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Old 29-10-2009, 06:25   #226
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I just found a power curve for my Yanmars that indicates that at my cruising rpm that delivers 6 knots the engine is delivering 15KW to the props. I had clearly been on the high side with my estimates.
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Old 29-10-2009, 09:32   #227
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Keep in mind that the prop efficiency of the present motor , saildrive and prop is 40 % at best and we work with 60 % prop efficiency .
Our props turn slower and we use a DAR of 73 % with 4 blades.
This is possible because of the torque of the electric motors this is maximum with 0 RPM
We also use forward facing props that operate in undisturbed water increasing the efficiency with 10 % over rearward facing props.

Greetings
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Old 29-10-2009, 11:10   #228
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Bill,

When you say 15kw, are you looking at your engine's power curve or the propeller absorption curve at that rpm? The power curve will give you what the engine is capable of producing at your cruising rpm, which will always be higher than what is actually used (otherwise you couldn't accelerate). Your actual power required to push your boat 6kts may be much less measured at the prop.

Brett
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Old 29-10-2009, 11:36   #229
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Quote:
Originally Posted by fastcat435 View Post
Keep in mind that the prop efficiency of the present motor , saildrive and prop is 40 % at best and we work with 60 % prop efficiency .
Our props turn slower and we use a DAR of 73 % with 4 blades.
This is possible because of the torque of the electric motors this is maximum with 0 RPM
We also use forward facing props that operate in undisturbed water increasing the efficiency with 10 % over rearward facing props.

Greetings
Gideon
Despite whatever testing has been done to arrive at these figures they remain targets rather than proven, since unless I'm wrong there still hasn't been a Fastcat launched with the Green Motion system?
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Old 29-10-2009, 11:45   #230
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www.re-e-power.com

I'm considering an E-Pod 3000 (RE-E-POWER Electric Propulsion for Marine Applications) for my Tartan 30. The E-Pod has a regenerative capability to recharge battery banks while sailing. They also now make an outboard motor version.

Any insights would be appreciated.

Thanks,

Jim MacDonald
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Old 29-10-2009, 12:20   #231
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Undoubtedly, electric propulsion is fabulous for many reasons both ecologically and comfort/convenience. But there is one big problem - where are you going to get the electricity to run the motor? The E-pod spec sheet shows average cruise at 100 amps at 48 volts. At max power it uses 200 amps. Where are you going to get 100 up to 200 amp-hours or more to replace the power you just used each hour?
- - The answer in this thread many pages ago seems to be a large generator based on a infernal combustion engine. Conventional storage batteries will be flattened in a short time at those current draws, not too mention heat generated by massive discharge. To eliminate that you need massive battery banks - and the generator. If you or future scientists/engineers solve the problem of batteries in a cost-effective manor without relying upon tonnages of lead - then diesels can kiss their smokey butts goodbye. Until then buy a 15hp or 20 hp outboard and hang that on your transom while you are waiting for the big "breakthrough" to filter down to Walmart prices.
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Old 29-10-2009, 12:59   #232
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I would not hesitate to use a genset to power the electric drive when I run out of juice. The thing I would be afraid of is lightning damage to the electric propulsion motor.

cheers,
Nick.
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Old 29-10-2009, 13:05   #233
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Originally Posted by LtBrett View Post
Bill,

When you say 15kw, are you looking at your engine's power curve or the propeller absorption curve at that rpm? The power curve will give you what the engine is capable of producing at your cruising rpm, which will always be higher than what is actually used (otherwise you couldn't accelerate). Your actual power required to push your boat 6kts may be much less measured at the prop.

Brett
I'm looking at the propellor power output from the graph at the following link. SAIL DRIVE-3JH3CE
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Old 29-10-2009, 13:38   #234
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LtBrett, you have an interesting point about what it can produce vesrus what it s really using. I usually cruise at 2950 RPM (80% MCP) and at that speed at roughly 15KW at the prop and 26 KW at the flyweel I should be using about 6.5 liters per hour to maintain that speed assuming I'm reading the specific fuel consumption graph correctly as grams/KW/HR. I typically refuel on long trips at about 40 hrs and pretty much use 56-60 gallons depending on water conditions for both engines. That is a 7 Kt cruise speed. If I run on 1 engine I use about .75 GPH at 6 kts. So in fact I'm using only about 3 liters per hour per engine. So If I'm calculating this correctly 3 liters per hour I'm producing about 12 KW. I'm just not sure if the specific fuel consumption curve is measured at the engine or at the prop. If it's at the prop things are not too far off, but if it's at the engine then I'm actually using only about 6KW at the prop.
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Old 29-10-2009, 23:40   #235
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I removed the Tartan 30's Atomic 4 gas engine. I have a 12V house battery bank and plan to have a completely separate 48V battery bank to power the E-Pod (using solar panels/wind turbine/E-Pod regeneration for battery charging .... possibly adding a water turbine).

I plan to use a "kicker" in combination with the E-Pod for entering/exiting marinas/anchorages and for emergency maneuvering. I don't plan to do much "motor-sailing" per se.

Since I'm new to this forum, I hadn't searched any threads/posts prior to my initial post .... but now have located previous mention of the E-Pod (The Hurdle's focusing on sailing, boating, sailboat racing, diving and other family activities.), a reading of which indicates that the E-Pod should suffice for my needs.

I could probably get by with just a kicker motor (which I'd also use for my dinghy), but then I'd have to carry more fuel, etc. The E-Pod would add weight (especially the batteries), expense, and reduce my storage space (which is already at a premium). But the added convenience and safety afforded by the E-Pod keeps gnawing at me.

Either way, it's a compromise ..... so for the short-term I guess I'll see if the kicker suffices, and if not, then add the E-Pod.
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Old 30-10-2009, 05:17   #236
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This is one I had not seen before. I think diesel-electric solution for propulsion is getting closer with solar & wind for house usage.Pure battery for emergency & limited time use. Sail for the rest. see SolidNav :: Alternative to Diesel Engine - Electric Sail Boat & watch the video on the site as well. I will be interested to see how my new props with the propspeed works out over the next year re growth as it would be nice to be able to stay with conventional shaft setup.
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Old 30-10-2009, 12:11   #237
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Hi Bill, I had considered the SolidNav unit as a direct replacement for my Atomic 4 engine but due to space constraints thought the E-Pod 3000 (mounted beneath the hull) might work out better for me ..... I did keep the original engine mounting bases in place just in case (for either using the SolidNav or a diesel engine down the road).
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Old 02-11-2009, 11:03   #238
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Phish Phart,

I strongly urge you to search the Electric Boats Yahoo Group site concerning RE-E-Power. Some re-e-thinking might be necessary.

The web location is : electricboats : Electric Boats
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Old 02-11-2009, 18:02   #239
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The old method of measuring output from engines was the water brake, which is a lot like a propeller in water.

There are a lot of electric drive vessels around, including the huge cruise ships, and a lot of articles on the web which state higher efficiency as a main benefit.

A submerged motor is well cooled, and mechanically simple. Care and attention to waterproofing is vital of course, the operating voltage will kill you very nicely is a salt water environment.
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Old 02-11-2009, 21:14   #240
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Phish Phart,
I strongly urge you to search the Electric Boats Yahoo Group site concerning RE-E-Power. Some re-e-thinking might be necessary.
The web location is : electricboats : Electric Boats
Do you have a specific message in the group you linked to? I cannot find anything in that group except a one line statement about one instance where an installation was not done correctly. Please expound on the suggestion you made that there might be more "negative" aspects of the "e-pod". I am working with a friend who needs something like the "e-pod" and we would like to hear everything we can from those who are using it.
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