Under Stern Rudder on Sea Kayak

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Daker
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Under Stern Rudder on Sea Kayak

Post by Daker » Mon Apr 16, 2018 3:15 pm

Does anyone have experience of having retrospectively fitted an under-stern rudder to a sea kayak and able to advise on the success or otherwise of doing so ?

I've recently been paddling a surfski a bit and am very impressed with their manoeuvrability on the rudder particularly when surfing either beach waves or deep water swell, which is of course where 'skis very much come into their own.

Being mainly a sea kayaker and preferring the load carrying capacity and closed cockpit style, I'm interested to know if fitting an under-stern rudder to a suitably fast sea kayak would give anywhere near the performance downwind of a ski.

My experience of over-stern rudders is that they are fine for gentle directional changes when touring but don't come anywhere near the turning ability that a ski has, but whether that is down to the hull as much as the rudder I don't know.

I totally accept that a permanent rudder will mean launching / landing requires more care but I try wherever possible not to get into my boats until floating so pretty sure I can live with that and also have an idea for a quick release rudder system in mind.

Thanks a lot.

pathbrae
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Re: Under Stern Rudder on Sea Kayak

Post by pathbrae » Mon Apr 16, 2018 6:58 pm

Have a look at the "Skudder" set-up which is a combined retractable skeg / rudder.

https://vimeo.com/107470449

and

viewtopic.php?t=120769

I'm not sure about retro fitting them though.
Karitek used to do a skudder kit which could be retro fitted but I don't see it advertised any more.
You coiuld give Geoff a call at Karitek or drop him an e-mail - he might be able to point you in the right direction
So much sea - so little time to see it.

Nick Gates
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Re: Under Stern Rudder on Sea Kayak

Post by Nick Gates » Wed Apr 18, 2018 10:17 pm

Fitting the rudder would require a small access hatch.
Glass in a half height bulkhead to support the rudder tube. Glass in the tube. Fit the shaft. Machine up a tiller from stainless or aluminium.

However, all that work, hit an unexpected shallow spot or get some weed caught around it and you will wish you hadn't bothered. They are very vulnerable.
Ummmm

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Re: Under Stern Rudder on Sea Kayak

Post by Daker » Thu Apr 19, 2018 8:37 am

Thanks for the comments.

I don't think it would be possible to buy a complete retro-fit P&H Skudder and, as you say Karitek stopped making their system a while ago I believe. I remember a discussion with Geoff a number of years ago where the pistons had become prohibitively expensive, although TBH I suspect the blade size on that was not really large enough for what I want.

As for whether its worth it, that will remain to be seen which is why I'm interested to hear from anyone who has done so and whether the under-stern placement is any more effective than a standard over-stern arrangement - - - - anyone ?

pathbrae
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Re: Under Stern Rudder on Sea Kayak

Post by pathbrae » Thu Apr 19, 2018 5:47 pm

From K1 paddling days, under-stern rudders were much smaller than the over-stern blades but were just as effective. I suspect a lot has to do with the rudder being positioned further forward and turning moments etc but I'm sure some of teh more hydro-dynamically literate posters on here will be able to describe exactly what the gains / losses might be. Certainly, under-stern equipped boats always seemed to be a bit faster than the equivalent with an over-stern.
So much sea - so little time to see it.

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Jim
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Re: Under Stern Rudder on Sea Kayak

Post by Jim » Fri Apr 20, 2018 5:32 pm

You get more turning moment at the end, but you get losses where the blade of an overstern breaks the surface (on a low aspect foil I seem to recall you can lose half the lift?), and an overstern will come out of the water more often in waves.

I have never fitted or used one on a kayak, but the simplest method is to glass a tube vertically through the hull and mount the steering gear above deck. All we used to do for flying fifteens was glass a tube in the rear before fitting the bulkhead, no extra support for the tube, mind you the hull was foam cored everywhere with ply core in way of the keel - I think just foam at the rudder tube though, it has been a few years...
Hiding the steering gear makes it a lot more complex.

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Re: Under Stern Rudder on Sea Kayak

Post by Aled » Sun Apr 22, 2018 10:45 am

A surfski rudder setup as a retrofit would be possible - glass in a tube from deck to hull and have the steering T bar above the deck. It would involve routing the steering cables up onto the back deck (pipes?), and probably the hardest part would be aquiring, making or adapting a surfski rudder with a rod long enough to span from below the hull to above deck.

Mac50L
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Re: Under Stern Rudder on Sea Kayak

Post by Mac50L » Sun Apr 22, 2018 11:17 am

The VImeo link - "Andy Butler talks us through the revolutionary [ Oh really? ] Venture Skudder system, available on the majority of the current range of kayaks [ since when? ] and offering unparalleled performance for recreational kayakers, no matter where you want to paddle!"

Actually the "skudder" was designed here in New Zealand about 3 decades ago by Don Currie and he fitted them to a couple of imported plastic Skerrays. So nothing "new" about it.

The same with the rudder by KajakSport, 90 degree raise and lower (instead of 270 degrees) which Don designed about the same time. We'd been commercially building them for a decade before KajakSport "patented" it and then a decade later Sea-lect also "patented" it. Same with the Smart Track rudder. I made those for my first 2 kayaks in 1985 and ~1998. "Quick and dirty", as they say, very easy to make and fit but liable to be damaged easily in a surf landing. I used the 90 degree style for everything else after that.

So basically, it has all been done before but an over stern rudder is so much easier to build and fit plus no lost space for gear in the aft compartment as happens with a skeg / skudder..

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