JEM
As I understand foil technology, it reduces the habit of “stalling” when deflected. A flat rudder under deflection stalls, and creates turbulence that saps speed.
It would seem that the less the rudder has to be deflected to correct for windage, the less the forward speed would be reduced.
Jim
Not a Fluids Physicist, but I play one on TV
Rudder shapes
A few variations, courtesy of HUKI. All foils, 3 high aspect, 2 grass shedding:
http://www.huki.com/mod_pages/oc1_images/rudders_full.JPG
Very nice, thanks,
I guess we are forced to conclude from all those choices that some work better than others, performance-wise.
Mike
For different conditions - none "better"
Longer for bigger water (more powerful control), shorter for flatter (minimal drag), straighter for clearer waters, angled for grass/weed/kelp.
Those extremes should explain the existence of the intermediate sizes/angles for “general use”.
Well, yeah, but the question at hand,
of course, is does one give up anything with the grass-shedding versions as compared to a vertical one of similar depth and area.
Mike
Obvious answer is…
…weed shedding is better in weeds, high aspect in clean water. High aspect isn’t going to be more efficient if it’s fouled regularly.
Actual efficiency in the real world is more important that technical efficiency inherent is a design. Choose you tools according to the task at hand, and the job gets done most efficiently.
Ok, try this one on for size,
what’s better, a weed-shedding understern rudder or a vertical overstern rudder.
Technically, of course. Everybody already knows none of this stuff really matters.
Mike
Sorry, you don’t have a clue!
Elaborate, please.
I’m only asking questions.
Mike
Your either…
… playing with me (I’m done) or missing the obvious point about conditions being what’s important.
Another foil vote
– Last Updated: Oct-30-04 12:26 AM EST –
If you must have a rudder, get a foil rudder much less drag.
I don’t play here
– Last Updated: Oct-28-04 12:17 PM EST –
I may have been a little flip with that comment, sorry about that. I really would like to understand the technical issues. I can make my own judgement on whether they matter to me or not, based on where and when I paddle. That's where that comment came from.
I look at a kayak hull and like to think about something going nicely through the water, causing little turbulence and turbulence drag. Unfortunately, often some appendage has to be speared into the water to help them go straight. What is the best answer? Thought it was a skeg for awhile, but now I find that skeg boxes cause turbulence drag, some designs more than others apparently. I don't like the idea of that. Don't like rudders either, but perhaps they can be better than skegs, depending on the implementation.
And then there's Mariner's idea (may not be "their" idea, really) of a built-in skeg. Have to admit that's pretty appealing, but there doesn't seem to be a lot written about those boats in comparison to other more popular ones. They seem to be far more swede-formed than many, so it makes direct comparisons difficult. I keep thinking about, and talking myself out of, trying to slap something like that on the aft keel of my Caribou to see what it does.
Mike
Full time skeg?
When you only need one part time? Not very efficient either.
But then, a rudder is in some ways acting like a full time skeg - so if it’s not needed it would be shifting balance toeward leecocking - and you would need to use stering input to correct that. More iefficiency, unless the boat has been specifically desigened for a rudder (many kayaks, all racing hulls, and surf skis).
All this is small stuff though.
Yeah, that’s why I keep talking
myself out of it. But I find I want more directional stability with my boat the majority of the time I’m out there. I’ve gone to half-skeg much of the time, as I mentioned somewhere else.
My very first test paddle with the boat was up a quiet creek, no wind, no waves, alongside the dealer in another boat. Was moving along pretty good, though did have to make minor path corrections fairly frequently. Assumed it was just lack of experience.
Part way along, just for fun I put the skeg down. My first reaction was, yuck. I heard gurgling, felt drag, immediately. I took comfort in the many usenet posts that said the boat didn’t need a skeg, most of the time. I believe I could put 20 lbs somewhere in back as an alternative, but then I thought I was buying a 50-lb boat, not a 70-lb boat.
Here I am at the end of the first season and still wanting some tracking help, most of the time.
Thing I like about the Mariner concept is the built-in skeg pretty much takes itself out of the picture when you lean the boat, which you do for turns anyway. Only contributes when the boat is level. Seems almost perfect to me. On the other hand, such a low-draft skeg probably needs much more surface area to be effective than a fin skeg. More drag, though who knows how much.
Mike
How many miles…
…have you put in in your one season?
More importantly, how many on a typical paddle?
Do you paddle at a fairly steady rate over distance and maintain straighter courses, or are you a stop and go sightseer type?
This sounds a lot more like basic tracking issues, that self resolve with mileage, than equipment issues.
The Pintail I recently got is not known to be a strong tracker. Just the opposite, hence the nickname “Pinwheel”. I put my girlfriend in it (she will be in her “first season” for several years as rarely as she paddles) and she did OK, but it did snake around a lot on her (her other boat is ruddered and masks things like this). I got in and paddled around and thought it tracked fine.
Difference is a lot more mileage (realtively - not compared to the big boys here) in a few more boats over a couple years (with no “season” here) - all un-ruddered (except ski - which I’ve yet to really paddle much) - and what that’s done to my stroke. Unless Greenland paddles somehow magically aid tracking (she was using a euro L)!
As has been said here many times: Skeg should be used for wind/wave balancing - so you’re not pushed off course by the weather It really isn’t to help you keep course against your own paddle inputs (tracking). Same can be said of a rudder, but since it corrects for wind AND helps you turn - most do both with one.
If it helps you to use 1/2 skeg all the time - do it! Better than ballast, but 1/2 seems a bit much. I set Kim’s at 1/4 and she noticeably straightened out. Try backing it off a little at a time until not needed - over next season.
Talk to Grayhawk and the other 'bou owners about your particular situation. I was brand new to SINKs when I tried one and thought is tracked pretty good - but that was on a pond.
PS - the 'bou’s hard chines are already giving you some of the handling characteristics of a built in skeg, and may be better at resisting crabbing.
Maybe you’re just a rudder guy. That’s fine too.
For me, the rudder/skeg choice has a lot more to do with the boat and type of paddling done than the paddler though.
I’ve gone somewhere over 100
miles, perhaps 150. I’m just a once-a-weekend few-hour paddler, managed to get out most weekends since late May. Lately I’ve been exceeding 10 miles per outing, a couple over 14. Not much compared to many, I know. This is my first year paddling a single.
I try to maintain 4 mph or better pace water speed, but need to rest occasionally. Do like to sight-see too. I can keep the boat going straight if I really focus on it, I can tell when it is starting to veer and make corrections. I don’t like having to focus on it that much all the time, that’s the problem. It doesn’t have to get off-line much for the skid-out of the back to really get going.
The tracking just feels unstable, like you have to “balance” it. I’m sure this is partly why the boat is quite responsive to turning while edging. If I could change that just a little towards the more stability, slower turning end of the spectrum, I’d be happy.
It could just be me, but one of the SK testers said the same thing, so I take some comfort that it isn’t just me.
The usual solution to this is some weight in the back, I tried 9 lbs of scuba weights all the way to the stern, and hated the result, too much front-end bobbing. Gave up on that and tried to learn to like the skeg halfway down. Still having trouble with it, the boat simply glides better without it, no question. Less than halfway I don’t notice that it did much, but then it isn’t a very big skeg.
I guess next I’ll try a 3 lb weight in the stern, to see what that does. Maybe it takes less of a trim change than I think.
Mike