Rudders—what makes them "hydrodynamic?"

[SWriverstone]

Okay, here I go again with another random technical question (thanks for your patience!)...

Regarding rudders, I've often heard of one rudder or another being "hydrodynamic." This is a term I've always been dubious of...because I've seen it applied to rudders that appear to have no design features that make them any more "hydrodynamic" than another rudder that doesn't bear this label. So I wonder: what exactly makes a rudder "hydrodynamic?"

Also, because we all know hull stiffness makes a difference in the speed of a kayak (a softer, flexible hull won't be as efficient), doesn't this same rule apply to a rudder? Example: isn't a stiff metal rudder blade going to turn more efficiently than a plastic rudder blade that flexes?

Also: most kayak rudders I see are generally just made from a piece of plastic or metal that is a uniform thickness, e.g. the edges all the way around the blade are the same thickness and squared off. It would seem that to make a rudder "hydrodynamic" you'd want the leading edge of the blade (that's in the water) to be tapered...or maybe rounded (like an airplane wing)? But I don't think I've ever seen a kayak rudder blade designed like this.

And is there any advantage to rudders that are elliptically shaped and rounded on the bottom...versus rudders that are rectangles or parallelograms and squared off on the bottom?

Is "hydrodynamic" just a BS marketing term?

And one final thing I'm pondering: shouldn't rudders for bigger/longer kayaks be bigger? (Wider, or longer, or both?) won't the longer/wider boat require more turning power to produce the same "snappy" rudder turn as a shorter kayak? I ask because most rudders I see seem to be a single, generic size. (Which may be because a 1-3 foot length difference in boats really doesn't mean anything to a rudder?

 

[CPS]

On my Stellar I have a foil rudder blade, which is a stiffened nylon with exactly those airplane wing like shapes you're describing. Also, I found the stock rudder small, and often in the air while paddling in gnarly waves.
I opted for a larger version of the same style of rudder blade, which has a bit more drag but also more oomph when turning. Especially under sail.

 

[JohnAbercrombie]

But I don't think I've ever seen a kayak rudder blade designed like this.

They are pretty common nowadays.
Also check out surfski rudders which are even more 'evolved', and come in different sizes- swappable for paddling in different conditions.
I do recall reading that there wasn't a great advantage in foil rudders vs flat blades for touring boats, but I don't have a reference handy.

I ask because most rudders I see seem to be a single, generic size.

There are 'Regular' and 'Tandem' blades available for the SmartTrack rudders, and those (foil shaped) rudders are standard on a lot of modern sea kayaks. (As @CPS mentions above...). It's pretty common to use the tandem rudder on larger solo boats. Swapping blades only takes a couple of minutes.

Longer and loaded boats, and 'straight tracking' boats take more effort to turn, but the rudder is out at the end of a longer lever, so it gets complicated.

 

[CPS]

I do recall reading that there wasn't a great advantage in foil rudders vs flat blades for touring boats, but I don't have a reference handy.

I would absolutely believe it. At the speeds kayaks go I don't think the turbulence of a 1/8" thick piece of aluminum is going to amount to much versus a nicely rounded shape.
The SmartTrack foil blades look sexier, and really, that's what it's all about.

I recall, and similarly don't have a reference handy, that angling a rudder blade past a certain angle causes it to 'stall' and act more like a brake. Yet most foot pedal setups enable a relatively large rudder angle.

 

[SWriverstone]

The SmartTrack foil blades look sexier, and really, that's what it's all about.

LOL - they do look cool!

Part of what prompted me to ask about rudders is because (in the land of low-brow rotomolded boats, LOL), I have a 2008 Wilderness Systems Tsunami 165 that has a rectangular 1/8" metal rudder blade. On that boat, this rudder works great—I can make a subtle adjustment and see the boat respond instantly...or I can step on a pedal hard and the boat responds crisply with a fairly small-radius turn.

Then I got a 2014 Tsunami 175, and noticed that it has a black plastic rudder blade (also about 1/8" thick). I was a bit dismayed that I could easily bend (flex) the plastic blade...and as if to underscore my concern, the rudder feels sluggish on a 17'6" rotomolded kayak. It doesn't seem to enable subtle course adjustments...and stepping hard on a pedal results in a decidedly less snappy turn (I'm like "Okay, you can turn any day now!").

So I'm looking to replace the rudder on this boat...and the SmartTrack system (with the tandem blade) is looking like a good option.

 

[CPS]

If you want it to retract fully onto the deck you'd want to check out the 'Hybrid Foil' rudder housing. Mine is the 'Compact', which has a nicer, metal housing. The blade sticks up vertically when not in use. I just always deploy it.

The sluggishness might also be the 175 being, well, more sluggish than the 165.

 

[JohnAbercrombie]

I recall, and similarly don't have a reference handy, that angling a rudder blade past a certain angle causes it to 'stall' and act more like a brake. Yet most foot pedal setups enable a relatively large rudder angle.

Yup - I think that angle is about 30 degrees from the centerline.

 

[JohnAbercrombie]

The blade sticks up vertically when not in use. I just always deploy it.

My Smart Tracks are like that - I'm with you on the rudder use: "it's a rudder boat; put the rudder down"....

 

[JohnAbercrombie]

So I'm looking to replace the rudder on this boat

Just make sure this all-too-common situation isn't causing the sluggish rudder response!

 

[JohnAbercrombie]

If you want it to retract fully onto the deck you'd want to check out the 'Hybrid Foil' rudder housing.

The Tru-Course rudder is another one that slides (not rotates) up on to the deck. That's what I put on my Mariner Max.
I've seen some problematic setups with that Hybrid rudder where the spring was arranged to flip the rudder up and the cord locked the rudder down - good luck when you hit that rock!

 

[CPS]

Yes, the spring retraction system is idiotic. Far better to have to haul it up but have the spring assist with deployment and provide impact absorption capability.

 

[red kite]

LOL - they do look cool!

Part of what prompted me to ask about rudders is because (in the land of low-brow rotomolded boats, LOL), I have a 2008 Wilderness Systems Tsunami 165 that has a rectangular 1/8" metal rudder blade. On that boat, this rudder works great—I can make a subtle adjustment and see the boat respond instantly...or I can step on a pedal hard and the boat responds crisply with a fairly small-radius turn.

Then I got a 2014 Tsunami 175, and noticed that it has a black plastic rudder blade (also about 1/8" thick). I was a bit dismayed that I could easily bend (flex) the plastic blade...and as if to underscore my concern, the rudder feels sluggish on a 17'6" rotomolded kayak. It doesn't seem to enable subtle course adjustments...and stepping hard on a pedal results in a decidedly less snappy turn (I'm like "Okay, you can turn any day now!").

So I'm looking to replace the rudder on this boat...and the SmartTrack system (with the tandem blade) is looking like a good option.

The 175 has a longer waterline than the 165. If you have the same / close surface area of the rudder blade, I'd expect the turning responsiveness of the 175 to be slower due to more sideway / farther forward water resistance of the keel line?

My memory is a bit fuzzy going more than a decade back, but 2014 could be the first year of Confluence's revamped rudder system? Those first couple of years had quite some QC inconsistencies. And, caring for a couple dozen of WS fleet boats at the time, I personally wasn't too fond of some of the new material and design choices.

 

[red kite]

The Tru-Course rudder is another one that slides (not rotates) up on to the deck. That's what I put on my Mariner Max.
I've seen some problematic setups with that Hybrid rudder where the spring was arranged to flip the rudder up and the cord locked the rudder down - good luck when you hit that rock!

KayakSport's Navigator rudder is similar to the Tru-Course. It can be ordered with two different blade lengths. https://kajaksport.fi/product-category/rudder/

 

[SWriverstone]

The sluggishness might also be the 175 being, well, more sluggish than the 165.

Haha yep, there is that! It's an almost entirely rockerless design. (But tracks great!) "Extreme North American" design, LOL.

Yup - I think that angle is about 30 degrees from the centerline.

I just push mine until it sounds like a toilet flushing back there, then back off a bit. LOL

The 175 has a longer waterline than the 165. If you have the same / close surface area of the rudder blade, I'd expect the turning responsiveness of the 175 to be slower due to more sideway / farther forward water resistance of the keel line?

That, plus see my comment above about it being a rockerless boat. If I stand on one side of the cockpit rim in the water, I can almost get it to lean...but it still barely turns, LOL. But I didn't buy it to turn—just to haul massive amounts of gear in a straight line for many miles and generally be bombproof.

 

[SWriverstone]

QUESTION: Not having ever used the SmartTrack rudder pedals...it's hard for me to imagine how they work in practice. Do you need to be barefoot or wearing neoprene (soft and flexible) booties?

Do you keep the stationary part of the pedal under the center of your foot, then just rock your feet forward to turn?

Is it finicky and difficult to get the hang of? Or really easy?

 

[Twempie]

QUESTION: Not having ever used the SmartTrack rudder pedals...it's hard for me to imagine how they work in practice. Do you need to be barefoot or wearing neoprene (soft and flexible) booties?

Do you keep the stationary part of the pedal under the center of your foot, then just rock your feet forward to turn?

Is it finicky and difficult to get the hang of? Or really easy?

The SmartTrack system works as well, if not better, than any other rudder system. As for operation, you push the top half of the pedal assembly to move the rudder. The bottom half of the pedal assembly is for bracing. It's intuitive.

I've had a SmartTrack pedal/rudder system on my Looksha IV HV for a more than a couple of decades, it was an option when I ordered the boat from Necky (as a free replacement for my dropskeg Looksha that couldn't be repaired). This was around the time the SmartTrack system was awarded a bunch of prizes for an innovative design.

Last year, I acquired a 17' "regular sized" Looksha IV, and immediately swapped out the original stairmaster pedals for a pair of SeaLect braces/pedals, keeping the original rudder for now.

BTW I rarely use a rudder unless I'm tired of ferrying on one kidney, lazy, or perhaps taking a photo, and believe it doesn't hurt to have a rudder as a backup. There's room in the HV/SmartTrack for my discontinued Chota MukLuk boots. The 17' Looksha is a little tight around the feet, so I go with booties instead.

If I were to start from scratch with a new pedal/rudder setup, I'd go for the SmartTrack rudder with SeaLect pedals.

SmartTrack Pedals on my old Looksha IV HV

SeaLect Pedals, modified from the original stairmaster strap-pedals on the new to me Looksha IV

 

[CPS]

If I were to start from scratch with a new pedal/rudder setup, I'd go for the SmartTrack rudder with SeaLect pedals.

That's what I've got in my Stellar. I wasn't happy when the the Smart track pedals so swapped them out. It took some creativity because the studs are a bit too short, but nothing too dreadful.

 

[SWriverstone]

So wait, does the whole pedal tilt with the SeaLect pedals? (Like the accelerator in a car?)

Nevermind, just looked at a closer pic, looks like the whole pedal does tilt. I think I'd like that better than the split-pedal system, but I've never used either.

As an aside, everyone seems to complain about the "sliding track" rudder pegs as not giving you anything to brace against. I've learned to brace hard (and easily) on mine—I just vary my foot pressure to change rudder position...then push against both pegs equally and they don't move. Not a big deal...(but I'd still probably like these pedals better).

Sprint kayaks used to have just a wood dowel between your feet that you pushed side-to-side...(not sure if they still do?)

 

[Twempie]

So wait, does the whole pedal tilt with the SeaLect pedals? (Like the accelerator in a car?)

Nevermind, just looked at a closer pic, looks like the whole pedal does tilt. I think I'd like that better than the split-pedal system, but I've never used either.

As an aside, everyone seems to complain about the "sliding track" rudder pegs as not giving you anything to brace against. I've learned to brace hard (and easily) on mine—I just vary my foot pressure to change rudder position...then push against both pegs equally and they don't move. Not a big deal...(but I'd still probably like these pedals better).

Sprint kayaks used to have just a wood dowel between your feet that you pushed side-to-side...(not sure if they still do?)

Yes, the SeaLect pedal is one piece and the SmartTrack pedal is a split into two pieces. They both work as well as each other, I just prefer the SeaLect because they feel more solid and have fewer moving parts.

 

[Twempie]

That's what I've got in my Stellar. I wasn't happy when the the Smart track pedals so swapped them out. It took some creativity because the studs are a bit too short, but nothing too dreadful.

Was the rudder swap/replacement relatively easy? I'm thinking it's been while since I've grazed my knuckles, and need a project.