Best tandem kayak rudder options.

Newbflat

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I have a (new to me) Seaward Passat G3 and the rudder and the rudder is floppy, loos and worn out. Ideally I would like to replace it with a new rudder with a foil blade. I really dislike flat plates so I’ve been searching and not coming up with anything other than SmartTrack rudders. I haven’t been that impressed with the number of parts in them and have seen a number of them fail. Anyone have any other ideas? a really long foil would be super. … I wish Onno still made double rudders, they were sweet.
 

Mac50L

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I always make my own, the Daggerboard design (scroll down to it) -

Providing the front and rear edge are parallel any foil shape will fit. Admittedly the pictures do show a flat plate blade. Though the blade slides in grooved plastic, you could replace those with grooved pulleys if you wanted to. One of the great advantages of this design is when pulled up it can't fall overboard as the pull-up string keeps it straight and can be locked to hold it.

Also the pedals as there are some poor designs, the sliding pedals being the worst
 

mick_allen

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Is this the type of G3 rudder you have?
3b-PassatG3b.jpg


if so, as the essence of a basic, decent rudder approach is all there, I'd just re-furbish it as best as possible.

If the rudder blade is not foiled and is say a flat aluminum plate, don't be so sure that a foiled blade is really of any great benefit:
to be sure hydrodynamically shaped foils provide measurable benefits, but most kayak use should involve minimal movement for minimal course correction rather than at the extremes . . . and interestingly for rapid course changes a readily stalled 'foil' will be more beneficial than one that attempts to maintain a less useful turn rate.

but what the heck, just add some filler on the sides and reshape or replace the blade as Mac50L suggest, tighten a few bolts or replace the studs, fill in and redrill out-of-round holes, etc. and repaint.
 

Newbflat

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Yes, it is that rudder. My experience with a foil on a touring boat showed that it can turn much more aggressively with less input, and has more controls when just a few inches in in the water assuming you don’t over correct and stall it. I have lots of experience with foils and not so good a foil on Surfski’s and it makes a BIG difference in how the boat handles. A good foil like a DK rudder can be transformative in how one preformed over a stock less than perfect foil. I’m not expecting anything big on a touring boat but I’d should be more controllable paddling down wind if it wasn’t essentialy a drag device.
 

mick_allen

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I'm sure you have great experience, but that rudderblade has characteristics that'll overcome most foil blades [that I see on kayaks] for that use.

For one, there is much more area than typical ; second,the length provides much more immersion possible [obviously with the area]; third, the blade almost looks 'shaped'; fourth, the rotator housing PLUS the transom base can provide the best blade stability - providing the best foil/blade control or stability compared to typical pinhead rudders; and fifth, typical ordinary big double kayak paddling will not require or really be able to provide rapid course correction; oh yeah, and sixth that immersed wide-ish blade chord will provide more control and less stalling than higher aspect ratio blades.

Of course the above is all crap playing around the edges - but basically pointing out that the bones of a decent rudder are already there - and like mentioned, it's easy, easy, easy, to just make other blades to whatever myriad of characteristics you wish to have or test.
 

Mac50L

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One other thing is the rudder pedals. Full foot pedals can be balanced, hinge level with the ankle so you can brace hard against the pedal but be putting no input to the rudder blade. The rudder lines are just loose. This means the blade is in the water at minimal drag. Any steering is just tipping a toe / top of the foot, forward. Aggressive steering is also easy to do if needed.
 

Newbflat

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I'm sure you have great experience, but that rudderblade has characteristics that'll overcome most foil blades [that I see on kayaks] for that use.
I will never understand why the sea kayaking world had basically given up on the benefits of a properly shaped foil on boats with rudders. Foils are better in every way and in some ways it’s not subtle. My biggest guess is they are hard to make properly and no one seems to care.. (wrongly). It’s even the same on Surfski’s which really benefit from a proper NACA foil. I can’t think of one company that offers one, some are close but they all blow it on having a pointed leading edge.

mick_allen continuing:
For one, there is much more area than typical ; second,the length provides much more immersion possible [obviously with the area]; third, the blade almost looks 'shaped'; fourth, the rotator housing PLUS the transom base can provide the best blade stability - providing the best foil/blade control or stability compared to typical pinhead rudders; and fifth, typical ordinary big double kayak paddling will not require or really be able to provide rapid course correction; oh yeah, and sixth that immersed wide-ish blade chord will provide more control and less stalling than higher aspect ratio blades.
A well designed foil doesn’t need more area below the water to have more force than a flat plate. Flat plates create very little lift when turned so they need substantially more attack angle and drag to creat the same force as a foil with significantly less angle of attack and drag… and It’s not subtle. Foil-ish rudder SmartTrack transom mount have the same blade depth as the existing rudder at around 16-17” from the pivot so reach is not lost. Foils do not need to be high aspect, that’s only a cross sectional equation expressed in a NACA number . Aspect and profile like elliptical or a straight tip shape are a different subject. There is no attack angle where a flat plate out preforms a foil no matter the aspect, except drag.

mick_allen continuing:
Of course the above is all crap playing around the edges - but basically pointing out that the bones of a decent rudder are already there - and like mentioned, it's easy, easy, easy, to just make other blades to whatever myriad of characteristics you wish to have or test.
If I had any sort of shop space these day I would, I would order a 20” DK, NACA 0012, tapered from 6-4” and modify a Feathercraft K2 rudder to accept it. But I live on a 600 square foot house boat with no shop. Might give it a shot if Don Kiesling can make the rudder.

I’ve owned and races an Epic V10 double and V8 double and swapped a number of rudders around. With the standard Epic elliptical rudder the V8 double was a barge, especially if not actively surfing fast and on a good size wave. Swap to a 9” 15° Sweep DK rudder of the NACA 0012 foil of my choosing and it’s is like night and day. Much more powerful with very little input and far better surfing at off angles. It also has much better feel when surfing diagonally so you can walk the line between staling and control, and it regains flow after a stall easley without needing to turn the rudder back to center to initiate flow again.

Yes I understand I’m asking about rudders for a Passat G3 and not a surfski, but the principles is the same, a well executed foil have a lot of power with little drag. It would be of great help if racing an empty Passet on a down wind leg and needing to catch surfs at an off angle or straight for that matter, or needing very little input to correct for strong wind and waves quartering off the bow. It would also make it easer to take advantage of more aggressively turn and controls the boat while loaded helping your ability to take advantage of following seas/surfing. Sea kayaks don't turn as quick as skis solely because there stern are much looser, even more reason to have a rudder on a double sea kayak that has the power to turn it powerfully when needed without just slowing it down.
 
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mick_allen

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So, requirements are foils, emphasis on boat usage when unloaded, racing, and angled surfing with additional aggressive turning also required when loaded . . . . not quite a typical double usage, so emphasis on previous thoughts shifted.

Pulling out what's applicable from before:

Firstly as your requirements are so harsh, you need a maximally stable rudder structure - one function for the duty [loading and unloading - say angled surfing] and the other for reliable controlled control inputs. ie no flop and no stall inducing accidental overdeployment inaccuracies. no humming nor yawing here, neh?
So as mentioned, unlike most, that rudder housing you have can give blade stability - right down to the waterplane - interestingly completely unlike the feathercaft II rudder housing . . .
SeawardII-FeathercraftII.jpg

and secondly, it sure seems [just a judgement] to me that the 25" seaward blade [24" from pivot?] reaches deeper below the waterplane than a 16" blade - to give control - can't control what you can't touch?

and thirdly as a foil is a requirement and a basic 12% one at that, just add a little micro and epoxy on the sides of that blade on your kitchen table, with just one cardboard section cutout to match it all and . . .
and like mentioned . . . just make the shape to whatever myriad of characteristics you wish to have or test.
And if you really want control at the extremes, widen the blade, forget the elliptical and drive that wide foil as deep as you possibly dare, you can always pull it out on the go, to what ever little bit of drag you want, right?
 

Newbflat

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So, requirements are foils, emphasis on boat usage when unloaded, racing, and angled surfing with additional aggressive turning also required when loaded . . . . not quite a typical double usage, so emphasis on previous thoughts shifted.
Again, why is this so hard to accept. There is no reason why sea kayak rudders shouldn’t have proper foils and solid reasons why they should. There is no down side.

Pulling out what's applicable from before:

Firstly as your requirements are so harsh, you need a maximally stable rudder structure - one function for the duty [loading and unloading - say angled surfing] and the other for reliable controlled control inputs. ie no flop and no stall inducing accidental overdeployment inaccuracies. no humming nor yawing here, neh?
So as mentioned, unlike most, that rudder housing you have can give blade stability - right down to the waterplane - interestingly completely unlike the feathercaft II rudder housing . . .
Not sure why you think my needs are “so harsh”… pretty standard racing requirements really. By my measurements the Seward blade tip sits about 16” under water, the other 9” are out of the water and up to the pivot. My feathercraft double rudder on my Feathercraft K2 is only an inch shorter to the pivot. The pivot rides in the same hight above the deck on both kayaks so they can pivot onto the back deck. So the Seward rudder is effectively one inch longer. As for tightness in the system it might be a wash, the feathercraft plate is thicker but not as well supported, the Seward plate flexes more.

and secondly, it sure seems [just a judgement] to me that the 25" seaward blade [24" from pivot?] reaches deeper below the waterplane than a 16" blade - to give control - can't control what you can't touch?

and thirdly as a foil is a requirement and a basic 12% one at that, just add a little micro and epoxy on the sides of that blade on your kitchen table, with just one cardboard section cutout to match it all and . . .
A proper foil is a lot more complicated than that and to work effectively it needs to be very precise. In particular, the leading edge‘s shape is critical. If you mess up the first thing the water touches it wrecks everything else down stream. If you have a ski I highly suggest you try a good rudder if you are running stock, it can be a game changer. The place most OEM rudders blow it is the leading edge.
N

And if you really want control at the extremes, widen the blade, forget the elliptical and drive that wide foil as deep as you possibly dare, you can always pull it out on the go, to what ever little bit of drag you want, right?
Having spoken to DK rudders I’m having a rudder made. Likely a NACA 0009. 16” or so. It will be attached to the bottom of the Seward rudder as I think I can snug it all up… Here is a picture of one he did for his Passat G3 for the Smarttrack rudder on it.
97A49096-D528-4B07-9A24-F017C639B455.jpeg
 
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Mitch

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You may want to contact Steve at Nimbus. He has been making foil rudders the last couple years.
 

Mitch

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Just read your last post. Good to see that Don K has a solution for you.
 

mick_allen

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"why is this so hard to accept"
I have no idea . . . it's your requirement. I thought that you'd asked for ideas in the OP:
  • - the first idea was use the existing housing but with it set up properly to brace the blade,
  • - second was with the good setup utilizing the existing what I thought was a big blade that might be adequate - turns out I'm incorrect but I don't have your blade in front of me, and you require a foil shape
  • - third was modify that blade to a foil shape,
  • - fourth was make a blade to whatever shape you wish [obviously a foil shape]
To me, it seems like you're using the first idea and then the third and fourth idea combined, but purchased.
. . . and I don't find that difficult to accept at all: seems fine to me.

Anyway, show us a sideview of what the final result is and what your reactions are - sounds interesting.
 

mick_allen

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It’s all about the Reynolds number . . .

So out of curiosity I wondered – what really is the difference in performance between a flat plate and a basic NACA type symmetrical foil? Was it even a close choice in some circumstances or was it that “foils are better in every way”, as is reasonably thought?

. . . and it seems as if it depends! - on the velocity of the water past the rudder: it depends on the width of the rudder combined with the speed of foil type: – the speed length ratio or the Reynolds Number . . .

A typical rudder is about 3” or 7.5 cm wide and for this post’s purpose let’s say the speeds involved go from 1mph to 10mph which give a Reynold’s Number range of 2.44 x 10^4 = 24,000 to 2.44 x 10^5 = 240,000 [3mph gives a Reynolds Number about 80,000 for that rudder].

So the typical discussions about flat plates vs foils show performance graphs that look something like this for Coefficient of Lift versus Angle of attack. I couldn`t find a graph for a symmetrical NACA foil, but for the sake of argument it’d be safe to assume they’d be fairly similar [but slightly lower lift coefficient] and the reason for considering that foils give superior results. Here we see 2 foils giving higher lift coefficients plus stalls delayed compared to a flat plate. Interestingly, the flat plate has a wider stall envelope than the foils.

foil-comparisons2b.jpg


So something like that is what one would expect . . . for higher Reynolds numbers. But kayaks operate over a speed range and the lower speed range falls under LOW Reynold’s Numbers – say 3mph and below – and here is the shocking result . . . flat plates perform equivalently to foils and at real low speeds, it even appears as if they outperform foils! I've included a paper showing and discussing these effects:

here's the abstract:
LowReN-airfoils copy.jpg



and here's interesting results at ReN 20,000 to 80,000:
LiftCurves.jpg


Now this is not the whole story: there’s drag to consider as well as many discussions I’ve read about flat plates having quick and unpredictable stalls versus the more predictable foil type that initiates at the tail of the foil. But it really points to the fact that a flat plate rudder for general kayaking is essentially an effective, economic and reasonable choice. Who’da thunk?

[edited to add: the paper is about control surface effectiveness as control surfaces have to operate in either direction and so for this case are symmetric, ie NACA 00xx type foils. The suffix xx12 and xx06 refer to the foil chord thickness that these foils have at the 20% chord location [if I remember correctly] from the nose. ]
 

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Mac50L

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Thank you Mick for that.
There is the question of drag but I still say the rudder should be floating at zero degrees until a turn (course correction) is wanted with proper full-foot pedals. They give "feel" as well as foot support. They allow slack rudder lines and allow the paddler to know if the lines are slack for a "floating" blade.

Next, blade support. The support shown in the two pictures is minimal or low. The Daggerboard style has the blade supported on the leading and trailing edges and just about nothing sticking up above deck level.

Added to this, during retraction, it can't go anywhere other than straight along the deck and then locked there, where as the pivoted rudder can land with its tip over the side and then become a liability.

That means if Newbflat is looking at all the options and the "best" type, the style he is suggesting isn't the best and I'd consider that more important than whether it had a foil or flat-plate shape.
 

mick_allen

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1st take:
. . . the question of drag but I still say the rudder should be ["floating" clipped] at zero degrees until a turn
I haven't looked into it, but here are a couple of considerations:
- if you have a setup that allows quick retraction - wouldn't just retracting it [flat or foiled] for most easy anticipated paddling make the least drag of all? Is that the main beauty of a stern hung rudder?
- if you couldn't readily retract in racing AND the anticipated [including maneuvering] conditions were predictable and mild wouldn't a flat plate be immearsurably superior as the frontal drag area of a flat plate is infinitesimal compared to the much thicker [and therefore draggier] foil, even say a NACA xx06?

2nd take: "floating" added
. . . the question of drag but I still say the rudder should be floating at zero degrees until a turn
that means feet not touching the controlling pedals or parts of pedals - which I'm not sure most would be able to do or resist, heh heh. Plus the rudder pivoting would have to be placed quite forward in order for it to 'float' or 'weathervane' directly in line with water flow to minimize deployment drag - ie it has to incrementally deploy in order to be made to 'float'. [edited to add: I think this argument I just made is crap: with the rudder being able to pivot readily any drag employed to make that easy weathervaning would be incredibly small. . . so I retract, heh heh]

For blade support, the daggerboard style cartridge has the ability to hold the blade well, but then the cartridge is the issue:
- if it is a pinhead cartridge, then the cartridge has the same old wobbly pinhead long unsupported [above waterline] issues
- if it is a transom hung rigidly placed cartride then is does have good blade support down to the waterline. But then on retraction, the blade has to go vertically up in the air - and more prone to damage, vaning, etc.

for straight line retraction, the daggerboard type does align centrally along the deck, but the retraction line then has to be centred along the deck as well . . . so there's no big reason why a pinhead couldn't be designed with a 2"- 3" nose extension toward the bow and have a similar result - just more plastic.
 
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kayakwriter

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Just adding my anecdata experience with rudders here. I used sails on my previous and current rudder kayaks, so I'm using the rudder to hold a course, with constant subtle corrections while underway. On both boats, I've fitted the SmartTrack rudder system. It does have the disadvantage of only pivoting up 180 degrees, so it's vertical at the stern, rather than 270 degrees to lay flat on the rear deck, surf rudder style.

The pro of the foil shape is definitely reduced drag and a far higher angle of turn before it starts to stall. The drag is so low that on both my single kayaks I upgunned the rudder blade to the bigger "double kayak" size, with no appreciable loss of speed and a very noticeable increase in "bite" and ability to hold off-wind courses.

YMMV.
 

Mac50L

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1st take:

I haven't looked into it, but here are a couple of considerations:
- if you have a setup that allows quick retraction - wouldn't just retracting it [flat or foiled] for most easy anticipated paddling make the least drag of all? Is that the main beauty of a stern hung rudder?
Yes and if Daggerboard type no centering needed as it by default is centered as it is retracted.

2nd take: "floating" added

that means feet not touching the controlling pedals or parts of pedals
NO.
The feet are hard against the pedals. It is tilting the feet that actuates the turning.

- if it is a transom hung rigidly placed cartridge then is does have good blade support down to the waterline. But then on retraction, the blade has to go vertically up in the air - and more prone to damage, vaning, etc.
Not the Daggerboard style as it is rotating to the deck when less than half retracted. It is the revolving type that waves in the air to fully vertical. Another Daggerboard style advantage.

for straight line retraction, the daggerboard type does align centrally along the deck, but the retraction line then has to be centred along the deck as well
The retraction line comes out of a hose / tube where the end of the blade ends up on deck. The retraction tube is under the deck on all of my kayaks.[/quote]
 

CPS

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On both boats, I've fitted the SmartTrack rudder system. It does have the disadvantage of only pivoting up 180 degrees, so it's vertical at the stern, rather than 270 degrees to lay flat on the rear deck, surf rudder style.
They do make an over-stern style as well. The housing is plastic and I find it doesn't operate as smoothly as the metal ones though.
 

mick_allen

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NO. The feet are hard against the pedals.
I think yes . . . I specifically am referring to whatever controls the rudder actuation: the 'controlling pedals or parts' - ie whatever actuates the rudder, has to be feet off or no windvaning.
Toe-wigglers2.jpg


Not the Daggerboard style . . .
There are multiple daggerboard 'styles'. But a transom hung daggerboard cartridge is rigidly attached to the transom and therefore has to slide vertically like this:

SlidingDaggerbd-vertical.jpg


Which is completely unlike the sliding pinhead which has more potential issues:
SlidgPinhd-Issues.jpg
 

Newbflat

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Please educate me on the low Reynolds numbers. What exactly do they equate to in actually speed. My interest is to have a ruder that is both more powerful (more lift) with smaller input, and to preform better at higher speeds like surfing or sailing fast. I see nothing that would make me think a plate is better, or even close.
 
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