shaping rudder

[ironjaws]

Hey fellas... Trying to find info on sharpening and rudder shaping. Heard somewhere a rounded bottom that is sharp on the leading edge is what you want. Anyone can give me an example of a company that makes the perfectly shape rudder. Seems like a few variations exist, and I would like to know how different designs differ in function.

[m4a1usr]

I have never seen a company offer a rounded bottom leading edge, as its not a super important requirement, however it does tend to offer certain advantages. Usually its choice based. And as I said. Not every hull needs to have the bottom edge rounded. None of my riggers rudders are rounded. But a couple of my hydros are. I can post a pic if you want? The whole front leading edge, at least the part under water, should be sharp. And the edge should be filed from both sides. Dont do just one side.

The racers who run SAW typically run a knive sharp rudders. Others will chime in more experienced then me.

John

[Boaterguy]

you should be scared to put pressure on he rudder because it is sharp enough, never changed the shape of a rudder, although I have never tested if one type is faster or not, it shouldn't matter unless you need an extra millisecond.

[ironjaws]

From what reading i was doing I have found that the bottom front should be round, and the bottom edge also sharp so the boat doesn't plane on the rudder. Also the leading edge sharp, of course. But I am wondering before i do this stuff, if it will have any negative effects. Finding people calling it a wedge rudder. The edge is sharpened short and aggressive so the water that hits the leading edge is directed away from the sides of the rudder and create less drag.

[m4a1usr]

From what reading i was doing I have found that the bottom front should be round, and the bottom edge also sharp so the boat doesn't plane on the rudder. Also the leading edge sharp, of course. But I am wondering before i do this stuff, if it will have any negative effects. Finding people calling it a wedge rudder. The edge is sharpened short and aggressive so the water that hits the leading edge is directed away from the sides of the rudder and create less drag.

Go to the Aquacraft UL1 section and read the tips and improvements thread. There is a nice description from Mike Z or commonly known as "Grim" and you can read his words. After all he designed the critter. He recomends what you are seeking.

John

[ironjaws]

Ya. it looks like they applies his theory to the pro boat impulse 31 rudder.

[m4a1usr]

This is the recommended rudder mod for the UL1.

John

[ironjaws]

I have seen that rudder mod. But what about shaping it more like a "shark fin" turned upside down? The rudder wouldn't be flat on the bottom... The bottom leading edge would start high and swoop down to the rear bottom edge. After some research I haven't come across any sure thoughts. Was looking at some REAL race boats trying to get some ideas... They seem to use a WEDGE style more often. Not many use the FLAT rudders.

[m4a1usr]

Tapering and sharpening the entire bottom of a wedge rudder would cause lift. Thats not really a needed effect. Even the rounding of the bottom leading edge causes some lift but not as much as doing the width of the rudder. Not to mention you would lose the rear eddy behind the flat trailing edge and would increase drag.

John

[ironjaws]

here's the real deal. unfortunately it is covered.