Couplings and inboard drivelines are used to transmit the torque of the engine to the propulsion device.  Depending on engine size and the propulsion unit, a variety of couplings and driveline configurations can be used.

Universal jointed drivelines allow for engine/propulsion unit offset and axial movement.  However, there are strict alignment procedures for installation of universal jointed drivelines.  Working angles of each joint must be equal and each joint must be in the same plane.  Universal jointed drivelines mount securely at each end with a slip joint in the center.  Please see the section on Universal Joint Drive Shaft Details.

H-Joint Couplings are similar to the universal jointed drivelines.  These couplings do not have any slip in the driveline, but slip on the input shaft of the ASD.  The use of H-Joint couplings depends on the input shaft of the propulsion unit.

Companion flanges are used to connect the universal jointed drivelines to the  input shaft of the propulsion unit.  These flanges are secured to the input shaft with the nut and washer supplied on the propulsion unit.

Gearbox adapter flanges may be required to match the output flange of the gearbox to the flange of the driveline.  These units provide the correct bolt patterns and pilots for the two items connected and may also be required to eliminate interference between components of the gearbox and the driveline.

For many applications it is advantageous to design and manufacturer the drive shaft with the end fittings that will directly match the marine transmission or the ASD unit.  Advantages include the reduction of weight and additional components in the system.

Direct couplings are used where space is a premium and the Engine/propulsion unit can be in direct alignment.  Alignment issues are critical with direct couplings as they are limited on the amount of misalignment they can accommodate.

The selection of couplings and Inboard drivelines for propulsion systems is based on propulsion system size, engine size, gear ratio, duty cycle and installation considerations.  All H/RI Universal jointed drivelines are balanced to the maximum rotational speed of the system.

Universal jointed drivelines are measured flange to flange and are made to customer requested length.  The minimum length of each driveline is shown in the description.  

Multiple piece drivelines can be used for excessive drive shaft length requirements.  Support bearings will be required at various lengths along the drive shaft.  Where the shafting penetrates bulkhead, bulkhead bearings can be used to support as well as offer a water tight penetration.

H/RI recommends the use of safety guards on all drivelines.  It is the responsibility of the boat builder to ensure adequate safety guards are installed on all rotating machinery for the safety of individuals as well as the vessel.

TORSIONAL ANALYSIS

A torsional vibration analysis is strongly recommended by H/RI for  installations where drivelines of excessive length or deep reduction ratios are used.  It is the responsibility of the boat builder to ensure that all components in the propulsion system are compatible and that the natural frequency of such components does not occur within the operating speed range of the system.  Usually the engine suppliers will perform this service.  H/RI will supply this service for those cases where your engine supplier can not provide a torsional analysis.

BASIC RULES FOR UNIVERSAL JOINTS

THEY MUST WORK IN PAIRS.  A Universal joint, working at an angle, will vibrate if it is not canceled by another joint at the opposite end of the shaft, working at the same angle and in the same plane. 

JOINT ANGLES MUST BE EQUAL TO WITHIN ONE DEGREE.  Joints working in pairs will vibrate if they are not working at the same angle to within one degree. 

YOKES MUST BE IN PHASE.  Joints, working in pairs, will vibrate if their yoke ears are not in the same plane to within two degrees. 

MAXIMUM JOINT ANGLE AND RPM COMBINATION CANNOT BE EXCEEDED.

A shaft, between two joints working at an angle, will accelerate and decelerate as the shaft rotates.  The higher the RPM and the greater the angle, the higher the rate of acceleration and deceleration.  As the rate increases, it will cause a vibration.