Rudder Fence

[Dave]

I have a C27 and am interested in pro and con comments on the use of a rudder fence....(a horizontal appendage attached on the rudder about 3 in. below the static water line)...Do they help in steering or what????? Do they help in gaining speed? Are they worth the expense and effort?

 

[Trevor]

Dunno Dave...

I read your post a week ago and wondered what the heck a rudder fence was... seems not many other folks know either! Sounds interesting though - maybe post some more details?

 

[D]

not fast enough

The rudder fence has been used on some multi-hulls to overcome the loss-of-control that is experienced at higher speeds. The 'fence' seems to prevent the blade from cavitating and losing its ability to 'bite' ... You probably wont be experiencing that problem ...in all probability Your Cat 27 will not reach the 15 - 17 kts where this is a problem .... fair winds !!!

 

[Garry @ S/V TASHTEGO]

Fence

When the rudder is generating a lot of lift the pressure on the after side may be so low that air is sucked down along the rudder causing it to loose lift. This is called ventilation and a rudder fence is installed to prevent this. The condition is most serious in racing boats broaching under spinnaker. As the previous post noted, a CAT 27 is not likely to suffer much from ventilation.  Cavitation is a more severe phenomenon where the pressure on the aft side of a prop is so low (nearly zero) that bubbles filled with water vapor form. When they reach an area of slightly higher pressure these bubbles collapse violently and can erode most materials including stainless steel. I can't imagine a CAT 27 experiencing cavitation although my 30 HP ;-) Atomic Four if driven hard might do it just before it exploded.