Prop, and rudder relationship

[runzwithsizorz]

The trailing edge of my rudder is an inch passed my prop. Can this effect thrust? and/or steering? Am I worrying too much?
I know aesthetically it *looks* a whole lot better when they are even, or the rudder is slightly ahead.Also think my rudder is
too long, (almost 3" deeper than shaft), if I shorten it should I leave it squared as it is now? or can round the leading edge
just a bit? It always seemed to me that by doing so, the rudder would be less inclined to snag on stuff.

[SirBudman32]

Don't round leading edge you want it sharp like a knife.

[JIM MARCUM]

I'd cut the rudder down so about 1 1/2" is below the bottom of the prop shaft. If the water pickup is exposed on the tip, seal it with a dab of thickened epoxy (add shredded fiberglass until it's like wood putty). I use a 8" rouge wheel to sharpen the rudder like a knife from the bottom tip to 1" above the waterline. Have the the cuts to prove it. JIM

[runzwithsizorz]

Don't round leading edge you want it sharp like a knife.

I guess I said that wrong. I did not mean dulling the edge, but sweeping back/tampering/rounding off, the bottom part of the rudder from for, to aft. Like this, only just a bit more so.

ose-80052.JPG

[SirBudman32]

sharp leading, round bottom, square on the back.

[JIM MARCUM]

Do not round off the rudder tips. Sharp leading edge, flat bottom parallel to the water, trailing edge flat with sharp edges. Objective is to cleanly shear thru the water without unecessary drag. JIM

[JIM MARCUM]

Do not round off the rudder tips. Sharp leading edge, flat bottom parallel to the water, trailing edge flat with sharp edges. Objective is to cleanly shear thru the water horizontally without needless drag. JIM

[runzwithsizorz]

I'd cut the rudder down so about 1 1/2" is below the bottom of the prop shaft. If the water pickup is exposed on the tip, seal it with a dab of thickened epoxy (add shredded fiberglass until it's like wood putty). I use a 8" rouge wheel to sharpen the rudder like a knife from the bottom tip to 1" above the waterline. Have the the cuts to prove it. JIM

Unfortunately, the water inlets are really low on this rudder, so I can only trim off a little bit more the an inch. I *could* re-drill the inlets, (this is a dual pick-up), higher but that's a lot of work for half an inch. I use J&B weld BTW.

[JIM MARCUM]

Thats fine. I wouldn't screw up the twin inlet rudder, just eliminate any excess length to reduce hydrodynamic drag. JB Weld is cool too. Good luck with your build. JIM

[Fluid]

Guys, shortening the rudder could be absolutely the wrong thing to do. The drag penalty is minor at normal oval speeds, and you will lose a lot more speed if you have to use a lot of left rudder trim to keep the boat going straight. The rudder is all that keeps the transom from drifting to the right from prop walk on many hulls once they are at speed. Not enough side resistance to prop walk from the rudder blade and you may need a lot of left trim = drag. The "best" way to find out the minimum amount of rudder a particular hull needs is to keep trimming off the rudder in 1/4" steps until you have gone too far, then buy a new rudder and cut it just a bit longer.

Too, on deep vees with the rudder on the right, banking left into a turn means most of the rudder comes out of the water = minimal control. Lay the boat on its bottom left side and see how much rudder is in the water. A good minimum is 1-1/4", more doesn't hurt. All this worry about drag and we forget that we still have to control the models......

[JIM MARCUM]

Jay is absolutely right. My recommended rudder length of 1 1/2" below the bottom of the strut was intended for cats only, and even then aiming at those looking for the absolute max speed with thier setup. If you are happy with how your boat handles & it's speed - leave it alone. Want less drag - listen to what Jay wrote on steps to fix it. JIM

[runzwithsizorz]

GOT IT, Thankz guyz. I must say i rather admire Fluids' approach,------- fix it till ya break it.