In article m,
Martin Underwood wrote:
This is probably an incredibly naive question, and I apologise if it's a
FAQ, but it's one of those things that I was pondering on in an idle
moment.

Why is it that on all boats, the rudder is at the back rather than the
front of the boat? Is it:

- because a rudder at the front simply wouldn't work properly to steer the
boat?

- because a rudder at the back gives greater manoeuvrability, in the same
way that dumper trucks on building sites have rear-wheel steering whereas
cars and lorries have front-wheel steering?

Your last point first: cars and boats/planes operate differently. There is
no dynamic lift or disturbance of laminar flow to account for when steering a
motor vehicle...

Whilst travelling forwards, the centre of lateral resistance of a pure hull
without fin or rudder will be well forwards of the mid-length, its location
determined to large degree by such things as distribution of drag/unit area
along the hull surface (which falls quasi-exponentially from bow to stern).
A conventionally-placed rudder will then much reduce or eliminate the
tendency of the stern to swing sideways.

You can determine the approximate centre of lateral resistance by applying
the hanging bow rudder (or hanging draw) strokes. The bow rudders will
require considerably more resistive force than equivalent stern rudder
strokes. At certain speeds it is necessary to move the blade further
forwards in order to attain a reasonable turning effect.

The main reason for not having a rudder (or a fin) at the bow end is because
it disrupts the efficient run of the boat, and will not, generally be able to
turn the vessel about the CoLR. A stern-mounted or under-stern rudder will
be able to do this.


Allan Bennett
Not a fan of circular reasoning

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