum at Boat Design where technically competant foks seem to hang out, not that there aren't technically knowledgeable folks here.

There are threads that seem to indicate the flat torque curve for EM should be considered, so use a bigger higher pitched prop, but that was in the context of a big motorsailor many times the displacement of cruising cats.

I wonder if anyone has worked on this in a formal way? Has anyone seen discussion of this anywhere, like on a prop manufacturer website?
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Old 18-07-2014, 07:01   #394
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Re: Electric Propulsion on Catamarans

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Originally Posted by cwjohm View Post
So does this not mean that we go from the backup redundancy of two diesels on a cat to a single point of failure in regards to the generator. Surely, murphy's law will dictate that at the crucial time when power is needed to get out of a sticky situation, will be the time when the generator needed to cut in to replenish battery power and generator failure at that time could be catastrophic.

What am I missing?
A series hybrid system (single generator, 2 electric motors) cuts in half the redundancy of a typical twin diesel cat. However, a parallel hybrid system (twin diesels with twin e-motors) doubles the redundancy of a typical diesel cat.
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Old 18-07-2014, 07:24   #395
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Re: Electric Propulsion on Catamarans

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Originally Posted by DotDun View Post
I obviously have other criteria, but range at reasonable speed shares #1 spot on the list.

Other criteria include:

Cost
Simplicity
Reliability
Longevity of the system
Redundancy
Availability of parts
Availability of technical expertise
The Yanmar parallel hybrid system meets all of your criteria:

RANGE AT REASONABLE SPEED: switches between twin diesel power and electric power as battery level changes-longer range than with non-hybrid system assuming same size diesel tank.
COST: Very little cost difference when compared to typical set up of twin diesel propulsion engines plus a diesel generator. One poster in this thread stated that a large solar array is required for a hybrid...it's not required, it's just a smart investment and the bigger the better. Cost goes up as battery size and solar size goes up...but so does efficiency.
SIMPLICITY: No trying to design the system from scratch...genius engineers have done that already. And it's as simple as the Toyota Prius set up...just a small electric motor between the diesel and the shaft that can be on or off when you choose.
RELIABILITY/LONGEVITY: Yanmar diesels are proven...electric motors we all seem to agree are quite reliable. The system has been tested and has been in use on real boats in the real world. Oh, and it's warranted by Yanmar.
REDUNDANCY: The parallel system has 2 diesels and 2 electric motors. That's twice the redundancy of a typical cat set up. If one of any of those fails, you have 3 other sources of propulsion (beyond your sails). Each system acts as a generator when under way or at anchor, so if one side fails, you even have a back up generator. Repair at your leisure, plus a safety net after a safety net after....
AVAILABLILITY OF PARTS/TECHNICAL EXPERTISE: I had the same concerns when ordering our new hybrid boat. I have emailed the genius engineer who created this system and he emails me back right away...each time. He suggested a few extra parts to keep on board that even a guy like me could easily unplug and plug in the new one. Not only is he available, but Yanmar trained techs are. Parts for these hybrid systems are becoming stocked in several parts of the world. But, worst case...you have to wait 2 weeks for parts to be shipped; see redundancy above.

I don't think there is a series hybrid system that could meet all of your criteria which is exactly why I didn't choose one. But this parallel system most certainly does.
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Old 18-07-2014, 08:48   #396
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Re: Electric Propulsion on Catamarans

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Originally Posted by bryguy67 View Post
The Yanmar parallel hybrid system meets all of your criteria:

RANGE AT REASONABLE SPEED: switches between twin diesel power and electric power as battery level changes-longer range than with non-hybrid system assuming same size diesel tank.
COST: Very little cost difference when compared to typical set up of twin diesel propulsion engines plus a diesel generator. One poster in this thread stated that a large solar array is required for a hybrid...it's not required, it's just a smart investment and the bigger the better. Cost goes up as battery size and solar size goes up...but so does efficiency.
SIMPLICITY: No trying to design the system from scratch...genius engineers have done that already. And it's as simple as the Toyota Prius set up...just a small electric motor between the diesel and the shaft that can be on or off when you choose.
RELIABILITY/LONGEVITY: Yanmar diesels are proven...electric motors we all seem to agree are quite reliable. The system has been tested and has been in use on real boats in the real world. Oh, and it's warranted by Yanmar.
REDUNDANCY: The parallel system has 2 diesels and 2 electric motors. That's twice the redundancy of a typical cat set up. If one of any of those fails, you have 3 other sources of propulsion (beyond your sails). Each system acts as a generator when under way or at anchor, so if one side fails, you even have a back up generator. Repair at your leisure, plus a safety net after a safety net after....
AVAILABLILITY OF PARTS/TECHNICAL EXPERTISE: I had the same concerns when ordering our new hybrid boat. I have emailed the genius engineer who created this system and he emails me back right away...each time. He suggested a few extra parts to keep on board that even a guy like me could easily unplug and plug in the new one. Not only is he available, but Yanmar trained techs are. Parts for these hybrid systems are becoming stocked in several parts of the world. But, worst case...you have to wait 2 weeks for parts to be shipped; see redundancy above.

I don't think there is a series hybrid system that could meet all of your criteria which is exactly why I didn't choose one. But this parallel system most certainly does.

This is certainly getting better looking.

Compare to 'typical' coastal cruising.

7 weeks, 1100nm, 91 gallons of diesel with ~100 hours on the genset. The genset was used to charge batteries, hot water, and AC. There were a few nights the AC/genset ran all night.

The genset averages ~.25/gal. per hour, so assume 25 gallons of the 91 was generator. Hence, 66 gallons or ~$330 worth of diesel. If we do that 3 times a year, that's ~$1000/year for fuel. It isn't even a consideration in the cost of boat ownership. Extrapolate that into full time liveaboard, and you're looking at ~$2500/yr for propulsion fuel.

How many years does it take to get back the additional cost??
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Old 18-07-2014, 17:07   #397
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Re: Electric Propulsion on Catamarans

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Originally Posted by BigBeakie View Post
Yamez4u,

Yeah! Thank you, that is a great suggestion. I am hearing so many crazy things from propeller companies that, you're right, I better sort this out myself.

So he talks specifically props fr electric motors and the considerations specific to EM's?
Most of the formulas are concerned a with peak running hp/kW and shaft rpm, so would not change much from electric to diesel. You obviously could skip any section on idle stall speeds.
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Old 18-07-2014, 17:18   #398
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Re: Electric Propulsion on Catamarans

HI bryguy

I looked at the Yanmar Hydbrids, but the cost was significantly more, and the power production significantly less, than diesels plus generator.

I have no doubt however, that this is the way of the future
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Old 18-07-2014, 19:21   #399
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Re: Electric Propulsion on Catamarans

I have doubts this is the "way of the future". ANY solution that relies on fossil fuel will at some point become so expensive that alternatives will be a "no choice" decision. FWIW I doubt the addiction to fossil fuels will be seriously addressed for a long time, judging by the willful ignorance of some governments we could name, but the realisation that oil is too precious to burn will eventually seep in.

It is ALREADY an issue in some parts of the South Pacific, (where we want to cruise for 10 years or so), with a trend line that indicates it is in the very foreseeable future, not decades away. I heard recently about a motor cruiser (diesel) that failed to get fuel somewhere because of lack of supply, and they barely made it to the Phillipines.

A parallel hybrid system (with its super duper redundancy) without fuel is dead in the water if becalmed. No problem, patience is a virtue.
A boat that harvests the sun & wind and stores the fuel in adequate batteries has a few more options. I would rather be slower but reliable than becalmed for too long.
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Old 19-07-2014, 01:25   #400
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Re: Electric Propulsion on Catamarans

In reference to cruising at 1 knot below hull speed on solar power:

Quote:
Originally Posted by yamez4u View Post
Agreed.

I don't have to guess. Even with my heavy 13 ton boat and a somewhat inefficient hull design (semi-displacement ) We are talking a 1972 41 foot Chris-craft Commander, one of the heaver fiberglass boats ever built, I can cruise at 4 knots on a sunny day with my 3kw array with no draw on the battery bank. But even with no sun my range with my 48kw battery bank would be around 100 miles at the before noted 4 knots.

I still have room to improve my numbers. But given that my boat is kind of a worst case as far as boats to convert, almost anyone else should get much better numbers. The Cats we are talking about could have 5kw or even 6kw solar arrays. I would expect there solar cruise speed to be 5-6 knots.
Finally, someone else who actually uses solar power to push their boat. It really is awesome and really does work well.

Quote:
Originally Posted by valhalla360 View Post
Your 5% statement is misleading at best. Those batteries that get 70% efficency hold a tiny fraction of the power of a single gallon of diesel. Then you overlook the costs associated with generating the power. Even with solar, there is the cost of producing the panels which drastically reduces your 70% number. More importantly, there isn't enough room to put on enough solar to maintain solar for any reasonable time period.
Lets run some rough estimates at efficiency:

solar panel efficiency: 15%
electric motor/controller efficiency: 90%
lithium battery efficiency: 90%
Propeller efficiency: 85%

Overall efficiency: 10%

Now for a diesel system:
diesel engine: 30% (efficiency over it's range is not as good as electric)
after powering cooling pumps, alternators, etc: 90%
typical efficiency of diesel powered yacht propeller (because it's way too small): 25%
efficiency refining crude oil into diesel: 40%
efficiency after subtracting transport costs: 90%
efficiency of producing crude oil from sunlight: 0.2%

Overall efficiency: .0048 % efficient

Solar electric system is so far more than 2000 times more efficient.

It's so far off it's not even funny, it's just annoying people actually do something so wasteful.

Yes, it costs something to produce solar panels electric motors etc.. but it's a lot less than it costs to produce a diesel engine an all the infrastructure required by it (refineries, fuel transport vessel) etc..

Quote:
The big prop (or sculling oar) isn't why you need very little power to go 1.5kts. You need very little power to go 1.5kts because it takes very little power (electic or diesel) to go 1.5kts.
Actually it's for both reasons. The sculling oar is 80% efficient. Try using a kayak paddle to pull the yacht and your efficiency is down to 40%. It does work it's much harder.

Quote:
Originally Posted by DotDun View Post
On my boat, I figure that takes ~26hp. How many watts from solar panels would that be?
You figured wrong. It takes no where near 26hp, that number is based on an inefficient system (see above) Efficiently around 4-5 hp which at 760 watts per hp or so, do the math.

Quote:
Originally Posted by handmer View Post
Is there a reason not to use the existing prop from Torqeedo?
Yes, because it is designed for their requirements, not yours. You might also notice the earlier torqeedo propeller then they went back to a traditional model...
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Old 19-07-2014, 05:57   #401
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Re: Electric Propulsion on Catamarans

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Originally Posted by boat_alexandra View Post
In reference to cruising at 1 knot below hull speed on solar power:

Quote:
Originally Posted by yamez4u View Post
Agreed.

I don't have to guess. Even with my heavy 13 ton boat and a somewhat inefficient hull design (semi-displacement ) We are talking a 1972 41 foot Chris-craft Commander, one of the heaver fiberglass boats ever built, I can cruise at 4 knots on a sunny day with my 3kw array with no draw on the battery bank. But even with no sun my range with my 48kw battery bank would be around 100 miles at the before noted 4 knots.

I still have room to improve my numbers. But given that my boat is kind of a worst case as far as boats to convert, almost anyone else should get much better numbers. The Cats we are talking about could have 5kw or even 6kw solar arrays. I would expect there solar cruise speed to be 5-6 knots.
Finally, someone else who actually uses solar power to push their boat. It really is awesome and really does work well.
I'm suspicious that a 41' boat has a hull speed of just 5kts.

Quote:
Originally Posted by boat_alexandra View Post
Lets run some rough estimates at efficiency:

solar panel efficiency: 15%
electric motor/controller efficiency: 90%
lithium battery efficiency: 90%
Propeller efficiency: 85%

Overall efficiency: 10%

Now for a diesel system:
diesel engine: 30% (efficiency over it's range is not as good as electric)
after powering cooling pumps, alternators, etc: 90%
typical efficiency of diesel powered yacht propeller (because it's way too small): 25%
efficiency refining crude oil into diesel: 40%
efficiency after subtracting transport costs: 90%
efficiency of producing crude oil from sunlight: 0.2%

Overall efficiency: .0048 % efficient

Solar electric system is so far more than 2000 times more efficient.

It's so far off it's not even funny, it's just annoying people actually do something so wasteful.
Amazing isn't it! So inefficient but yet so cheap!

Quote:
Originally Posted by boat_alexandra View Post
Yes, it costs something to produce solar panels electric motors etc.. but it's a lot less than it costs to produce a diesel engine an all the infrastructure required by it (refineries, fuel transport vessel) etc..
You forgot the most important part of your efficiency ratings - COST!

The engine/drive train retail cost for a complete repower for my boat is $18,200 (+ labor). I supplied estimated fuel cost for propulsion for a full-time live aboard at $2500/yr. Yep, got to add $$ for oil changes.

Since most sailboat cruisers won't accept the restriction of a total solar/electric aux power system (lower speed, daylight only, and not enough range), there will be a diesel generator big enough to cruise using electric power.

So, figure the uptake in capex for a electric power including a large enough diesel generator, figure in the small gains in being able to move the boat in/out of the harbor without starting a diesel and tell us how many years it takes to break even.

Then, add in the frustration factor if your electric system breaks while in a location where only diesel support is available.

Believe me, I'm not against solar/electric. I'm against using incomplete/false data to sell it. If you have the desire to spend your money on it, please go for it. Every time someone buys a system, it moves that date when it makes sense for the rest of us a little closer.
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Old 19-07-2014, 10:17   #402
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Re: Electric Propulsion on Catamarans

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Originally Posted by cwjohm View Post
HI bryguy

I looked at the Yanmar Hydbrids, but the cost was significantly more, and the power production significantly less, than diesels plus generator.

I have no doubt however, that this is the way of the future
Hmmmm...Perhaps it's more on a re-power vs. new construction? I know that the cost difference on our new construction was minimal.
Twin 5KW generators (via the E-motors) would be less power production than a diesel generator that is larger than 10KW I suppose. But I like that my generators can be powered with the wind (hydrogenation) when I'm sailing...using no diesel.
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Old 19-07-2014, 10:32   #403
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Re: Electric Propulsion on Catamarans

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Originally Posted by BigBeakie View Post
A parallel hybrid system (with its super duper redundancy) without fuel is dead in the water if becalmed. No problem, patience is a virtue.
A boat that harvests the sun & wind and stores the fuel in adequate batteries has a few more options. I would rather be slower but reliable than becalmed for too long.
I agree with so much you say...so don't take this wrong: But the above quote is simply way off base. If a parallel hybrid runs out of gas it is NOT becalmed...not any more than a serial system. A parallel system CAN be powered by the electric motors alone at typical no-wake speeds by using the energy that is stored in the batteries. It won't cruise as fast as a serial hybrid because the E-motors are smaller; but not becalmed either. Solar and hydro-generation (while sailing) fill the batteries back up and that stored energy CAN be used for propulsion. Same as serial. I don't argue against serial hybrid systems; parallel and serial both have advantages and disadvantages. Parallel just happens to be my final choice after researching both. It fits MY needs best. With the type of sailing you'll be doing and your strong belief systems, I think you're making the best choice for you with the serial hybrid. For many people, an all diesel system is the best choice for them.
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Old 19-07-2014, 11:13   #404
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Re: Electric Propulsion on Catamarans

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Originally Posted by DotDun View Post
You forgot the most important part of your efficiency ratings - COST!
I came up with some arbitrary systems, so feel free to make your own

Keep in mind the electric system has unlimited range where the diesel system is limited to the amount of fuel you can carry forcing you to make stops in areas you would rather avoid. Both systems have approximately the same power.

Let us run some rough estimates at cost:

3kw of PV = $3000
3x 48v 50a mppt = $900
6kwh of LiFePo4 = $4000
2x mars etek 0907 motors = $750
2x brushless motor controllers = $600
high current copper wiring and connectors (normally can be salvaged for free) = $200

assuming custom molded large size propellers running from toothed belts going into the water between the hulls, no stuffing box is needed, no drag when under sail and it is possible to use a wide range of propellers depending on the speed and if powering or generating for maximum efficiency. Pedal power adaptation also highly efficient. The cost to build this is ~ $100 and a bit of time.

Total cost: $9550

Now for the diesel system:
2x beta 13hp motors - $8400
2x folding bronze propellers - $3000
cost of fuel - varies depending on use and location
cost of parts/oil etc - your guess is better than mine
amount of time tinkering with engine - often longer than engine free sailors spend waiting for the wind
cost of living in a future world which has an atmosphere that humans, mammals and millions of other species face extinction - incalculably high


Now you can see the difference in cost of $9550 or incalculably high.

There are many configurations possible which are cheaper or more expensive for electric drive systems. Diesel systems are all the same price.
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Old 19-07-2014, 11:50   #405
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Re: Electric Propulsion on Catamarans

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I'm suspicious that a 41' boat has a hull speed of just 5kts.
It is not. The hull speed for a 41 Chris-craft which has a water line of 35 foot is 7.9 knots. But the weight of my boat and the semi-dispasment hull are not ideal. Given that we are talking about much lighter cats with displacment hulls which could hold solar arrays that are twice the size I have. I think he is pretty much on the money with his estimate of 1 knot below hull speed for a cat.

There are a few cats out there with large arrays and electric motors, maybe one will wonder in here with there numbers.
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