In the past, rudders were either mounted on the trailing edge of a fixed keel … or they were mounted as far to the stern as possible (considering linkage, rudder logs, tiller space/placement or steering wheel quadrant size.
In many cases, rudders are transom hung which obviously provides the greatest distance from the keel. Some transom hung rudders are seen with fairing at the keel depth, which is designed to provide a bit of added advantage for the water flow along the keel and back and around the rudder. Tra<s><font color=“red”>m</font id=“red”></s>nsom hung rudders are often viewed as having “unpleasing” flow with turbulent water rolling out from under the keel of the boat and upwards - often climbing up the sides of the rudder, much like a surface piercing foil.
Meanwhile, hull hung rudders found under the hull of the boat are intended to reduce the turbulence at the top of the blade, as water streams back along thehull and the rudder surfaces.
Transom hung rudders have an advantage that they can be easily raised (or tilted) for shallow water and beaching. It is interesting to note, that many high speed planing dinghies and small multihulls (skiffs, racing class dinghies, etc.) all continue to use the transom hung rudder. Whether class rules have made it so, whether they have or haven’t been challenged, or whether the added few feet further aft of the keel/center/dagger board provide an added advantage is a question I am pondering.
Are there factors and formulas that are used for locating rudders from the keel? Does a rudder that is a greater distance from the keel promote a more stable direction and straighter hull “tracking”? or - Does a rudder closer to the keel offer better and faster tacking at the disadvantage of very sensitive steering?
I have witnessed on the <font color=“red”>big</font id=“red”> cat, the distance between boards and rudder seems to increase the area of lateral resistance and slow rudder response. I also have been sailing extremely fast downwind, only to find myself with overly sensitive steering (so called “sportscar” steering where it was very easy to oversteer). Was this oversteering a result of hull speed through the water - the distance between rudder and keel, or simply my imagination?
This brings us to our little boats and optimum rudder locations. Would dual rudders (bow/stern) also result in oversteer - or is there enough distance that the hull between both rudders would act to hold directional stability?
Are there any lessons to be learned from both transom hung and under-hull rudders, single or dual, close or maximum distance from keel or boards - or is surface drag a more important issue which prevents experimentation or testing of distances between keel and rudder or numbers of rudders?
The most current issue of Model Yachting (US 1 Meter section) indicates some rule questions regarding transom mounted rudders versus “Len<font color=“red”>g</font id=“red”>th Over Al<font color=“red”>l</font id=“red”>” definitions, and I am curious if any will push the envelope and try a one meter with a transom hung rudder - and see what performance gains there might be - if any.
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