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

Wheel Removals

Sadly, as you’ve probably already learned the

hard way, propellers have a fine propensity

for locating and making contact with mas-

sive, usually jagged, hard objects. It’s a rare

boat that doesn’t need its prop pulled and

reconditioned at least once or twice. If hav-

ing to pull a boat’s rudder to remove the prop

shaft can send a mechanic into the farthest

reaches of imaginative swearing, I can assure

you that having to do the same simply to

remove a prop will transport him to a state

just about indistinguishable from apoplexy.

Simply, the distance from the aftermost

tip of the prop shaft to the face of the rudder

blade has to be at least^1 / 2 inch (12 mm)

greater than the fore-and-aft length of the

propeller hub. As a rule, hub length, fore and

aft, is 18 to 20 percent of diameter. So with a

20-inch (500 mm) wheel, you would need at

least 4^1 / 2 inches (112 mm) from the end of the

shaft to the rudder blade. You should, how-

ever, check the hub length against the pro-

peller manufacturer’s specs.

Sail Rudder Refinements

Of course, not all single-screw craft have bal-

anced rudders like that for single-screw

powerboats. If the rudder post is right up at

the leading edge of the rudder, then the lead-

ing edge should be curved or cut back slightly

to permit pivoting the rudder over and sliding

the shaft by it. This arrangement is shown in

Figure 12-22. Indeed, this brings us to some

of the considerations of propeller apertures

in rudders for such craft. The left-hand fig-

ure of this drawing shows the ideal arrange-

ment. It’s clear that with the rudder over, you

can pull both the shaft and the prop with

ease. Less obvious is that this is the best—or

nearly the best—configuration for steering.

In this case, most of the rudder blade remains

pretty much behind the propeller when the

helm is put over.

A Sailing No-No

Now look at the center drawing in

Figure 12-22, where the propeller aperture is

cut almost entirely out of the rudder. This sort

of configuration is amazingly common. Pulling

the shaft and the prop is no problem here, but

visualize what happens when the rudder is piv-

oted to one side: the blade is no longer behind

the propeller. For good control under power,

the prop wash simply must impinge directly

on the rudder blade. Cutting the rudder away

to make a prop aperture destroys any chance

of this. Even worse, as you can see, the rud-

der area has been substantially reduced, mak-

ing for poorer steering under sail as well.

A Removal-Proof Setup

The right-hand drawing in Figure 12-22 shows

another propeller aperture configuration.

Here steering is superb—it’s the best configu-

ration, even better (very slightly) than the

left-hand drawing. In this arrangement,

there’s no loss of rudder area at all, and the

rudder is always perfectly centered behind

the wheel. The problem though—and it’s a

PART FOUR:RUDDERS AND STEERING SYSTEMS

Figure 12-22.
Traditional
sailboat rudder
apertures