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| 55 Nordhavn Case Study, Valkyrie - Nordhavn 5502 |
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When I bought my boat, Nordhavn had not perfected
the correct prop size for the new 55’s with a John Deere engine.
Being hull number 2 required numerous tries by the commissioning team.
I ended up with a prop that would work and allow the engine to reach
close to its correct rpm. This prop ended up being a 38”d x
34”p. But I was convinced that I was not getting the performance
or the economy as advertised by Nordhavn. This is what started the
search that led me to Troy at Wildcat Props. During my haul
out in the spring of 2007, I took my prop to Troy. He suggested adding
additional pitch. I was on a tight time table to go back into the
water as most haul out are. Troy was great and very accommodating
of my time constraints. He took a great amount of time explaining
to me how diameter, pitch, number of blades and skew all work together
to get the best performance for your boat. To accommodate my time
constraints, we modified the existing prop to get the rpms at wide
open throttle correct. The performance was improved.
However I was still convinced I did not have the correct size prop.
So I took running data at every hundred rpm from idle to wide open
throttle with the modified prop. I sent this to Troy in the early
spring of 2008. Troy then ran the numbers and suggested a 42”d
x 30.5”p 5 blade prop. I knew a 42”d would fit because
that was the diameter of the original prop delivered with the boat
before it was cut down during commissioning. The more I thought about
what Troy was proposing, the more convinced I became that we were
going in the right direction. I ordered the new prop and was astounded
at the results! Not only was I amazed with the performance and speed,
but also with fuel economy. Thanks to Troy this new prop not only
gave me better performance but will pay for itself quickly in fuel
savings.
Working with Troy was a pleasure. Not only did he figure out the correct
prop for my boat, but he also suggested a marina for quick haul out
and delivered the new prop directly to me at the marina yard. Thanks
Troy for all your help! ~ Don Bitting
Valkyrie - Nordhavn
5502 |
| In the chart below you will find the background
information for various prop sizes trying to get it right: |
Engine: John Deere 6081
M3 with 330BHP at 2300RPM peak torque speed is 1200RPM
Transmission: ZF Marine model W325 with a ratio of 3.958:1
reduction left handed
Shaft: 3 inch diameter stainless steel Aquamet 17 with a standard
SAE taper |
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Prop
Size
|
%
Load
|
Max
RPMs
|
| Boat
Delivered
|
42
x 38
|
100%
|
2125
|
| Same
Prop Modified
|
39
x 35.5
|
100%
|
2230
|
| Same
Prop Modified Again
|
37
x 32.5
|
80%
|
2350
|
| New
Prop
|
38
x 34
|
95%
- 97%
|
2350
|
| WildCat
Modified
|
38
x 35.5
|
100%
|
2340
|
Data with WildCat
modified prop done during calm seas with less than 10 knots
of wind.
There might have been small current, but it would have been
the same during test data.
|
| RPM
(+ or – 10)
|
Knot
|
%
Load
|
GPH
|
| 600
|
3.3
|
21%
|
.4
|
| 700
|
3.7
|
|
.6
|
| 800
|
4.4
|
25%
|
.8
|
| 900
|
4.8
|
|
1.2
|
| 1000
|
5.3
|
31-32%
|
1.6
|
| 1100
|
5.8
|
|
1.9
|
| 1200
|
6.2
|
32-33%
|
2.3
|
| 1300
|
6.6
|
|
3.3
|
| 1400
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6.9
|
36-37%
|
3.8
|
| 1500
|
7.4
|
|
4.6
|
| 1600
|
7.8
|
37-38%
|
5.2
|
| 1700
|
8.2
|
|
6.1
|
| 1800
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8.5
|
45%
|
7.4
|
| 1900
|
8.8
|
|
8.7
|
| 2000
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9.0
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56-57%
|
9.3
|
| 2100
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9.2
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|
11.3
|
| 2200
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9.4
|
78%
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12.7
|
| 2300
|
9.6
|
100%
|
|
| 2340
|
9.7
|
100%
|
16.6
|
Below you will find the run data after my new prop was
installed. I am very pleased with the results. I now run at a slower
RPM and burn less fuel or run the same RPM and go faster. It took
me a long time to get to this point but it was worth it. This change
should pay for itself with the price of diesel, I could have saved
300+ gal of fuel this summer alone if this had been installed before
I left for Maine.
Engine: John Deere 6081 M3 with 330BHP
at 2300RPM peak torque speed is 1200RPM
Transmission: ZF Marine model W325 with a ratio of 3.958:1
reduction left handed
Shaft: 3 inch diameter stainless steel Aquamet 17 with a standard
SAE taper
Prop: ZF Prop 42” diameter 30.5” pitch 5 blade
with 80% DAR and 30% skew |
| RPM (+ or –
10) |
Knots
|
% Load
|
GPH
|
| 600 |
3.3
|
21%
|
.4
|
| 700 |
3.8
|
24%
|
.6
|
| 800 |
4.4
|
28%
|
1.0
|
| 900 |
5.3
|
31%
|
1.3
|
| 1000 |
5.8
|
32%
|
1.6
|
| 1100 |
6.4
|
33%
|
1.8
|
| 1200 |
6.8
|
33%
|
2.3
|
| 1300 |
7.4
|
34%
|
2.9
|
| 1400 |
7.8
|
37%
|
3.8
|
| 1500 |
8.3
|
37%
|
4.5
|
| 1600 |
8.7
|
38%
|
5.2
|
| 1700 |
9.0
|
40%
|
6.1
|
| 1800 |
9.3
|
48%
|
7.5
|
| 1900 |
9.6
|
55%
|
9.2
|
| 2000 |
9.9
|
60%
|
10.1
|
| 2100 |
10.1
|
73%
|
11.9
|
| 2200 |
10.2
|
88%
|
14.1
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| 2290 WOT |
10.3
|
100%
|
16.5
|
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Contact WildCat Props!
Custom propeller configurations are also available on request. Should you
require assistance in selection of a new propeller suited to your vessel,
restoration-repair of your existing propellers or prop tuning-maintenance
please contact WildCat Props. |
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