The auxiliary rudder or pendulum rudder of a windvane gear effects the course correction either a. directly (auxiliary rudder system), or b. indirectly (servo-pendulum and double-rudder systems), the deflection of the windvane in the latter case causing the pendulum rudder to swing out sideways and, in turn, pass this motion via lines to the main rudder, where it carries out the corrective movement.
An auxiliary rudder is an additional steering rudder which makes steering movements independently of the main rudder. Auxiliary rudders may be up to 0.27 m2 / 3 ft2 in area. The ratio of main rudder area to auxiliary rudder area should be no greater than 3:1. Bear in mind here that the main rudder area has to be sufficient to steer the boat even under engine. The auxiliary rudder, on the other hand, is only called upon to make minor corrections. It does not have the same steering function as the main rudder and can therefore be smaller.
The ratio of main rudder area to auxiliary rudder area is ideally 3:1
Pendulum rudder to main rudder proportions: the lever effect is the key to this system
A pendulum rudder generates servo forces by swinging out to one side. These forces are transmitted to the main rudder. The amount of force produced is determined by the length of the pendulum arm from its pivot point to bottom end of the pendulum rudder. This distance, known as the power leverage (PL), is usually somewhere between 150 and 200 cm / 60-80 in. Pendulum rudders are about 0.1 m in area.
A trim tab pivots sideways to move the trailing edge of the rudder to which it is attached. Trim tabs are normally less than 0.08 m / 0.85 ft in area and can be attached to main or auxiliary rudders or pendulum rudders.
Prebalancing a rudder blade, which involves moving the rudder shaft to a position about 20% aft from the leading edge, reduces the force needed to turn the rudder. This effect is the same as the sudden increased weight on the tiller when a dinghy rudder pivots up after touching the bottom. As soon as the rudder drops back into its vertical position, the balance is restored and the load on the tiller drops to almost nothing again.
Almost all modern yachts have a pre-balanced rudder blade. This is a bonus for all types of windvane gears because a more easily turned rudder allows the gear to work properly with weaker windvane steering impulses. The obvious result of this is better light air performance.
If the pre-balancing procedure is overdone and the shaft is positioned between 22 and 25% aft, the rudder blade will be unsettled and will tend to swing out. In extreme cases the rudder blade may end up turning the windvane instead of the other way around.
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Lets start by identifying what exactly certain boats are. Sometimes the terminology can get lost on beginners, so well look at some of the most common boats and what theyre called. These boats are exactly what the name implies. They are meant to be used for fishing. Most fishing boats are powered by outboard motors, and many also have a trolling motor mounted on the bow. Bass boats can be made of aluminium or fibreglass.