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. Video Show Contrasts video - optional 11 April 2017 Rolls-Royce Naval Marine Walpole, Massachusetts Hilmar Stefansson – Chief Engineer (retired)

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.

Controllable Pitch Propellers

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

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 RPM @ 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

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

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

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 +/- 14.1 FPT

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

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

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

Gen I Bolt Tool

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

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”

Thank You!