1. Controllable Pitch Propeller Blade Bolt Design
The Point
Rolls-Royce is literally synonymous with Quality. This is a tremendous challenge for everyone in the company. Our customers know what Rolls-Royce means and expect no less.
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11 April 2017
Rolls-Royce Naval Marine
Walpole, Massachusetts
Hilmar Stefansson – Chief Engineer (retired)

2. Background
Rolls-Royce owns and operates a large Marine Division offering Ship Propulsion Products to commercial and Naval customers
Products include
Gas Turbine Engines
Diesel Engines
Propellers
Controllable Pitch (CPP)
Fixed Pitch (FPP)
Waterjets
Thrusters
Rolls-Royce Naval located in Walpole, Massachusetts specializes in the design and manufacture of Naval Controllable Pitch Propellers and Large Waterjets.

3. Controllable Pitch Propellers

4. Controllable Pitch Propellers
Product Range
Diameters from 10 ft to 23 ft
Four and five blade configurations
Blades and hub casing are Ni-Al-Brz (stainless Steel optional)
Powers from 1500 HP to 60,000 HP
Propeller consists of
Individual Blades secured to a central Hub Mechanism
Hub can rotate all blades about their radial axes hence changing pitch – about 60 degree rotation available
Propellers rotate in one direction only
Reverse thrust is accomplished by reversing pitch Blade bolts are subject to high cycle fatique

5. Controllable Pitch Propellers
Most heavily loaded CP Propeller is the US Navy DDG 51 Class (Burke Class) Destroyers
50,000 HP
17 ft diameter
165 full power
4,200 lb Blade weight
DDG 51 design is an upgrade from CG 47 design
CG is 40,000 HP, 4,200 Lb Blade Weight

6. Controllable Pitch Propellers – Hub Mechanism
Blade Bolts
- 8 per blade

7. Generation I Blade bolts (Moregrip Design) D
In use since early 1970’s
Three US Navy Ship Classes (DD963, FFG7, CG47) – 40,000 HP, 130 ships, 200 propellers
Design Features
Material is K-monel
Rolled threads and fillet after age hardening
Hydraulically stretched, installed, pressure released, and stretch measured with dial depth gage.
Analytical studies backed up by extensive testing:
Model Scale testing
Full Scale Bolt fatigue testing
Instrumented Sea Trial on Propeller critical components with strain gages

8. Generation II Blade bolts
In use since late 1980’s
US Navy DDG 51 Class – 50,000 HP, 75+ ships, 150 propellers
Material is Inconel 718 (originally Kmonel)
Design Features:
Rolled threads and fillet after age hardening (same as Gen I)
Large fillet under bolt head
Reverse taper threads
Shank length elongated (softer “spring)
Shank OD and ID reduced to allow for larger fillet
Loads
64.7 +/- 5.4 FPA,
65 +/ FPT

9. Generation II Blade bolts
Conventionally Torqued, and Stretch measured with dial depth gage. Stretch is criteria
Required due to smaller ID
Analytical studies backed up by extensive testing:
Model Scale testing
Full Scale Bolt fatigue testing
Instrumented Sea Trial on Propeller critical components with strain gages

10. Blade Bolt design process
Obtain Propeller Particulars
Power, RPM, Diameter, ship resistance data, wake data
Generate Propeller Blade Design
Run CFD to determine Full Power Ahead steady and alternating hydrodynamic loads
Select hub size
Build 3-D Cad Model
Hub, Blade, Blade Bolts

11. Blade Bolt design process – cont’d
Run FEA using Full Power Ahead loads
Scale results with DDG measured stresses for Full Power Turn
Using S-N curve
Determine cycles to failure at each stress condition
Use ship operating profile to determine cycles at each condition.
Determine life of component using Minor’s Rule
Life > 30 years = PASS

12. Gen I Bolt Tool

13. Additional Design Requirements
Copper Flashing applied to threads
Acts as a thread lubricant to prevent galling
High affinity for hydrogen
100% NDT
LPI new production bolts using wet fluorescent dye
LPI tested at any maintenance period before re-installation (usually water washable red dye)
any indications are rejected

14. Problems No fatigue failures
Some bolts have been found loose or missing
Installation error?
Preload increased about 20%
Hydrogen Crack
One ship with manually adjustable Impressed Current System
“over-protection”

15. Thank You!