Sunday, February 21, 2016

Re: [Electric Boats] Why gear reduction?

 

Gentlemen,   hopefully to help show how pitch effects performance on an electric drive, here are a couple of tables I complied from readings I took on my sailboat Chiquita, a C&C 29  Mk 1, in 2014, the first year of my conversion. As indicated in the heading information I have a 12" diameter PYI Max 2 blade feathering prop in which I can adjust the pitch of the blades when out of the water. 

The first table is an average of four test runs, in/out, in flat water, with no tide or current and the pitch set at 10 inches as recommended by PYI for this initial installation.   

The 2nd table is under the same conditions a little later in the year, with the pitch set at 7.2 inches.  Note the significant reduction in energy requirement for the same throttle setting.  Also note however, the correspondingly reduced speed and maximum speed.   I chose to reset to the 10" pitch to retain 90% of my original hull speed with the previous Atomic 4.  A further note for comparative purposes, my original pitch setting with the 25 hp Atomic 4 the electric drive replaced, was 6.4 inches or 16 degrees and max speed  in flat water was 5.7 knots.

This coming season I plan to set a 11 and possibly a 12 inch pitch and due further tests.

Electroprop E-7

Owner:

Jamie Storey

Shediac, NB

Canada

Propeller:

PYI  Max 2 blade

Boat Name:

Chiquita

FIN Keel

feathering adjustable

Make & Model :

1977 C&C 29 Mk I

Pitch:

10 inches

24 degrees

Displacement

7,600 lbs

Shaft Seal:

New PYI Dripless

LWL

23.58 ft

Controller:

Sevcon 4

LOA

29.6 ft

Throttle:

OEM Controls Dial

Batteries:

4 x 215 amp Odssey PC1800 FT

Volts:

48

 

Average -  Based on Last Four Trials after motor and new dripless seal worked in 2014

Flat Water

Throttle

Setting

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Amp draw

2.5

6.5

12.5

19.3

31.3

45.5

70.7

Knots

1.6

2.0

2.6

3.3

3.9

4.4

5.0

RPM

602

837

1061

1266

1500

1720

2003

voltage

(estimated)

51.3

51.1

50.9

50.6

50.4

50.1

49.2

Power

(Kw)

0.13

0.33

0.64

0.98

1.58

2.28

3.48

Notes -  1.  Slight vibration of prop at 4.5 throttle

                 2.  RPM's  oscillate slightly after 3.5 throttle so we took average

 

 

Average -  Based on Two  Trials in/out after Pitch reduced to 7.2" or 18 degrees.

 

Flat Water

Throttle

 

2.0

2.5

3.0

3.5

4.0

4.5

5.0

Setting

 

 

 

 

 

 

 

 

Amp draw

 

2

4

6

10

16

24

34

 

 

 

 

 

 

 

 

 

Knots

 

1.4

1.8

2.1

2.5

2.9

3.6

4.1

 

 

 

 

 

 

 

 

 

RPM

 

603

828

1022

1260

1480

1768

2008

 

 

 

 

 

 

 

 

 

voltage

(actual)

51.3

51.1

50.9

50.6

50.4

50.1

49.2

 

 

 

 

 

 

 

 

 

Power

(Kw)

0.08

0.18

0.31

0.48

0.78

1.20

1.67

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I uploaded a couple of pictures of the prop and the throttle to add to the explanation :

 

Jamie

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Posted by: Avalon@nbnet.nb.ca
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