Let's talk rudders

mick_allen

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That skeg rudder system looks similar enough (but a bit bigger) to what surfskis use as standard, as far as location and blade size.
I think it should work in a similar fashion as well.

i wouldn't be comfortable having that on any extended/exposed trip. Just looks too fragile.
From sidehits maybe, but as the blade is 50% shorter than most pinhead rudders and if the other mechanism uses material that is the same size as pinheads or stern mounts - wouldn't this understern have at least some substance similar to any other rudder?

The main concerns (for me) with understerns are whether housing damage compromises hull integrity or whether severe rudder damage leaves it bent and exposed below the hull compromising paddling. However I think that these possibilities just have to be accepted if choosing understerns and that a provisional safety measure would be a breakaway blade below stress causing box failure.

Prijon got it right with their foil-shaped rudder.
Is this the one you mean?:

Prijon-WingRudder.jpg


It has an elegant nature to it (certainly nicer than most sternhung or pinhead rudders) but is unusual in that it looks like a typical pinhead but uses a stern mount for the pin. It takes advantage of the low position by having the mid-blade inserting into the mount stabilizing the blade while deployed, but is odd that it has such a short pin and such a weird long rear bracket combined with the extended rear housing. Very high aspect blade, 'balanced' rudder - may be why the the throw has been limited.
 
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gnarlydog

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Mick, one would think that the size of the Karitek Skeg/Rudder would be sufficient - but probably must be the location that makes it less effective.
Possibly the range is not that great either ( I did not play with it on dry land and check the side to side movement).
I also did not use it as to correct the weathercocking (rather moderate, on an Explorer) but it did not give me the turning direction that other ruddered kayaks would.
Possibly it might work for weathercocking, but so does a simple skeg.
I did not have a chance to test in following seas to determine if the rudder action is sufficient to forego corrective stokes when the kayak is broaching.
Talking to a guy that has owns an Exporer with the Kari-tek hydro skeg, his verdict was: not worth it.
 

mick_allen

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Possibly the range is not that great either ( I did not play with it on dry land and check the side to side movement).
This is a very interesting comment/question. I also now wonder what the range actually is? Certainly understern rudders are complicated and the less range the easier to make work consistently. hmmm.

And it also is strange - in conjunction with Rider's comment that the range is small for the Prijon rudder too. (and funnily enough, would be 'designed' for entirely different reasons)
 

rider

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I think range is limited with any gas-pedal style system, a function of simple geometry. I installed the Seaward system on my Elaho HV i had, very workable installation after some minor modifications made, very servicable, but limited range.
Notice, because of the shape of the bracket and blade of the Prijon rudder, the blade pivots around it's center, as opposed to pivot being way in front of the blade. I believe it makes a noticeable difference in reducing drag.
On the skeg-rudder, my main concern is hull damage around the box on impact. Ending up like the Bismark with a bent rudder you can't really fix on the go isn't a great prospect either.
Problem with neat pretty things that are meant to go into a neat slot , come out, turn, and go back up, is they don't usually work near as good once bent and field-straightened.
 

mick_allen

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range is limited with any gas-pedal style system, a function of simple geometry.
If the system is designed together, it can be fine. But rudders with wide wings combined with a short throw gaspedal will not have as much. And the gas pedal itself does not necessarily have to have a short throw - it is just easier to make it that way. (for example, I think the sealine gas pedal type system has a decent throw)

However in your case, I originally just suspected it might be designed that way because high aspect blades stall before low aspect - but on further looking at the picture, i notice the side wings are extremely, extremely small compared to other usual rudders! So maybe the prijon pedals just don't have a lot of movement to them after all. It would be interesting to compare the throw distance of the 3 decent models (seadog, sealine and prijon). I leave the seaward out as it does not self-adjust like the others.

Notice, because of the shape of the bracket and blade of the Prijon rudder, the blade pivots around it's center, as opposed to pivot being way in front of the blade. I believe it makes a noticeable difference in reducing drag.
Unless it changes the shape of the rudder blade, there's no reason for less drag. I think what you're experiencing is that you can't deploy the blade at too great an angle - which keeps the drag down.
Most rudders are easy to deploy at large angles - that just add lots of drag for no big benefit.

Ending up like the Bismark with a bent rudder you can't really fix on the go isn't a great prospect either.
this might not be completely fair as I have read on other forums of typical rudders getting over deployed or crunched and then having to awkwardly paddle for an extended period of time before getting to shore to deal with it. Can happen with any of those mechanical bits we use.

On the skeg-rudder, my main concern is hull damage around the box on impact.(cut)
Problem with neat pretty things that are meant to go into a neat slot , come out, turn, and go back up, is they don't usually work near as good once bent and field-straightened.
I think you're dead right on what you say above, however I also think that those concerns just have to be accepted if one chooses an understern rudder - whether retractable or fixed. There are many, many regular boat understern rudders out there that do huge service under many conditions for many different types of boats. One way of looking at it - that many of us have wooden kayaks here - and we take certain precautions to not have them bashed about as much as when we use our plastics - so it is not so much of a stretch to see someone exercising the same sort of restraint with an understern.

Like think of how unrestricted you feel in a plastic boat without a rudder of any type. How does your attitude change when you have a rudder on the back and you're around other yaks or rocks or close to shore? I think that type of attitude change would be natural with an understern.

obviously from the above, I love the idea of understern rudders but sadly realize that they come with some unavoidable considerations.
 

Tootsall

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rider said:
Notice, because of the shape of the bracket and blade of the Prijon rudder, the blade pivots around it's center, as opposed to pivot being way in front of the blade. I believe it makes a noticeable difference in reducing drag.
Pivoting the rudder around it's central axis has the effect of balancing out the forces that would otherwise try to straighten it back out into alignment with the keel line: reduces the effort needed to hold it at any particular angle.
 

mick_allen

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Pivoting the rudder around it's central axis . .(cut) . . reduces the effort needed to hold it at any particular angle.
this 'central' zero moment axis is typically assumed to be at the 25% chord point. Unless electronics are used, most 'balanced' foil designs use an axis somewhat less than this - so at least some feel feedback in the control is maintained.

My question is , is it really desirable to have less feel and more touchiness in the rudders that we use? Aren't they fairly so low in feel, that reducing or eliminating this feedback is the reverse of what we need? And isn't this especially the case for a high aspect ratio, lower stalling angle foil? I like the appearance of this prijon , but I also see confusion.
 

Tootsall

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Mick, what you say is true: I'm using the example of a flat, symmetrical blade with no foil for simplicity.

The only real reason I can think of for a balanced pivot foil or blade is that by reducing the effort needed to pivot and hold the rudder, one could reduce the length of the torque arm required and thereby obtain an increased angle of deflection with a minimal pedal motion: as may be the case in the pivoting foot pedal design.

The downside (s) as you point out are the increased "sensitivity", lack of feedback and possibly need for stronger pivot bearings. (And, naturally, more complexity in the "flip up" mechanism).
 

Telkwa

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Hey, rider -
Can you tell us what problems you ran into adapting the Seaward lockout foot pedals? I'd like to try this on my Telkwa. From the pictures on their website, it looks like it might be a relatively straightforward swap.
 

Doug_Lloyd

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Re:
Jurfie said:
What about a recessed slot (like a skeg box) on the back deck (rather than the hull) for a rudder to flip up and into? It can be sloped slighty towards the stern to drain. That would get the rudder "sail" off the back deck when up, and also prevent...ahem...an uncomfortable re-entry. If I'm not mistaken, Seaward's slider rudder deployment system doo-dad keeps lines off the deck. The narrow part at the stern is a less usable space anyways, so it wouldn't be a major loss of storage space...just a thought.

(The above idea, if found to be a good idea, is copyrighted by the author, June 10, 2008. All royalties go to me. :wink: )
image.jpg


image.jpg


http://nadgeekayaks.com.au/sea-kayaks/nadgee-solo.html

Looks like the rudder slot is a reality now.
 
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mick_allen

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Hey, your favourite company was halfway doing this over a decade ago with the C-Trim rudder:

VCP-C-Trim1a.jpg
 
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Doug_Lloyd

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mick_allen said:
Hey, your favourite company was halfway doing this over a decade ago with the C-Trim rudder:
Yeah, on their double. The Aluet II. That was the longer C - Trim rudder blade. That was the blade length I used on my early Nordkapp HS to achieve a deep draft rudder. There are a few kayaks around that have a slot like that but not as deep as the Nagee.
 

mick_allen

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Adding to the compilation of slotrudder types:
Venture,P&Hskudder1a.jpg

Venture Kayaks announced this a short while ago - blurb at bottom mentions a Pyranha/P&H patent.

http://www.venturekayaks.com/news/?p=282

and from above in a sit-in kayak:

Venture,P&Hskudder1b.jpg

The resolution looks fairly clunky with the rudderpost penetrating up through the deck. And like the lettman (although I cannot tell for sure as for the lettman) it looks like a hunt-and-peck retraction with a centre-detent. ie not a self centering on impact mechanism.
In the first picture, the keel-line is not continuous so there must be some larger cutout for size of the rudderpost and "shock protected joints".
 
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mick_allen

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I just realized that I also didn't include Bjorn Thomasson's concealed rudder:

http://www.thomassondesign.com/nyheter/nya-kajaken-och-nya-funderingar:





This is virtually identical in concept to the previous P&H Venture rudder (how would that patent be defended, heh heh) but Bjorn has concealed the tiller under the decktop and shaped the rudder shaft drum to fit the hull bottom instead of leaving a raw hole like the Venture does. When deployed and turned there would be hull turbulence, however.
Also semi hunt-and-peck non auto-centering, but I think there is a detent or balancing on the lines to help centre before retract.

(edited to add: actually the pedals are fixed, but flexible - so therefore when toes are off the pedals, the rudder centres: only then is it aligned and able to retract)

..
 

mick_allen

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The recent adventure kayak mag had a picture that was slightly more informative of the rudder shaft for the Venture skudder - in the post just one removed above:

VentureSkudder.jpg


You can just just just see the bottom of the rudder shaft with the hinged and captured blade (at the very top of the pic). As well you can see a retract line that is outside the rudder shaft so on can infer because of the small hull cutaway (right where the line is) that there will be a little wear and chafe of that line (with the rudder going up and down when fully angled ? !!). Because there is no visible deploy line, there likely is a bungee or deploy line that is internal to the shaft.

Not nearly as complete a solution as Bjorn's Thomassons (with both lines internalized and not subject to the excessive wear), but halfway cleaner than the lightspeed approach. I haven't yet heard of any centering solution, so that may be from mind melding or equalizing lines feel or memory or detent - or may not even be addressed at all.
 
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JohnAbercrombie

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Another DIY rudder by Rune Eurenius (for a Bjorn Thomasson Sea Racer):



Some details at http://www.thomassondesign.com/en/news/exciting-rudder-solution
Rune used a bike pedal for the bearing.

Looking at Bjorn's rudder concept: In an email Bjorn T. reminded me that a 'drum/pulley' is actually better than a 'bar' for attaching lines to the rudder stock, since with a bar the turning moment changes as the pedal is pushed further.
 

mick_allen

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a 'pulley' is actually better than a 'bar' for attaching lines to the rudder stock, since with a bar the turning moment changes as the pedal is pushed further.
The advantage is probably not so much with the increased rudder deployment with smaller pedal deployment (which is certainly a factor to consider) as it is the continual cable bending and flexing to account the changing tiller position versus that of where the cables insert into the hull. Probably not a big deal in any case, but one more factor to look for in a more completely designed rudder.

Another topic, but the similar change from rotational deployment to linear actuation is another issue that is very often overlooked in skeg deployment. Pull/pull skegs are easier to set up for this as only a few push/pull cable skegs confront this issue. Reg Lakes skeel does it best, but its side entry requires a cumulative close side tolerance that is much less than the cable diameter and Nick Schade's skeg does it (or at least addresses it) but only on the deploy cycle. Most others completely ignore that rotational/linear issue.
 

mick_allen

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Karitek Rope ‘skeg rudder’

I just noticed this year old vimeo, by Mick MacRobb of Flat Earth Kayak Sails, demonstrating the new rope version of the discontinued Karitek hydraulic ‘skeg rudder’:

housing3.jpg


aspects that I note:
- still uses the double cassette box approach. I presume this is to allow revisions to skeg or future hydraulics.​
- large housing to rudder size ratio.​
- spring(bungee likely) deploying so a single line retracts.​
- seems about 30 - 35 deg max rudder throw - which is fine as a rudder is more a drag device with further angles.​
- amazingly quick self-centering. It seems to self-centre after only about 5 degree of retraction. That could be a future wear issue on the retract actuator or when quick hits.​
- a much simpler and likely lower cost approach than the hydraulic version.​
- with the tiller throws being similar to regular rudders, alternate pedal systems or suppliers should work.​
- as in all slot rudders, internal deck rope/cable routing may be in conflict with interior deck ht, hatch opening and gear, etc. (This is unavoidable unless other awkward means (or kayak specific means) are utilized)​
[2021 - edited to add that Mick MacRobb was a unique character and his death a great loss to our community]​
 

JohnAbercrombie

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Thanks for that link and info, Mick.

Interesting idea- I'm curious when (and if?) they get it into production and what the price will be.
Not very suitable for any boat with a low back end, though, from the looks of it.

I ended up choosing a SmartTrack stern hung rudder for my current project (and first 'rudder boat'..."the horror"! ;-) )
 
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