rudder tuning

I've got an Evo with 4 inch and 7 inch rudders, I believe.

They're both quite thick, right to the trailing edge--very non-hydrodynanically shaped.

Has anyone experimented with sanding these down to a shape less likely to stall and with less drag?

Eric

I have a Mako6, was not satisfied with the new Fenn rudder, replaced it with an old Fenn rudder. Less stalling now.
I allways sand the edges, I like a nice smooth curve on the leadind edge and a knife sharp trailing edge... don't really know if it performs better but I sure have to be carefull when handling the ski...

I would like to solicit advice on the correct position of rudder pedals.
Initially I have set my Mako6 pedals almost vertical and keep almost constant contact with them - even potentially working one against the other when balancing.

I read elswhere on this forum that this may be the cause of snapped rudder cables - wearing at the adjustment point.

Should I be setting my rudder pedals up so that when my heal contacts the foot plate I need to stretch my toes forward to use the pedal?

I have an E-V12-U with both a regular 6", and a 9" surf rudder. While both rudders were possibly better shaped than the previous posters' rudders, I still had issues with the minor flaws they had. So, I took file and a sanding block to them both. This has seemed to have helped prolong the flow over the rudders in rough conditions. Both rudders were somewhat unfair, both along the seam lines, and the surfaces as well. Took a file to fair the seam lines, a sanding block to fair the surfaces. Faired with epoxy/carbon powder additive to fill in the hollows and molding defects. Then sanded again down to 800 grit. Lightly filed the trailing edge normal to centerline plane to create a fine, sharp, squared section. The results are splendidly smooth and silky rudders that perform better than anything one could purchase.

But I think that both rudders may have too thick a section. This may have been designed into the foil to allow for acceptable performance with the type of finish quality that the lower-cost manufacturing processes afford. I have not checked or profiled the sections of the rudders to compare to any of the NACA foil templates, but it would be difficult at best to do this anyway, as thickness ratios could have been modified in the design process. But I guess one could come close to the template used in the foil. At any rate, I believe that a thinner-sectioned, turbulent flow-tolerable foil with good quality surfaces could provide more than sufficient lift in turbulent conditions, and provide a measurable drag reduction as well, compared to the foils currently provided by the ski manufacturers.

I put the rudder peddles just barely shy of parallel with the board, tops slightly angled towards the paddler. That way I can stomp on the board without putting too much pressure on the peddles. Any further forward than that and I believe I would have real control issues in the multidirectional chop and big waves.

Jonojnr wrote: Should I be setting my rudder pedals up so that when my heal contacts the foot plate I need to stretch my toes forward to use the pedal?

I have tried that, but it aint working for me. I found it difficult to control the ski in a downwind with chop also coming from the sides. I have it now halfway between vertical and the inline with footplate position, and that seems to suite me the best.

I'm having trouble envisaging why you need anything more than a couple of degrees of rudder in the open ocean.

The only time I find I need any large amount of lock is to spin the thing around a tight U turn.

I find that leaning the boat or dragging the paddle will hold a line without slowing the ski down as much as a large dollop of rudder, but this only really comes into play when coming back in through the break.

So in what conditions are you having to use large amounts of rudder in the open ocean?

Around the cans, the sooner you can turn around and paddle back the other way is time and distance cut from the course. A ski with more rocker will get around the cans much quicker and with some lean, my epic seemed to turn a lot quicker than my Stellar SES. Neither ski turn as quick as my Beachcomber with a lot of rocker, my Breaksea turns on about par with the Epic V10L.

Using too much rudder can act like a brake. Use less rudder and more sideways leaning in downwind conditions. Lean left to turn right and vice versa.

Jonojr, your pedals should be vertical or slightly past vertical. The aim is to not put pressure on the pedals during the stroke.
The pressure should be at your heels. Pedal pressure during the stroke causes micromovement of your rudder and this is slow. You only need to push the pedals with your toes a small amount to turn the boat downwind. Also "lean left to go right" downwind is a recipe for falling off. A ski is like a big surfboard, lean the way you want to turn, use your paddle and small amounts of rudder. The lean left thing to go right is a flat water kayak technique that doesn't translate well downwind.

I second what Dicko indicated on the leaned, carving turns on waves. Yes, on flattish water leaning the opposite direction does induce an asymetric volume distribution that will create a yaw moment, enabling a tighter turn. Try that going downhill and leaning down the face, you will most likely plant your face if you don't brace, but you'd be bracing on the wrong side for the turn, and you'd just get planted anyway. Use your rudder judiciously. Even kayakers use a kind of rudder when going downhill... but they prefer to call it a paddle.

Doug at SagaKayak.com wrote:
But I think that both rudders may have too thick a section.

the thicker (fatter) the blade the better (less drag also)they work whilst turning , and if the foil X section is good with nice edges it will also make minimal drag when straight.