Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Universal Joints

Neither the standard old-fashioned universal
joints (also called Cardan or Hooke’s joints,
Figure 3-6) nor modern CV joints can take
thrust well, at least not much. Hence the sepa-
rate thrust bearing. Before CV joints were
available, some small fishing boats, like dories,
actually used a single universal joint to make
retractable propeller installations (Figure 3-7).
You can get away with this on an old 10 or
20 hp (7 to 15 kW), one-lung, make-and-break
engine, but not on anything much bigger.
Figures 3-7 and 3-8 show the old retract-
ing propeller arrangement used for years by
fishermen in Nova Scotia to allow them to

beach their boats. Note that under load the

universal joint is straight. It works well

enough like this in small boats with limited

torque and thrust, but I wouldn’t try this on

300 hp (220 kW).

Double universal joints, by the way, must

be installed with equal angles as shown in

Figure 3-9 when used in pairs—as they

should be. If the angles are mismatched you

can actually rip the universals apart from tor-

sional differences. CV joints don’t have to fol-

low this rule, but I like to lay them out this

way if I can, just to be on the safe side.

To ensure that the balls in the bearing all

rotate fully—for proper lubrication—Aquadrive

Chapter 3: Transmission Geometry, CV Joints, Stuffing Boxes, and Engine Mounts and Beds

Figure 3-5.

Engine installed

on rigid mounts

Figure 3-6.

Jackshaft with

universal joints.

The proper term

for this shaft is a

“Cardan shaft,”

and the joints are

“Hooke’s joints,”

but many refer-

ences use univer-

sal joint, Hooke’s

joint, and Cardan

joint interchange-

ably to refer to a

single one of these

joints. (Courtesy

Halyard Ltd.)