Alternative Propulsion Thread

[George Wade]

Originally Posted by Rising Star

Skipmac,

Comparing an electric motor to an ICE (internal combustion engine) is comparing apples to oranges.....

Comparing an electric motor to an infernal combustion engine is like comparing a teenage python to a day old treefrog...

[James S]

Originally Posted by s/v Jedi

Come on James, you can do better.

My Google search for a 50hp electric traction motor returned 34,900 hits. The first page shows two links that got my attention:

An electric Mini Cooper with 4 motors of 160 hp each, one for each wheel:
Electric Mini: 0-60 in 4 Seconds: It Has Motors In Its Wheels : TreeHugger

City Electric Motor will ship you a 25-25,000hp electric traction motor same day:
City Electric Motor Company Inc.

No, that part is easy.

ciao!
Nick.

Your right Nick...If I was doing it today it would be a different story, but as I said in my first post, "when I was re-powering" that was two years ago.
From what I had learned cooling was an issue and finding quality water jacketed motors wasn’t that common.

The Mini Cooper sounds like fun!

[fastcat435]

Having an electric motor to propel your boat is very well possible, using it to regenerate the batteries is possible , storing 3 hours of run time is possible depending on the batteries used. Having a back up generator is a good idea specially on long trips where wind can be absent for days ( unless you are no in a hurry )
Using regeneration, solar, wind and shore power are all part of the Green Motion system that will be launched in 3 months time , it is not cheaper than any diesel solution but it is environmentally friendly, produces no noise sooth or smoke.
Each hour of power by batteries means at least 4 hours of regeneration costing some speed. The cost over a 10 year period depending on how much a boat is used would come close to the diesel alternative. there are however more advantages going electric hybrid, the weight can all be placed closer to the center of gravity. In case of the Green Motion system the complete drive system is lifted from the water decreasing drag stopping propeller growth and leaving no true hull holes that could eventually leak

There are advantages to going diesel but there are certainly more advantages in going hybrid electric , I have never seen a diesel motor refill its own tank while sailing.
Our full series of inboard water cooled and underwater motors will eventually range from 8 up to 25 KW , comparable from 24 to 75 hp.

[David M]

I'm really not trying to give you a difficult time Gideon, I just think it is important that everyone know the facts. 25 kilowatts is equal to 35.5 horsepower and not 75 horsepower. Eight kilowatts is equal to 10.7 horsepower not 24 horsepower.

There is no difference in conversion to thrust if a propeller is being turned by a diesel engine or an electric motor. Shaft horsepower is the same thing regardless of the source of power. Kilograms of thrust generated will be the same as well.

Online Conversion - Power Conversion

Please give me a public response if you believe that I am in error. I have always admired your boats and your knowledge of sailing but I think this needs an explanation.

[fastcat435]

you are very right David a hp is a hp however the location where it is measured is different between a diesel and a electric motor
With a diesel the power is measured at the end of the crankshaft so it does not take into account the reverse gear , the sail drive losses or hull p bracket bearings and thru hull bearings , the alternator and a few more items costing energy.
A 30 hp saildrive will maximum give around 23 hp at the prop.
A saildrive or shaft drive prp is not the ideal companion for the diesel since the max torque of the diesel start around the 2200 rpm for that reason a prop is chosen small so the diesel will not stall when engaging gear.
With a electric motor torque is maximum at o rpm so a bigger prop can be used
For instance in Fastcat number 3 we have used 2 x 4.5 KW Solomon electric motors giving this cat a top speed of 6.5 knots , when setting the 30 hp sail drives to 2300 rpm creating 22 hp we get 6 knots 4.5 kw equals about 6 hp yet with using this 6 hp the FastCat is faster than its 22 hp equivalent, the solomon system uses a universal joint hull bearings and a p. bracket all costing a bit of power how much is a guestimate but probably 10 % , in the Green Motion system these bearings and universal joint are not needed .
In the Team Heiner 38 a new downscaled volvo ocean 70 equipped with a 6 KW green motion motor we reach 7 knots , the same as what is expected with a 20 hp saildrive.
The larger slow rotating prop ( max 1200 rpm )has a higher efficiency than the fast rotating sail drive prop (1800 rpm)
Team Heiner 38 - Technische details
gideon

[David M]

Gideon,
We are talking shaft horsepower here. Which of course is the horsepower where the propeller attaches to the shaft.

Your statement, according to your own numbers, is that a 75 horsepower diesel engine measured at the crankshaft is the equivalent of an 35.5 horsepower electric motor measured at the propeller shaft. So what you are stating is that (75 minus 35.5) 39.5 horsepower or 52% of the horsepower generated by a diesel engine is lost in the transmission of power to the propeller shaft. Are you certain about this? The dirivetrain power loss percentage you provide are no where near what I have learned through my naval architecture classes regarding power loss through drivetrains on ships and boats. Usually its closer to a 7%-15% loss due to friction

Also, for a propeller that is already correctly matched to the boat, changing out to a different style propeller does not change the efficiency by that large of a percentage. If there really was that great of difference in efficiency, most people would be using that design.

I'm really not trying to start something here, just trying to get the facts. Since you are marketing your boats to our members, I think they are owed a detailed explanation of the differences in horsepower that you described in your first post.

[jjtctaylor]

Hi Gideon,

How much more testing before you make Green Motion drive pods generally available to the public ? Update your website and perhaps show at METS or other trade shows ?

Battery storage will still be an expense and barrier to some applications, but many are looking for "reliable" options for the drive AND controller themselves. Heat and condensation are still issues with some designs.

Your last test should be the lightning strike ! Any electric drive owners out there have feedback on lightning risks to electric drive proposals?

JT

[s/v Jedi]

I think the gearbox equals 10% loss. The alternator takes 1 hp for each 30A generated at 12V and Gideon estimates losses for cutless bearing, shaft-seal etc. at 10%.

So, let's take a 75 hp diesel with 120A alternator. We loose 4 hp at the alternator, 71 left. We loose 10% in the gearbox, 63.9 left. We loose another 10% in the bearings etc. so we are left with 57.5 hp at the prop. Shocking already I think, but not down at 35.5 yet. But now the difference of the prop itself. I have no clue about how much difference that makes, but when you go significantly larger and slower turning, I think it might be a big difference, but almost 40% ? I just don't know.

ciao!
Nick.

[David M]

I would like to hear Gideon's figures on how 52% of the power of a diesel engine is lost between the crankshaft and the propeller shaft. I think it is a fair question to ask.

The propulsive efficiencies of various types propellers varies of course, but not by huge margins when you match the correct style propeller to the application. In other words, you would not attache a propeller designed for an outboard to a shaft of a 330HP diesel, then change out the propeller for a 24X24 four bladed bronze and then say you had a huge percentage change in propulsive efficiency by changing out to a different propeller.

[jjtctaylor]

Originally Posted by David M

So what you are stating is that (75 minus 35.5) 39.5 horsepower or 52% of the horsepower generated by a diesel engine is lost in the transmission of power to the propeller shaft.

I Don't think Gideon is saying that. Based on my own experience. There are a bunch of sub-optimization done to make boats work. The props are NOT sized for max cruise, but a balance between stalling the engine when changing gear and over-rev top end. I am not sure what is going in a big ship if the props go to stop and then change gear, but there is a load they have to handle. Diesel-electric takes cake of that switch without over-taxing the motor. That is a loss. Same with alternators and other attachments. SO my 27 horse yanmar does about as well as my 15hp dinghy outboard. I think outboard HP is measured at the prop, not the crank. The diesel engine manufactures do not want to cite specs that affect their product, so use lowest common denominator - crankshaft with no losses.

You can definitely do better as well with a larger slow moving prop. And as always can do best with a clean prop.

JT

[s/v Jedi]

Yes, it is that stalling of the engine when shifting into gear with a big prop that compromises optimal prop selection with a diesel (diesel max torque is at high rpm). An electric motor has max. torque at 0 rpm so no need for that prop selection compromise.

ciao!
Nick.

[David M]

I'm just trying to get it clear in my head what he does mean and then apply basic laws of naval architecture and see if the numbers add up. I do want to be fair and I do want to see that our members are getting all the facts. So far, we do not have all the facts but I am sure Gideon will be providing them soon enough.

[jjtctaylor]

Just curious David what happens in larger ships that are not diesel-electric to handle the start-up loads at zero rpm ? Do they have an aux motor and transfer the load ? Cause I bet the marine architecture specs are only running losses.

I also expect scale has a great impact, as the larger props and shafts have massive inertia and momentum, but as percentage of power might be less.

What do you think ?

JT

[scotte]

Originally Posted by fastcat435

it is not cheaper than any diesel solution but it is environmentally friendly

Originally Posted by fastcat435

The cost over a 10 year period depending on how much a boat is used would come close to the diesel alternative.

According to some links/articles, having a FastCat with the Green Motion system is advertised as costing the same as a FastCat with a conventional diesel engine - i.e. a "no-cost" upgrade. Is this no longer the case?

Originally Posted by fastcat435

storing 3 hours of run time is possible depending on the batteries used

Also, previously it was said that the Green Motion system will have 12 hours of runtime without charging. Am I correct that has now been downgraded to 3 hours (or less)?

Just curious about the facts of this boat and system, and looking forward to the pictures of the systems and the independent reviews of it.

[Pblais]

I see an awful lot of cruisers who go to docks every night when travelling, and we all know that most boats rarely spend a night away from the dock.

I wouldn't spread that around too much. We like it that way.