mick_allen wrote:
...under hull location(s) so always in water in waves etc, and underhull retraction so no windage...
Is there such an animal Mick?
I call such an animal the ‘slot rudder’. For us designers, the slot-rudder is the holy grail that has been continually searched for with many funny and weird results - there are many fits and starts and half attempts and false attempts and goofy attempts and possible realizations.
Here are some of the steps by others along the way:
Integrated Rudders
So called as they supposedly integrate with the hull lines and when unused, do not add any extra drag to the hull other than the hull itself. Unfortunately the rudder is always exposed, the hull requires either zero rocker for the rudder to be effective in
any way and as they are so ineffectual they tend to develop little extra blobs on the bottom or side. The less developed of these cases also expose the rudder horns, cables and fittings:
some examples:
mirage:
more info at
http://www.mirageseakayaks.com.au/product_rudder.html
epic kayaks 18x sport:
more info at
http://www.epickayaks.com/products/details.aspx?nid=663&cid=3371
illusional Slot Rudders
These are rudders that give the
illusion of retracting into a slot in the hull – but only if viewed from a distance and directly from the side. Upon further inspection, one sees there is in fact a large pie shaped or larger depression in the hull that the ‘rudder’ can ‘hide’ away in no matter what angle it is deployed at . And in this pseudo ‘retracted’ position, the rudder and its depression still are a depressing drag. And as with the ‘integrated’ rudder above, the less developed instances also expose (and immerse) cables and joints and fittings.
Some examples:
Extreme Interface:
more info at
http://www.lightspeedkayaks.com/about_rudder.html
another self design version from a guy down under, also with the obligatory large pie shaped bottom hole.
(editor: links and jpg lost)
Pietsch
Also has the usual big hole or depression in the bottom. And as the rudder ‘post’ itself has to move, likely a little more play has to come into effect than otherwise expected (this is a surmise). I doubt that the receiver can be in constant contact with the post – an extra failure mode or sideplay circumstance.
more info at
http://www.pietsch-hansen-kajaks.de/steueranlage.htm
delusional Slot Rudder
lettman – hard to really see in the pdf but something like a slotrudder is shown. Deploy lines hidden, I think - but don’t understand quite what’s going on – it seems incomplete. Doesn’t appear to be any realignment mechanism, so must be some kind of indicator if in alignment so then can retract. Either it or I am having delusions here.
info on the pdf file at
http://www.lettmann.de/archiv/service/LMKatalog2005K367.pdf
[ed. - link is lost, but here is the view]
goofy Slot Rudder
zolzer has a funny flex scoop rudder with exposed lines running down each side of the blade. The exposed line must make it quite draggy and as the ‘rudder’ probably curves to deploy, not very effective. This is one of those ideas that should have been worked on a little more in the sketchbook.
more info at:
the zolzer website
a possible real Slot Rudder:
Geof Turner at Kari-tek has come up with what might be the first real commercial slot rudder. Unfortunately, the resolution is extremely cumbersome with housings within housings – so one gets a wide slot with a bulky skeg box, multiple hydraulic lines and cylinders, and inside awkward moving parts on top of the skeg and at the footpeg. However, he undoubtedly has a solution to at least one fundamental part of the slot rudder conundrum – the auto realign retraction. There is not enough info that i/ve seen to assess how well other aspects of the slot rudder are achieved, but this approach seems is a major step in the right direction.
sideview:
parts view
more info at:
http://www.kari-tek.co.uk
..
For me, ‘slot rudders’ should meet the following criteria:
- completely internal rudder assembly with only a slot in the bottom of the hull
- absolutely no extra required hull or keel protruberances so hull can be as rockered or smooth or shaped as desired for any other reasons than the rudder.
- absolutely no exposed lines or cables or rods or attachment points either below or on top of the yak to catch or cut or interfere or tangle.
- not necessary, but say can deploy to as much as 45deg ea side
- slim slot flush to bottom of hull, only as wide as the rudder blade (clearance added only if desired for anticipated sand/gravel jamming conditions – I would choose minimal clearance and possibly mount rudder 1- 2” off keelside- be interesting to test)
- an automatic self aligning mechanism for the rudder blade to automatically and instantly insert into the slim hull slot. Will auto align and deflect if hit by moderate sea obstructions or by the user quickly panic ramming the rudder up with no thought to how the rudder is deployed when initiating . This is a complex mechanism and I would accept that big impacts or side impacts will cause the same damage as if a skeg.
-as this alignment mechanism is so fundamental – say some redundancy to ensure realignment on retract.
- the internal rudder steering mechanism should be in constant engagement for minimized sideplay, minimized jamming, and minimized failure.
- the internal mechanism not much bulkier or heavier than a typical skegbox with an additional steering yoke and lines or cables or rods.
- design refinements to minimize weed contamination of the rudder axis in the deployed mode. (but no protruberance on retract)
- options of typical fully articulated rudders or the more stronger true skeg rudders (where the trailing edge of the skeg articulates – like the rudder of an airplane). Both operate and retract similarly. (these are not necessarily interchangeable options)
- options for high or low aspect depending on the duty expected. (these are not necessarily interchangeable options)
- apply to most hulls by just cutting slot and gluing in the box .
- allow typical skeg deploy knob with any type of rudder pedals or foot deploy, retract and steering - self adjust.
-the potential for making very small, light (and likely fragile unless exotics mat’ls) for racing application.
We are in the times in which the above specifications are beginning to be realized - the holy grail is almost at hand and is certainly within reach.
-mick
