T-Pain Is On A Boat: Re: [Electric Boats] Re: Arrival of Motor and Controller

Thanks for interesting info about propellers James!

This has been one of my most difficult subjects to understand in my electric boat project. Even the local "propeller expert" could not help:-/

The present propeller might be quite good i hope. It is relatively large, and slow turning: 400rpm at 4 knots for my 3500kg displacement boat. The diesel engine is a relatively large and heavy one: 32hp mercedes om636 (50 years old) so i guess it has quite a lot of moment of inertia helping the startup..

I am planning to use a relatively large motor (three phase siemens motor from a norwegian produced Think car), rated for 51Nm continously. Coupled direct drive. I hope it will manage! Full testing of motor characeristics is not finished since i have problems getting communication with the inverter with the prehistoric software...

But if i should change propeller: larger, slow turning, cupping and large area is better i understand. What about number of blades?

And the shaft angle is also something to consider. Is this difficult to alter this? There might be some issues with leakage when not correctly done i guess...

Regards Bendik, Norway

Sent from Yahoo Mail for iPad

On mandag, desember 14, 2015, 6:53 p.m., James Lambden james@electroprop.com [electricboats] <electricboats@yahoogroups.com> wrote:

Electric Propulsion is generally not supported by current propeller models. Many of the old guard refuse to acknowledge the inherent efficiency of electric propulsion.

We converted a boat named "Snow Lily", a Tartan 34 of 12,000 lbs. It takes 4.3 KW to push this boat at over 6 knots. Yes that is around 6 horsepower. Run that boat on any diesel propeller calculator and you will find hugely different numbers.

Current modelling of propellers includes current ways in which diesels are installed in boats. These boats have high angles of their drivetrains, close proximity to the strut and to the rudder.

I recall from a few years ago, Dave Gerr, as head of Westlawn School of Yacht Design, posted on the Masthead, the publication of the school, effectively that EP didn't belong on boats at all. Multiple emails I sent on this subject to him have not been returned.

The best way of arriving at the correct propeller for EP at this time is by looking at boats that are currently working with EP.

EP closes the gap on diesel because of efficiency. Efficiency is very closely related to how much slip a propeller has. I liken it with a car stuck in snow…. the tires spin but the car doesn't go anywhere. A large propeller has traction and does not waste power.

Our standard propeller with a 5 KW drive unit has 14 inches of pitch, about 85% blade area ratio, and cupping on the propeller. This results in top speed achieved at 750 rpm compared to a diesel top speed of 1200 rpm. With almost half the slip, you can see why we can achieve such great overall efficiencies.

The fact is that an electric motor is far better suited to turn a propeller than a diesel can ever be, because it takes torque to turn a propeller, which is where electric motors with speed reduction rule. It is impossible for a diesel of gas motor to turn the big propellers we can use with Electric. They simply do not have the torque or rotational momentum to turn a big propeller. We commonly use a propeller on our electrics that is meant to be turned by a diesel of 20 times the horsepower!

Eventually the old guard will wake up to this reality and start supporting EP, but don't hold your breath on that one. It is not the old guard that will make the change, it is the young guard that will demand it, and when that happens the sail boat builders will follow suit.

It is my goal that by 2025 half of all new recreational sail boats are powered by electric and hybrid technologies. When you consider what our group does to facilitate a conversion, and the passion that our group has for this technology, I think this is easily possible.

It would be so much easier to build a boat from scratch with EP, than what we have to do to convert a boat. Currently sailboats are designed around interior layouts and the propulsion is an after thought. The motor is stuffed way back under the companionway, exits at a high shaft angle, the propeller is very close to the strut which puts turbulence into the forming vortex, robbing the propeller of efficiency. The rudder, close behind the propeller further affects the vortex too. Lead batteries which have come a long way in the last 5 years are heavy, but can easily be substituted for lead in the keel.

If a boat builder wanted to build an electric boat that had great range it would be simply a matter of designing around the propulsion system efficiency first. And this could result in a far nicer interior layout than what is currently possible, because EP motors can be so much smaller than diesel. Take for example Electroprop's new Racer drive which weighs only 50 lbs and is so small you could put it into a small suitcase and carry it around with you. This enables a builder to put the motor in ever smaller compartments, or install twin motors.

Feedback from customers that are inquiring about EP for new builds indicated that the builders do not want to build electric boats because they are afraid that the boats will not perform to the satisfaction of their owners. This is not unfounded as many of the earlier conversions done years ago were very poorly done, and many of these motors were pulled out and replaced with diesel. But take a good look at those conversions and they are not anywhere close to the quality and efficiency of the components available today which enjoy overall efficiencies significantly higher, components that are much smaller, and builds that will last a lifetime. Sooner or later, a brave builder will start leading the way with a factory built electric or hybrid boat. Its just a matter of time.

So my advice is to simply disregard the information that is readily available for propellers. There are some rules of thumb out there about the different attributes of propellers that are worth considering… like the difference between 2, 3 or 4 blades, cupping etc. But the formulas used to calculate power for a diesel or gas sailboat do not apply to EP.

Remember that on average, a diesel motor installed in a sailing vessel is around 10 or 15 % efficient, with much time spent in the single digits and when idling to warm up…. a big 0 percent efficiency. Compare that to electric propulsion with speed reduction being around 80 to 85 % efficiency now and you quickly get the picture. And there is no need to wait for the motors to increase in efficiency. We will get incremental increases in motor efficiency, but at the very top if we compare to Tesla's claim of 97%, there is only 10 to 15 percent to go. Motors will get smaller and more powerful that is true, but its not advancements in motor technology that will result in more range, because the most we can get is 15 or so percent gain from improvements in overall motor efficiency. The real advancements will come from higher capacity batteries and more powerful, smaller, range extenders, all of which can be made to use with existing motor technology.

All of this applies to sailboats. Power boats are still better served by diesel. Sailboats are one application where electric and hybrid technologies shine because of the very low power requirement due to the fact that a sailing hull is so easy to push through the water. Electric Power boats will come of age when the hulls are made to be more efficient, but for now, most power boats require the diesel due to the high power requirement of inefficient hulls that are designed for planing and not designed for displacement speeds.

There is hope on the horizon though with Nigel Calder being very instrumental in looking at the EP industry and being quite supportive of this technology. Now we just need to get everyone else on board.

James

www.electroprop.com

James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103

805 455 8444
jlambden: Skype

www.electroprop.com

james@electroprop.com

On Dec 13, 2015, at 1:53 PM, DAN HENNIS dhennis@centurytel.net [electricboats] <electricboats@yahoogroups.com> wrote:

Try the online catalog at Glen-L, they sell the bible of prop. It is by David Geer and is called simply, "Propeller Handbook", and sells for under $20 bucks. I am ordering one and am told it is the best to have and use in your marine library. I have been wrestling with the same issues with my E/M (electric marine) conversion, and am a lot closer to being "in the marina"(not the ballpark) with diameter and pitch.
Dan

----- Original Message -----
From: Hannu Venermo gcode.fi@gmail.com [electricboats] <electricboats@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Sun, 13 Dec 2015 10:38:12 -0500 (EST)
Subject: Re: [Electric Boats] Re: Arrival of Motor and Controller

Does anyone have any links to actual data re: efficiencies with slow,

large props ?

On 13/12/2015 14:15, moriartybob@yahoo.com [electricboats] wrote:

> Electroprop includes a large prop with most of their kits. I passed on

> that for now and am going to see how things go initially with my

> somewhat large, fixed, 2-blade prop. I need to haul the boat for a

> bottom job in a few months and will then decide whether to go with a

> bigger prop and maybe change the planetary gear reduction from 3:1 to 5:1.

> Lots of fun. Should be going live in a few weeks.

> --Bob Moriarty

--

-hanermo (cnc designs)