Rudder Design

Well, just to provide another point of view, I recall this guy who has changed his rudder from flat plate with wedge to naca profile, and was extremely enthusiastic of his new rudder: http://www.boatdesign.net/forums/boat-design/rudder-design-31745-2.html#post364878

 

Installing a wedge effectively makes the chord line longer, as far as flow sees it. This means it'll act like a larger rudder.

In this application, it's quite unlikely you'll notice much difference from a flat plate to a wedge to a 00 NACA section. From a technical stand point, yes, the NACA, followed respectively by the wedge then the flat plate, will show measurable differences, but unless you have a particularly efficient trawler design, you'll never notice it.

 

Following the reasoning of PAR, I think it makes no sense to say that a NACA profile, for a rudder blade, is more effective than a flat plate. Of course it is. The issue is imo whether, for a trawler, with a maximum speed of about 14 knots and working 60% of her time at no more tan 10 knots, it is worth placing a rudder "so effective".

 

Important to read my latest post in that thread
http://www.boatdesign.net/forums/cl...r-lloyd-gl-rules-free-28404-2.html#post647307

 

There's a big difference between a leisure boat looking for the highest speed from limited amount of power, trying to reduce drag, and a usually overpowered heavy displacement fishing boats requirements.

Looking at that link, the rudder was too far from the prop to start with [ both vertically and horizontally] to use a flat plate effectively anyway, and it was also probably too small.

Another important issue is that a larger rudder operating at smaller angles is a better scenario for L/D than a small rudder at large angles.

 

Delays stall, and it also reduces low incidence drag . Trailing wedge angle should be 20 to 30 degrees.