Improving Stellar SR G1 rudder

3 weeks 4 days ago - 3 weeks 4 days ago #30429 by MCImes
Hey Guys,
I have read the Stellar SR G1 stock rudder is not the greatest (mine is approx 2008 vintage for reference). My experience confirms this, as I feel the boat broaches easily even when under maximum rudder, and also the rudder has a "mushy" feel. The response is not crisp. I feel it has 'give' in it before it corrects.

1. I have heard a different rudder improves the response of the boat. What is your preferred rudder? (brand or style)?
2. Would replacing the rudder lines with stainless cable improve the mushy feeling? or some other solution?

Any other thoughts on how to improve the SR G1 rudder?

Thanks in advance!

Current Boats: Stellar SR Gen 1 Advantage
Past Boats: Epic V10 Gen 0 Performance
"When you've done something right, they wont know you've done anything at all" - God from Futurama

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3 weeks 4 days ago #30430 by Dicko
The early stellar rudders had the post at the leading edge. They simply didn't work. They cause the boat to wander, were hopeless on waves. Also the posts were very weak where they are welded at the base and have a tendency to break with the slightest knock. Just buy a new standard rudder. I am fairly sure they will fit straight in. You can remove the post and set it further back, but its not easy and getting the placement right is hit and miss.

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3 weeks 3 days ago #30439 by RedBack
As Dicko said, the first Stellar rudders were truly dreadful.

The second series is better and for flat water racing they are actually quite good, - their narrow profile generating very little drag in circumstances where only small changes of direction are required.

For downwind racing however, they have four problems: Sweep, Taper, Depth, & Profile.

The sweep (almost 30 degrees) means that as the stern of the ski comes out of the water when you're on a runner, steering effectiveness reduces dramatically because the amount of rudder in the water reduces at an even greater rate.

The taper of the rudder (from 130mm at the top to 50mm at the base) conspires with the sweep to further reduce the rudder's active surface area when on a wave.

At 200mm in depth, the standard rudder (particularly in conjunction with its sweep and taper) is marginal at best. For downwind conditions, a 230mm depth would be more effective.

Finally, the profile of the standard Stellar rudder is great for reduced drag at straight ahead or shallow turning angles, but not for manoeuvrability on runners. The narrower the profile of a rudder, the lower the angle of attack before it "stalls". (A rudder is simply a wing that generates "lift" in the direction of turn.)

If you take measurements of the Stellar rudder and plug those into a rudimentary CFD program, you'll probably find it produces its greatest lift (turning force) at about 15 degrees AoA. Beyond that, the lift drops dramatically and becomes zero (stalls) before 20 degrees. At this point, the rudder becomes virtually ineffective except as a "brake" simply slowing the craft down until the flow reattaches, at which point the rudder will suddenly "bite" again.

By increasing the width of the rudder by just a few mm, lift at the same angle of attack can be increased, more angle can be used before lift drops away and the onset of stall delayed to probably 25 degrees.

Yes, drag will be increased with a "fatter" rudder because of both increased frontal area and increased wetted surface area, but in downwind conditions, this would be more than offset by the added manoeuvrability and "surfability" afforded by a different rudder.

Sorry, - that was a (very) long-winded way of saying that you need a larger rudder with a different shape and profile to be effective in downwind scenarios.

Try Peter from Orka in South Africa. I put one of his rudders on an SES and it transformed the boat in lumpy conditions, particularly when having to work diagonally across the direction of the swell to get to the finish point.

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3 weeks 3 days ago #30441 by Dicko
Agree with all Redback says except I was using an Epic surf rudder modified to fit my current ski (SEL). The width of the rudder created so much drag it felt like I was dragging weed. Control was better, but in reasonable downwind it just affects the run of the boat too much. If you were in large downwinds maybe. I have just bought a new stellar surf rudder and the profile is half as wide as the Epic. The drag and speed reduction is minimal. Have only used it a couple of times in smallish wind chop and haven't tried it on a good downwind, but it feels like a rudder that you could leave on the boat all the time. The Epic rudder only came out when conditions were right.

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3 weeks 2 days ago #30455 by MCImes
Very helpful. Thank you guys

Current Boats: Stellar SR Gen 1 Advantage
Past Boats: Epic V10 Gen 0 Performance
"When you've done something right, they wont know you've done anything at all" - God from Futurama

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3 weeks 2 days ago #30456 by Newbflat
I can speak directly to this seeing as I had a SR (gen 1) and changed the rudder to a MUCH better rudder. To cut to the chase I would send Don Kiesling an email
( [email protected]) and get a rudder from him.

I never liked my Stellar rudder and it was a balanced one, not the first gen with the post up front. I have strong feelings about Stellar rudders (and most other manufacturers) and the standard 8” and the newer 9” Downwind rudder suck imho. They have terrible leading edges and it’s ALL about the leading edge... well, mostly. I swapped the 8” standard rudder in my first gen SR to a 9” 15° "gorge special" from Don and it totally changed the behavior of the ski. No more broaching, much more precise and immediate controle and much improved ability to surf diagonally, night and day really. This apply to my current gen SR as well. It seriously changed that ski from being a below average surfer with the 8” rudder to a super one with the same 9” 15° "gorge special". I have had a bunch of his rudders over the years and they have never failed to preform better than stock rudders on ever ski I have used them on. Some more than others but transformative In my Stellar skis. Also a big improvement in my Swordfish S over the stock 8”.

Here is a couple of photos of a DK 9 inch 15° wide cord "gorge special" that lives on my SR. It’s compared to the Stellar 9” Downwind rudder. Honestly I never got to test the Stellar rudder as it wouldn’t fit the new SR I had just bought as the shaft was too big and wouldn’t fit in the ski. But, I would venture a guess that it wouldn’t preform well as the leading edge is a totally and unacceptable mess. It literally has a pointed edge from being run on a belt sander with two facets. The pictures don’t really show just how bad it is. It’s garnered to loose flow over the rudder the moment you furnish it much and will most likely stall quickly and induce broaching. Compare with the perfect NACA foils leading edge on the DK rudder (on the left) ... it’s night and day and you can feel it on the water. Don now offers quite a few options who talk to him and se what he recommends now. I’m totally happy with the 9” 15° wise cord "gorge special" for a proper big Downwind rudder. It’s a big rudder and is aggressive but the SR is so stable it’s great. Swap it to my SEL and it’s light with the toes or it will throw you out of the ski. But he can make what ever you want.


Current: Stellar s18s excel
Stellar SR excel (gen2)
FENN Swordfish S carbon hybrid
Stellar SEL excel (gen 2)
Epic V10 Double Performance

Had:
Stellar SR (gen 1)
V10 sport (gen 2)
V10 (Gen 2)
Beater SEL (gen 1)
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2 weeks 2 days ago #30553 by Dicko
Just want to throw in a few thoughts on the Stellar surf rudder now that I have used it for a few weeks.

To start with, it is the ugliest rudder I have ever used. It is ridiculously thin.

Secondly, I think it is actually faster than the standard rudder. There is no discernible difference between the standard rudder and the surf rudder with regard to drag, and if anything may feel slightly quicker in the water. Previously I was using a modified Epic rudder, but was reluctant to use it because unless the wind was howling it simply slowed the boat too much.

I have used the new rudder a couple of times in small- moderate downwind paddle and it controls the boat well. It definitely adds to the primary stability of the boat and definitely improves the tracking of the boat. The best part is that I just leave it on he boat full time now without any drag penalty. Thought this may be of interest.

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1 week 4 days ago - 1 week 4 days ago #30610 by Watto
Last post first - Dicko I agree the Stellar surf rudder minimal if any drag difference from standard and yes there is improvement in handling and stability. The latter most noticeable in my SES, go from the standard then to the surf rudder a bit like changing boats.

Post beforehand of Newbflat absolutely spot on! Hey love that table timber under your Keising rudders - looks like our West Australian jarrah, surely none in Seattle? While stability difference for me between the surf Keising and surf Stellar is indeterminate, control difference is enormous! As I've been out of action from shoulder op for almost four months now (sigh) I haven't used the larger Keising rudder in big conditions. My initial concern yet to be determined is its steep angle and potential weed collecting. However the smaller standard rudder a huge improvement - much more immediate response, didn't stall in wind up to 20 knots.

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1 week 2 days ago #30620 by Newbflat
Watto..

Not jarrah, it’s Teak. But you can get Jarrah here and I have mane some bookshelves with the stuff... it lovely.

Oh yeah, it’s a weed magnet for sure. That’s just the trade off for a long straight and steep leading edge. In exchange you get more aggressive and precise steering do to powerful lift. The Stellar 9” Downwind rudder is even steeper than the DK. But it’s so thin with a strange thickness taper that doesn’t look like a proper NACA (4 digit) foil and the leading edge such a mess it’s all wasted. The other thing I like about DK rudders is the last 2 inches or so of the rudder is not elliptical. When that rudder is in the air in short steep waves and only the tip touches the water the DK rudder has more power.

Current: Stellar s18s excel
Stellar SR excel (gen2)
FENN Swordfish S carbon hybrid
Stellar SEL excel (gen 2)
Epic V10 Double Performance

Had:
Stellar SR (gen 1)
V10 sport (gen 2)
V10 (Gen 2)
Beater SEL (gen 1)

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4 days 4 hours ago #30637 by MCImes
Thanks again guys. Looks like I will be asking for a DK rudder for christmas! Im excited to try out an improved boat when my drysuit arrives and hand has recovered in a month or 2.

Till then ill just look at the water with lusty eyes and watch millers run videos :)

Current Boats: Stellar SR Gen 1 Advantage
Past Boats: Epic V10 Gen 0 Performance
"When you've done something right, they wont know you've done anything at all" - God from Futurama

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2 days 15 hours ago #30641 by Lippstreu
i have messed around with rudders quite a bit over the years and have discovered that they make a huge difference in handling of the ski especially downwind. In my experience theory and practice coincide very well in rudders in that an elliptical rudder of about 14% thickness is the most effective. Reducing sweep and increasing the aspect ratio both increase effectiveness but at the cost of the rudder tending to "bite" and whip the tail around a bit on runs.
The one thing I would question is whether the thickness of the rudder is as noticeable as suggested. A reasonably clean rudder should not account for more than 5% of total drag of the ski and even doubling the thickness from 8% to 16% (the very extremes of thickness should not vary the rudder drag by more than 20%. By implication it is being suggested that drag differences of 1% are readily felt.

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11 hours 34 minutes ago #30648 by owenfromwales
Thought people might appreciate a shot of the nifty tri-nut that Don makes for his rudders. At present I don`t think these lock nuts can fit onto an original Stellar shaft (imperial v metric), but that could change in future. Either way, they work really well and it's so nice not needing some sort of socket.

189cm 90~100kg
Present skis:
2017 Stellar SEI 2G
1993 Gaisford Spec Ski
1980s Pratt Spec Ski
1980s UK Surf Skis Ocean Razor
Previous
1980s UK Surf Skis Ocean Razor X 3
1987 Kevlar Chalupsky (Hummel) (Welsh copy!)
1988 Kevlar Double Chalupsky
1992 Hammerhead spec
2000 Fenn copy
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