Trans RINA, Vol 153, Part A1, Intl J Maritime Eng, Jan-Mar 2011 SHAFT LOADS ON AZIMUTH PROPULSORS IN OBLIQUE FLOW AND WAVES


H Amini, and S Steen, NTNU, Norway (DOI No: 10.3940/rina.ijme.2011.a1.199) SUMMARY


A range of model experiments have been carried out in calm water and waves for an oil spill vessel model with twin tractor azimuth thrusters at different heading angles and advance coefficients in the large towing tank at the Marine Technology Centre in Trondheim, Norway. Propeller shaft bending loads have been measured using a shaft dynamometer capable of measuring all shaft side force and bending moment components as well as propeller torque and thrust. The results include the loads on the propeller shaft with and without the presence of a ship hull model at the same heading angles and advance velocities in order to study the wake influence from the ship hull on the hydrodynamic loads. Results show that the ship hull wake has a much stronger effect on the propeller loads when the propeller is azimuthed outward from the ship hull centreline than inward. Measurements from the experiments in waves are also presented for the same thruster model in a straight-line course for both the head and following sea states under different wave conditions. Larger bending loads are found in head sea conditions compared with the following sea conditions. Generally it is found that the shaft bending loads and lateral forces are quite large, which is important to consider in the mechanical design layout and for dimensioning of components.


NOMENCLATURE A w


C0. 7


D p f z


f y


* Fy


* Fz


Fr J KT  


n D T


2


K nD Q


Q


25 p


K fy  K fz  Kmy  Kmz 


m y m z


 


n D f


y


2 4 p


n D f


z


2 4 p


 


n D m


y


2 5 p


n D m


z


2 5 p


4 p


* n Wave amplitude (mm)


Blade element chord at r = 0.7R


Propeller diameter (m)


Vertical force on propeller (N)


Horizontal force on propeller (N)


Total horizontal bearing force (N)


Total vertical bearing force (N)


Total radial bearing force (N)


Advance coefficient (-) Thrust coefficient (-)


Torque coefficient (-)


Propeller horizontal force coefficient (-)


Propeller vertical force coefficient (-)


Propeller horizontal moment coefficient (-)


Propeller vertical moment coefficient (-)


Propeller horizontal moment (N.m)


Propeller vertical moment (N.m)


Q R p T V a W p


 


gL Fn Va


RnD C 0.7np /0.7 1.  2


Shaft rotational speed (rps)


Propeller torque (N.m) Propeller radius (mm)


Propeller thrust (N)


Advance velocity (m/s) Propeller weight (N)


Water cinematic viscose coefficient (N s m-2)


Propeller heading angle (deg)


Froude number (-) Reynolds number (-)


INTRODUCTION


Azimuth propulsors include both azimuthing thrusters and podded propulsors. Pods have an electric motor integrated into the


unit, propeller shaft, while in


directly connected to the azimuthing thrusters the


propulsor powering machinery is located inside the ship hull, which drives the propeller through a system of shafting and bevel gearings [1]. Also, the size and shape of the housing of the azimuth thrusters and podded propulsors are usually different, with the pod housing being significantly larger than the typical azimuthing thruster housing.


It is the puller type of azimuth thruster that is addressed here. Note that although the focus here is on the puller type of azimuthing thrusters, the hydrodynamic loads related to oblique inflow are more or less the same for the pusher type azimuth and for podded propulsors. The


©2011: The Royal Institution of Naval Architects


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