Re: Ang.:Re: [electricboats] Electric Drive Installation - Some Data

Again, the flat blades of the feathering prop do not behave like the more ideal blades of a proper fixed prop with regards to pitch and slip and the associated calculations.  You can check with J-Prop for more specifics on all that.  they have tables and such. Mine is an 18" on a 63mm hub.


The control system you pondered with knotmeter input could be implemented with some basic microprocessor bits like an Arduino.  I have some ideas for that with some push button functions like fwd-slow to neutral to high reverse for 3 seconds for docking.  Knotmeter input might be problematic for that sort of control at low speeds.  but there are lots of possibilities with control systems.  So long as it doesn't take time away from sailing.  And for now I am more concerned with the implementation of the cooling system.  I am closer to optimized on the rest of it than I expected.



Dan Pfeiffer

 

On 2021-07-24 1:43 pm, Carsten via groups.io wrote:

Ok, when the actual pitch is known, then the rpm per knot can be calculated.

The motor rpm can then be set accordingly.

For a 13.5" pitch prop, it will be about 90 rpm per knot, as far as my head calc tells me.

Just a guideline.

Actual performance (minimum power use) - yet unknown ;-)

That's where the tests comes in.

 

Then, if the motor shows to use very little power, then it might be possible to connect a speed log output (NMEA) to the controller, so it can control the spinning automatically ?!?

Wouldn't that be something new ?!

 

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På søn., den 25. jul. 2021 klokken 2:04, Dan Pfeiffer

<dan@pfeiffer.net> skrev:

Yes, I follow the meaning regarding prop spinning.  Just add enough power to spin it without driving the boat.  Some call that making the prop invisible.  More relevant to a fixed prop I think but I will experiment.  Playing with those settings turns out to be quite a bit more fuzzy in practice than in theory.  Everything is much more dynamic in actual use underway with the vagaries of wind and waves as you are making adjustments to power input and reading the results. 

 

Dan

On 2021-07-24 12:45 pm, Carsten via groups.io wrote:

 

Wow, Dan, you fingers must be glowing now !

It's 1:45AM here, so I'll read all details below tomorrow.

 

Just two things - you may contact your controller manufacturer for hints of how to program the "soft" change in direction.

I will need to do that too, as I am going to convert my saildrive, which is not as strong as your shaft drive.

It should be made to do it corrent and smooth, even in a "crash" situation (kicking from full ahead --> full astern).

How to do it - I don't know (yet).

 

For braking the prop - of course you'll need some brake to let the prop feather.

But some say, that when you let the prop follow the sailing speed (spinning same speed as the waterflow passing by the prop) then it is even more smooth than being feathered. But uses a small amount of power, of course. This is of course nonsense to do with a diesel, but it's possible when going electric.

It would be interesting for us coming users (with fixed props too) to see, how much power you actually need for letting the prop spin when sailing eg. at 5-6-7-8 knots :-)

I hope that you follow my meaning ?

 

Carsten

 

 

On Saturday, 24 July 2021, 23:53:46 GMT+8, Dan Pfeiffer <dan@pfeiffer.net> wrote:

 

 

RPM added to chart.  Should have done that from the start.  Thanks.


PROP
That's an interesting idea about optimizing pitch for preferred cruise speed rather than for matching max motor speed to hull speed.  It might be different and might get the motor operating at a better efficiency.    It's a nice advantage for me that I already had this feathering prop and can tinker with the pitch settings. 

An issue with the feathering prop is the ability of the motor to go very quickly from fwd to rev.  The blades on the prop rotate on the hub and if the transition is too fast they slam.  I think too much of that could damage the prop.  I have two plans to deal with that.  First is to program acceleration curves into the controller that keep it from transitioning too fast.  Second is to make a linkage from the control lever that has a much more significant detent for neutral or maybe that locks in neutral and requires you to pull another small lever to go out of neutral to fwd or rev. 

 

I don't recall the exact measurement of prop tip to hull but it is a bit more tan the 15% dia.  There is some prop thump at high speed.

WATER PUMP/COOLING
I already have a speed controller to try on the raw water pump.    I would also like to map another output on the Sevcon controller to turn on the cooling pump at a higher temp than the first output so I can have two stage cooling.  Or maybe I can set up a thermostat on the second.  Not sure yet. 

At full power the water pump noise is pretty well masked by the motor/belt noise.  And I am going to add a finned cooler with a small fan to the coolant side of the system.  I think with that I won't need the raw water pump until I am pushing 6+ knots.   Some type of oil cooler for a car plumbed in line with the heat exchager.  Like this:
http://static.summitracing.com/global/images/prod/large/hda-403_w.jpg



THRUST BEARING
I chose the 5207 bearing because it is sealed and it doesn't allow for angular movement of the shaft.  Between that and the pilot bearing I added the shaft is held rigid in the reduction gear assembly with less than .001" of runout.   I think that is critical to keep the belt running true on the pulleys.   Being a sealed bearing means I didn't have to have a housing that is filled with oil and would have needed some type of lip seals on the shaft.  The 5207 is specified for radial and axial loads in both directions.  Static load capacity is 6200lbs.  RMP max is 7400.  Axial capacity is taken as 30% of static.  Load from the prop at max is on the order of 600 lbs from what I have found (that's bollard pull).  My max RPM of the prop is 800.  So I am at about 33% capacity for axial load and 11% capacity for RPM with this bearing.    I'll tear it down at the end of the season and get a look at the bearing for any wear issues. 

I would have used that big SS trailer hub for the bearing but in my case there was not room as it would have added several inches to the reduction gear assembly.  But I think it would have been more than strong enough and it would have been excellent for holding the shaft true in the assembly.   And keeping the shaft running true is necessary for keeping the belt running true on the pulleys. 

Look at these transmissions made for the Motenergy motors.  They all use two bearings (like the one I used for a pilot bearing) to keep the shaft true.
https://www.kit-elec-shop.com/gb/engine-mounts/4765-transmission-bracket-for-boat-v9-50-a-222mm-50mm-shaft.html

Here's some video of testing of my assembly:
http://dan.pfeiffer.net/10m/electric_motor_video.htm



TORQUE and FEEL
The electric makes the boat accelerate faster (useful in docking).  It's not a huge difference but it is distinct.  It winds up to speed faster too.  My Volvo had a 100lb flywheel.  But that turned out to be something of an advantage in keeping from slamming the feathering prop.  So be careful what you ask for? 

The boat tracks better with the electric motor on my boat.  This is probably because the prop is now right handed.  It was left handed with the diesel and the shaft is offset to starboard.  So prop walk is now countering the shaft offset. 

One issue is that I may need a shaft brake to lock the shaft and let the prop feather for sailing. It tends to spin in small surges while sailing.  I am not sure yet what is going on with that but I think the brake may be the solution.  I know the Sevcon can be programmed with a brake function (for automotive applications) and maybe that would be a solution depending on how much power that takes.  Maybe I can lock it with that function and then apply a mechanical brake to hold it. 

This will need to be sorted out because the ironic reality is that I have spent all this effort/time/money on an electric drive that I would rather never use.  My first priority is sailing. The motor is an unfortunate necessity that facilitates sailing.   Sailing is the goal.



Dan Pfeiffer

On 2021-07-24 12:12 am, Carsten via groups.io wrote:

 

Impressive, Dan !

From 2 to 3 blade prop, that's the way ! The J is a nice prop.

When your hull is clean, you could try to tune the pitch, when testing at your preferred speed.

This could optimize the power use.

Please post us, if you find that the change to pitch has a noticeable effect.

 

To make your chart tip-top, maybe you could incorporate your motor RPM in the tests.

We know that you run 3:1, then the prop rpm is easily calculated.

 

What is the distance between your prop blade tip to the hull, when fitted with this 18" prop ?

Some say 15% of prop diameter is good, others don't.

 

If you think the water pump is noisy, maybe the pump rpm could be electronically controlled ?

No need to run at full speed, when just a little cooling is required. Saves power too.

 

I see, that you didn't chose a spherical double roller bearing, like the SKF 22207E (for radial and axial loads).

If you face any trouble with your ball bearing (noise or wear), you can always change it.

How is the torque feeling with this electric motor, compared to the diesel ?

I guess it's giving a real push now, from zero !

 

Carsten

 

On Saturday, 24 July 2021, 11:52:16 GMT+8, Dan Pfeiffer <dan@pfeiffer.net> wrote:

 

 

For coolant I went with the recommended 50/50 glycol/water.   The system took apr. 2 liters total after I got a lot of air out of it. 

The big filter to the right in the photo is the raw water strainer.   Water in from seacock at lower right, to strainer, to pump, to vented loop, to heat exchager, then back overboard.  The intake is oversized for this application so I have extra capacity for a future diesel genset. 

The coupler is a standard flange unit (Buck Algonquin 50mc004150)  that I modified by machining off the boss and machining in a counter bore to fit the boss on the coupler on the prop shaft. 

The thrust bearing is a 5207-2RS double roller angular contact ball bearing with 2 rubber seals.   Like this:
https://thebigbearingstore.com/5207-2rs-5207-zz-radial-ball-bearing-35x72x27/

It is set in an aluminum housing that I made.  There is a shoulder on the shaft that transfers the forward thust load to the bearing from the aft side and a threaded collar on the forward side  that handles reverse loads.   The shaft is stainless steel.  There is a pilot bearing on the front end of the shaft.  My runout measured on the order of .001".

I turned the cooling on at about 55 or 60C.  I never tried to feel the motor case to see how hot it was. 

Motor temp sensor is in the windings and is read by the Sevcon controller. 

the 18" prop is standard on the boat.  Original was 2 blade fixed 18, I don't recall the pitch.   The feather prop I have is a 3-blade J-Prop and I have the prop pitch set at the #9 index which corresponds to a pitch setting of 13.5".  That's all a bit nebulous and the flat blades of the feathering prop don't behave like a curved fixed prop.  I took the setting I had used with my diesel and 2:1 reduction and picked wahat I thought would be right for the 3:1 reduction of my belt drive (motor RPM is 2400 like the Volvo diesel was).  So I am running the prop at 2/3 the speed I was with the diesel.  Seems lie a good match so far.  I might try setting #10 to verify things.  I can change the prop pitch setting i the water by diving on the prop. 

 

I'll get some clean bottom data as soon as the proper weather opportunity comes for me to clean the bottom. 

Dan

On 2021-07-23 9:18 pm, Carsten via groups.io wrote:

 

Great job, Dan !

 

Man, now you make me ask questions !

 

Did you solve your coolant type issue, and what was the outcome ?

 

What is the big filter for ?

 

What final solution do you have for the coupling/thrust bearing ?

 

What was the temperature of the motor itself (the housing) before the cooling turned on, handwarm or hot to feel ?

And where is your temp sensor located on the motor ?

Is the 18" prop bigger than standard for this boat ?

What is the final pitch (if you adjusted) ?

2 or 3-blade ?

 

If you get a chance for a dip, a completely clean hull will provide better comparison data.

I'm so exited, as your setup will be almost similar to mine.

 

Cheers to your work !

Carsten

 

 

On Saturday, 24 July 2021, 03:11:24 GMT+8, Dan Pfeiffer <dan@pfeiffer.net> wrote:

 

 

I have my electric drive running and I have some data.  I still have some details to sort out and there are some anomalies in the data but it's a start. 

See attached for details. 

Dan Pfeiffer